Oxford_Hippo

Hi,

few problems with the brakes/brake fluid on our new ( or at least recently bought ) UK 993 C4 cabrio, 1995 model year.

Problem 1
When I bought the car the ABS light was coming on intermittently,
but filling the brake fluid seemd to solve the problem..or so I thought.

Week later ( last saturday ) topped the fluid up to 5mm above the Min. Mark.

Tonight - checked level again, and it was 5mm BELOW the Min. Mark - after only about 50 miles of driving - so guess there's a leak somewhere....

Problem 2:
Buzzing Noise in the cabin.
Get a loud ( deepish ) buzzing noise when I first turn the ignition, to position 1 - so dash lights etc. all on, but no engine turn.
Seems to come from the front of the car.
Buzzing noise goes after the engine has been running for few seconds - so thoughthis must be the ABD/ABS pressurizing iteself? - but it does not sound like a 'healthy' noise!

Tonight ( car battery flat after 3 days of parking after a 'good' drive - so will hunt through posts on battery drain )
But - had bonnet / trunk open so I could boost start the battery tonight,
This worked
But - heard loud buzzing coming from the ABD unit in the trunk

In true amateur mechanic fashion I gave it a gentle 'tap' and it stopped buzzing!
but it felt like the vibration was coming from under the ABD cover,
and felt / sounded too loud to be just an ill-fitting plastic cover.

Went for 20min drive to charge up the battery,
Stopped to fill up the tank.
Checked the brake fluid - it was below the min mark - so topped it up - as described above.
10 mins later on the drive home the ABD and ABS light came on
fraid I can't emember if I was braking at the time.

Found the other threads here ref. ABD/ABS faulty connections - so will try those

My main concern is the deep buzzing noise, and vibration from the ABD.

Does the ABD unit have motors / pumps that could be causing this?
I'll be able to have a closer look tomorrow, and take the ABD cover off.

Thanks for any suggestions.

ps - despite all this still, enjoyed geting back in the car and the drive tonight!

geolab

It looks like you have a leak and should be looked into BEFORE driving the car anymore.
The sound you are hearing is most probably the pump re-pressurising the system, since the leak is letting brake fluid out.
The ABS and brake lights on the dash are two distinct lights. Which one is lighting up?

Any problem with the brakes should be solved before driving.
Have you checked under the 4 corners if there was oil somewhere ? whilst the leak should be minimal.
BTW, the pump stopped not because you tapped on it, just a coincidence.

g_murray

Sounds to me like you definitely have a fluid leak somewhere. The battery is going dead because the ABS pump is (constantly?) running so as to maintain pressure. Filling with fluid to then have it go low only after a few hours is a definite tell-tale. You need to bring the car into your favorite mechanic to have the 'problem diagnosed'. The brakes on a 993 are very powerful -- and very necessary -- don't lollygag with this one. This needs addressing now.

Ger.

Oxford_Hippo

Hi Geolab and g-murray

thanks for the speedy answers,

The recent ( yesterday problem ) was BOTH ABS and the ABD lights on at the same time.

Went for a ( cautious ) drive today.

ABD and ABS lights came on briefly after about 5 mins - just as I was stopping at the shops.

Then, about 10 mins later, restarte the car to continue my journey - and hey presto - no ABS light, and no ABD light - at , nada, and have driven ( still cautiously ) for about 3 hours today......I think it must have been the way I 'tapped' the ABD box yesterday!


yes - before I'm reminded - I agree brakes can't be left to luck - so will get mechanic to check it at the weekend.
Thanks for the help
Tim

g_murray

Quick question/reply: when was the last time the fluid was *changed*?
Stuttgart recommends the fluid be *changed* every 2 years for normal driving. A LOT more frequently if you track the car.

I've removed the ABS cover (the black platic bit between the battery and the 'driver's footwell area') in past times for concours preparation, and, I gotta tell ya, there's very little in there than can 'jiggle around' or come loose.

I sincerely hope you don't need a new ABS pump coz those things are $$$.

It's possible there is or was a (lot?) of trapped air in the system and the extra fluid you put in has 'taken its place'. The pump may have been continually operating because it was trying (constantly) to build pressure -- which is hard to do when there's compressible air (not incompressible brake fluid) in the lines.

I would start with the simple stuff first --
i) check for leaks
ii) check for loose brake-bleed nipples (a distinct possibility)
iii) if the fluid is 'ok' then just bleed the brakes to remove air
iv) also check for the existence of the 'waxy' stuff during your bleeding
v) if the fluid is OLD or has been 'beaten on' then purge the system completely and replace with brand new (e.g. ATE super blue) fluid, etc. etc.
vi) check the WEAR on the brake-pads ...do they need replacing? ..which would cause the fluid level to drop (altho' not in THAT short a period of time).

If the above DOESN'T "work out" for you ...then a trip to the mechanic might be on the cards after all - both for your overall health ...and peace of mind.

Ger.