Vacuum Pump Woes - 1980 240D

[1980240d]

Hi All,

I am having some unusual issues with vacuum pumps on my 1980 240d. I recently had a pump come appart on me. It looked like the cam follower finally gave out. The connecting rod that drove the vacuum piston actually sheared off. Not the best design seeing that alot of that metal drops right into the engine!

I replaced the pump and cam with used spares I had. This pump worked great for 10 days, but then failed. When I opened the pump up, I was supprised to find that the connecting rod had pulled/pushed its way through the piston. The piston was NOT seized.

This seems like an odd failure to me. What could cause this? Are there different pumps with different stroke lengths? Are the cams that drive the pump different? I did do a quick measurment on the lob height, and they appear to be the same. Could it be an issue with the IP or gear that drives the pump? Is there a specific way the cam is suppoed to mount to the gear? I mount the pump in the only orientation that looks possible - with the pump port at about 1 o'clock.

I did notice that the pistion structures are different. The first pump piston was actually a sandwich structure - Flat steel plate that mated to to aluminum pistion -squuzing the ring setup beween the two. The second pump was just a single piece aluminum piston which had the o-ring and "ring" pulled over it.

The pump is the newer style with a single port. The care is a 4 speed manual. Mileage is somewhere close to 300K.

Any insight would be great!

Bill