I was planning to be out with the 964 crowd today in Wales, UK for some great driving on great roads.

However, on the way there, about 2 miles before the meeting point, the brake pressure warning light came on and the beeper started to sound but, i still had good braking. We arrived, chatted for 30 mins and got back in the car. The warning light was on but no beeping and still good brakes. After about 10 miles though we started on some twisty roads with undulations when, as i went for the brakes, the pedal was stiff and right at the top of the travel.

Well, that was the end of that. I managed to get the car home and started on the books and searches.

I have checked there are no leaks near the booster and that fuse 15 isn't blown so i'm hoping it is going to be relay R51.

My R51 has a 964 code to it but i wondered if there was a VW/Audi/cheaper/easier to obtain alternative relay parts that would fit? Is there also any way to check that the relay is or is not working before buying another?

Also could anybody suggest what, if not the R51, could be wrong with the braking system to cause this. The car has been off the road for four weeks or so and the wheels have been off in that time but i've not been near the brakes.

Any help as usual would be appreciated.

 

I think you are going to find that your hydra boost pump has failed....

 

Check that the plug on the pump has not come loose. Happened to me in a race once.

 

Which plug on the pump are you referring to? Everything seems to be as it should but i can't get hold of an R51 relay for a few days just to test if it is that.

Is there a way of bypassing the relay - i've heard stories of bypassing the DME on n/a cars using paper clips. Would this work to get the pump running?

 

Here is the electrical layout of the relay.

Can i bypass this somehow to get the motor to run without the relay in place to run a simple test. I tried tonight but my High School physics must be rusty - the paper clip i used to bridge the circuits melted the rubber gloves i was wearing

 

In the front trunk, the pump should be mounted to the very front of the tub. On the passenger's side of the pump, there will be an electrical plug near the bottom. If the battery is lose and shifts a bit, it can knock the pump and dislodge the plug.


You could bypass it, but the problem with bypassing it is that the motor will run all the time. This is fine to do with your fuel pumps, but I would be concerned doing it on the pressure pump. If you did bypass, you would want to use a jumper to connect the opposite sides of the relay. You only need to do the hot circuit (i.e. there are four plugs that come out of the bottom of the relay...you only need to connect two together). It should be the opposite sides you connect. So in your 1st picture, jump the leads on the left right, or the front back. You'll know when you get the right ones, as the pump will start running.

 

I seem to recall Adrian mentioning that is the pump runs constantly over 2 mins it will burn out, might wanna consider that prior to letting it run on.