993tt neophyte question:

What is that vibrating noise coming from the dash? Occurs while is running and driving, lasts 5 seconds or so each time, and seems to cycle very frequently, like every time I slow down, after hard braking, and just plain whenever.

I assumed it was the brake booster pump cycling, but couldn't find any threads on this being well known to owners in the 993tt forum. My searches led to the faulty ccu motor fan as the culprit in the 993 forum.

Thoughts on the cause and whether the frequent cycles is expected and normal? Btw, my brake pedal is firm and no problems with performance. Thanks!

 

The early 96 brake booster setup is noisy, and you hear and feel it. That said, mine only cycles occasionally unless I'm in traffic or doing lots of around town driving. It also feels less to me like its in dash as under the pedals, but close enough.

If you determine this is the case and you don't have the updated parts, you can purchase them for about $450 and retrofit pretty easily.

 

thanks, i do have an early my96 version. build date was actually 6/95. and yep you're right, i hear/feel the cycling much more often while city driving.

quad, sounds like you haven't retro fitted yours either? i'm wondering what the difference in performance would be with the updated part, and whether anyone thinks if the more frequent cycling is a sign of impending part failure?

 

I have not updated it as 450 for the supplied parts doesn't fit within my cost/benefit guidelines. My car isn't a daily driver so it's not real annoying.

The retrofit parts are new lines and some different mounts and such. Nothing that would affect performance.

Not sure why yours runs more frequently though

 

If you're hearing the brake booster pump frequently, you could have a failing pump - it's having to keep cycling to maintain the pressure. Unfortunately it's a very expensive Porsche [only] part.

 

if you need one, this is probably the best price you find. Maybe make a lowball offer.

http://www.ebay.com/itm/Porsche-911-...823d94&vxp=mtr

 

Thanks for the link. If the pump does fail, I should expect warning light and a stiff pedal, yes?

 

If the pump does fail you will crash, probably. OK, so you may be lucky, but if the pump fails you will have effectly no brakes - it won't be a case of standing on a stiff pedal a little harder.

When my pump began failing on my old 993C4 I didn't get to the total failure stage - the pump just seemed to be buzzing away far more frequently (ordinarily you may hear it maybe only once on a journey after the initial start up). I don't recall any warning lights though - I guess there was just sufficient pressure being retained.

 

don't think so. there has to be a safety built in.

 

Here's a quote from another forum:

"My brakes failed yesterday, i had ignored the warning light on the dash but only for about 10 miles then parked up, on setting off again the brakes disappeared, the pedal was as hard as nails and could not be pressed , absolutely NO brakes at all over 2 mph , called the AA they took me home .
Don't be a fool "like me" if the warning light comes on STOP THE CAR IMMEDIATELY !!! it could have been curtains for me yesterday."

...and another:

"I had a similar problem a few years ago, in a 964 i had. i was going alot quicker and it was quite scaring. doing about 50 mph and no brakes when i pressed the pedal. But i had no warning lights come on.

Originally i changed the relay, which was expensive from porsche as i could not find a used part. that did not work and porsche would not take the relay back.

The brake booster pump was a nightmare to source, porsche roughly wanted £1600 for the booster. My car was off the road for about 3 months utill i could find one used, even that cost about £600. Once installed straight away back to normal."

Seeminigly there's no 'safety backup'.

 

I find this extraordinarily hard to believe.

 

Agree, it's a booster, not the complete brake mechanism. Without it, the system will be unassisted, but functional. My logic says that would make the brakes hard to push but with greater effort, still able to function, albeit suboptimally.

 

My understanding is there are two brakes left after the warning light comes on. I think I read it in the owners manual but don't quote me. Given time there is always downshifting and the e-brake. Yikes!