TomCA911

Hello Fellow Rennlister!

Long time lurker and first time Porsche owner (91 964 C4 Manual Coupe). So I've owned this car for approximately 1 year and everything ran well until I started the car yesterday and I got the brake light, 4WD warning light and beeping horn in the car. My last drive was 1.5 weeks ago and everything seems to function properly. Only thing different was it was an "extra spiritied" driving and braking (not on track).

I warmed up the car for approximately 15 minutes, warming lights stayed on. Then took it for a short drive around the block.

Question 1 - Car ran fine, but the brake peddle was super hard and it took a lot to stop the car. Any thoughts or tips?

I read a hand full of topics on this and most recommends topping off the brake fluid reservoir.

Question 2 - Sorry, dumb question here... The brake fluid in the reservoir is currently light blue color. Since I don't know the history of the brake fluid type/brand, is it ok to top it off with a light yellow fluid (Pentosin or ATE)?

Thanks in advance for your reply!
Tom

Pacific German

Blue is ATE Super Blue fluid. DOT classified it as an illegal for North America. Its okay to mix with other suitable fluids.

TomCA911

Thanks Pacific German for the reply.

Yes, I did read somewhere that the blue fluid is no longer distributed here in North America. This leads me to believe my brake fluid is way past due for a flush. I hope topping it off temporarily (w/ yellow fluid) can help with the braking until I can get a proper flush.

Anyone else experience the super hard brake peddle?

wkoperwhats

It sounds like the hydraulic pump has failed. This is the pump that provides power for brake assist, ABS, clutch and 4WD diff locks. Wait until morning, turn the key to accessory (not to start) and you *should* hear the pump pressurizing the hydraulic system. It will shut off in about 30 seconds. I can hear mine easily from inside the car. If you don't hear the pump, I'd first check fuses, then move on to testing the power plug at the pump itself. It's located behind the removable plastic shroud against the front of the car on the driver's side of the frunk. Hope this helps.

Cheers.

968norway

If the hydraulic pump is not functioning do not drive the car. As you have already experienced, braking becomes very difficult, it says in the manual it is virtually impossible to stop the car without hydraulic pressure.

Hopefully it's a fuse, after that you should check the pressure switch.

TomCA911

wkoperwhats - I followed the steps you outlined this morning and you are correct, there is no pump pressurizing sound that I am used to hearing. I need start looking into the fuses and down the checklist.

968norway - Yes, after noticing the hard brake pressure, I moved the car super slowly down the street hoping something would change. I wouldn't drive it more than I already have. I do hope it's only a fuse and nothing more serious.

I will be doing more researching on fuse's and things to check down the list, but if anyone here has something good to share or a link I should be reading, please post it.

wkoperwhats

If you have a voltmeter, pulling the plug (it's one of those with the metal clip that you press in to release) and looking for voltage might be the easiest solution. RicardoD's excellent DIY writeup on bleeding hydraulics (here) has the perfect picture to help you find the correct connector.

TomCA911

Update - I did check fuse (#15) and (#16) and both seemed ok.

I also checked relay 34 (ABS System) and relay 51 (Pump, Brake Booster). Although they looked fine, when I pulled relay 51 (the tall silver one), there seems to be a rattle inside. I doubt this is normal, but I don't know what normal is

I did reach out to Ricardo who graciously offered to help flush my system, however since I am unable to drive the car, I have to get the ABS pump situation sorted first.

I hope it is just a bad relay. I still have no pump pressurizing sound when I turn the key (not starting the car).

me964

not normal

you should



did you check the 40amp fuse for the pump ?

.

TomCA911

me964 - I did check the 40amp fuse which seems fine to the eye (this fuse is really old looking), but I should swap it out just in case. The fuse is white and non-translucent, so I can only see the top of it unlike the other fuses in the box. I'll report back once I get a new fuse and relay in.

Harry Apps

Your fuse box should have a fuse-tester in one of the relay sockets - look for the slots and a green LED on the top.

TomCA911

Thanks a bunch for chiming in. I learned something new again today. I was looking at that slot but didn't realize it is a testing slot. I will give it a try.

RicardoD

Wish I had one of those C4 ABS testers that Cajunfan is working on! Even has a relay tester in it.

https://rennlist.com/forums/964-foru...or-orders.html

I just placed a down payment for one but this is the kind of tool that would help in a situation like this.

Kappi2907

Buy a multi-meter and download worshop manuals.
80% of testing on the 964 cam be done with a miltimeter.