ABS Problem 964

voodoo964 · 02-13-2008, 08:50 AM

HI,

I've noticed my ABS light coming on along with the regular warning light and the speedo drops to 0. This happens infrequently but is started happening more and more. The lights then go off and everything works as normal.

The lights came on again today while pressing the brake and the pedal pushed in further like the abs had been turned off...

I requested having my fluid changed at my last service - the guys said it was a timely job so they just checked the boiling point on the fluid and said it was fine.

Any advice? how hard is it really to do this job and i guess this would be the best place to start?

Thanks

colo964 · 02-13-2008, 09:04 AM

In the past I had some luck in fixing ABS light problems by cleaning the ABS sensors - tends to be some metal filings built up after 15 yrs+. I don't recall all the symptoms at the time, but it is cheap and easy. I just may work.

voodoo964 · 02-13-2008, 09:33 AM

Thanks - i will give that a try!

rsrmike · 07:12 PM

voodoo, colo964 is right about metal filings affecting the sensors. The most common sympton of dirty wheel speed sensors is a slight uneccesary engagement of the ABS, usually when first applying the brakes after changing direction. i.e. reversing out of a parking place. The metal filings tend to stand "on end" as they are being pulled against the magnetic sensors. They also tend to "lean" towards whatever direction your moving as the hubs can brush them with the trigger wheel ever so slightly. As you change direction and hit the brakes, sometimes the "flutter" of these filings can freak out the sensor signal ever so slightly at which point you get a slight abs "bump" However, it sounds like you may have multiple problems. First off, the speedo only reads off the left front wheel through the abs speed sensor. It is possible this sensor is bad but not likely. I have seen them go bad but they usually either work or they don't. I have seen ABS Relays go bad and that is a much more likely intermittent problem. Have you been jump-starting the car recently perhaps? This can have a negative effect on these relays. If the relay goes out it would shut down the system, trigger the lights, and kill the speedo. It would not however, affect the pedal feel. You should feel the same pedal feel with the ABS on or off. You could test this by removing the relay from the central electric panel and testing the pedal feel. Just be sure to use the same conditions each time. You could possibly have a mechanical/hydraulic failure inside the ABS Hydraulic unit in the front that would most cetainly affect pedal feel but not neccesarily trigger a warning light unfortunately. And would certainly not affect the speedo operation. Is your car a late 964? If so the late 964 and early 993 are prone to an unusual problem of a gunky builup in the bottom of the brake fluid reservoir. The problem originated when Porsche decided to use a new brake fluid called "long life 200" or "type 200" and stretched the brake fluid change interval from 2 to 3 years in an effort to reduce maintenance costs supposedly. They still vented the brake fluid reservoir to the outside of the car through a little vent tube. Unfortunately, something didn't work well in this setup and some sort of reaction started to occur. The end result is a milky white buildup most visible in the bottom of the brake fluid reservoir. Porsche's recommended fix for this is to replace the reservoir with a new updated style that is sealed and vents through the cap. They also recommend replacing the brake master cylinder and ABS hydraulic unit as well. This type of failure is much more common on the 993 but the 964 is not immune. As you can imagine this is big $$. I've recently personally experienced a very temporary brake failure in a 964 that occured immediately after an abs engagement on a dirty spot in the road. The brake pedal was slightly "spongy" as if it needed flushing before, then all of a sudden the pedal feel was virtually non-existent. After stabbing the pedal repeatedly, it sudden came back and was stiffer than before. They have been flawless ever since. I find this a little scary particularly due to the fact that the car in question is a RUF RCT capable of 193 mph!! I would first examine your ABS relay. Perhaps even pop the cover off and check for any hot spots on the circuit board. You can even smell it and see if it seems burned. If so replace it and see what happens. I would also look in your reservoir and check for milky crud. Remove the cap and pull the little screen out with pliers(PITA). Stick a screwdriver down to the bottom and see if it is thick and gross looking. If so I would at least replace the reservoir and make sure you have the new updated parts before I even considered flushing the brake fluid. You don't want to push more of this crud into your braking system. Stick with a good brake fluid and flush it at least every two years under road use. This is just my two cents from my experiences, I hope it helps. Good luck!!

voodoo964 · 02-14-2008, 02:25 AM

Cheers mike!

I'm spending my Saturday rebuilding the gearboxes for the soft top, i can now add a few more jobs to that - lets hope i get it all done.

Its a December 93 964 so it s one of the last before the 993 took over , the issues you've specified could very well be the cause!

I've had a lot of hassle with my battery so I've been using a booster up until i got a new one last weekend - i guess this could cause problems for the relay.

Anyway i'll go through all the bits and see if i can knock it out.

Thanks for the advice!

btw - i contacted RUF Germany last year about having my car brought up to RUF RCT evo spec they quoted me €60,000($88,000) for the engine alone!

rsrmike · 02-15-2008, 09:08 AM

My God! $88,000??!!?? Man, it's very nice but not THAT nice considering what you can buy for $88K. I think the man that built this car spent $19K?? for the engine part anyway, many years ago.

Let me clarify I don't own the RUF, it's owned by a friend of mine who recently purchased it from original owner. I'm just in the process of rebuilding the top-end for him, the brake glitch was on the way to my house.

I think you probably have a failing ABS relay but I don't think that affects pedal feel. Just in case you missed that part in all my jibberish. Good luck with your projects. Are you fighting broken brass gears in the top lock motors? Mike

voodoo964 · 02-21-2008, 04:25 AM

when i bought the car the roof closed with a bit of a thud, since its my first i didn't really notice something was wrong. i eventually found out that only one of the mechanisms was not connected! so i took the whole system apart to see why it wasn't. it turned out that the threaded plates which the gearbox attached to on the chassis had been broken off by the force. a buddy of mine made up some new plates with nuts welded to them and he riveted them to the chassis last sat. i rebuilt both gearboxes and testes without attaching the roof. the one we had "fixed" was making some crunching noises so i'll have to spend another sat trying to diagnose why the gearbox isn't working - i'm guessing theres some give on the main gear - hopefully i wont have to replace!

yeah 88k is crazy money - might try and get a turbo 965 at some point instead