SOLVED! replaced front caliper, now pedal goes to floor

niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
I replaced my front passenger side brake caliper as my old one was sticking and was dragging noticeably. after replacing, i had my wife help me bleed the caliper. I have bled the brakes on ALOT of vehicles over the years, so i know what i'm doing. The problem is that now after bleeding them, I have an extremely soft pedal. So soft in fact that you can push it all the way to the floor. You can pump it fast and get some pedal built up but if you sit for a few seconds, then the first push goes all the way to the floor. Later this week, i will try bleeding the other 3 wheels in hopes that fixes it. Is there any way that this could have caused the master cylinder to go bad? I am at a loss here. A month ago I replaced the drivers front caliper for dragging and I had no issues bleeding it and the pedal was nice and firm afterwards. And while the fluid did get a little low during bleeding, it didn't run dry before i added more.
 

gmcman

Member
Dec 12, 2011
4,656
Just some tips and this is irrelevant to your knowledge, I'm just going to say it .

Are you sure the master cylinder is full?

Did you use a new crush washer?

Can you pump up the brakes with the engine off and eventually get a firm pedal?

Did you bleed the brakes with the engine off?
 

niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
yes, the master cylinder is full. i used new crush washers. if i pump them with the engine off, then yes it eventually gets firm but if i let it sit a few seconds or so then it is soft again. yes i bled them with the engine off. but now if i start it then they easily go clear to the floor unless i pump them fast a few times but then after sitting a few seconds it will go to the floor again.
 

Mooseman

Moderator
Dec 4, 2011
25,184
Ottawa, ON
Did the master cylinder drain out while you were swapping the caliper? You might have to bleed all four wheels. Another possibility is air got into the ABS system somehow. Usually that requires a high end scanner or Tech 2 to activate the ABS motors however some have had success with just going on a dirt road and slamming the brakes and bleeding the brakes again.
 
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niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
I'm pretty sure the master cylinder didn't go empty but i'll first bleed all 4 wheels and see if that fixes it. I can't activate the abs motors because the abs light is on so hopefully bleeding all 4 wheels really well will fix it. i just didnt know what chance there could be that this caused the master cylinder to go bad. On the plus side, i discovered it has newer clean looking brake fluid in it. I hate these stupid aluminum calipers!
 

gmcman

Member
Dec 12, 2011
4,656
Something else comes to mind in regards to the master cylinder. When you first start bleeding, you want to pump up the brakes with about half pedal travel until the pedal feels firm. You don't want to forcefully press the pedal until it stops against the end of it's travel, this could possibly damage the seals in the master cylinder.

Perhaps there's a chance this could have happened?

Last time I had spongy brakes with nobody around to help, I cracked all 4 bleeders and ran a clear hose into 4 containers and let them gravity bleed for awhile. Ran most of the old fluid out then had someone help with bleeding all 4 wheels.

With a functioning ABS, and all 4 wheels in the air, I was able to cycle the ABS by lightly clamping vice grips on one front brake hose, then using 4WD ran it up to about 20 MPH then applied the brakes.

How does the brakes feel when you try to slowly move the vehicle? Does it seem normal? The brake pedal will feel different with the engine running.
 
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mrrsm

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Oct 22, 2015
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Your Mechanical Acumen is NOT being challenged here... But In Post #3, you provide the Best Evidence of what has gone wrong if you "Filled The Master Cylinder"' but perhaps Did NOT Bench Bleed it prior to installing it.

This First Step is the ONLY Method that will solve this problem based upon the symptoms you have described. Please remember this ... ALL Master Cylinders require Bench Bleeding in this manner prior to any Installation:

Proper MC Bench Bleeding Procedures:


The Second step requires Regular Brake Line Bleeding Techniques by following the Bleed Order of RR, LR, RF LF in the Brake Bleeding Sequence and Frequently Topping Off The Master Cylinder prior to moving from One Wheel to Another in order to prevent the MC from accidentally scavenging in Air.

CHRISFIX is a GMT Nation Member ...and THIS is the Best How-To on Brake Bleeding EVER:


PS...

Please tell your Spouse to "Hold the Brake Pedal Down" for the entire time that that you have Opened Up the Bleeder Fittings. Then yell to her when the Fitting is CLOSED to lift her foot and allow the MC to draw in Fresh Fluid and proceed with pumping the Pedal hard each time afterwards.
 
Last edited:

JerryIrons

Member
Dec 20, 2011
434
I replaced my front passenger side brake caliper as my old one was sticking and was dragging noticeably. after replacing, i had my wife help me bleed the caliper. I have bled the brakes on ALOT of vehicles over the years, so i know what i'm doing. The problem is that now after bleeding them, I have an extremely soft pedal. So soft in fact that you can push it all the way to the floor. You can pump it fast and get some pedal built up but if you sit for a few seconds, then the first push goes all the way to the floor. Later this week, i will try bleeding the other 3 wheels in hopes that fixes it. Is there any way that this could have caused the master cylinder to go bad? I am at a loss here. A month ago I replaced the drivers front caliper for dragging and I had no issues bleeding it and the pedal was nice and firm afterwards. And while the fluid did get a little low during bleeding, it didn't run dry before i added more.

You are getting a soft pedal with the engine off right? Couple of things to try:
- clamp down the rubber hose on the caliper you just swapped out, and then try pumping up the brakes. Be careful you don't damage the rubber hose. You can even try this on all calipers one by one to see if you have a problematic caliper.
- bleed all 4 wheels, usually air in the system causes this but not always
- you can put caps on the master cylinder where your 2 brake lines connect, maybe one at a time, to test how your master cylinder is working. If you do this, you will admit air into the system, before the ABS unit, so then you need to bleed all 4 wheels, engage ABS on gravel road several times, then re-bleed all 4 wheels.

It is possible to blow the seals on an old master cylinder with an aggressive bleeder helper who bottoms out the pedal, but in all honesty has never happened to me, and my bleeder helper is a teenage son.
 

niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
I didnt press the pedal any harder than usual when i've bled brakes on vehicles before but i guess it's possible that the master cylinder couldnt handle it. I will try bleeding the other 3 wheels first and if it still doesnt work then i suppose i'll replace the master cylinder. Is the dorman or brand that napa and oreilly's carries good enough for this or should i splurge and get the acdelco one?
 

niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
another thing to point out. after i bled the new caliper and was able to pump up the pedal then i started it but noticed immediately that the pedal went clear to the floor. so while it was running i rapidly pumped it fairly hard Alot of times trying to figure out the pedal. once i got some pedal built up more firmly then i was pressing fairly hard to see if i could get it back to the floor. when i couldnt, then i'd pause for 5-10 seconds and try again and it would immediately go to the floor until pumped up a few times. I have never been quite this vigorous with a brake pedal before, so does this sound like i may have blew out the master cylinder? i priced the store brands vs acdelco on amazon and they can be had for the same price, so obviously i'll go with the acdelco even though i'll have to wait for it. I will still spend the time to bleed the other 3 wheels with the hope that gets it working...
 

niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
also, i could try to activate the abs by hitting the brakes on loose gravel or dirt but with the abs light on constantly, i'm afraid the system wont activate...
 

Mooseman

Moderator
Dec 4, 2011
25,184
Ottawa, ON
Sounds more to me like you still have air in the system. It's the classic symptom of air in it. I'd do the pinch off each line test to see if air is trapped in a particular caliper starting with the new one.

Just thinking out loud here. What if the new caliper pistons are retracting too much when you let off the pedal? When you pump the pedal fast, it doesn't have time to retract so it firms up. The pinch off test would isolate that caliper.
 

budwich

Member
Jun 16, 2013
2,019
kanata
check the caliper / brake disc alignment to ensure that disc seated correctly against the caliper AND the rotor.
 

niceguypmp3

Original poster
Member
Oct 31, 2020
60
iowa
ok, an update! it's fixed!!! i decided to start bleeding the other 3 wheels and started with the drivers front caliper that i had replaced a few weeks ago. right away there was ALOT of air in it on the first push of the pedal. we tried a few more times but no more air. got in it and now a nice firm pedal. started it and now it's a nice pedal like it should be. Dont' ask me how air got in the drivers front caliper when it was the passenger front caliper that i changed yesterday lol. Thanks for the help everyone! On the plus side, it should get better mileage now. Even with that caliper dragging so badly that i could barely turn the tire by hand, i still got 20 mpg on saturday with a 120 mile trip. Now i can see what my mileage jumps up to because that caliper has been dragging ever since i got it. i've only put about 300 miles on it since buying it.
 

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