94 corolla brakes lock up

[mr_mahoney]

1994 corolla brakes start dragging then lock up. Wait a few hours then drive off to repeat issue.

- rt front caliper was replaced
- rt front brake hose was replaced
- rt front wheel bearing was replaced
(issue remained)

thouroughly cleans guide pins on rt side

- cleaned master cylinder and replaced fluid for fresh new (master cyl and front lines)

Issue remains

Questions:
- how do I rule out the proportioning vavle?
- how do i rule out the power brake booster?

I would love to know what others who had brakes locking up on a Toyota found as a solution.

Thanks for anyone willing to share. Car has been down for 3 months with this issue.

The only thing that seems broke is the master cylinder resivoir cap. It is so spongy that it will not alway stay in place and the little plastic piece keeps dropping out. (is it a check valve of sorts?)

[Bitter]

brake hose? is the other side working too?

[ganda1f]

Originally Posted by mr_mahoney

- how do i rule out the power brake booster?

When the brakes do start dragging/lock up, I would stop, shut off the engine and press the brake pedal a few times to deplete the vacuum in the booster. Then see if the brakes release. With the vacuum depleted I can't see how the booster could apply any force on the brakes.

[mr_mahoney]

I drove the car yesterday for about 15 minutes and the car kept getting slower and slower. I stopped and felt most heat coming from the front right wheel (left side was not putting out heat).
I jacked up the right side of the car and confirmed the wheel was locked up.
- with the engine running, I unhooked the vacuum line to the booster (and plugged the hose so the engine would not rev) = wheel still locked up

- I cracked open the bleeder on the front right caliper to releive pressure and = wheel would turn free

Conclusion - the fluid would not return to the master cylinder, keeping the caliper extended.

- I took off the proportioning valve and cleaned it with brake cleaner and compressed air. = valve is clean (funny thing I learned - the brake system is divided into left and right, unlike most US cars have front and rear systems. So the front port on the master cylinder supplies juice to the left side and the back port supplies juice to the right side.

- The front left side does not go to the proportioning valve, it just goes to a t and then to the front left wheel.

Since the proportioning valve is clean, I am now going to put on a new master cylinder. I will keep you posted.

[ganda1f]

Originally Posted by mr_mahoney

- with the engine running, I unhooked the vacuum line to the booster (and plugged the hose so the engine would not rev) = wheel still locked up

Did you also pump the brake pedal a couple of times? Just unhooking the vacuum line will not deplete the vacuum in the booster. The booster has a one-way valve to keep the vacuum whenever the intake is not under vacuum.
The brake circuits are diagonal, right-front and left-rear are on one circuit, left-front and right-rear on another.

Come to think of it, another reason to rule out the booster is the fact that only one wheel is locking up. I cannot imagine how the booster could only cause *one* wheel to drag and not all.

Is your left-rear wheel OK? Perhaps there is some blockage in the line to right-front?

[mr_mahoney]

Good thoughts. I will test again. Any other ideas to try? What other parts could it be?

The right front has had two new calipers on it, a new rubber brake hose, and a new wheel bearing and the wheel still locks up. (caliper won't release)

[Bitter]

new slides?

[mr_mahoney]

Yes, new slides.

The last time it locked up, I cracked the bleeder and the caliper retracted. Something is not letting the fluid back to the reservoir.

[speedy25]

Time for some brake system schooling. I have encountered this problem many times and I'm surprised so few know about the compensating port. Ever notice when you do some bleeding or other work and see a a squirt or bubbles coming up into the reservoir? This is the port WORKING. The port is uncovered when the brakes are "off." This is to allow brake fluid to return to the reservoir. Yes brake fluid DOES expand when hot just like almost everything.

The port can be clogged by debris, or the brake pedal can be misadjusted so the piston does not return to its home position. Both will cause brake lockup WHEN HOT.

Now you know what to look for.

-SP

[mr_mahoney]

compensating port - is this the tiny hole or the larger hole at the place where the reservoir connects? ( I did clean those holes very well when I had the master cylinder apart)

pedal returning to home position (thus letting the piston inside return home. - one article stated to place a small amount of putty or clay where the rod pushes in on the outside of the piston. Bolt it up and remove again to make sure little bit of clay remained between rod and piston. (if it was pushed clear thru, then adjust accordingly.

So in short:
- clean compensation ports
- adjust pedal/and or/ rod so piston returns to home position

"brake schooling" - I admit I need all the help I can get. I am so thankful you guys are taking time to share your experience!

[mr_mahoney]

Very nice article explaining the functions of a master cylinder:
http://www.autoshop101.com/forms/brake02.pdf

Good illustration on compensation port as well

[speedy25]

Originally Posted by mr_mahoney

"brake schooling" - I admit I need all the help I can get. I am so thankful you guys are taking time to share your experience!

Work smart!

Your brakes are the only thing between you and an accident!

You posted the right kind of reply so you should be able to make repairs properly.

-SP

[speedy25]

I'll also add another item that I had not heard of until recently.

For some reason the compounding/construction of modern brake hoses have caused a new problem that also manifests itself as brake drag. The hose comes apart internally and gets blocked. Depending on how it degrades it can block the flow of fluid in one direction or both. Keep this in mind when you are working on your cars that have funky brake problems.

-SP

[Bitter]

My next guess up the line was going to be a bad master.

[mr_mahoney]

Thank you JESUS !!! The brake system is finally fixed.

A new master cylinder fixed the issue.

Thanks to many prayers, the support of this forum, and the Good Lord above, I got the brake issue resolved last night.

- I first put the system back together and blew into the right front metal line, hoping to get some bubbles back into the master cyl. - NOTHING
- I then unhooked the back metal line from the master cyl. and I then could blow through it (much fluid came out)
- I then hooked the metal line back up and could not blow into it. - I suspected the compensation port was being blocked (since I cleaned it all out the other day)
- Next, I bled it one more time. (althought the master cylinder never did quite act right)
- I simulated a drive while up on jacks. (left car in PARK), but I let engine run for about five minutes and pumped the brakes 20 times or so
- checked right front wheel and it was locked up tight.

I put on the new master cyl, bench bled, hooked up, bled again.
.....and simulated my test again - wheel always was free after braking !
YES !!!!

Drove it around the neighborhood for about 10 minutes and it ran great. Popped it into nuetral a few times and car coasted free.

Thanks to all the guys who took time to share their knowledge with me. This car belongs to a family with two children and they had it down for over 3 months. They were running out of money to put into to it and the "mechanics" that worked on it before me did not do a good job.

I talked to God alot during this process and asked for help. He gave me the patience and piece of mind to stick to it and keep calm while not throwing any wrenches. Not to mention, weather at night here in Indiana has not been pleasant.
I encourage any mechanic who is frustrated to no end, to stop and ask God for help. He has always given me the ablility to get the job done when I asked for His help. You guys are part of those answered prayers. Again, I say "Thank You".
If you want to read my other mechanical moments of God helping, check out my blog at: http://www.gearheadgospel.com/

May God bless you in times of Repair and Despair
-Shawn