Menu toggle

ABS causing a wooden brake pedal and crash

R

RLambert

PCGB Member
Member
Bit of background first, coming down to Castle Combes Quarry corner at 140mph on the first proper lap in the Club Race, I hit the brakes and got a solid brake pedal, pressing harder didn't slow the car much so I whacked the back of the car in front, lost control and then bounced off the barriers. There is a lovely video clip on you tube, look for Porsche Club Crash Quarry.

Anyway, in the 2nd race I was getting the same thing but if I came off the brakes and reapplied them the woodeness went away. I didn't have this problem in qualifying.

So after discussing my accident down the pub last night, it was suggested that this was a known problem with ABS cars and the long bumpy straight leading down to the corner. This is upsetting the ABS somehow but by tapping the brake before the corner, the ABS sorts itself out and the brakes are fine.

Has anyone else heard of this phenomenon ? And if so how can the ABS cause a solid feeling pedal ? I've had a quick google for it but didn't find any info.

A couple of the other club racers have also had 'strange' things happen with the brakes at the same corner.

The car is a little battered by the way but I went on to get 2nd in the 2nd race and was the fastest 911 so I guess that means the wheels are still pointing in the correct direction!



 
Met someone at a trackday in July driving a 964 C4. His brakes 'failed' at a downhill braking point - approach about 120 into apex about 30. It felt as if the servo had failed and the amount of effort to press the pedal was sky high. Turned out to be the ABS relay (I think) had worked loose in the fusebox.

Not sure if this is similar to your incident? Not looked at you tube but am guessing you were the red car - I was watching from Camp?
 
Yes, that was me in the red car Ade. How did the accident look from your perspective ? I hope it was entertaining!
 
Like Ade, I've heard of this on a C4. I think the main difference between their brake system and our simpler C2 system is that we don't have a brake booster pump (but someone might correct me on this). This thread on Rennlist has a number of pointers about a hard pedal:

http://forums.rennlist.com/rennforums/964-forum/20389-hydraulic-brake-pump-failure.html?highlight=+hard+pedal

If we discount the possiblity of a booster pump failure then that leaves other suggestions like failure of the pressure switch (again I'm not sure if a C2 has one), ABS relay or simply a low fluid level (maybe because of going downhill).

Ouch to your hit and double ouch to the yellow 911 clouting you afterwards! Remind me to cross CC off my list of must do tracks!

p.s. How's the fuel surge problem?
 
Hi Steve,

Yes the yellow 911 crashing into me was the icing on the cake. Tim, the driver did come and apologise afterwards which was good of him. I was just in the wrong place at the wrong time.

Your thread talks about the electric pump failure which wouldn't be an issue for the C2. I did find another thread that blamed dirty or dodgy wiring on the ABS sensors so I'll have a look at those.

As for the fuel surge, I don't have a fix other than loading it up with fuel. I'm going to look at a swirl pot but I think the extra weight of the pot, pipes and the reserve fuel negates most of the weight saving of running lower tank fuel so that's probably not an option.

Apparently of all the UK tracks, Quarry is the corner that has the most track day crashes, so whilst CC is a brilliant track and definitely worth trying, it can bite so you do need to be careful!
 
A bit distant! To say the least.

When I noticed the damage on the yellow one, as it continued to race, I guessed there had been contact. Given the amount of tyre smoke from his car in the braking zone it was inevitable he would never make it round.

Keep forgetting the C2 and C4 brakes are so different.......

CC is a great track! Avon Rise into Quarry has so many posibilities, especially given the approach speed. Not sure I would like it in race conditions though with a pack of other cars all going for the same bit of Tarmac.

Been there this morning for the pcgb trackday - viewing only though. Last trackday I did there (in the rally car) I span on turn-in for Camp - first session in the rain and still on worn A048R tyres. Quick swap back to horrible road tyres made the rest of the day far more controllable.
 
I've posted this on Rennlist for you to see if anyone can come up with any more ideas for you.

http://forums.rennlist.com/rennforums/964-forum/590255-abs-causing-a-wooden-brake-pedal-and-crash.html
 
Thanks Steve, I've just been reading the responses. Rennlist does seem to have a huge following and the forum users are very helpful.

I checked all the ABS sensors yesterday the the front ones were very gunged up with metal filings and dirt so I've cleaned those off. The outer casing to the wiring to the front sensors has melted a bit due to the proximity of the disc but the wires seem intact.

I'm going to check that the relay is a nice tight fit and that the ABS ECU connection is good and clean.

 
Yes, there were some good responses. I think you can discount the responses about the pressure switch causing some people problems as I believe that's only found on the C4 and turbo hydraulic boosted systems and not the vacuum boosted systems of the C2. I thought it was interesting that some C2 owners had experienced the same effect on bumpy roads. So maybe even when everything is working perfectly it's an inherent problem that you have to drive around, as you did in the second race.
 
I've read of a similar issue on the Lotus forums:

"The problem is when one wheel senses a different speed while loosing contact on a rough road surface during braking, the system locks up giving you reduced braking and a hard peddle until you lift your foot and reapply braking pressure.."

"Happened to me and two others in the mountains on last years Stelvio trip,its fking scary as the pedal goes solid/you dont slow down until you back off and re-apply.
Basically happened when going downhill quite briskly,braking hard and hitting rutted/very bumpy surfaces."


http://www.pistonheads.com/gassing/topic.asp?h=0&f=15&t=809432&nmt=Lotus%20known%20Ice%20Mode%20ABS%20Brake%20Issue%20is%20Not%20Alone
 
You must log in or register to reply here.

Posts made and opinions expressed are those of the individual forum members

Use of the Forum is subject to the Terms and Conditions

Disclaimer

The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

Porsche
Lockton
Pirelli
Officially approved
Oracle Finance
WEX Esso
Collecting Cars
Archant Dialogue
Back
Top