Help Guys!!!

I purchased a 1988 C4 Convertible about a month ago that had been sitting for a year and a half after the owner had died in a motorcycle crash. The car runs and drives great and just seems to need some TLC after sitting so long. My current problem is the right front brake is dragging. I have replaced the pads, rubber brake line at the right front wheel, and now the caliper. I have also bled the brakes but nothing has fixed the problem. I have read some posts about the ABS Modulator causing this problem but I don't want to keep replacing parts that will only get more expensive as I go. If I do a Google search I find ABS Modulator, Relay, and Pump so I'm not sure which item if either will fix my issue. Any suggestions or ideas would be greatly appreciated!

Thanks Guys.

 

pull the abs fuse and see if it still does it.

 

Have you cleaned and re-lubed the guides in caliper bracket ?

 

I looked in the owner's manual Saturday and I don't remember seeing a fuse marked ABS but surely there would be one so I'm gonna go back and check that. I did clean and grease the slides when I installed the new caliper last week but your question did give me an idea to check to see if it's the slides or something hydraulic. When I install the caliper I can push the pin in with my hand but I have to wiggle the caliper a bit to get it to slide into the slot between the bracket and the bottom of the brake pads. I think I'm going to remove the caliper from the mount bracket, place a 1"x4"x12" piece of wood between the pads and have someone press and release the brake pedal and see if it holds pressure or releases. Obviously if it releases then the pads are binding in the bracket but if it holds then I have a hydraulic problem. Thanks for the replies, I'll update this evening if I get to work on it.

 

Okay guys here's the latest. I came home today and removed the caliper from the bracket but did not disconnect the brake line. I placed a 1"x4" piece of wood between the pads to make sure the pistons did not push all the way out. I did not start the car or even turn the ignition switch on to make sure the electrical part of the ABS system was not energized. I had my son mash the brake pedal and it took several pumps before the right front brake engaged. When it did engage it would not release until I opened the bleed port. I looked in the Haynes repair manual I have and there is no fuse listed for the ABS. My next step is to start looking for a schematic of the brake system. Any ideas of what to look at or where to start?

 

Brake hose. The inner lining of the brake hose can collapse and act like a valve in your arteries. Run the same test you did before with the block of wood then loosen the brake hose at the frame. If the caliper doesn't retract then your brake hose is bad.

 

in your fuse panel, there's a fuse marked 'brake fuse' , behind your battery there should be one marked ABS, behind your drivers seat below the storage bucket, you're abs controller has a large red wire for power. I'm voting on the brake line 'rubber' being plugged, also

 

If it is the hose change all 4 they are 24 years old and a very basic safety item. It would not be a bad idea to just change them anyway.

 

Vette's ABS system are year specific. The FSM (factory service manual) for your specific year tell you to "bleed" your caliper positions in a specific order to avoid having air trapped within the "maze" like components of your brake system. I recommend, before you begin further part swapping, re-bleed the brake system according to your year specfic FSM instructions. If your rotor is "warped" from dragging you'll need to take care of that also.

 

I guess at this point the best thing for me to do is get the Factory Service Manual because the Haynes manual the previous owner's widow gave me just doesn't cut it and I'm not gonna keep throwing parts at it. I replaced the following items in this order; Front Brake Pads, Right front rubber brake hose, Right front caliper. My fuse box does not list a fuse for the ABS so if there is one it is located elsewhere. I don't think the rotor is warped yet, the brakes just don't release fully. They release enough for the wheel to turn but drag enough to heat up the pads and rotor enough for you to smell them as you walk by and you can feel the heat if you put your hand near the wheel. None of the other wheels do this.

 

I would re-examine the basic hydraulic system ie. hoses, calipers. ABS causing a brake drag (especially when key is off) is almost a non-occurrence as the normal position of the valving inside the unit is open.

FYI, just because you got a new caliper/hose from you local auto parts store does not mean it is good. Almost all of those calipers are remanufactured to questionable standards.

Are any of the other wheels having the same drag? Take the wheels off to compare to your RF.

 

I was thinking the same thing, that without the switch in the "ON" position the valves would be spring loaded to the open position to allow for normal braking in the event of an ABS failure. I'm gonna start over with bleeding this weekend and bleed all of the wheels really well and try to make sure that is not causing my problems.

 

I hope he figures it out.
I am now having the exact same problem with my right front 1988 C4 brake pad dragging due to not backing off and making the wheel hot to the touch. It doesn't happen with any of the other 3 wheels.

 

Okay for anyone else that has this problem here is what finally worked for me. If you read through the thread you will see I bled all of the brakes, checked fuses, replaced the front brake pads, replaced the right front brake line, replaced the right front caliper and re-bled the brakes after each action. None of this worked! What I eventually did to resolve this problem was to order a 10 mm brake "T" fitting and two 10 mm 15" braided steel brake lines from a VW site. I removed the cover from the ABS Modulator on my 1988 convertible which was located underneath the car just behind the driver's seat. Once I removed the cover I identified the main brake line coming from the master cylinder for the front brakes and the two lines going from the ABS modulator to each front wheel and disconnected them. I bypassed the ABS modulator for the front brakes only using the "T" fitting and the two braided steel lines I had ordered online. I also plugged the empty ports on the ABS Modulator to prevent dirt and water from entering the valve. I followed up with bleeding the brakes as you normally would. What this did was bypass the modulator for the front brakes only and eliminate ABS for the front wheels. I AM NOT telling or suggesting anyone do this and DO NOT take responsibility for anything that results from anyone doing this!!! I am simply explaining what I did on my car that worked for me. If interested below is a link to the VW site I ordered my parts from. http://www.pacificcustoms.com/mm5/me...w=&range_high=

 

After reading your post and having the same problem I decided that was what I would do, went to the brake shop to pick up some fittings, yeah not so good, if you bypass any safety feature on a vehicle ins will not cover, I found the problem with mine, I took it apart, their are three coils that operate chopper motors, lots of very small parts, one works the back brakes, and one each for the front brakes, inthe bottom of the chopper motor for the brake I was having the problem with was a small broken spring, the way they work is when you energize the coil the chopper motor turns and interups the fluid going to that brake, it does this very fast and that is why we feel the pulse, the spring holds the bottom of the chopper motor off the bottom, it was broke so the motor could not return to the open position, from what I have read the abs is supposed to fail open, I have read about others that have had the same problem, in my case it did not allow enogh fluid to the caliper and it would not reliese all the way either.

 

this is a very interesting post.. what was your eventual fix, and did you take any photos..

thanks for sharing,

 

my fix was replacing the small spring that supports the very small chopper motor. this iis where the ABS motor is located[ATTACH][ATTACH][ATTACH][ATTACH][/ATTACH][/ATTACH][/ATTACH][/ATTACH]

 

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Were did you find a spring?

 

well after looking on line and checking all the auto and brake shops I walked into the machine shop located in the building where I work and one of the machinist had just bought a big bag of assorted springs ranging from very very small to larger sizes, I found one in the bottom of the bag, I took one of the other chopper motors apart so I could check the load strenth of a good spring to the new one, presto.