Odd issue with brakes.

[bennieRohde]

So my buddies got a 2000 S10 blazer (Trailblazer trim) I've been helping him go through.
We bled the brakes and the pads/rotors all seem fine. The calipers were replaced by previous owner with aftermarket sport type calipers that all seem to work as far as we can tell.
The issue - when braking, generally while moving slow like through a parking lot. Sometimes the brake pedal just isn't there. You can go to the floor and get nothing. Can't find any leaks in the reservoir or master. (We also replaced the master because the old one was raggedy. It may have worked but was sad. or anything that says "I'm the problem" so far. Couldn't find an issue with the booster but I'm not familiar with them and am not 100% sure what all to look for.
Highway driving and hard braking seem fine. Rarely ever lose the pedal. It works as normal. Only when going slow.
Is this some kind of vacuum issue from the booster or something ?
Thanks.

Mod edit: Changed the model and moved the thread to "Other GMT"

 

[Redbeard]

Sounds like the master cylinder didn't get bench bled or it has gone bad. With the master cylinder going bad one doesn't usually have a leak, the brake fluid bypasses the orings and stays in the system. Hence no visable leaking. Was this same problem occuring before changing out the master cylinder? And what brand master cylinder did you change to? Many many parts on this platform do not like aftermarket brands installed on them. This does not sound like a booster going bad. When a booster goes bad one just has to STAND on the brake pedal because no extra assistance is giving while braking. Until this braking issue is resolved I would keep the trailblazer parked.

 

[mrrsm]

This Video is a Great Primer on How to Bench Bleed the Master Cylinder and Purge Hidden Air Pockets prior to its installation:

How to Pressure Bleed ANY GM or GMC Brake System with FULL Step By Steps:

How to Perform a Pressurized Brake Bleed on ANY GM Vehicle

I thought it would be a good idea to break out this “Pressurized Brake Bleeding Procedure” from the other Brake Repair Work involved with my 2000 Chevrolet Silverado 1500 Long Bed Truck. I think this Procedure stands out from all others because it is THE Fastest, THE Easiest and THE Most...

gmtnation.com

The last consideration is the necessity to use a Tech 2 or other High End Scan Tool to Purge-Bleed the EBCM-ABS System:



Dr, Shock takes us through all of these Step By Steps:

 

[Chickenhawk]

I am guessing your friend has a 2002 Trailblazer, not a 2000. Plus, I can't think of any aftermarket "sport-type" brake calipers for our platforms. Just the expression "aftermarket sport-type calipers" scares me. It makes me think of all those cold-air intakes and magnetic fuel line enhancers that do nothing except cost money. Can you provide more details on these calipers?

By the way, I help test police cars on road race tracks for part of what I laughingly refer to as "a living" plus I have had my Trailblazer on the road race track (with a couple of suspension tweaks suggested to me by GM Police Division) and have never seen or heard of sport-type calipers, unless you are talking about those regular calipers that are powder-coated with red paint. (The paint adds at least 5 mph to the top speed of course. Everyone knows that. LOL.)

 

[TJBaker57]

So my buddies got a 2000 trailblazer I've been helping him go through.

So, since there is no "2000 Trailblazer", the GMT360/370 Trailblazer platforms' 1st year was 2002, is it possible this is a 2000 "Blazer" with the "Trailblazer" trim package?

 

[TollKeeper]

Unless he meant a 2000 Chevy Blazer...?

The only S-Series that got the GMT360 nameplate is the GMC Envoy.

 

[mrrsm]

Any Member who lives in the shadow and under the Constant Threat of a Pyroclastic Mud Flow coming from a Volcanic Eruption of Mount Rainier ...gets a Full, Free Pass for this "Year 2000" Faux Pas from me... realizing the Sheer Irony of the name of that Mountain being one and the same to the one from the GMT360 Platform as... The Buick Rainier.

Volcanic Hazards at Mount Rainier | U.S. Geological Survey

Because of its elevation (4,392 m), relief, hydrothermal alteration, icecap, glacier-fed radial valleys, and proximity to encroaching suburbs of the Seattle-Tacoma metropolis, Mount Rainier is the most threatening volcano in the Cascades. Its next eruption could produce volcanic ash, lava flows...

www.usgs.gov

 

[TollKeeper]

@mrrsm - Wrong thread?

 

[mrrsm]

Nope...

 

[TJBaker57]

Unless he meant a 2000 Chevy Blazer...?

I was thinking of this, which even has "TrailBlazer" written on the side, but is not one of "our" Trailblazers.



The image is from....

Chevrolet S-10 Blazer - Wikipedia

en.m.wikipedia.org

 

[TollKeeper]

But the "TrailBlazer" on those is just an appearance package... 1999-2001 for the Blazer and 1998-2000 for the Jimmy.

Kinda like the Trailblazer NorthFace Edition.

 

[TJBaker57]

But the "TrailBlazer" on those is just an appearance package...

Yes, and it might be confusing to someone who does not own the vehicle but is simply helping the owner,,,, like the opening post of this thread stated.

And it at least appears there are upgraded aftermarket brake components for the 2000 Blazer.

 

[bennieRohde]

Sorry for such a late reply fellas. I'll send a photo soon. It is a 2000 Chevy blazer. Not trailblazer.

I'll also get a name of the brand of caliper. They are bright orange ish red. Heavy duty looking. Looks like they came that color new not painted over.

I am guessing your friend has a 2002 Trailblazer, not a 2000. Plus, I can't think of any aftermarket "sport-type" brake calipers for our platforms. Just the expression "aftermarket sport-type calipers" scares me. It makes me think of all those cold-air intakes and magnetic fuel line enhancers that do nothing except cost money. Can you provide more details on these calipers?

By the way, I help test police cars on road race tracks for part of what I laughingly refer to as "a living" plus I have had my Trailblazer on the road race track (with a couple of suspension tweaks suggested to me by GM Police Division) and have never seen or heard of sport-type calipers, unless you are talking about those regular calipers that are powder-coated with red paint. (The paint adds at least 5 mph to the top speed of course. Everyone knows that. LOL.)

Haha this is pretty funny. And maybe they are that kind of brake caliper. I was taking a guess because the previous owner also put a cold air intake, exhaust, z28 rims and drag radials on this thing man. Hahah. -_-

Sounds like the master cylinder didn't get bench bled or it has gone bad. With the master cylinder going bad one doesn't usually have a leak, the brake fluid bypasses the orings and stays in the system. Hence no visable leaking. Was this same problem occuring before changing out the master cylinder? And what brand master cylinder did you change to? Many many parts on this platform do not like aftermarket brands installed on them. This does not sound like a booster going bad. When a booster goes bad one just has to STAND on the brake pedal because no extra assistance is giving while braking. Until this braking issue is resolved I would keep the trailblazer parked.

Yes it has the issue before it was changed. And they got bled pretty good but we plan on doing it hopefully this weekend again and seeing if it will help. And what does the term bench bled mean?

I'll have to check on the brand. Believe it was literally something like brake masters. Something basic like that.

He's actually driving it every day. I told him to park it ! He is stubborn. I'm trying to finish helping him put his suspension on his jeep too so he can have that ready for winter. And maybe drive that till we solve the brake issue.

Mod edit: Merged posts to clean up the thread. Please try and respond in a single post.

 

[Mooseman]

Moved the thread and edited the model in the first post to clarify the vehicle.

I would try to do a bleed of the ABS using either a capable scanner (preferred) or, going on a dirt road and stomping on the brake pedal to activate the ABS. I would then do another bleed at each wheel. I would also do a bleed of the master cylinder FIRST, which can be done with it mounted and using the brake pedal, same as the bench bleed.

 

[bennieRohde]

Okay. I'll do that this weekend and go from there.