86 Front brakes locking after MC rebuild
#1
Race Car
Thread Starter
86 Front brakes locking after MC rebuild
86 928 Vin 860677
I had the rear brakes lock up and had the brake master sent out to be rebuilt. I was told the rebuild seals were not available for my year so decided to send it out.
Upon return the rear was fine but the front was now locking up. I returned the mc and was told the spring was installed backwards. Installed and front was still locking up. Upon removal of the Mc I found the C-clip came off the back and sent it out again.
I have the same problem fronts are stuck.
My troubleshooting consists of the following:
Drivers front caliper pressure released by opening bleed valve, that freed both fronts
on applying the brakes same outcome locked up.
Removed brake rod to check for preload still locked up.
Unbolted the Master from booster and still locked up.
My understanding is that the master rest position is not allowing air to return to the reservoir, pedal is rock hard. The Abs has been disabled for years and I did check the proportioning valve for any sediment.
I have not found any replacement apparently my vin 60677 is a split year. Any feedback if I’m missing something, a reference on another rebuilder or an availability of a used one will be greatly appreciated.
I had the rear brakes lock up and had the brake master sent out to be rebuilt. I was told the rebuild seals were not available for my year so decided to send it out.
Upon return the rear was fine but the front was now locking up. I returned the mc and was told the spring was installed backwards. Installed and front was still locking up. Upon removal of the Mc I found the C-clip came off the back and sent it out again.
I have the same problem fronts are stuck.
My troubleshooting consists of the following:
Drivers front caliper pressure released by opening bleed valve, that freed both fronts
on applying the brakes same outcome locked up.
Removed brake rod to check for preload still locked up.
Unbolted the Master from booster and still locked up.
My understanding is that the master rest position is not allowing air to return to the reservoir, pedal is rock hard. The Abs has been disabled for years and I did check the proportioning valve for any sediment.
I have not found any replacement apparently my vin 60677 is a split year. Any feedback if I’m missing something, a reference on another rebuilder or an availability of a used one will be greatly appreciated.
#2
Rennlist Member
Is this one of the failure modes when the spring is not the correct length? @Mrmerlin has a lot of information on here about what needs to be done to (certain?) master cylinders if they are rebuilt. Perhaps it's worth seeing if you can find some of his posts on the issue.
Good luck
Good luck
#3
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Is this one of the failure modes when the spring is not the correct length? @Mrmerlin has a lot of information on here about what needs to be done to (certain?) master cylinders if they are rebuilt. Perhaps it's worth seeing if you can find some of his posts on the issue.
Good luck
Good luck
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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.
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!
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!
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Mrmerlin (01-12-2023)
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Mrmerlin (01-12-2023)
#5
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86 928 Vin 860677
I had the rear brakes lock up and had the brake master sent out to be rebuilt. I was told the rebuild seals were not available for my year so decided to send it out.
Upon return the rear was fine but the front was now locking up. I returned the mc and was told the spring was installed backwards. Installed and front was still locking up. Upon removal of the Mc I found the C-clip came off the back and sent it out again.
I have the same problem fronts are stuck.
My troubleshooting consists of the following:
Drivers front caliper pressure released by opening bleed valve, that freed both fronts
on applying the brakes same outcome locked up.
Removed brake rod to check for preload still locked up.
Unbolted the Master from booster and still locked up.
My understanding is that the master rest position is not allowing air to return to the reservoir, pedal is rock hard. The Abs has been disabled for years and I did check the proportioning valve for any sediment.
I have not found any replacement apparently my vin 60677 is a split year. Any feedback if I’m missing something, a reference on another rebuilder or an availability of a used one will be greatly appreciated.
I had the rear brakes lock up and had the brake master sent out to be rebuilt. I was told the rebuild seals were not available for my year so decided to send it out.
Upon return the rear was fine but the front was now locking up. I returned the mc and was told the spring was installed backwards. Installed and front was still locking up. Upon removal of the Mc I found the C-clip came off the back and sent it out again.
I have the same problem fronts are stuck.
My troubleshooting consists of the following:
Drivers front caliper pressure released by opening bleed valve, that freed both fronts
on applying the brakes same outcome locked up.
Removed brake rod to check for preload still locked up.
Unbolted the Master from booster and still locked up.
My understanding is that the master rest position is not allowing air to return to the reservoir, pedal is rock hard. The Abs has been disabled for years and I did check the proportioning valve for any sediment.
I have not found any replacement apparently my vin 60677 is a split year. Any feedback if I’m missing something, a reference on another rebuilder or an availability of a used one will be greatly appreciated.
I'd be looking for another rebuilder, also.
Actually, once they told me that they had assembled it with a spring backwards, I would have been done.
That whole "brake system" stuff needs to be fairly proper.
Last edited by GregBBRD; 01-12-2023 at 05:45 PM.
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GUMBALL (01-13-2023)
#7
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Buy from reputable 928 suppliers like 928 International and 928sRus. We both sell rebuilt Brake Masters.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
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#8
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I believe that 928 International still had a couple of brand new masters, in stock.
If not, I certainly do.
If not, I certainly do.
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monkez (01-12-2023)
#10
RL Community Team
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How old are the brake lines? They swell and narrow inside and prevent fluid from passing backwards and the pads from releasing.
Here's a picture of the cracked and hardened rubber lines cut open that I removed from an 81 Euro S compared to the stainless ones I installed.
Look closely as there's more rubber insider the reinforcing braid.
Here's a picture of the cracked and hardened rubber lines cut open that I removed from an 81 Euro S compared to the stainless ones I installed.
Look closely as there's more rubber insider the reinforcing braid.
#11
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How old are the brake lines? They swell and narrow inside and prevent fluid from passing backwards and the pads from releasing.
Here's a picture of the cracked and hardened rubber lines cut open that I removed from an 81 Euro S compared to the stainless ones I installed.
Look closely as there's more rubber insider the reinforcing braid.
Here's a picture of the cracked and hardened rubber lines cut open that I removed from an 81 Euro S compared to the stainless ones I installed.
Look closely as there's more rubber insider the reinforcing braid.
We call it: "Hardening of the brake lines", in reference to the old medical diagnosis of: "Hardening of the arteries."
New brake lines are almost mandatory these days.
However, the change from rear brakes locking to front brakes locking, when the master was rebuilt, doesn't scream "brake lines", unless the rears locking up was an incorrect diagnosis.
#12
Race Car
Thread Starter
I have the S4 brakes newer SS lines problem occurred after rebuild.
I was under the assumption that the kit was not available for my year and vin, found a post recommending this company for a rebuilding. I’m already close to $400 into it with shipping charges new is going for the $800 range.
I was under the assumption that the kit was not available for my year and vin, found a post recommending this company for a rebuilding. I’m already close to $400 into it with shipping charges new is going for the $800 range.
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RennHarry (01-14-2023)
#15
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