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Old 03-24-2003, 05:57 PM
erubin erubin is offline
Registered User
Join Date: Mar 2003
Location: Los Angeles, CA
Posts: 445
vacuum pump and brake booster

Several months ago I bought a 1982 300D turbo (W123). I've taken care of a host of minor problems but got stumped on the vacuum pump. Let me run through my findings and my suggested fixes and hopefully someone reading this can help:

After replacing a few pneumatic lock components I now have a leak free lock system (per my vacuum tester). The problem is that the brakes feel under power assisted and the door locks stop functioning after a few hours with the engine off.

I measured the vacuum pump as 17" Hg with the booster hose plugged and the rest of the hoses plugged. This isolates the system to just the pump. This seemed too low as I was expecting 20-23"Hg per my memory reading through other postings. With the brake booster conected the vacuum is only 11" Hg and the gauge needle is flickering. From this I decided both the vacuum pump and the booster needed work.

I bought a $50 rebuild kit for my pison air pump. I took the pump off the car and inspected the rocker bearing which looked perfect so I went ahead and rebuilt the pump with the 3 new check valves, pison seal and used all the other parts in the kit (see attached photo). After reinstalling the pump I now have no vacuum! This time instead of taking off the pump from the car I just took off the pump cover. It looks like the pison seal that sits over the o-ring sliped off the piston. I cleaned everything and put back the old (but undamaged) piston seal back on. Again 0" vacuum. I have now ordered a new (or rebuilt?) vacuum pump for just over $200. I've rebuilt many hydraulic and some pneumatic systems in the past and never had so much trouble/bad luck.

I assume things will be much better with the new vac pump except my wallet. Has anyone had a similar problem rebuilding one of these piston vacuum pumps?

I will probably still have a brake booster problem with a vacuum leak. Can the booster be repaired with new seals, grommets, etc? Does the entire booster ever ned to be replaced. How do I determine what needs replacing?

Thanks for your help,
Attached Thumbnails
vacuum pump and brake booster-piston-vacuum-pump-rebuild-kit.jpg  
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