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NEED HELP Brakes locking up again

Discussion in 'Brakes' started by Realism, Jun 29, 2016.

  1. Realism

    Realism Well-Known Member

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    Hello again and welcome to revenge of the braking system.
    Previously (in an older thread) I had some issues with my front calipers not fully releasing. Replacing the flex lines helped them to let up. Since then, I've been trying to decide who to go with for new rotors, calipers, and brakes. Settled on: Calipers = ACDelco pro Rotor = ACDelco advantage Pads = AcDelco pro ceramic 2 calipers+2 rotors+front pads = $277 (rockauto ground shipping of $41) = Total $318 :stars: That is a chunk of change for shipping and mid tier parts.
    Not 100% confident in my choice and I am open to suggestions. They were selected piecemeal since the only full kit rockauto carried was Powerstop, and I couldnt find much review and opinion on them.

    However, the main point of this thread is that I am yet again having brake caliper issues with ALL FOUR.

    So after replacing those flex lines, the calipers let up allowing me to drive without locking up, giving me some time to decide and get parts ordered. 105 yesterday, late afternoon I head out for some errands, on my way to my first stop (2 miles away) I notice that it feels and sounds (barely) like my front calipers were getting tight again. Pull into the office parking lot and check the heat of the wheels with my hand. Rear wheels are a bit warm, which I assumed was just because of how bloody hot it was outside. Using that as a base line, I test the fronts. They are much warmer than the rears, so I'm like great, note to self, make final decision and order those parts tonight.

    An hour later I leave and drive down to the store about 2 miles away. Just about there and I get a fast yellow, so I end up braking hard, stopped, and then lifted my foot off the pedal to gently reapply just in case the heat of the hard stop convinced calipers to lock down. When I press the pedal back down, it is hard. The rest of my driving back home I noticed that the brake pedal is hard and super sensitive, like no give to it. I get about 1/2" of travel before I feel the brakes grab tight and the pedal doesnt travel any further than maybe 1" inch. While getting it back home, I could see higher RPM's just to get up to speed (35 mph), but it must not have been fully locked because when I took my foot off the brake, it would slowly creep forward. Felt the wheels when I got home, the rears felt almost as warm as the fronts did when they were acting up and even had brake dust on wheel (never did before), the front wheels were hot enough that touching longer than a brief second would have left burns.

    This leads me to assume that the root cause was not the flex lines or calipers. The only change between then and now was an oil change, although it has been doing this high idle at start for a while - jumps to 1500 RPM and drops to 900 slowly over 20 seconds before taking another 20 seconds to drop down to the normal 650.

    Going to do a brake boost check and pull the TB for cleaning (did it 12 months ago). Not sure if the master could be bad, I thought when the MC is bad it gives spongy no brake instead of the hard grabber I'm getting now.
    Sorry for the novel :readrules:
    Summary:
    Hard feeling sensitive brake with 1/2"-1" total travel. Grabs quick. All four feeling not releasing. Wheels are hot, with fronts near scorching.
     
  2. Sparky

    Sparky Moderator

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    For rotors/pads I like the Brakemotive stuff. They have an ebay store.
    I just get my calipers etc from the local parts stores usually, that way I can take my old ones in for the core charge and not ship stuff.

    Regarding the lockup, if it is all 4 it makes me wonder if you've got something like a master cylinder issue or perhaps the ABS block acting up. Go out on some loose-ish surface and slam the brakes on to get the ABS to fire and see if that helps at all.

    Of course, checking for brake booster operation is a good idea too.
     
  3. Realism

    Realism Well-Known Member

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    What would you recommend for calipers from local places?

    Abs I have wondered about, since the brake fluid was black last year when I took over maintenance and changed it. Will pulling the abs fuse have an effect if the problem lays with that?

    I always thought the MC made brakes squishy like air in the line does when it goes bad. Could the dirty brake fluid from before have damaged the seals in a way that it makes for non-releasing calipers?
     
  4. gmcman

    gmcman Well-Known Member

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    When you replaced all your brake hardware, did you replace or clean/lube the two guide pins on each caliper?
     
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  5. Sparky

    Sparky Moderator

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    I've just gotten reman from Advance Auto. Never had an issue with them.

    Pulling the fuse won't have an effect as that just won't let the ABS fire. If the block is gunked up you want to fire the ABS and/or flush the fluid out of it.

    A bad MC could make them squishy, but I'm just thinking it isn't retracting right or something maybe. Trying to leave no stone unturned despite being unlikely, ya know?
     
  6. Realism

    Realism Well-Known Member

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    Negative. Only hardware replaced was both flex lines in the front. If it was just one caliper being an issue, I would suspect the guide pins and check them again. However, it is highly improbable that all four calipers would suddenly have guide pin issues at the same time.

    Advanced auto - copy that. I had considered them, since I do have one somewhat nearby. I will try getting the ABS to kick on too, as far as flushing it, how is that done?

    Right - explore every possibility. Wanting to work from most to least likely, or easier to check perhaps. Testing and replacing the MC is the last possibility/course of action I want to do, since its such a pain in the . . .
     
  7. gmcman

    gmcman Well-Known Member

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    Generally when the brakes are dragging, they tend to fade more and aren't as sensitive.

    Just a thought....How many miles are on the front hub and bearings, have they ever been replaced? A worn hub and bearing will sound or feel like grit in the wheel or like you have mud tires.

    Does the brake pedal fully retract when you lift your foot? Pull the pedal back until it stops and see if it returns.

    Here's something I tried to cycle my ABS brakes, worked well. I would clamp all 4 lines and try....not all 4 at once though....:biggrin:

    http://gmtnation.com/forums/threads/cycling-abs.15166/#post-493265
     
    Last edited by a moderator: Jun 29, 2016
  8. AWD V8

    AWD V8 Well-Known Member

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    Affecting all 4 wheels... a possible ABS module issue, but...

    First check that the brake pedal returns all the way to the top. You should feel a bit of closeness at the top at rest. This is the free play between the pedal push rod and the master cylinder piston. The master cylinder needs this clearance to allow the brake fluid to return to the reservoir. If this clearance is not there the pressure will remain in the system causing dragging/overheating brakes. This is a simple push rod adjustment.
     
  9. MRRSM

    MRRSM Gold Supporter

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    There have been some instances involving GM Disc brakes in which there has been an insufficient offset necessary for the Caliper Brackets to be able to roam comfortably in and out ...without getting jammed against the Disc itself. And so...The GM Engineers came up the idea of using various thicknesses of OEM Shims that moved the entire Brake Mounting Hardware further away from their ordinarily closer inboard position. By doing so...these Shims provided enough OEM strength and stability to allow the Caliper Brackets to move away from the Heat Expanded Rotating Discs by adjusting the narrow space more evenly, giving the Rotating Brake Discs AND the moving Caliper Brackets the freedom from becoming jammed against each other.

    I think a quick search on eBay might reveal these for Shims are for sale...and even if they are not specific to your particular application...if they will fit in between the mounting locations and held in place with the 18MM Bolts that are kind of a standard size ...their Quality of Manufacture and their ability to be installed safely might allow the Disc-To-Bracket relationships more correct positions when the Brake is released and the Caliper Brackets move outboard. I'm thinking that this is the specific problem involved here. Hope this idea has merit.

    http://www.ebay.com/itm/Wilwood-Cal...ash=item3d1dec8b4c:g:7C4AAOSwdj9XT3yA&vxp=mtr


    EDIT:

    Conversely... I believe there is also a series of Ultra Thin Shims that can move the Discs themselves further outboard if the space that is locking is on the interior sides of the Caliper Brackets. In any case ...as Einstein often pointed out, "It makes no difference whether you are the Passenger on the Train ...or the Man standing in Train Station near the Tresle.... From a relativity perspective... You are BOTH moving away from each other ...at the Same Speed..."
     
    Last edited: Jun 29, 2016
  10. gmcman

    gmcman Well-Known Member

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    I agree the brake pins aren't as likely but they definitely need to be free moving. I would start with the brake booster then the master cylinder before going to the ABS.

    You can make a few stops then bring the vehicle back home with the engine still running, or just apply the brakes a few times when cold...then lift up the front end and see if the wheels are dragging. Then take a screwdriver or body pin tool and pry the check valve from the brake booster. This will release a lot of vacuum and cause a vacuum leak but then check the wheel and see if it turns easier.

    If the brake lights stay off, then the booster could be hanging up. You could also loosen the bolts on the master cylinder slightly and allow the master cylinder to extend from the booster and see if that loosens up the wheel slightly if pulling the check valve won't cause any changes.
     
  11. Realism

    Realism Well-Known Member

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    125,000 miles. No idea if they have ever been replaced, but it is possible since it was clipped on the passenger front corner at some point and was repaired before we bought it.
    Brake pedal fully retracts. Checked it even by trying to lift up with my foot, wouldnt go any higher.

    Not sure what you mean by closeness.

    Good advice. Things I will try this evening when it cools down a bit.

    I did take it out to my storage unit to retrieve my tools. 6 mile total trip. With laser thermometer I temped the rotors before for a baseline (given it was in the sun), checked at storage. Pedal was still the same hard feeling. Rears were about 135, passenger front 160, driver front 165. Noticed that even fully pressed down felt like the brakes werent catching that quick and taking its time. Driving back I tried the fire the abs as best I could from 35mph. Didnt feel it kick in when I slammed on the brakes, then again I've only ever felt them kick on once in the entire time having it and that was on ice two years ago. Brake pedal felt normal when I did this, meaning it felt not hard and sank down like it normally would. All braking after this was met with the same hard brake feel.
    Parked at home, checked temps again. Rears about 150, passenger front 195, drivers front 210.
    Brake boost check came out normal. With it in park, on or off, the brake pedal feels close to normal, but when it is engaged the brake is much stiffer.

    I am concerned with the effect the heat buildup from this brake issue, (current and past) could be having on other components. Can this destroy the wheel bearing? There are a few other things that need to be done to the envoy, mostly suspension stuff and this weird sliding on ice type feeling when turning and some steering wander that may be from a bad alignment. Really want to fix it back to factory shape, but if it looks like its going to need lots of $$$ now and a bit more $$ in the next few months, I will have to consider options.
     
    Last edited: Jun 29, 2016
  12. xavierny25

    xavierny25 Platinum Supporter

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    20151113_145823.jpg
    That small front end damage could have done something like this causing your issues.
    These are from a set of caliper and brackets from an tbss I picked up months ago I'm glad I took everything apart before I put it all together on my voy. The tbss was in a front end crash and this is only a small piece of the damage.
     
  13. AWD V8

    AWD V8 Well-Known Member

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    If the pedal is at rest in the top position, no foot on the pedal, if you grab the pedal and gently move it up and down, you should feel a bit of looseness at the top before it feels like it is beginning to apply pressure. This is the clearance of the push rod on the pedal to the piston in the master cylinder. It should rattle a wee bit. If you don't have looseness, about 1/16" - 1/8" it means that the piston in the master cylinder may not be fully retracted and letting the pressure out of the system.
     
  14. gmcman

    gmcman Well-Known Member

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    Honestly 200 deg for the rotors surface isn't terribly abnormal after a few good stops. Now if the wheel itself was 200 deg that would be a problem.

    You also seem to have an even temp across each circuit, granted the fronts are warmer but left to right they are even while being biased to the front.....which seems normal.

    If you are rolling on a flat surface with no pedal pressure, does it slowly stop with no jerkinesss or does it have a slight "bump" when it stops.

    Just a couple thoughts ...this is important, did you clean all the oily film off the rotors when you installed them with brake cleaner?

    I have to ask this.....not implying anything but do you brake with your left or right foot? I have known people to brake with their left foot and inadvertently rest their foot against the brake pedal.
     
  15. Realism

    Realism Well-Known Member

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    Yeah. My drivers front caliper had a pin that was bent a bit like when I checked and replaced the caliper and pins last year.

    AWD V8: Okay. Yeah there is a bit of looseness then, about 1/2" maybe of travel before feeling the brakes start grabbing. dont have any rattle though.

    Good to know about the temp there then. Wheels were only about 160ish in front, rears much less.

    Just rolling along without giving gas it does start slowing to a stop on its own. Havent had any slight bumps when it does. Only bump in the last year or so has been an occasionally from behind feeling when your U-joint is telling you to pay attention to it.

    Cleaned rotors with it when re-installed.
    Right foot.
     
    Last edited by a moderator: Jun 29, 2016
  16. coolasice

    coolasice Well-Known Member

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    I would try blocking off the booster vacuum line and release any built up vacuum in the booster, then take it for a short slow drive to see if the brakes are still acting the same...
     
  17. gmcman

    gmcman Well-Known Member

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    Keep in mind braking will be severely diminished after the first stop, best to do in a open parking lot.

    I took mine for about a 5 mile drive, had about 5 or 6 red lights. Here's the temps of my brakes on the left side, right side was very close to these readings.

    Realism....Your brake temps don't seem to be too far from the norm.

    Brake temp1.jpg
     
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  18. Realism

    Realism Well-Known Member

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    Ha, that's absolutely brilliant! Thanks for the thermal imaging assist on the temps. Eases my mind about them causing other issues due to heat output.
     
  19. Sparky

    Sparky Moderator

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    Here's the thing though, if your temps are in line, that means your brakes aren't getting stuck on, meaning... well, something else is going on.

    The fact that the truck slowly moves at idle in gear with the foot off the brake also does indicate also that they aren't dragging, or at least not badly.

    I'm starting to lean towards the power assist being screwy. Not sure where to look exactly for that though.
     
  20. Realism

    Realism Well-Known Member

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    They drag, but not bad enough to completely stop wheels from turning, plenty of excess brake dust on the worst offenders.
    I was leaning in that direction and looked to see what I could find on the booster.
    vacuum is good and the valve checks out okay. No leaks. I did find mention of the sensitive brake pedal a few times in connection to the brake booster's internal hub being cracked which causes it to be either fully on or off. The slightest pressure to the pedal is enough to cause the brakes to start locking up.

    Few other things to check in the morning too. Including loosening the MC from where it mounts, if i get any let up then I can try some washers as shims to give space. Would be strange since I've never even touch the MC other than to put fluid in.
     
  21. MRRSM

    MRRSM Gold Supporter

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    I know this would be a laborious effort but... Is there any chance you could elevate the vehicle level on four Jack Stands... Pull off the Wheels/Tires and have some one sit in the driver's seat and mash the Brake Pedal while you inspect each wheel for anything mechanically amiss...or misaligned?

    Here are Two Service Bulletins that may also have additional clues to the cause which ties in with some of the impressions mentioned by @Sparky :

    TECHNICAL SERVICE BULLETIN Reference Number(s): 04-05-25-002E, Date of Issue: March 11, 2009 Affected Model(s): 2004-2007 Buick Rainier; 2002-2006 Cadillac Escalade, Escalade EXT; 2003-2006 Cadillac Escalade ESV; 1999-2007 Chevrolet Silverado Classic; 2000-2006 Chevrolet Suburban, Tahoe; 2002-2006 Chevrolet Avalanche; 2002-2007 Chevrolet TrailBlazer, TrailBlazer EXT; 2003-2006 Chevrolet SSR; 1999-2007 GMC Sierra Classic; 2000-2006 GMC Yukon, Yukon Denali, Yukon XL; 2002-2007 GMC Envoy, Envoy XL, Sierra Denali Classic; 2004-2005 GMC Envoy XUV; 2002-2004 Oldsmobile Bravada Supercedes: This bulletin is being revised to add step 2 to the procedure and update the Parts and Warranty Information. Please discard Corporate Bulletin Number 04-05-25-002D (Section 05 - Brakes). Related Ref Number(s): 04-05-25-002, 04-05-25-002A, 04-05-25-002B, 04-05-25-002C, 04-05-25 -002D, 04-05-25-002E ARTICLE BEGINNING CONDITION Some customers may comment that the ABS light is on. Upon further inspection, DTCs C0265 and C0201 may be set in the brake module. It is also possible for DTC U1041 to set in other modules. There may also be a loss of communication with the brake module. CAUSE A poor connection at the EBCM ground is causing unnecessary replacement of brake modules. IMPORTANT: The EBCM ground is different for each application. Refer to the list below for the proper ground reference: Midsize Utilities = Ground 304 " SSR = Ground 400 " Fullsize Trucks and Utilities = Ground 110 " CORRECTION IMPORTANT: Do not replace the brake module to correct this condition. Perform the following repair before further diagnosis of the EBCM. Perform the following steps to improve the connection of the EBCM Ground: Remove the EBCM Ground. The EBCM Ground is located on the frame beneath the driver's side door. If multiple grounds are found in this location, the EBCM ground can be identified as the heavy (12-gauge) wire. 1. Page 1 of 1 ABS Light On, DTCs C0265, C0201, U1041 Set and/or Loss of Communication with Bra. 5/5/2009

    TECHNICAL SERVICE BULLETIN Reference Number(s): 08-05-25-005, Date of Issue: October 01, 2008 Affected Model(s): 2006-2007 Buick Rainier; 2006-2009 Chevrolet TrailBlazer Models; 2006-2009 GMC Envoy Models; 2006-2009 Saab 9-7X; 2006-2009 Isuzu Ascender Models Related Ref Number(s): 08-05-25-005 ARTICLE BEGINNING CONDITION #1 NOTE: This bulletin provides information on two different conditions. Some customers may comment on a Service StabiliTrak indicator light along with a Service StabiliTrak message displayed in the DIC. Upon investigation, the technician may find DTC C0196 set in history. CONDITION #2 Some customers may comment on a blinking StabiliTrak indicator light along with a StabiliTrak Active message displayed in the DIC during normal driving conditions. No DTCs will be found with this concern. CAUSE This condition may be caused by a software anomaly within the electronic brake control module (EBCM) that allowed the yaw offset to be falsely learned. CORRECTION Correction Do This Don't Do This Reprogram the EBCM. Do not replace the yaw sensor or EBCM for this condition. IMPORTANT: From the controller list, select " VSES Vehicle Stability Enhancement System Control Module.&Quot; If routine diagnosis using SI does not reveal any obvious cause, reprogram the EBCM using SPS with the latest software available on TIS2WEB. Refer to the Service Programming System (SPS) procedures in SI. As always, make sure your Tech 2 is updated with the latest software version. WARRANTY INFORMATION (EXCLUDING SAAB U.S. MODELS) For vehicles repaired under warranty, use:


     
    Last edited: Jun 30, 2016
  22. coolasice

    coolasice Well-Known Member

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    Before shimming anything you need to try disconnecting the vacuum hose and see if the drag is still present...
     
  23. Realism

    Realism Well-Known Member

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    Interesting. Didnt have any of the lights on, I will take heed though, but since you mentioned it, I did do a full code scan and checked for the TSB mentioned codes. Nothing matches, however, I do have the following codes history status. If it means anything.

    Powertrain Codes:
    U1197 Lost comm with security control system
    U1000 class 2 data link malfunction
    c0300 rear propshaft signal circuit malfunction
    c0306 motor A/B circuit malfunction
    C0374 general system malfunction
    c0379 front axle system malfunction c0380 mode switch power circuit low
    C0550 ECU malfunction
    B0770
    B0775 four wheel drive high range (4HI) indicator circuit
    B0780 four wheel drive low range (4LO) indicator circuit
    B0785 two wheel drive high range (2HI) indicator circuit
    B0790 transfer case neutral indicator circuit
    B2725 ATC mode switch circuit malfunction
    U1301 Clas 2 data link high

    Door module:
    U1064 lost comm with body multiple control system (right rear door)

    Driver seat module codes
    U1064 lost comm with body multiple control system
    U1016 lost comm with engine control system
    U1160 lost comm with convenience control system
    U1161 lost comm with convenience control system.

    Not sure if these mean anything or are past codes.
     
  24. Mooseman

    Mooseman Moderator

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    They could have been from a temporary condition or when the battery was disconnected. U1000 seems to always appear. They usually take a long time before they clear completely from history. Just clear them all and recheck once in a while. I wouldn't worry if they aren't current.
     
  25. Realism

    Realism Well-Known Member

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    I wasnt either. I've cleared them before, but they always show back up when I rescan all modules. Its funny though, the CEL that has been tossed for the "gas cap" issue never shows in history. Oh well, no worries.

    This morning I went out and listened well for the sound of any vacuum leaks while running, checked for leaks while operating brake pedal. Lifted the front off the ground and tried to spin both wheels. Did video it, but not sure if its all that useful. Drivers side rotated about 12 inches after I let go. Passenger side went about 3 times the distance. So maybe half a revolution for passenger and not even a quarter for the drivers side.
    With it up I pulled the booster vac hose off - no change in wheel resistance. started vehicle and still no change. (I forgot to take the valve off to check that, will do that when I can later). No brake lights come on with the stickiness btw. Blocked the vacuum hose and pressed brakes a few time. No change.

    I loosened the bolts fixing the MC to the booster, giving about 3-4 mm of free play on both sides (1/8" or so). No change in wheel resistance. operated brakes a few time while running. No change.
    With the vehicle running I got under and cracked the bleeder valve with hose over it. Brake fluid escaped (no air bubbles), while open I rotated the tire and it felt easier - continued rotation further than before, but not the full free spin it should (accounting for piston). Closed bleeder and rotates more freely still. Figure okay.. So I do the same to the other side and it also frees up, with same results. * I did notice two things to take care of under there: the abs line on drivers side is before the main brake line so its tucked behind the main, not pinching it or anything like that; passenger side I noticed that when im turned to the far right the flex line actually rubs on the tire, no damage yet, but will use a zip tie to pull it away a little. *

    Cracking the bleeders helped retract the pistons some. They are new flex lines, so no issues there, but seemingly hydraulic related. Wasnt able to get to the rear wheels, but will double check them even though Im beginning to wonder.
    That drivers front has always been the worst offender, is this due to it being the first in the circuit? Prior to this, all was well until it started hitting over 100 degrees, fast brake and poof, we have issues.
    Does it sound more MC related now? Not sure how or what else to check in relation.
     
  26. gmcman

    gmcman Well-Known Member

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    You are almost descrbing a normal braking system.....disc brakes run at nearly zero clearance....the pads will drag slightly.

    Does your steering wheel shake when braking?

    Are you in 2Hi or A4WD?.....should be 2HI.

    Have you verified fluid level in front and rear diff and transfer case?

    Has transfer case fluid been replaced at the 50K mile interval?

    Brake dust is normal for certain pads, not necessarilly directly correlated to dragging brakes.

    Can you take a pic of the brakes and caliper as they are on the vehicle, can you take a pic of the pads removed from the caliper?

    Are the pads mounted correctly? I ask this because I have seen some crazy mistakes.

    You really need to check the guide pins.
     
  27. Realism

    Realism Well-Known Member

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    2Hi. No steering wheel shake during braking, but wheel does have a small degree of play either way, maybe 5 degrees left or right. It does pull slightly to the left while driving and a slight wander from bumps if i dont fight the wheel, more noticable at higher speed. Been that way since I got an alignment in January (not too pleased, steering wheel wasnt set straight either), arm bushings need to be done.
    Front diff I filled in May, rear diff and transfer case was last checked by a shop the ex would take it to, nothing noted in their report about them, but I probably should check myself, since this is the same shop that said they changed the brake fluid, when in fact it was black as sin when I changed it 3 months later.

    50k transfer fluid change - no idea, we got it in 2013 with 112k on it, 125k now.
    True brake dust is to be expected, but it has been excessive.

    I will take some current ones of the calipers and brakes mounted in daylight and post them. I did upload a video of wheel resistance. mostly for my own before and after comparison,

    Was working on them earlier in May, mounted correctly with all proper. replaced the calipers in october I believe.
     
    Last edited: Jul 4, 2016
  28. coolasice

    coolasice Well-Known Member

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  29. Realism

    Realism Well-Known Member

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    Finally got a few to get out there on it.
    Transfer and differentials are full, rear could due with a change. Checked and cleaned the ABS sensors, double checked wheel bearings, made sure brake light switch wasnt causing issue. Looked for a way to adjust the push rod, but according to what I keep coming across there is no way to adjust.
    Checked rear wheels, they are rotating okayish, so its for limited to the front two.
    Tried to look down into the MC reservoir to see if there a swollen valve or something protruding and preventing pushrod from seating all the way (being under 6' does have its disadvantages) used floor jack to give me a boost :smile: There is still some black residue from the old fluid coated to some parts on the inside, more concerning was something I never noticed. If i angled the light just right, it looked as if there were little swirls in the brake fluid. Forgive me, but the closest and cleanest I can describe it would be to say its like the edges of a giant ball of spit in water, with the swirling trails, almost transparent but not quite. I'm assuming this to be moisture content, not sure how its gotten itself in there, certainly not suffering from low compressibility.
    Took pictures at Gmcman's request. Current are uploaded here http://imgur.com/a/jAZYK

    Double checked the slide pins and had someone operate the brakes. I did notice that the bottom pin boot was not extending near as much as the upper. Watching while the brakes were depressed it appears that the boot is allowing air out, sucking the pin further in, but not letting air in. So I think I may pull the pins out and see what can be done, possibly replacing the boots. This doesnt explain the passenger side though. Just on a random idea, I took a sharpie and made lines along the rotors to see where the contact is greatest. Drivers side with the one pin is contacting more on the inner section of rotor. unequal slide pin issue, yeah I can see that. Passenger side has equal contact, fully removing the lines in two passes.

    Thinking of rebleeding the system and replacing the reservoir. If an ABS module was gummed up, I wonder if its worthwhile to d/c the steel line going to one of the front wheels after and before the module, checking to see if the caliper eases.

    Sparky: Try as I might, I could not get the ABS to kick on

    Coolasice: I did consider that, thank you for the link. Would a salvage yard brake booster be sufficient or is it one of things you'd best get new? I would test new if it wasnt a party foul to return if it wasnt the problem.
     
    Last edited: Jul 4, 2016
  30. gmcman

    gmcman Well-Known Member

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    Thanks for the pics, everything looks good. The inboard rotor surface looks thin but not terrible...pads have good even wear.

    Did you see my post about cycling the ABS? If you have 2 jack stands for the front and a floor jack for the rear diff it's easy to do.

    I will look at my front wheels tomorrow but yours almost appear to be rotating fine. If the guide pin is sticking, that could cause a slight drag on the pads. Doesn't take much to slow the wheel.....the slightest excess pressure will slow the wheel.
     
  31. coolasice

    coolasice Well-Known Member

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    I would think new would be the way to go because you don't know the condition of a salvage unit...
     
  32. Realism

    Realism Well-Known Member

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    I did read over your post on cycling the ABS. Was saving that for last as I am on a slight grade.

    Monday evening I went and pulled the front slide pins. Cleaned and sanded any grit/rust, re lubed (used Syl-glide this time) pins and just under the the lip of the piston boots. Compressed the pistons fully. When taking the passenger caliper off I heard noise when one of the pistons was no longer in contact against the pad and immediately pushed caliper back down thinking the piston was trying to push out of the bore. Not 100% sure if the noise was indeed that, but I did let more fluid out before trying again (I noticed some of that light particle stuff in the fluid as it was passing to the bleeder container). Passenger was more difficult than other side to press back in. Would be nice to test the pressure on each line to determine if there is unequal pressure.

    After putting it all back together, the sensitive brake issue has gone away, but it has been cooler, so it leaves me wondering if the 100+ outside temps could be having an effect, will keep my eye out for that. Wheels spin a more freely than before, but they did when I replaced the flex lines in May. I can still hear the contact of pads on rotor and needing more rpm at lower speeds to get up. It looks like the pins are pulling the caliper against the outer pad, making it have the contact. Noticed for a short time after doing this, my vehicle wander felt like it went away. Ruling out a few things, I'm left with some questions.

    If compressing the pistons frees the extreme grab and alleviates the sensitive brake pedal (if only temporarily), then does this mean there is blockage since it would be forcing fluid backwards?

    Why would brake operation over time (or a single quick hard brake application) cause the calipers to compress harder and not let up, lending to the sensitive pedal?

    Is external temperature a factor?

    In what position are the slide pin boots supposed to be?
    I have tried to find the answer to this one for a while now. Unsure if they are supposed to be fully extended (without caliper on) with an air pocket in the bore or if they are supposed to be inserted and the air evacuated to create a vacuum. If there is air pocket, it pushes the piston section away from inner pad, but pulls tight against the outer pad, causing it to be applied to the rotor. If it is a vacuum, it would cause the outer pad to not be pulled against the rotor, but would pull the piston side against the inner pad, causing it to make contact with the rotor.
    I've tried to get it about the midline judging by pictures of a fully assembled AC Delco caliper + bracket on rockauto.

    How much lubricant should go into the bore before the slide pin goes in?
     
  33. Sparky

    Sparky Moderator

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    Not sure on some stuff, but...

    Slide pin grease - I just smear it evenly on the pin itself with a decent coating but nothing too crazy (don't want it causing the pin to not insert fully). THen I spin the pin when it is in the bore to spread it around.

    I've always gotten most of the trapped air out from behind the boot but not been too bothered about a bit of spring to the pin. I think either way you do it the excess air (or vacuum) will be balanced out as the brakes are far stronger than the slight vacuum or air pocket are.

    I'm still leaning towards some sort of blockage acting like a check valve someplace further up the line.
     
  34. gmcman

    gmcman Well-Known Member

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    When you apply the brakes, the caliper will slide, then retract. You are likely seeing the caliper returning to it's resting state. Also, the pads will rest on the rotors when the brakes are not applied causing drag.

    I finally took a video of both my front wheels after a 5 mile drive, the right side drags slightly more than the left, likely due to the splined disconnect, maybe not but keep in mind with 4WD, not only do you have brake pad drag, but axle shafts and the front diff.

    I feel what you're seeing is normal, remember, my brakes function properly and yours ran slightly cooler than mine.

    If you're not getting any immediate pull to one side when applying the brakes, after the brakes have been warmed up...and no abnormal pad wear, I still believe they are working normal. Maybe not what you're used to, but they act just as mine do.




     
    MAY03LT likes this.

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