Vacuum pump rebuilding, diaphragm type

[derburger]

My vacuum pump is exhibiting the classic signs of pre-failure. Oil is getting into the air filter which is a recent development, and there is an oil leak from the pump, which leaked when I bought the car. No signs of vacuum failure, though. I have a few questions about this job, since my haynes manual is sketchy on the topic, and there aren't many posts about the R&R of the pump. My vacuum pump is the diaphragm type, with the vent hose going into the air filter housing on the top.

1. For removal of the pump: remove the PS pump belt, disconnect air hoses, and the 5mm hex bolts and the pump, correct? I'll degrease it first, and clean the hex bolts. Is there a trick, or easier way to do this?

2. There are two rebuild kits sold:

A diaphragm seal kit, and the check valve repair kit.

Is the replacing of seals pretty straightforward in the diaphragm type vacuum pump? As in, I should be able to R&R these parts that I see in the pump. My main goal is to stop the oil leak and the oil in the air fiter, maybe I should replace bearings "while I'm at it" too. What's the standard procedure for rebuilding the pump?

3. Since the "oil drain separator check valve" is the same valve sold in the check valve rebuild kit, and the oil separator system causes leaks when the valve fails, I should replace that valve when I change the oil pan gasket, which also leaks.

4. I know MB gaskets don't require any sealant, but I want to be sure there will be no leaks. I'll use a torque wrench on the bolts for the proper torque, tightened in a star pattern. I've heard of a spray adhesive that helps with gaskets, what is the popular one to use for these jobs?

Anyone do this job before? It looks about less difficult than AC compressor R&R.

[IMG]http://www.***************/secure/PartImages/0015860743.jpg[/IMG][IMG]http://www.***************/secure/PartImages/068198819.jpg[/IMG]

[derburger]

Bump. Anyone rebuild the old style vacuum pump?

[rrgrassi]

IIRC, bgkast rebuilt one.

[Diesel911]

The Factory Service Manual has instructions on rebuilding all of the different types of Vacuum Pumps.

But if you are careful how you take it apart I think yours is just "assemble in the reverse of disassembly".

There has been more than several cases of Vacuum Pumps not working after being rebuilt. This was due to the O-rings in some rebuild kits not being fat enough to seal the little Check Valves.

I have a Piston type Vacuum pump but when I took it apart I sheared off 2 of the screws. To get the rest off I appled heat via a Propane Torch and penetrating oil.
I never got the 2 broken screws out and used a light coat of Silicon Sealant around to edge to compensate for the missing screws; with no problems.

[derburger]

If the o-rings in the rebuild kits were too small, I think some people just re-used the ones from the vacuum pump. I don't have the FSM anymore since it was taken offline and I haven't bought the CD. Fortunately, the skinnerbox.steaky website with the manual and the PDF's are on archive.org so they can still be used.

I'll order the diaphragm kit and the 2 check valve rebuild kits, so I can replace the check valves in the vacuum pump and the oil separator check valve, since it's the same valve in both applications. I see in the FSM where to replace the diaphragm by removing the hoses and cover on top of the vacuum pump. Are the check valves on the inside of the vacuum pump, where the pump meets the engine? There isn't a section in the FSM on replacing the check valves that I can see.

[vox_incognita]

Vacuum pump diaphragm replacement pix

On changing diaphragm,the manual on earlier models(w115) suggests the lid to be tightened on a pre-tensioned diaphragm (2mm follower lift IIRC)-a special fixture has to be made in the shop etc.I suppose by not doing this the diaphragm would go south sooner than expected.Follow the instructions carefully.
This is a service info sheet by the manufacturer:

http://www.ms-motor-service.com/ximages/pg_si_0025_en_web.pdf
P.S.-2,6 mm preload :
http://web.archive.org/web/20030804201252/skinnerbox.steaky.org/123_DISK2/program/Chassis/43-620.pdf
...I believe one could pre-load the diaphragm without the fixture anyway...

...never knew skinnerbox was still on the net,thanks !!!

[kerry]

When I rebuilt a diaphragm pump on my 77 300d, I did not have to remove anything other than then fan shroud. No need to remove the whole pump, just the front cover. Check valves are under the small cover on the front cover. I did check o-ring sizes. It's a 2 hour job at the outside.

[mobetta]

I used an air ratchet to remove a vac pump, really makes life easier.

[derburger]

Good stuff, thanks for the information. The FSM (the skinnerbox FSM is still online, but at archive.org) tells to use a special tool to pre-load the vacuum pump, and maybe without it the rebuild does fail quicker. With the pump still on the car I suppose it would do the same thing as the special tool. I ordered both check valve rebuild kits so I can use one of the extra valves for the oil separator, when they get there I'll see which brand has the better o-rings for the rebuild. The vacuum pump is leaking oil from the gasket, apparently it was a failed re-do of the gasket when the P.O wanted no oil leaks. I think I'll rebuild the pump while it's on the car, then remove it to replace the gasket. I'll use a torque wrench and FSM torque values since I don't want a leak or failure.

[Stevo]

A couple things, didn't read the whole post so not sure if this was covered. Be very careful undoing the allens on the pump. The bottom one is easy to round out as its difficult to get a straight shot at. The two "down" parts of the 'roller coaster track" on the timing device need to be "up and down" when you install the pump (so you dont have to compress the pump spring) I made a board with a 8+- inch piece of angle iron to compress the spring while working on the pump. DONT put to much torque on the center bolt, dont ask how I know