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Brakes locking up/holding when driving?

Tiny
JUSTIN0604
  • MEMBER
  • 2008 MAZDA 3
  • 2.3L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 135,000 MILES
The vehicle had a spongy brake symptom so diagnosed a bad master cylinder. Did 4 wheel bleed twice to make sure good fluid and no contaminants. Did ABS bleed then took for test drive. Within less than 2 miles and braking twice the brakes started to hang to the point brakes started smoking and had to keep RPMs up to get back to shop. Back in the air and found release of pressure by opening bleeders at wheel allowed wheels to spin freely. Did another 2 full system bleed and ABS bleed again tested vehicle on stands in shop several attempts worked great no wheels on vehicle. Put wheels on and got back on the ground took for drive again. Also, released pressure this time at master cylinder lines. Fluid immediately came out as if you were bleeding it. Then took for test drive. Within 2 miles brakes locking up. All 4 are doing this not just front or rear. Got it back to the shop and opened lines only at master cylinder and again fluid came back out like bleeding it. I would also add that when we first inspected the spongy brake issue you could see fluid had been leaking between the master cylinder and brake booster. The replacement master was bench bled before putting on car. It is an Oreilly's master cylinder. Just want to know if the booster could have got fluid behind the diaphragm to cause this problem or faulty new master cylinder? Need help ASAP to get back to the customer by tomorrow morning please and thank you!
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Thursday, May 25th, 2023 AT 8:15 AM

11 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,959 POSTS
Yes, the booster is most likely the problem, here is a guide to help and instructions in the images below to help you change it out:

https://www.2carpros.com/articles/a-comprehensive-guide-to-fixing-automotive-brakes-locking-up

There are two primary components you might want to focus on: the master cylinder and the brake booster.

Faulty Master Cylinder: Since you recently replaced the master cylinder and the problem arose, it's possible the new master cylinder could be faulty. Though not common, it does happen. In your case, since the brakes are locking up, the issue could be with the master cylinder not properly releasing pressure when the brake pedal is released. It could also be an issue with incorrect installation or an incorrect part, but given your thorough approach, which seems less likely.

Brake Booster: If brake fluid has gotten into the brake booster from the failing master cylinder, it could cause problems with the vacuum assist, resulting in excessive brake pressure and leading to the symptoms you're describing. If you suspect this is the case, the booster will need to be replaced, as it's very difficult to effectively clean brake fluid out of a booster.

Check out the images (below). Please let us know if you need anything else to get the problem fixed.
Images (Click to make bigger)
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Thursday, May 25th, 2023 AT 4:44 PM
Tiny
JUSTIN0604
  • MEMBER
  • 6 POSTS
Thank you, Ken L! As an update, we did another master cylinder following the exact same technique as we originally described. Got even more in depth and more thorough just to be sure we missed nothing. I test drove it approx 3-4 miles no problems at all. Customer picked up this morning and drove approx 8 miles only to have the brakes lock up again. It is being towed back to the shop today but not sure what else to do. I will try the booster to be sure that is not the issue. Is there anything else I may be missing? Something with the ABS valve that would cause all 4 to fail at the same time? Something with ABS at all? I have never in my 20+ years had this type of issue and am truly beside myself as I take great pride in doing brakes as my number one goal to safety of vehicle. Thanks for any more input!
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Friday, May 26th, 2023 AT 10:44 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,262 POSTS
Hi,

I noticed we haven't been in touch for a couple of days. Have you been able to make any progress? We are interested in knowing.

Let us know.

Take care,

Joe
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Sunday, May 28th, 2023 AT 7:52 PM
Tiny
JUSTIN0604
  • MEMBER
  • 6 POSTS
I responded to Ken L and didn't get an answer that I saw.
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Sunday, May 28th, 2023 AT 7:54 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,262 POSTS
Hi,

Sorry about that. I will forward this to him. On the other hand, I read through your reply to him. Have you replaced the booster or inspected it for brake fluid getting into it?

Let me know.

Joe
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Sunday, May 28th, 2023 AT 8:46 PM
Tiny
JUSTIN0604
  • MEMBER
  • 6 POSTS
I have the booster ordered and should have it Tuesday when we get back in action. Thanks for checking in. There was fluid leaking out between the m/c and the booster before I replaced the original m/c. The booster is last and hopefully will fix this issue.
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Sunday, May 28th, 2023 AT 8:58 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,262 POSTS
Hi,

Sounds like that could be the issue. If you have a chance, let us know if that resolves the issue.

Take care and thanks for the update.

Joe
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Monday, May 29th, 2023 AT 12:19 AM
Tiny
JUSTIN0604
  • MEMBER
  • 6 POSTS
We replaced the booster today. This issue is better but not completely resolved. The brakes seem to build pressure as you drive but only so much then they stay there. It does still have them dragging but not as bad as before. It seems that pedal travel would be the issue, but I do not see any way to adjust the pedal, booster or M/C so not quite sure how I could adjust pedal travel or rod travel? Any ideas? Thanks!
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Tuesday, May 30th, 2023 AT 3:34 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,262 POSTS
There really isn't an adjustment. I attached the directions for the pedal inspection below for you. That is the only thing I have in my manual as far as inspect/adjust.

If the brakes are building pressure when driving, it sounds like you could have a caliper hanging up. When you get out of the vehicle, do you feel excessive heat from any of the wheels? Brake fluid will expand when it gets hot and that can cause the caliper to slowly engage. Do me a favor. Do this.

After driving and having the issue, lift one wheel at a time and see if there is excessive resistance. If there is, open the brake caliper bleeder to see if the caliper releases.

Try that and let me know.

Joe
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Wednesday, May 31st, 2023 AT 6:46 PM
Tiny
JUSTIN0604
  • MEMBER
  • 6 POSTS
Thank you, Joe! I have tried that and always all 4 are dragging/locking up. I have also loosened both nuts on m/c to booster which does release the pressure and allows the vehicle, all 4 wheels to free up. I believe what is going on at this point is the travel distance between the m/c and the booster on these aftermarket parts is not correct. I plan to pull them back off and replace them with Mazda parts as there are no other issues that I can find. When bleeding at all four corners I have great flow, no air, and release is good with all 4 wheels when applying and releasing the brake pedal before you start and move the vehicle. It only seems now to get to a certain point of dragging the brakes, again all 4, but not locking them up. I did get a new m/c seal with the new booster I put on so I put it on as well as the original seal that came on the m/c which spaced it just a touch from the booster but still sealed it off so no leakage of vacuum or pressure from the booster which is why I believe the brakes are not locking up as before and only seriously dragging. I have read more forums and found that these replacement m/c units from parts stores in particular do not have a good track record in especially with Mazda vehicles. I will continue some further tests while waiting on the dealer parts and will let you know what the results are when I find out. Unless you have other ideas? Thanks again for everyone's help!
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Wednesday, May 31st, 2023 AT 7:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,262 POSTS
Hi,

If you can loosen the MC and the brakes release, it absolutely sounds like you found the problem. Check to make sure something like the brake lamp switch isn't preventing the pedal from fully returning.

Let me know what you find. I'm interested in knowing.

Take care,

joe
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Wednesday, May 31st, 2023 AT 10:10 PM

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