86 5-speed brake master Abs disabled
05-16-2022, 05:46 PM
#1
Race Car
Thread Starter
86 5-speed brake master Abs disabled
86 5-Speed WITH S4 BRAKES
My both rear brakes locked up the heat melted the stick on wheel weights enough to fall off, after cooling down I was able to drive it on the lift.
Both wheels could not be turned by hand until ll I released the outer bleed screw. I have the S4 conversion brakes and the Abs is disabled due to front caliper refit, it has driven many miles with the abs disabled and do not believe this is the issue. I am looking into a rebuild kit for the master and inquiring has anyone bypassed the abs system to eliminate any possible issues? Any trouble shooting hints to narrow this down would be appreciated.
Thanks
My both rear brakes locked up the heat melted the stick on wheel weights enough to fall off, after cooling down I was able to drive it on the lift.
Both wheels could not be turned by hand until ll I released the outer bleed screw. I have the S4 conversion brakes and the Abs is disabled due to front caliper refit, it has driven many miles with the abs disabled and do not believe this is the issue. I am looking into a rebuild kit for the master and inquiring has anyone bypassed the abs system to eliminate any possible issues? Any trouble shooting hints to narrow this down would be appreciated.
Thanks
05-16-2022, 06:53 PM
#2
Team Owner
first of all get either a new or professionally rebuilt MC and possibly a new booster,
get new SS flex lines with S4 brakes you might need a different kit
the MC is not easily rebuilt BC its made to not be taken apart.
That said White Post can rebuild this part so thats what I would do
get new SS flex lines with S4 brakes you might need a different kit
the MC is not easily rebuilt BC its made to not be taken apart.
That said White Post can rebuild this part so thats what I would do
05-17-2022, 03:28 PM
#4
Rennlist Member
Why as the ABS disabled? Even with a caliper swap the ABS should be able to be retained.
That being said I don't see why you couldn't remove it if you intend to run without it functioning indefinitely. You would likely need to fabricate new lines from the master to the front flex lines and master to the T for the rears. .Depending on brake sizing front/rear you may also need to change your brake bias valve to tune the brakes one end from prematurely locking under hard braking.
That being said I don't see why you couldn't remove it if you intend to run without it functioning indefinitely. You would likely need to fabricate new lines from the master to the front flex lines and master to the T for the rears. .Depending on brake sizing front/rear you may also need to change your brake bias valve to tune the brakes one end from prematurely locking under hard braking.
05-17-2022, 04:56 PM
#5
Rennlist
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Why as the ABS disabled? Even with a caliper swap the ABS should be able to be retained.
That being said I don't see why you couldn't remove it if you intend to run without it functioning indefinitely. You would likely need to fabricate new lines from the master to the front flex lines and master to the T for the rears. .Depending on brake sizing front/rear you may also need to change your brake bias valve to tune the brakes one end from prematurely locking under hard braking.
That being said I don't see why you couldn't remove it if you intend to run without it functioning indefinitely. You would likely need to fabricate new lines from the master to the front flex lines and master to the T for the rears. .Depending on brake sizing front/rear you may also need to change your brake bias valve to tune the brakes one end from prematurely locking under hard braking.
Running the brake fluid through a non functioning part, which is designed to completely control the brake pressure, makes little sense, to me.
With full respect to Stan, I've yet to see a master cylinder/booster problem that caused the rear brakes to engage.....always seems to be the front brakes.
What is the history of the flexible brake hoses to the calipers? Common for these to get "hardening of the arteries" and only allow high pressure to pass....making the calipers not release due to the residual pressure that can not return. (Although both rears having this issue at the exact same moment is probably really rare.)
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greg brown
714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
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Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
05-18-2022, 10:35 AM
#6
Race Car
Thread Starter
Further testing shows this:
After Pressing the brakes with engine off several times the rears lock up. When either caliper when the outside bleeder is opened they now can be turned by hand. Opened vacuum to booster sat for a while so no vacuum but has no effect this is repeatable. The lines are stainless and not that old and fluid is clean. Don’t want to throw parts at it and running out of options for testing. There is an over pressure switch on the Abs the factory testing procedure requires a specific tool.
Observation if that rear calipers stay engaged unless either outside bleed valve is opened there is free play in the brake pedal as required.
After Pressing the brakes with engine off several times the rears lock up. When either caliper when the outside bleeder is opened they now can be turned by hand. Opened vacuum to booster sat for a while so no vacuum but has no effect this is repeatable. The lines are stainless and not that old and fluid is clean. Don’t want to throw parts at it and running out of options for testing. There is an over pressure switch on the Abs the factory testing procedure requires a specific tool.
Observation if that rear calipers stay engaged unless either outside bleed valve is opened there is free play in the brake pedal as required.
05-18-2022, 12:06 PM
#7
Team Owner
FWIW we had 2 cars in SLC with a similar issues of locking brakes ,
both due to adding different brands of fluids this caused the MC and calipers to have the seals swell .
Both cars required replacement of MC and the calipers rebuilt,
then swap the fluid out to ATE,
NOTE one car also had a booster filled with brake fluid so check for that issue as well
NOTE this issue took about 6 to 8 months to develop after new fluid was installed.
NOTE if you have a rear bias valve this can get plugged with corrosion and if refreshing the brakes,
is smart to also replace it.
both due to adding different brands of fluids this caused the MC and calipers to have the seals swell .
Both cars required replacement of MC and the calipers rebuilt,
then swap the fluid out to ATE,
NOTE one car also had a booster filled with brake fluid so check for that issue as well
NOTE this issue took about 6 to 8 months to develop after new fluid was installed.
NOTE if you have a rear bias valve this can get plugged with corrosion and if refreshing the brakes,
is smart to also replace it.
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05-18-2022, 09:46 PM
#8
Race Car
Thread Starter
Fluid has been in for a couple of years, I’ll check the booster, but from my observation as soon as I release the bleeder on either side they both release. This blockage seems to be coming from the Master going to do a little more testing then I’m going to pull it.
08-01-2022, 01:45 PM
#9
Race Car
Thread Starter
Update
I had the master cylinder rebuilt following the recommendations of this forum on who to use. After install now the locking problem has migrated to the front brakes. After about 2 miles of driving they just lock up. I had trouble bleeding master cylinder due to a bleeder screw that was leaking air, I replaced a bleeder and the problem is still there. At this point I could send the master back to be looked at or I missing something, or it’s completely to do with the ABS maybe a blockage. It’s just so odd that the Front is now the problem and the rear is fine, must be missing something or there’s something wrong with the Rebuild. Running out of things to check any ideas would be appreciated. Thanks
I had the master cylinder rebuilt following the recommendations of this forum on who to use. After install now the locking problem has migrated to the front brakes. After about 2 miles of driving they just lock up. I had trouble bleeding master cylinder due to a bleeder screw that was leaking air, I replaced a bleeder and the problem is still there. At this point I could send the master back to be looked at or I missing something, or it’s completely to do with the ABS maybe a blockage. It’s just so odd that the Front is now the problem and the rear is fine, must be missing something or there’s something wrong with the Rebuild. Running out of things to check any ideas would be appreciated. Thanks
08-02-2022, 01:44 AM
#10
Rennlist
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Update
I had the master cylinder rebuilt following the recommendations of this forum on who to use. After install now the locking problem has migrated to the front brakes. After about 2 miles of driving they just lock up. I had trouble bleeding master cylinder due to a bleeder screw that was leaking air, I replaced a bleeder and the problem is still there. At this point I could send the master back to be looked at or I missing something, or it’s completely to do with the ABS maybe a blockage. It’s just so odd that the Front is now the problem and the rear is fine, must be missing something or there’s something wrong with the Rebuild. Running out of things to check any ideas would be appreciated. Thanks
I had the master cylinder rebuilt following the recommendations of this forum on who to use. After install now the locking problem has migrated to the front brakes. After about 2 miles of driving they just lock up. I had trouble bleeding master cylinder due to a bleeder screw that was leaking air, I replaced a bleeder and the problem is still there. At this point I could send the master back to be looked at or I missing something, or it’s completely to do with the ABS maybe a blockage. It’s just so odd that the Front is now the problem and the rear is fine, must be missing something or there’s something wrong with the Rebuild. Running out of things to check any ideas would be appreciated. Thanks
Keeps the insanity level under 9 (on a scale of 1 to 10) when working on these cars....
Last edited by GregBBRD; 08-02-2022 at 01:46 AM.
08-10-2022, 06:20 PM
#11
Race Car
Thread Starter
Update, sent the Master back and requested to have it checked out due to the front brakes locking up. I called and finally spoke to the individual who repaired it to verify if there was an actual problem with the rebuild. Apparently he mixed up the front and rear springs not noticing that one was a larger diameter and corrected the issue. When it arrives hopefully things will be back to normal.