Michael Gibney

Hi, Loooking for some advice here.

My brake warning lamps came on, low brake fluid and or no pressure in ABS system so no power assist.

Found a leak of brake fluid under the pump and traced it to the little black plastic fitting that is held into the pump by a small stainless steel clip. The said plastic fitting was "melted" on the end that goes into the pump and was blocked off by its own melted material. I have made up a temporary brass replacement and bled the system and it all works fine but the question remains - what caused the melting? Common sense sais heat but how can that be because all else was fine and pump only works for a short time before building pressure so it could not be overheating.

Has anyone else had this happen?

Any suggestions to avoid a repeat?

Thanks

Rich W

Do a search on this. There was a fairly recent thread about a malfunction which will cause the ABS pump to run continuously and subsequently cause the brakes to fail (as you already know).

Adrian

Dear Michael,
The hydraulic boost pump has been running continously because the pressure switch on the pump has failed.
The plastic fitting melted, because the pump designed for a maximum running time of 2-minutes continous has massively overheated.
You will need to remove the whole pump, have the pressure switch and seal replaced and the pump checked out. If the pump ran out of fluid it is toast.
This is a safety issue which, by the way has nothing to do with the ABS. This must be repaired properly. The system is not working fine and by replacing the plastic fitting with the brass one you have actually paced yourself in some danger of running out of brakes when the pump fails completely. This will not take long.
Ciao,
Adrian
964C4
GT-2

Michael Gibney

Adrian,

Thanks for the info, what you have advised and the search I did after the first reply I had lead me to believe this problem must be approached in a comprehensive manner so I have put the car off the road and have removed the ABS pump and have sent it to a repairer for testing. The repairer is the one recomended by the Mercedes Benz dealers as the firm they use for the testing and repair of their pumps. Although I am expecting a "replace" outcome I can say that with the temporary brass fitting to get me home the pump reached pressure faster than it has in the past year that I have owned the car so the restriction must have been there for a long time, again evidence of a poor previous servicing, something I have seen too often on this car.

Thanks again.

Regards, Michael Gibney

Adrian

Dear Michael,
I hope you removed the Hydraulic boost pump not the ABS pump. The ABS pump is part of the ABS hydraulic unit.
Ciao,
Adrian
964C4
GT-2

Michael Gibney

Adrian, the unit I removed is the one in front of the battery, very close to the front of the car. This is where the plastic part was melted so I hope I got it right, thanks again.

Regards, Michael Gibney

Adrian

Yep that is the Hydraulic boost pump absolutely nothing to do with the ABS,
Ciao,
Adrian
964C4
GT-2