Dragging Brakes
Thread Starter
Heel & Toe
Joined: Mar 2008
Posts: 20
Likes: 0
From: Georgia
Dragging Brakes
Has anyone had this type of problem with their brakes? I have a 1992 convertible, LT1, that is all stock except for a ProCharger Supercharger. When the car gets up to normal operating temperature, the brakes begin to drag. I notice it when I come to a stop. The brake pedal gets hard with very little travel, but the car still stops pretty good. As I continue driving, sometimes the dragging will stop but the pedal stays hard with little travel. When I touch the outer part of the wheels the back wheels are warmer than the front, but none are alarmingly hot.
I had a code 71 so I pulled the EBCM, made sure the connections were clean, put it back in and cleared the codes. Still have the problem but no codes are present. "sys" is flashing on the speedometer screen. Replacing the EBCM is a last resort since it's so expensive. Are there any other things to try??
I had a code 71 so I pulled the EBCM, made sure the connections were clean, put it back in and cleared the codes. Still have the problem but no codes are present. "sys" is flashing on the speedometer screen. Replacing the EBCM is a last resort since it's so expensive. Are there any other things to try??
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
We’re just starting to wake up here on the east coast. 
Not an uncommon problem.
Most likely the actuator rod in the booster is to long. When things heat up parts expand and it starts pushing on the master cylinder piston. Take off the 2 nuts and pull the master cylinder back some. You need to increase the clearance to about 1/8 inch or so. The actuator rod has to be screwed back into the sleeve. You need to hold the sleeve lightly and screw the rod back into it about 1 or 2 turns.
Before you start you can jack a wheel up and see if it drags. Then loosen the master and see if it releases, then you will know your in the right area.
As far as your code 71 goes, I would clear it and see if it re-occurs. I have a 94 but I believe the 92 uses the same brake computer parts. You can’t clear the codes in module 9 (EBCM) by disconnecting the battery. You have to use sub menu 9.7 to do it and clear the code.
The flashing SYS indicated a CCM code has been set or more often the battery might be on its way out and the CCM does not like it, no code for that though. Additionally, an after market radio could make the SYS flash if the mod was not done.
Not an uncommon problem.
Most likely the actuator rod in the booster is to long. When things heat up parts expand and it starts pushing on the master cylinder piston. Take off the 2 nuts and pull the master cylinder back some. You need to increase the clearance to about 1/8 inch or so. The actuator rod has to be screwed back into the sleeve. You need to hold the sleeve lightly and screw the rod back into it about 1 or 2 turns.
Before you start you can jack a wheel up and see if it drags. Then loosen the master and see if it releases, then you will know your in the right area.
As far as your code 71 goes, I would clear it and see if it re-occurs. I have a 94 but I believe the 92 uses the same brake computer parts. You can’t clear the codes in module 9 (EBCM) by disconnecting the battery. You have to use sub menu 9.7 to do it and clear the code.
The flashing SYS indicated a CCM code has been set or more often the battery might be on its way out and the CCM does not like it, no code for that though. Additionally, an after market radio could make the SYS flash if the mod was not done.
Last edited by pcolt94; Mar 27, 2008 at 07:20 AM.
Advanced
Joined: Dec 2007
Posts: 52
Likes: 0
From: Waynesville Ohio
Also you should check that there is a one way valve between the booster and the manifold. The booster is only intended to recieve vacuum from the engine, when you are under boost you need to block that pressure from the booster. I don't know for sure that this is true on corvettes but I have seen this before with turbocharging other cars.
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Thread Starter
Heel & Toe
Joined: Mar 2008
Posts: 20
Likes: 0
From: Georgia
I adjusted the rod in the master cylinder. The brake pedal, of course, had much more travel, however I still have the problem once the car gets to operating temperature????? The pedal gets hard with little travel BUT sometimes it goes back to normal then back to the problem as I'm driving!
I may try m.martince's fix next.
I may try m.martince's fix next.
Pro
Joined: Feb 2005
Posts: 560
Likes: 0
From: Hamilton New Jersey
I adjusted the rod in the master cylinder. The brake pedal, of course, had much more travel, however I still have the problem once the car gets to operating temperature????? The pedal gets hard with little travel BUT sometimes it goes back to normal then back to the problem as I'm driving!
I may try m.martince's fix next.
I may try m.martince's fix next.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
You never said the car was pulling so that sounds like a global problem and eliminates a flex line blockage. I would say flushing is not a bad thing to do because you symptoms are some what strange. The booster could obviously cause a hard pedal and poor braking, but having a hard time making to connection of the brakes dragging which you indicated was your main problem.
You might have gone a bit to far in adjusting the actuator rod. You might consider re-visiting that when you get time.
I guess its possible the master could be doing something strange and not releasing pressure if its hot….just a guess.
But it would great if when the problem was happening you could get home, jack it up and really see what is dragging.
You might have gone a bit to far in adjusting the actuator rod. You might consider re-visiting that when you get time.
I guess its possible the master could be doing something strange and not releasing pressure if its hot….just a guess.
But it would great if when the problem was happening you could get home, jack it up and really see what is dragging.
Safety Car
Joined: Oct 2007
Posts: 3,816
Likes: 0
From: :45 minutes from everywhere / E-I-E-I-O
Has anyone had this type of problem with their brakes? I have a 1992 convertible, LT1, that is all stock except for a ProCharger Supercharger. When the car gets up to normal operating temperature, the brakes begin to drag. I notice it when I come to a stop. The brake pedal gets hard with very little travel, but the car still stops pretty good. As I continue driving, sometimes the dragging will stop but the pedal stays hard with little travel. When I touch the outer part of the wheels the back wheels are warmer than the front, but none are alarmingly hot.
I had a code 71 so I pulled the EBCM, made sure the connections were clean, put it back in and cleared the codes. Still have the problem but no codes are present. "sys" is flashing on the speedometer screen. Replacing the EBCM is a last resort since it's so expensive. Are there any other things to try??
I had a code 71 so I pulled the EBCM, made sure the connections were clean, put it back in and cleared the codes. Still have the problem but no codes are present. "sys" is flashing on the speedometer screen. Replacing the EBCM is a last resort since it's so expensive. Are there any other things to try??
But the code with the sys light too, is electrical.
Your wheel 'outer part' is too far removed from the rotor brake contact spot to conduct major heat, with out cookin' the bearings first, IMO...
Could residual vacuum be applying the brake through the booster diaphragm? This 'check valve' that turbogtu referred to is interesting...
Melting Slicks
Joined: Oct 2007
Posts: 2,310
Likes: 9
From: KB7TIF Ville NV
Well My 92 zr1 is doing the same thing. Cold its fine. The warmer it gets the more the brakes drag, all 4 drag and the rotors will get very hot.
Heres what I did, took some aluminum foil about 4 layers and built up a heat shield between the Master cylinder and engine. The master cylinder stays cooler and there is less drag on brakes.
Culprit- master cylinder.
When the master is hot to the touch there is drag when its cool its fine.
My local corvette shop just emailed me a said Wrong brake fluid or contaminated fluid.
Heres what I did, took some aluminum foil about 4 layers and built up a heat shield between the Master cylinder and engine. The master cylinder stays cooler and there is less drag on brakes.
Culprit- master cylinder.
When the master is hot to the touch there is drag when its cool its fine.
My local corvette shop just emailed me a said Wrong brake fluid or contaminated fluid.
Last edited by illenema; May 27, 2008 at 04:14 PM.
Instructor
Joined: Aug 2003
Posts: 139
Likes: 0
From: South Cave, Brough East Yorkshire
re: Dragging
Just thought I would post that I had the same problem on my 92 LT1 and finally sorted it out a few weeks ago - In my case it was also the master cylinder.
When hot it would drag the front brakes. When I opened either side caliper bleed screw - or the nut for the front line at the master cylinder it freed off the brakes at both sides - so i figured that pointed to more likely be the master cylinder than the brake lines.
Anyway replaced it and it has solved the problem.
I did all kinds of checks, plus adjustments on the pushrod, bleeding and flushing fluid several times - and even cleaning out the old master cylinder but it didint cure anythign til I got another master cylinder.
There seem to be quite a few posts on this and its often on 92`s - do u think there was a problem with some of the 92 master cylinders? My car has done 65k so not real high mileage though it may just be age related.....
Hope u get it sorted - Mine was like it when I bought it 6 months ago - it killed my gas mileage and I didnt realize how much it was effecting the acceleration especially in the higher gears!
Dom.
When hot it would drag the front brakes. When I opened either side caliper bleed screw - or the nut for the front line at the master cylinder it freed off the brakes at both sides - so i figured that pointed to more likely be the master cylinder than the brake lines.
Anyway replaced it and it has solved the problem.
I did all kinds of checks, plus adjustments on the pushrod, bleeding and flushing fluid several times - and even cleaning out the old master cylinder but it didint cure anythign til I got another master cylinder.
There seem to be quite a few posts on this and its often on 92`s - do u think there was a problem with some of the 92 master cylinders? My car has done 65k so not real high mileage though it may just be age related.....
Hope u get it sorted - Mine was like it when I bought it 6 months ago - it killed my gas mileage and I didnt realize how much it was effecting the acceleration especially in the higher gears!
Dom.
Racer
Joined: Jun 2007
Posts: 486
Likes: 0
From: Sandy Ut
I had this same problem with my 90. I know the front pads were low, and I replaced the front pads, and went to check the fluid and found it was nasty. On top of that the rubber caps were really swollen.... wrong fluid or contaminated fluid. I bled the brakes until I thought I had all the ick out, and the contaminated fluid. Still not much luck, so I replaced the master cylinder. It has not been about a year, and it is starting to come back. When to check, and sure enough the rear resivoir is now a dark color again. I am going to drain all the fluid, then blow all lines, and then put all back together. Going to replace the rear pads while I am at it, as they are starting to look thin. From there, if that does not cure it, I am going to have dive further into it, but I must say that the dirty and wrong fluid makes a ton of difference.
Thread Starter
Heel & Toe
Joined: Mar 2008
Posts: 20
Likes: 0
From: Georgia
I think we have this problem figured out. 
The more I research it, the more I come back to the master cylinder and brake fluid.
I am going to buy a new master cylinder and completely flush the lines. I feel confident this will cure the problem. I will let you all know how it works out.
Thank you all for your great input!!
The more I research it, the more I come back to the master cylinder and brake fluid.I am going to buy a new master cylinder and completely flush the lines. I feel confident this will cure the problem. I will let you all know how it works out.
Thank you all for your great input!!
