fahad al ghanim

I'm facing a huge problem, just finished my RWB 964 build and I keep having the rear brakes sticking whenever I've been driving the car for a while. At first I thought it was a problem with the brake calipers so I changed them with new set of rear brake kit from FVD motorsports. I also changed the brake booster but still im facing the same issue.

If someone has any ideas please let me know!

cobalt

What wheel widths and offsets. I was told but don't hold me to it that heavy negative offset wheels will mess with the ABS system. Otherwise we would need more info regarding the actual symptoms.

Corrected to read negative offset sorry about that.

fahad al ghanim

It has a 964 Super fender (RWB)
Front 10.5Jx18 -5
Rear. 13Jx18 -31

I dont know if it helps but tires size is:
265/35/18
335/30/18

Also for information the car is equipped with full Fab-Speed exhaust and headers, and some people say that the headers and exhaust should be wrapped for heat reduction. Im not sure if this might be the problem or not but recently the car actually caught minor fire at the rear end left side due to brake sticking but thank god nothing happened

Blu RS

I've been down this road before with rear brakes badly sticking on my 964 that occasionally sees track duty. In my case it was because the calipers were rebuilt with improper technique. I know that because I rebuilt them myself (twice over) and subsequently found out I'd made a crucial error or two during the rebuild process. (This last time, my third rebuild, I got it completely right and my guidance/insights are given below.) In my case, and almost certainly in your situation as well, the bore seals are the culprit causing the sticking. Your bore seals are ruined, they cannot recover in place, so therefore your calipers need to be rebuilt properly. Your bore seals either got ruined from overheating or you have rebuilt calipers where the seals likely were installed incorrectly. Incorrect seal installation causes the pistons to distort/torque the seals when the pistons were reinserted into the bores. That in turn causes the pistons to to fail to retract, which immediately causes the brakes to fail to release. All of the above happens almost immediately the first time the new brake installation is used with any serious brake pressure. And once those seals have been "cooked" by such serious overheating as to cause a fire, then the caliper has to be rebuilt regardless. Long story short, the resilience of the seal is what enables the piston to retract. If the seal is twisted in its seal land, or if the seal is hardened from overheating, then the resiliency is lost and the seal cannot assist the piston to retract.

Among all the issues associated with proper caliper rebuilding, here are some key "take-away" points I've learned. 1. Get true Brembo replacement seals, don't try to cheap out on this point. (Sources include FVD and HRPworld.com) 2. Replacing the pistons may not be necessary if the current pistons are in perfect shape with no nicks or scratches on the barrel sides. 3. The seals should be "pickled or marinated" for at least 4 hours in clean brake fluid before they are installed. Some references call for 24 hour saturation before use but I've found that at least four hours should be sufficient. Put them in a zip lock baggie and pour some new fluid in with them. Then make sure to turn the baggie over several times during the "marination" process. 4. Completely clean out the bore lands where the seals will be installed such that each bore land is completely clean and dry before any attempt is made to re-insert a new seal (I use Q tips to clean the bore lands). 5. Completely wipe off the marinated seal before inserting it back into the caliper bore. The seal should be completely dry and go into a completely clean and dry bore land. 6. Now that the caliper seal is back in the place in the caliper bore, lightly lubricate the protruding edge of the seal with fresh brake fluid. 7. Lubricate the bottom end of the caliper piston with fresh brake fluid. 8. Insert the lubricated piston into the caliper bore until it comes into contact with the bore seal, then gently rotate the piston in a small arc back and forth to make sure the bottom of the piston has good lubrication contact with the bore seal. 9. Gently but firmly press the piston STRAIGHT down into the bore being extremely careful not to push the piston much further than halfway in. 10. Now if you've come this far, then you know pretty well what all else needs to be done.

I've had so much frustration with sticking brakes that I'm delighted to be able to share these techniques I used to finally make a rebuilt caliper perform just like a new one. Hopefully you'll find my comments worthwhile in reaching a solution for your sticking rear brake issue. Good luck!

fahad al ghanim

Thank you blu rs for the information! But dont you think it’s impossible in my case since my calipers are brand new?
i used to have the problem with my old calipers but i bought new sets because they told me that the sticking problem is from the old calipers

cobalt

Disregard everything I wrote before. It sounds like A) your ABS is not functioning properly and B) by going with a wider tire being pushed out by well over 137mm you are effectively reducing your contact patch by narrowing and elongating it it by moving the tire so far past the center-line of the suspension. The lack of grip due to the reduced contact patch is most likely causing the brakes to lock up. You might consider having the ABS tested to see if it is working and possibly moving your brake bias forward to balance it out.

I am curious to see what you find out I wish I had more to offer you on this subject. I will look into this further and try to respond later if I find anything else out.

Blu RS

I agree that if indeed the calipers from FVD were new, and not rebuilt, then it would seem that your calipers (both old and new) were not the cause of the problem. However, once those calipers have locked up so badly as to cause a fire then they will almost certainly need to be rebuilt. That of course doesn't solve anything but just adds to your problems. Anyway, out of curiosity, will you please tell us which calipers and rotors you're running on the front and the rear? Also, can you confirm that the brake booster (and likely larger master cylinder) you installed was from a 993 or was it something else? Finally, did you remove or change the brake bias valve in the ABS system?

fahad al ghanim

Thank you guys for the help!So I thought the upgrading the rear brakes(that used to always lock) might solve the issue but its still locking after a long drive. Im running right now on front stock 964 C2 brakes and a big red kit(brembo) on the rear brakes. The master cylinder is a new 964 C2 one. No I haven't changed nor removed the valve. Does the ABS usually lock if i am rolling on an RWB alignment? Usually the alignment has a bit of a negative caliber.

cobalt

So why the change to larger rears without increasing the fronts. What is the dia of the pistons and rotor size? You could be moving the bias to far rearwards. I run 993RS brakes all around, big reds up front and larger piston medium S4 calipers with 322mm rotors rear in my WB TT 964. When my ABS isn't functioning or turned off it will lock up my rears 305 on 11ET5 rim. I would consider trying less air pressure in the rear and see if it helps. The reduced contact patch of the setup you are running with a larger caliper is most likely the culprit. You might want to go back to stock rears or consider big reds up front. I also run heavy negative camber front and rear.

jonathant

Emergency brake shoe stuck/dragging?

You mention a fire after a “long drive” (i.e. not a track session) with new FVD calipers. Could be the new calipers dragging but maybe less probable than something simple like an e-brake out of adjustment.

-nick

Have you changed the flexible brake lines? They can swell internally and easily cause a caliper to stick. Though given the extreme wheel offsets and stretched tires, maybe the locked brakes are spitefully protesting what was once a nicely engineered chassis?

rahulsingh

Hi, sorry to get into this thread, did you find the solution.., i am having same issue in rwb
thanks

Metal Guru

Unfortunately the OP is not the first RWB owner I've seen post with suspension issues.
In the world of automotive manufacturing, the two systems receiving the most attention from government regulators are fuel systems and suspension/steering systems.
RWB modified cars have virtually <zero> engineering development behind them AFAIK, making these cars a nuisance to own at best and dangerous in the worst case. There's a video somewhere on Youtube of a bunch of RWB owners in Japan doing an endurance race with their cars, which is insanely dangerous IMO.
Buyer beware......