Martin Hodgkiss

Hi all,
today I walked away from my 1990 964 c4 and heard a faint buzzing coming from the front. At the time I stupidly thought that it was the oil cooler fan.
The ignition was off at the time. I went in to the office to return an hour later to a non buzzing car. I drove thw car away and noticed the buzzing again only louder. I Popped the front bonnet and was met by smoke coming from the very front above the battery.
On closer inspection I found a king of pump under a plastic cover. I removed the cover to find a pump that was so hot that the plasic pipe feeding it had melted and was dripping fluid all over the battery.
I checked the resovoir to find one side completley empty.
The only way i could stop the buzzing was to disconect the battery or as I later found out , pull out the brake booster relay.
Pump seems to turn off when i squeeze the relay is it faulty??

Has anyone else experienced this or know what the problem is???

Thanks

Martin

ps the axel red light is now on all the time (4 wheel drive)

Adrian

Dear Martin,
Your C4 is now undriveable and you have some work ahead of you. That pump is the brake boost hydraulic pump. It is now toast. What has happened is that through relay R51 the pump has remained powered, overheated and melted the plastic return line. You will find that your luggage compartment may now be filled with brake fluid.
The relay, pump, pressure switch and plastic lines will all have to be replaced. Once this is done you will have to bleed the brake boost hydraulic system. As I said this C4 is now unsafe to drive and must be repaired before you go out again.
Ciao,
Adrian
964C4

Martin Hodgkiss

thanks Adrian, The pump appears to be working, so im hopeing its just a relay replacement and a then the system back up. Anyway the garage has just taken it away.
Any idea how much it would be? worst senario??

Thanks for your advice, spot on as always

Martin

Adrian

Dear Martin,
I have some bad news for you. The pump has been overheated and internally damaged. It may still appear to work but believe me it will fail you when you need brakes. These pumps are designed to run intermittantly and have a duty cycle. This is the 5th or 6th time I know of this problem and all but one person listened and got a new pump. The one person who didn't is very lucky to still have his 964.
I cannot stress strongly enough the need to have the pump pulled apart and checked/repaired or replaced.
I have no idea what the total cost is going to be but I would budget for circa £1,000 if you also replace the pump and the pressure switch which has also been overheated.
I would also recommend you be 100% sure of the cause before you accept the 964 back from the shop.
Ciao,
Adrian
964C4

Martin Hodgkiss

ouch.....
It's in good hands now, i'll just wait for this huge bill !!!!
Damn i'll have to sell a kidney.

Thanks,


martin

Adrian

Dear Martin,
The lesson to be learned from this incident is to learn the 964 or any other auto that anyone owns. There is only one fan which you could hear which is designed to operate with ignition off as a safety overheat protection only and that is the rear blower fan. If you have any other noises eminating from the 964 that you can hear when you walk away it is a good idea to turn around and investigate.
The oil cooler fan will not operate with ignition off if serviceable. Nor will the condenser-mixer fan.
I included in my book a few extra checks for C4 owners to carry out in the servicing schedule hopefully to avoid such problems. I re-read your post and I am sure that there would have been other possible clues to impending failure if you knew how to identify them. Complicated systems like those in the 964/993/996 etc require additional care and understanding. Most importantly understanding on how they work because they do not work like other cars. One of the joys of Porsche ownership is understanding that Porsche often have their own way of doing things. Plus the 964 is dry sumped and its oil system does not operate like a standard wet sump system does.
Ciao,
Adrian
964C4

Rocket Rob

I had this happen to me. The fault was a bad relay that cost me $2,000 for parts and labor. If you ever hear the ABS pump running after the ignition is turned off, I recommend pulling the fuse and then have the car taken to your mechanic immediately. Pulling the fuse may save you the cost of a new ABS pump.

Adrian

Dear Rob,
Brake hydraulic boost pump. There is an ABS pump installed and is part of the ABS hydraulic unit. These distinctions are very important because all road going 964s have an ABS pump but not all have a Brake boost hydraulic pump.
Ciao,
Adrian
964C4

ulfpc

I had the very unpleasant experience of pushing the brake pedal
to the floor without the car stopping. There was a big leak in
my hydraulic pump and brakefluid everywhere.

A bad hydraulic pump is a very big danger, so please be careful
and observant.
Ulf