'92 brakes stick when hot
03-26-2019, 04:13 AM
#1
Instructor
Thread Starter
'92 brakes stick when hot
I've searched and read all the threads here. I'd like to troubleshoot this problem and not just throw parts at it. It's not the calipers. Fronts seem more firmly locked than rears. If I crack a bleeder that wheel releases immediately. My next step is to get it locked up and crack the hose at the end away from the caliper.
While the fronts are locked and off the ground I took the master cylinder loose and they stayed locked so this has nothing to do with booster plunger length.
When they are sticking the brake pedal is very firm with less travel.
With the front off the ground and they are hot and sticking, I can turn the tires more and more easily as everything cools down and eventually they get completely free.
//////////////////////////////////////////////////////////////////////////////////////////////////////
My next step is to get them hot and sticking then crack open the hose end away from the caliper. My questions are do brake hoses swell up internally when hot and keep the fluid from traveling back out of the caliper? and also can hot internally swollen hoses make the brake pedal firm.
I've read all the threads and many people have changed calipers, the master cylinder, flex hoses, etc. and say they still have the problem but never return to tell if they ever solved it.
If I crack open the end away from the caliper and it releases then that hose is not the problem. Where do I go next? Loosen the hard line at the master? If fluid spurts out there and the brakes release then the master is the problem...right?
While the fronts are locked and off the ground I took the master cylinder loose and they stayed locked so this has nothing to do with booster plunger length.
When they are sticking the brake pedal is very firm with less travel.
With the front off the ground and they are hot and sticking, I can turn the tires more and more easily as everything cools down and eventually they get completely free.
//////////////////////////////////////////////////////////////////////////////////////////////////////
My next step is to get them hot and sticking then crack open the hose end away from the caliper. My questions are do brake hoses swell up internally when hot and keep the fluid from traveling back out of the caliper? and also can hot internally swollen hoses make the brake pedal firm.
I've read all the threads and many people have changed calipers, the master cylinder, flex hoses, etc. and say they still have the problem but never return to tell if they ever solved it.
If I crack open the end away from the caliper and it releases then that hose is not the problem. Where do I go next? Loosen the hard line at the master? If fluid spurts out there and the brakes release then the master is the problem...right?
The following users liked this post:
RUSHTK (04-04-2022)
03-26-2019, 09:01 AM
#2
If I read your post correctly, everything you said is correct. The rubber hoses do fail internally and would allow the pressure to release over time. I suspect they are the problem, this is a more common problem for the symptoms you described than a master problem.
03-26-2019, 10:46 AM
#3
Instructor
Thread Starter
Got more info. I drove/heated up the brakes just now and then jacked up the front. Both fronts locked up pretty tight but I can turn them...barely. I loosened the driver side rubber brake hose at the end away from the caliper and that wheel became instantly free. I then checked the passenger side front and it was free now as well.
So, to add a symptom, I can release pressure at the caliper/brake hose end away from caliper on either front wheel and it instantly frees up both fronts.
I have not checked the rears thoroughly.
//////////////////////////////////////////////////////
Is there something between the master cylinder and calipers? I read something about a anti lock brake module???
What's my next check? Release pressure to the front hard brake line coming out of the master? If that frees the wheels then it must be the master, right? And if they stay locked then it has to be whatever is between the master and the calipers...right?
////////////////////////////////////////////////////////////
More info: I just loosened the larger/forward hard brake line coming out of the master cylinder and the front wheels stayed locked up so that eliminates the master.
So, to add a symptom, I can release pressure at the caliper/brake hose end away from caliper on either front wheel and it instantly frees up both fronts.
I have not checked the rears thoroughly.
//////////////////////////////////////////////////////
Is there something between the master cylinder and calipers? I read something about a anti lock brake module???
What's my next check? Release pressure to the front hard brake line coming out of the master? If that frees the wheels then it must be the master, right? And if they stay locked then it has to be whatever is between the master and the calipers...right?
////////////////////////////////////////////////////////////
More info: I just loosened the larger/forward hard brake line coming out of the master cylinder and the front wheels stayed locked up so that eliminates the master.
Last edited by 2airtime2; 03-26-2019 at 11:14 AM.
03-26-2019, 02:42 PM
#5
Instructor
Thread Starter
That's what I'm thinking because I just did this: 1st I unplugged the connector coming out of the sidewall on the drivers side feeding it. 5 lights came on related to abs and slip. No change. I cracked open the RF hard line on the ABS module and both front tires freed up. I have also checked the rears, they are not sticking. Then I unplugged the plug on top of the controller and test drove, no change.
So, with no power going to the controller or the module the fronts still lock up after driving a few mins. The brake fluid must be moving a solenoid, but...since now I believe the problem is behind the drivers seat that doesn't explain why it's temperature sensitive. Could that compartment be heating up due to close proximity to the exhaust pipes? Maybe I need to leave that hatch open and have a fan blowing on it for the next test drive.
So, with no power going to the controller or the module the fronts still lock up after driving a few mins. The brake fluid must be moving a solenoid, but...since now I believe the problem is behind the drivers seat that doesn't explain why it's temperature sensitive. Could that compartment be heating up due to close proximity to the exhaust pipes? Maybe I need to leave that hatch open and have a fan blowing on it for the next test drive.
03-26-2019, 03:34 PM
#6
Instructor
Thread Starter
I found the problem!! It's the master cylinder. I assumed and it cost me some time but luckily no money. When I released the pressure at the master and it didn't release the wheels I moved on. Problem is I assumed the larger nut (of the 2 for the steel lines) went to the front...and it might...but, when I crack open the smaller one it immediately releases the front wheels. On mine, the larger nut is forward and the smaller nut is rearward. At this point I don't care which is which, I just know cracking loose the small one releases my front brakes.
I'll report back after I replace the master cylinder.
I'll report back after I replace the master cylinder.
The following users liked this post:
don hall (03-27-2019)
03-26-2019, 05:34 PM
#7
Safety Car
Before you replace that m/c, check the adjustment of the pushrod between the booster and the m/c. Your exact situation will be true if that pushrod is too long.
There is a vent port in the m/c that should be open when your foot is off the brake pedal. You should be able to see that port in the bottom of your reservoir, closest to the booster (if your fluid is clean). This vent port is supposed to relieve the pressure in your brake lines as the fluid expands due to heating during normal operation.
First, be sure nothing is blocking the return of your brake pedal. When you first move the brake pedal, there should be a small "spurt" of fluid from that port, that will cause a visible disturbance in the fluid as the piston moves to cover this port. You can do this test with the engine off, standing beside the car, and watching the surface of the fluid as you step on the brake pedal.
If no "spurt", your pushrod is too long. Remove the m/c from the booster, without removing the hydraulic lines from the m/c. Gently pull the pushrod out of the booster just far enough to grab the shaft. Turn the adjusting nut on the end of the shaft to reduce its length.
Please report back.
There is a vent port in the m/c that should be open when your foot is off the brake pedal. You should be able to see that port in the bottom of your reservoir, closest to the booster (if your fluid is clean). This vent port is supposed to relieve the pressure in your brake lines as the fluid expands due to heating during normal operation.
First, be sure nothing is blocking the return of your brake pedal. When you first move the brake pedal, there should be a small "spurt" of fluid from that port, that will cause a visible disturbance in the fluid as the piston moves to cover this port. You can do this test with the engine off, standing beside the car, and watching the surface of the fluid as you step on the brake pedal.
If no "spurt", your pushrod is too long. Remove the m/c from the booster, without removing the hydraulic lines from the m/c. Gently pull the pushrod out of the booster just far enough to grab the shaft. Turn the adjusting nut on the end of the shaft to reduce its length.
Please report back.
The following 2 users liked this post by Hot Rod Roy:
don hall (03-27-2019),
krackenvette (08-14-2019)
03-26-2019, 07:45 PM
#8
Instructor
Thread Starter
Before you replace that m/c, check the adjustment of the pushrod between the booster and the m/c. Your exact situation will be true if that pushrod is too long.
There is a vent port in the m/c that should be open when your foot is off the brake pedal. You should be able to see that port in the bottom of your reservoir, closest to the booster (if your fluid is clean). This vent port is supposed to relieve the pressure in your brake lines as the fluid expands due to heating during normal operation.
First, be sure nothing is blocking the return of your brake pedal. When you first move the brake pedal, there should be a small "spurt" of fluid from that port, that will cause a visible disturbance in the fluid as the piston moves to cover this port. You can do this test with the engine off, standing beside the car, and watching the surface of the fluid as you step on the brake pedal.
If no "spurt", your pushrod is too long. Remove the m/c from the booster, without removing the hydraulic lines from the m/c. Gently pull the pushrod out of the booster just far enough to grab the shaft. Turn the adjusting nut on the end of the shaft to reduce its length.
Please report back.
There is a vent port in the m/c that should be open when your foot is off the brake pedal. You should be able to see that port in the bottom of your reservoir, closest to the booster (if your fluid is clean). This vent port is supposed to relieve the pressure in your brake lines as the fluid expands due to heating during normal operation.
First, be sure nothing is blocking the return of your brake pedal. When you first move the brake pedal, there should be a small "spurt" of fluid from that port, that will cause a visible disturbance in the fluid as the piston moves to cover this port. You can do this test with the engine off, standing beside the car, and watching the surface of the fluid as you step on the brake pedal.
If no "spurt", your pushrod is too long. Remove the m/c from the booster, without removing the hydraulic lines from the m/c. Gently pull the pushrod out of the booster just far enough to grab the shaft. Turn the adjusting nut on the end of the shaft to reduce its length.
Please report back.
04-21-2019, 07:11 AM
#9
Instructor
Thread Starter
Well, good and bad. The master cylinder fixed my brake sticking when hot problem but now my brake warning (dash light) is on all the time. Also the service asr and service abs lights are on.
Another symptom with the old mc with sticking brakes was the pedal intermittently felt firmer or normal. With the new mc it feels normal all the time.
Another symptom with the old mc with sticking brakes was the pedal intermittently felt firmer or normal. With the new mc it feels normal all the time.
05-21-2019, 08:39 PM
#10
Instructor
Thread Starter
I've finally been able to drive the car a few times...sportily, and no more sticking brakes (MC was the problem). The service asr and service abs lights have gone off on their own. No idea why. The asr and abs are functioning fine as they always have.
The red, dash, brake warning light was on til I unplugged the single wire plug on the inboard side of the mc. I'm leaving it unplugged til I get a chance to troubleshoot that issue. The brakes are working fine without that plugged in.
The red, dash, brake warning light was on til I unplugged the single wire plug on the inboard side of the mc. I'm leaving it unplugged til I get a chance to troubleshoot that issue. The brakes are working fine without that plugged in.
05-21-2019, 08:45 PM
#11
Le Mans Master
Member Since: Dec 2005
Location: Where Woke Goes to Die
Posts: 8,194
Received 615 Likes
on
431 Posts
I've finally been able to drive the car a few times...sportily, and no more sticking brakes (MC was the problem). The service asr and service abs lights have gone off on their own. No idea why. The asr and abs are functioning fine as they always have.
The red, dash, brake warning light was on til I unplugged the single wire plug on the inboard side of the mc. I'm leaving it unplugged til I get a chance to troubleshoot that issue. The brakes are working fine without that plugged in.
The red, dash, brake warning light was on til I unplugged the single wire plug on the inboard side of the mc. I'm leaving it unplugged til I get a chance to troubleshoot that issue. The brakes are working fine without that plugged in.
Last edited by 81c3; 05-21-2019 at 08:45 PM.