Tackled the project today. Let me start by saying that the only conceivable way that this is a 1 hour project is if you are a MB-trained tech who has done dozens of these.

Started by disconnecting the vacuum lines. Easy enough. Removed the radiator hose so I could get into the area. Next I attempted to unscrew the 'top' of the vacuum pump to pull it and replace the diaphragm. No luck there. The radiator / fan / housing were in the way, so I couldn't get in there with a ratchet or screw driver. Might in theory have been able to take the top ½ off of with some bent arm (or whatever they're called - they look like an elongated S) screwdriver. Had I succeeded in doing so, however, there still would have been a zero percent chance of being able to replace the diaphragm at that point. Just too hard to get up into the space where the pump is located, even working from underneath the car.

I decided that rather than pulling out the radiator, etc., I should just take the entire vacuum pump off and work on it separated from the car. Cleaned the heads of the Allen screws off, sprayed a shot of penetrating oil on them, and eventually was able to unscrew the pump from the engine. That was only the beginning of the challenge. At that point I tried to slide the pump out past the fuel filter housing. No luck. So I reversed course and tried to take the pump out through the bottom. No dice there either. The opening of each space was too small to squeeze the pump through. I resorted to disconnecting all of the lines going to / from the fuel filter housing, unscrewed the house from its mount, and pulled the entire filter housing (w/ filter inside) off the car. Success! I could finally remove the vacuum pump from the engine compartment and work on it over to the side.

Sprayed the vacuum lines out with brake cleaner to flush all the nasty oil out of them. Worked well. Lots of oil up in them.

Took the top half of the pump off, and then opened the housing where the valves are located. Cleaned the housing out well (lots of oil in there - used brake cleaner and shop towels), and put in new O rings and new valves. Reused the springs, but I did clean them well first. Put that all back together without any problem.

Next I disassembled the bottom ½ of the vacuum pump. Removed the old diaphragm which had a decent size tear in it (don’t think I put it there when I used a screwdriver to pry the 2 halves open – the diaphragm had them stuck together, and it looked like a touch of silicone sealant might have been used). The bottom half was a mess. Cleaned it well (same drill) and then checked out the roller and ball bearings. The all looked good and rolled around nicely. Gave the bearings a small shot of WD40 to keep them lubed. Cleaned the disks that go in there too (one below and one on top of the diaphragm). Then I started to put the thing back together with the new diaphragm.

That is easier said than done. The roller assembly is spring loaded, and you have to push it up into the pump body to align the built in ‘nut’ (though its not really a nut, more like a nut-tube-whatever) with the center screw that keeps the diaphragm in place. I struggled mightily with that for about 30 minutes. I was ready to give up entirely when I decide to compare the new center bolt that came with the rebuild kit (diaphragm, bolt, washers, 4 of the 8 bolts that go around the edges of the diaphragm) to the old one that I removed when I replaced the diaphragm. Sure enough, the new bolt was at least a quarter inch shorter than the old one. @#$%^. Why can’t they send the right bolt! Cleaned off the old one and tried again to screw the diaphragm in place. It finally worked. Placed the top half of the pump on top of the diaphragm, aligned the holes, and started screwing in the 8 bolts that keep the 2 halves together. Tightened them in a star pattern, as others have instructed.

I did not, however, remount the vacuum pump and hook everything back up as I do not have a gasket for the pump. The old one stuck partially to the pump and partially to the engine. Had to scrape it off with a razor blade. Obviously can’t reuse it. Contemplated using gasket sealant instead of waiting to get a new gasket, but decided against that for now. I plan to order a new gasket tomorrow and have it overnighted, so I can try to work on it Tuesday evening after work. I feel like a fool for not having ordered it when I bought the repair kits and had them overnighted to me. It’s a $2 part!! What was I thinking?

I took a couple of pictures, which I’ll try to post. Start to finish I spent about 5 hours on this. It would have gone much faster had I known in advance which roadblocks I was going to hit, of course. But this is still at least a 2+ hour job IMO.

In the meantime, did I miss any important steps along the way? I assume waiting to get the gasket is the right choice – does anyone disagree? Once I hook everything back up, reprime the fuel filter, etc., is there anything else I need to do prior to trying to start her up?

Many thanks for the advice you all have offered so far. Please keep it coming! As I mentioned, I’m a complete novice and am just learning as I go.