Hello everyone. Thanks in advance for any help you may be able to offer. I have a 1996 "Cobra Clone", the whole drive train, computer, interior, is all from a 1996 Cobra. Recently the front brakes were "locking up" causing me to burn up the rotors and hoses. I took the car to a shop to have the brakes replaced and had the 10th Aniversary Cobra calipers and upgraded rotors installed on the front. Both front hoses were changed and I picked up the car. After driving it for about 10 miles the front calipers locked up again. I pulled over and got a tow back to the shop. I was then told it was the Master Cylinder and replaced that with the 1996 Cobra master cylinder. They took the car out for a test drive and it happened again. They told me they don't know what the problem is and can't fix it. The car has ABS disabled. I changed the rear axle to a non ABS 8.8 so there are no exciter rings on the back. I even removed the ABS fuse under the dash and the ABS Fuse under the hood hoping that that would somehow fix this. They shop says it must be the ABS module somehow malfunctioning even though it is not hooked up. When I drove the car home from the shop the brakes started to lock (it does it gradually, like there is pressure building) so I pulled over. I cracked the bleeder on the Master cylinder and the calipers released and I could see the car settle back. After another mile or so I had to stop and do this again. Does anyone have any advice on what I can do? I don't want to buy a new ABS module since the car does not have all of the ABS equipment. Does it sound like it could be the ABS module? Is there anyway it could be the power assist? Is it possible to cut out the ABS module and just run brake line or something? I am really stumped. Thanks for any help.
The ABS should affect it. You should have normal braking. It sounds to me like a bad "combo" valve..or proportioning valve. Are both fronts locking up or just one?
Both front are locking up. I had the prop valve replaced already. It is weird because if the car sits for awhile I can drive for 10 miles in the city before it starts to build pressure and lock up, once it locks up I can release the pressure at the Master cylinder. After I do that I can go another mile or two before it locks again. It is like there is a seal messed up in the ABS module and the master cylinder can push the fluid through just fine, but it doesn't allow the fluid to flow back out so easily causing the build up in pressure. This weeked I am pulling the ABS module out and am going to run new line in the front. It has to fix it because everything else is already new :P I have my fingers crossed anyways.
Im not too knowedgable on brakes but Maybe its the solenoids or vavles that the abs system uses?
Maybe they are defective and doesnt allow all the fluid back into the master cylinder, so pressure slowly builds up and lock up the brakes
Also have you tried putting the fuses back in and driving the stang? And obviously there is going to be a code since the rear does not have the rings, but if theres other abs problems more codes should come up with it.
I am taking the car into a Mustang Speciality shop that also happens to have a huge Mustang salvage yard. I was wondering if the power assist would be ok with the ABS setup completly out. It is the hydro-boost type that runs off of the power-steering fluid so I don't know if they make a non-ABS one or if the non-ABS systems used a Vacum type boost. I will post tomorrow as soon as I find something out. As far as the codes go, I used a Snap-On Diagnostic tool before the brakes went out. The ABS light was on due to the non-ABS rear and the only codes that came out where the speed sensors disconnected. Thanks for the input. I have worked on cars for awhile and have never had something stump me like this. You would think that since the brake system isn't that complicated, it would be an easy enough fix. My trial and error method has ending up costing me $1500 and I still have the problem :) At least I have some nice new 10th Aniversary Cobra Calipers out of all of this.
Ok. Quick update. I picked up the car from the Mustang shop today and they said that everything was working fine. I spent another $600 replacing the power assist (which they said was the problem) After about ten minutes of driving the front wheels locked up again. So now I have replaced EVERYTHING...except the disabled ABS module and the brake lines. I called them and they said to bring it back in on Tuesday. So do I demand that they put the old power assist back on and refund my money? I am getting sick and tired of shops telling me what the problem is and then charging me for parts and labor and in the end the problem not being fixed. I am in over 2K trying to fix the brakes and pretty much broke. I am getting frustrated with this and am ready to just sell the car. As soon as the brakes are finally fixed I am putting it up for sale and am never looking back.
hmmm....this is definately a tough one. Was any thing done to the brakes before this started? Don't think of this as a "pressure building" issue but more of a pressure release problem. When you take your foot off the pedal, the fluid should return to the master cylinder. There should be no pressure left in the lines. Yours is not doing that for some reason and is maintaining some level of line pressure. This is causing brake drag. (it won't be an ABS problem because the job of the abs is to release pressure) Things that I can think of that would cause pressure to remain in the lines would be a prop valve either wrong or not working, a bad master, or most likely, no "pushrod" clearance. Seen it several times with hydro. Is there any free-play in the pedal? If the rod is the wrong length, it won't let the master return fully.
...Almost forgot...I think the rest of the repair should be "on them". as they said that would fix it.
< Message edited by Stepman -- 5/23/2008 11:46:30 PM >
I had a similar problem on an old chevy a few years back it was only one side though.I called a brake specailty shop out in California they said when upgradeing any type of brake system it is a hit or mis deal.But any way it ended up being the caliper was locking up on the hanger even though it looked identical it was not compatible.Make sure your calipers are moving freely at the hangers and slide pins are moving. the caliper would apply the brake under great presure but hanger would bind caliper and would'nt allow the caliper to return (less presure when returning) Just an idea. Dave
Thanks for the responses. It is tough because pretty much all of the major components have been replaced. The calipers, master cylinder, prop valve, and now the power booster. I am going to take a look at it today to see if there is a kink of some sort that is visible. I was thinking that maybe that could be it. There is no play in the pedal. Nothing was done to the brakes before this started. As a matter of fact, I changed the rear axle in Michigan, drove the car to Colorado with no problems. After one day of being in CO this started happening and I burnt up my rotors and calipers and brake hoses. One side even briefly caught fire. That when I had it towed into a shop and it has now been about 2 months and I have not been able to drive this car. I really don't understand how it can be so hard to diagnose and fix. The ABS system is "disabled" but the fluid obviously still has to run through the module. I think if I cut that out and run all new line in the front the problem should be fixed. Every single piece of the front braking system would have been replaced. And then this car is going up for sale. Too bad too because I am still under 40k miles.
Posts: 146
Joined: 5/21/2008 From: NORTH CAROLINA Status: offline
the abs pump is glogged, i had this problem on a customers car, the abs picked up some trash some how and when you brake its clogging one of the lines, and not letting the pressure release back untill u manuely release it, tell someone to check your abs pump for blockage!
I can''t believe that. I won''t say it can''t happen because I had one that the peddle would go right to the floor (occasionally) on the first pump. The job of the ABS is to release the brakes, not hold them.
Also, with all those parts being replaced, it seems anything that was in there, would''ve been flushed out by now.
I can''''t believe that. I won''''t say it can''''t happen because I had one that the peddle would go right to the floor (occasionally) on the first pump. The job of the ABS is to release the brakes, not hold them.
Also, with all those parts being replaced, it seems anything that was in there, would''''ve been flushed out by now.
Actually...
The job of the ABS is to Hold, Release and Reapply the brakes for ABS assited stops. The ABS computer makes those decissions upto 15 times a second.
As for the posters problem, i agree with some of the other replies. It seems like the ABS accumulators are defective. Did you have them checked? Also, im sure you did this allready but are you recieving any ABS codes? Other reasons why disc brakes lock up is because of the power booster not have enough clearance from the master cylinder rod as well as some square cut seals not retracting the piston. When they installed the power booster, did they gap is from the master cylinder rod correctly? Thats where my money lays...
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Brake Problem, 4 different mechanics can't figure it out - 
