Indycam

If you have a stock 89-94 964 C4 please do a few tests for me .

1) After the car has been sitting for a long time and the hydraulic pressure has dropped way down , how many seconds does the pump run ?

2) After the pump switches off , how long before it switches back on ?
Please don't move the car or use the brakes . Just wait for it to go on again .

3) On the 2nd pump up , how long does the pump run ?

4) When you first switch on the car and the pump runs , check the fluid level drop in the front section of the brake fluid reservoir please . Measure carefully , how much it drops .

Adrian

Boy its cold outside, but I did the check for you Indy. I had to run my daughter to the railway station, early and it is snowing.

1). 45 seconds (sitting since yesterday).
2). It doesn't (waited 5-minutes), but of course I already knew it wouldn't.
3). It doesn't my systems needs 4 to 7 normal pumps before it cranks up. Heavy braking will bring it on after 2 or 3.
4). The total reservoir fluid level drop is hardly noticeable, maybe 1mm at most.
Note: If the total fluid level is correct. As the level in the reservoir moves towards the minimum level there will come a time when you will see the fluid level in the far right chamber actually drop.
Unfortunately as I have discovered a long time ago this level is still higher than minimum level required to set the warning light off on level ground. However you may start getting an erratic warning when the 964 is being thrown around or under heavy braking.

If anyone else answers these questions and the pump runs for more than 60 seconds then switches off, then switches on again without touching the brakes there is a problem. The system is supposed to hold pressure to 102 bar for a minimum of 3 hours.
Item 3 on the list is a tad subjective. It depends on how HARD you pump the pedal, but twice whilst standing still is not enough.

Check the fluid level and top up just slightly below MAX. Ensure this is done on level ground.
If you think you are losing fluid and cannot find the leak, you might want to check your transmission fluid level.
I have seen at least two C4s that had failed diff lock slave cylinder seals.
They worked fine it was just that they tended shared some of their fluid with the transmission. This is quite a slow process as well.

C4 owners should be aware that the accumulator is precharged. No such device has been used in a Porsche braking system before and its serviceable life age is not really known. Many of the brake pressure problems that will be seen now and in the future will be caused by the accumulator losing its charge. I can tell you I am sure mine needs replacement. Over the years it takes that little bit longer to reach full charge on the first start.
Ciao,
Adrian.

Marc Shaw

Indycam,

Results after 3 runs (ambitent temp 10C in my garage)

1. brake pump when cold: 31 seconds/30 seconds/32 seconds (ie. car had sat for a few hours before each trial)

2. it never went back on (I waited for 20 minutes)

3. brake pump when warm: 6 seconds/7 seconds/7 seconds (ie. switched car off for 5 minutes then back on again)

4. I never could see any change in the fluid level.

Marc

Adrian

Marc,
The system requirement from Porsche is that in step 2 it hold pressure for 3 hours minimum. Nobody is going to sit for three hours plus in their car waiting for the pressure to drop. If the pump stops and then comes on again quickly without touching the brake pedal, you should have the brake boost pressure warning light, exclamation mark and the warning horn/gong/buzzer and you know there is a problem.
I have been informed that this is some sort of test and results were going to be compiled, for what reason I really don't know. I thought the poster wanted some reference for his own 964 to work from.
If everything is perfect you should actually not see any change in the brake fluid level.
Ciao,
Adrian.

Marc Shaw

Thanks Adrian. I gathered that after your first post here but I had actually done these tests a few weeks ago at Indycam's request (before I knew it would hold for 3 hours) and I'm just posting them here now to add them to the collective knowledgebase he is attempting to develop about the braking system.

I guess we interprested #3 differently though in terms of what he was asking for. I did not pump the pedal to see how many pumps it would take before it ran again but rather, switched the car off and then back on again to see how long the pump would run with the system already pressurized (no brake pedal use at all).

Perhaps Indycam can clarify the question.

Marc

dfinnegan

I timed my pump a few times today:

after sitting overnight in sub-freezing temps (~28F): 27 seconds
a couple of hours later at ~33F: 9 seconds
after driving 30 minutes and then letting it sit in ~34F for 1.5 hrs: 12 seconds

I couldn't see any movement in the fluid level, but I didn't check every time

Cheers,
Dave

Adrian

Marc,
I have to be honest and see no value in such a test involving switching the engine off and back on again and seeing how long the pump runs for after the system is pressurised. What is going to be done with this kind of knowledge? Start telling people to test this and if certain parameters are not met based on Rennlist submissions, they are told their 964 is broken?
By the way all of these running times are seriously dependant upon brake fluid temperature.
My biggest complaint is that I would have appreciated being told in the post why the questions were asked.
I wasted a lot of time early this morning in -12C temperatures thinking I was helping somebody with a genuine problem and needed some base points (which are in my book anyway), and in the end it was for something else.
Teach me to read Rennlist before doing my chores won't it!
Note to self, next time stay in bed and give daughter the keys.
Ciao,
Adrian.

Marc Shaw

Adrian,

Like you, I have no idea what this info will be used for.

I just sat in my cold garage and measured the times.

I'm sure Indycam will explain when he returns.

Marc

mark lintott

No idea what the info is for either but I know mine takes between 25-30 seconds for the first start of the day after that its ready to go even after leaving from morning to late afternoon. It never sits still that long anyway - once its out of the garage its used as much as possible. Cold here too but no snow ....luckily.

Nice to see you posting again Adrian - where have you been last few months?

Cheers

Adrian

Dear Mark,
I am a full time writer now which takes up all of my time. I just finished my fourth book and submitted it to the publisher. The Ford GT Then and Now. Big book, lots of historical racing pictures. Quite a lot of Porsche content as well. Porsche AG were very helpful for this book as were Ford and Lola.
I am taking a little break doing some research. I have been commissioned (even been paid) to write a Biography. This has given me some time to do some of the things I used to do more often. However it won't last, because I have to start writing in earnest in the New Year. I also have to try and do the 996 book next year as well.
Ciao,
Adrian.

mark lintott

Hi Adrian,

Nice to hear from you. Sorry, not meaning to hijack the thread but when is the Ford GT book out? Another childhood icon (GT40) but would like to get a new GT if one came up in my part of the world.

Good luck with the up and coming publications.

Cheers

Adrian

July or August 2006.
The fun about this book is that I was given a new Ford GT to play around with here and in the UK and I got to drive two original Ford GTs (GT40s).
Chassis no. 1016 which came third at Le Mans in 1966 and 1078 which did not finish Le Mans 1968.
If think Porsches can be raw try these babies.
Ciao,
Adrian.

mark lintott

Chassis No 1016 must be the Buckmun/Hutcherson car from 66 Le Mans. Just finished reading Chris Amon's bio "Forza Amon" which covers that race quite well. Not sure what his Chassis No was though.

The chance to drive those cars would be reward enough (for me anyway) no matter how the book sales go! Look forward to the book though - I hope it's as detailed as the rest of your writings (!)

Cheers

Adrian

Chassis no. 1046,
Ciao,
Adrian.