Leaking diff lock pump

[brian williams]

A few days ago 2 warning lights lit up on my 1990 C4 as I was a couple of miles away from home. They were the diff symbol and the brake fluid level symbol.After putting it away in the garage I left it for a while then noticed a slick of some sort of oil from the front end. On tasting it (it tasted salty) I knew it was brake/hydraulic fluid. The fluid had drained out of the spare wheel well,so I pulled all the carpets etc out to find the front end swimming in fluid. I traced the leak to the end of the diff lock pump. Has anyone out there replaced the pump and how easy is it please? I have been informed that the replacement pump can only be supplied by a dealer, hopefully I can get some discount by being a PC member. Thanks in anticipation of any help!!

 

[Dave Wilkinson]

Brian,

The first thing to say is that the hydraulic pump you are referring to is not just for the diff locks - it's for the entire braking system. The pump is VERY expensive to replace, but it may not HAVE to be replaced. The common problem here is that the pressure cut-out switch on the end of the pump fails and, in doing so, prevents the pump from switching off when the correct pressure is reached. The pump then overheats and often melts the hydraulic piping leading to the pump itself - hence the fluid all over the luggage compartment.

The switch is available (964.606.904.00) as a separate part and is, obviously, MUCH cheaper than the pump complete. Only if the pump is burnt out is it likely to need replacement. If you replace the switch you will also need to replace the "O" Ring (999.707.094.40) and any damaged hydraulic piping.

Hope that helps.

Regards

Dave

 

[brian williams]

Thanks for this info. I haven't done much with the car, as busy helping other people with their projects. This morning I did start the car to check for leaks etc. and it didn't actually leak any fluid,although the warning lights were still on. I left it running for 5 mins. and still no leaks although I didn't actually operate the brakes at all. The pump seemed to be running so maybe it is just the switch, and I couldn't see any leaks in any pipes either,although when I first discovered the leak fluid was dripping down from the taped up wires/plastic pipe which runs across the front section of the "boot". What I need to know is how does the switch undo from the pump body? I can see the power connection to the switch and the wire clip that holds it on. The leak seemed to be coming from the black plastic area that enters the pump body. If I get the spares you suggest could fix it how are they fitted and what would I need to bleed to get things working correctly? I hope I'm not being too much of a pain but if I'm to try and fix it myself I need to be fully armed. Also there are 2 electrical connections, one at the top and one lower down, which is the switch connection?

 

[Dave Wilkinson]

Brian,

The switch is the green thing screwed into the top of the pump body. The switch is up near the top, the other connection will be to the pump itself.

BTW, it's recommended that the pump should run for no longer than 2 minutes. Under normal circumastances the maximum pressure should be reached within 45 secs to 1 minute, the pressure switch should then turn the pump off. DO NOT LET THE PUMP RUN LONGER THAN 2 MINUTES!!!! IT WILL DESTROY ITSELF.

As I mentioned in the first post, the heat of the pump will melt the plastic piping. Maybe the reason there are no more leaks is that there is no more fluid!!! You should not drive the car until you resolve this problem - there will be no brakes!!

Ideally you should use a power bleeder to bleed the system once it's repaired and you will need to bleed the clutch slave cyliner and the diff locks (for which a Bosch "Hammer" is required).

Good luck.

Dave

 

[brian williams]

I have now put a new switch on to the pump,what a job it was getting the old one off and the new one on as the fit was very tight! After putting it all back together there are no leaks and the pump did switch off after 45 seconds. I found an article describing the exact procedure via porsche964.com and bled the pump to the ABS reservoir bleed nipple.However,there are still 2 warning lights,the diff symbol and the ABS symbol. Any ideas what I need to do next? I did drive the car out of the garage for about 10 yards and they didn't disappear as usual,do I need to drive a bit further for them to go out or do I need to bleed any more things? Thanks in anticipation!