Rebuilt my Vacuum Pump 84-300D - PeachParts Mercedes-Benz Forum

cook · #1 12-11-2012, 09:07 PM

I recently rebuilt the piston vacuum pump in my 84 300D. I primarily followed the FSM instructions along with these instructions:
Rebuilding the vacuum pump on the 617.952

A few notes from my experience that may be helpful to others:

I removed my radiator fan and radiator shroud so I could have better access to the pump.

I used a wooden board to make a holder for the pump while I worked on it as referenced in the link above. Pictures of it are below. It was really simple to make.

The first picture is just the plywood holder with the bolts.

The second picture is the holder with the pump on it. Note that I put clean copy paper on the board to help keep the pump clean.

One thing that was not obvious based on everything I read was how thick the little piece of wood needed to be that is glued onto the board. I found that 3/4" worked fine. Once the MB rebuild kit arrived, the instructions listed almost the same measurement for the height of it. The little piece of wood presses the piston up in the pump so you can remove the bolt on the piston and not have it spring apart. The little block of wood is pushing against strong springs in the pump and keeps them compressed as you work on it. Then as you remove the pump from the board you slowly release the spring tension and once removed from the board you can easily remove the other parts as needed.

I used the genuine MB rebuild kit and everything fit right, as expected.

I did not use any gasket sealer on the gasket when I installed the pump back on the car. I made sure all the old gasket material was removed from the block and the pump. Both surfaces were shiny clean when I was done. That took a while to do.

I tightened the 6 pump mounting hex-head bolts to 7nm.

I also replaced the bearings in my pump while I was rebuilding the rest of it. Sorry, but I did not get any pictures of it.

And I checked the play on the timing device to see if the bushing was worn or not. I had hardly any play, so I do not expect any issues from bushing wear.

Everything is working fine and I have good vacuum now.

I hope this helps.

Diesel911 · #2 12-11-2012, 10:23 PM

Cool.

Did you see anything that was obviously worn?

Stretch · #3 12-12-2012, 03:44 AM

Did you have any trouble with the cover screws?

Mine were all corroded in place.

cook · #4 12-12-2012, 09:22 PM

I did not notice anything that looked worn in it. The piston walls looked smooth, no deep scoring. I just hope I would have noticed if something looked worn. The bearings looked fine too. They had the plastic race in them, but looked OK and all the bearings were in place. I replaced them anyway since there was over 350K on them.

I got all the screws off OK, 2 got slightly bent on the head where the screwdriver fits into it, but the rebuild kit included a new one, so I used that one to replace the worst one.

qwerty · #5 12-12-2012, 09:44 PM

Did you replace the inlet port check valve? (Contained in the nipple where the hard pipe connects to the pump.)

Stretch · #6 12-13-2012, 03:28 AM

Did you by any chance write the DIY in the linked thread?

Diesel911 · #7 12-13-2012, 10:54 AM

Quote:

Originally Posted by Stretch

Did you have any trouble with the cover screws?

Mine were all corroded in place.

I was a slow learner and sheared off 2 of mine.

After that Heat Penetrating Oil and I used a Hand Type Impact Wrench that you Hit with a Hammer left over from My old Motorcycle daze.

I never replaced them either. I just seald the edge with Silicon Sealant.

I did not rebuild mine I just went in and cleanded it out and I also put a little Silicon Sealant around the edges of the Valves in case the O-rings had srunk/compressed a little.

The other Member made a comment about the Check Valve. One lost some Vacuum due to the Check Valve. I removed and inspected it and sprayed it out with WD-40 and my Vacuum returned to normal. Later as above I took the Pump apart and cleaned inside.

If you buy the Piston Rebuild kit, the Arm Bearing end rebuild kit and an New Check Valve it will cost more than a New Vacuum Pump (a new Pump comes with a Check Valve) and because you rebuilt it yourself you will have no warranty.

Brian Carlton · #8 12-13-2012, 11:43 AM

Quote:

Originally Posted by Diesel911

If you buy the Piston Rebuild kit, the Arm Bearing end rebuild kit and an New Check Valve it will cost more than a New Vacuum Pump (a new Pump comes with a Check Valve) and because you rebuilt it yourself you will have no warranty.

.............and, you run the risk of a "maintenance induced failure" if you make an error in the assembly process.

Not worth the time, money or risk. Buy a new pump for $300 and be done with it. Not a bad investment for 250K miles.

jpizano23 · #9 12-13-2012, 03:01 PM

When I first took mine off two of the bolts got stripped it was on that tight. One of them I was able to get out with a larger hex key the other I had to drill out and then remove once the pump came out. When I took the pump apart two of the flat head screws didn't want to come out i had to drill those out too and then remove them, I replaced all of the screws on the vacuum pump when I was assembling it. I also replaced the all of the bolts to the engine block when I put it back on.

cook · #10 12-13-2012, 08:30 PM

Qwerty -- I did not replace the metal inlet port check valve. I cleaned it and it was working fine.

Stretch -- I did not write the article I linked to in my first post above. The original article is still referenced many places on the internet, and the cached feature of searches makes you think it is still there, but when you try to go to the article, it ends up being a dead link. So I was really happy to actually find the article -- it had been moved from its original location. That is 1 reason why I included it in this thread.

Stretch · #11 12-14-2012, 12:37 PM

Stealth bookmarking...

...nice! Thanks for posting it up anyway.