VACUUM PUMP FAILURE! Are you neglecting yours?? - PeachParts Mercedes-Benz Forum

Beagle · #11 06-20-2012, 04:04 PM

Thanks for the positive responses Guys

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Quote:

Originally Posted by Stevo

I pulled the vacuum pump just to check it and discovered the piston had broken through (later pump) the housing and that was due to a warn bushing that lives in back of the timing device. That warn bushing allowed the timing device to slam back and forth on the shaft hitting the engine block on one side and the vacuum pump on the other side. There was a deep grove in the block so that must have made some noise. I measured 2.5mm of slop that that timing device had to move. Thats what took out this one, I captured all the shrapnel before it did any harm. So I always check the end play of the timing device when the pump is off.

Steve

I believe that the root cause of almost all of these pump failures is a leaking vacuum system that results in continuous full stroke operation of the pump at high rpm. It is unfair to blame the play in the timing device assembly for taking out the pump when it is the pump that was responsible for destroying the intermediate shaft bushing in the first place. The intermediate shaft has negligible thrust of its own account.

It is probably easier to explain what I’m getting at by comparing the two separate scenarios of driving with or without a vacuum leak. Let’s look at a 200-mile journey first with no leaks:

1)You start up and after 15 sec at idle 25” is reached (FSM) and the pump then parks itself with the roller just kissing the cams. It stays that way as you drive off until you use you your brakes, then the roller dips into the cam a little way for no more than 10 sec to top up and then parks again. This continues throughout the journey. It would probably be an exaggeration to say the pump had been working for a total of 10 min of that 3-hour journey and non of it at full stroke. Both the pump and the timer have been having a very easy time of it.

A very different picture with leaks:

2)At start up the pump will never reach >25” and continues to pump at full stroke until the engine is turned off - it never parks. The level of vacuum reached will depend on the severity of the leak but it will give reduced brake assist. The real damage occurs at high rpm and full stroke for extended periods. It takes 57kg to compress the rocker to a full stroke and at high rpm the cam is thrashing the S#&T out of the rocker and those little 626 bearings while at the same time hammering the F/P shaft thrust bearing. This will continue uninterrupted for the full 3-hour journey! I leave the consequences to your imagination.

For Army...
Pump Piston Replacement

Vac Pump Removal

Quote:

Would you happen to have a more precise part number? Almost every 626 bearing that I have located is either shielded or sealed.

Qwerty
You will need to go to a specialist bearing store and get them to order two 6 ball open "precision" 626 for you. The 8 and 6 ball non-precision bearings are very common so be careful and make sure it is a top quality brand. Check their catalog.