Vacuum pump lesson learned

[tgingrich]

My vaccuum pump went south last week so I ordered a repair kit and thought everything went smoothly - until I had everything back together. I was only gettting 5-7 inches of vacuum. I was looking for new leaks in eveything - the brake booster, check valves, you name it. I tore the pump apart again and everything looked fine. Back together again this time with the cover gasket from the old pump and back on the engine. Same thing. Growing increasingly frustrated, I tore the pump apart again and looked at the old parts. Well, the valve seals from the old pump were three times as thick as the new ones, allowing the vacuum to leak over the new valves. Old seals in and everything works fine. It was two days from the time I took the pump apart and cleaned everything until I had the new parts for reassembly. Next time instead of burning up my sunday, I will compare ALL of the new parts to the old FIRST. Lesson learned. At least now I know my vaccum system is fine except for the door locks.

[whunter]

Been caught by that type of issue many times.

[tesavage]

Originally Posted by tgingrich

Well, the valve seals from the old pump were three times as thick as the new ones, allowing the vacuum to leak over the new valves. Old seals in and everything works fine. It was two days from the time I took the pump apart and cleaned everything until I had the new parts for reassembly. Next time instead of burning up my sunday, I will compare ALL of the new parts to the old FIRST. Lesson learned. At least now I know my vaccum system is fine except for the door locks.

I am incredibly relieved to read this. I've been having horrible vacuum problems of my own since I rebuilt my vac pump. I even ordered a new main vac line because the check valve in the old one wasn't sealing fully. (But it did sound amusingly like an oboe playing G upon blowing into one end.)

I've now traced the problem definitively back to the pump itself, but had no idea what it could be. Now I think I know. Having decided that the new valves were a little thicker than the old, I didn't think twice about using the new, thinner o-rings. The irony of the situation is that I lost one of the new o-rings and reused an old one, later opening up the pump again to install the new ring when I found it a day later.

Anyway, thanks for answering my question before I had a chance to ask it!

Tom

[tgingrich]

I swore I heard mine leaking too. I fought the temptation to cut the main vacuum line to try to get an accurate reading - I disconnected the line at both the brake booster and the pump and got very low vaccum directly from the pump. Then I reconnected the brake booster when it hissed upon disconnection, plugged both vacuum lines at the valve/splitter with new hoses and golf tees and still got the low vaccum. I wouldn't accept the problem was the 'newly' rebuilt pump. It was.

[James L]

So what worked? the new o-rings are the old? I am getting ready to do this on my 1984 300SD as my rebuild kit will be here friday! Can you walk me through it!! I have the MB cd and it talks about a special clamping tool?

[tesavage]

Originally Posted by James L

So what worked? the new o-rings are the old? I am getting ready to do this on my 1984 300SD as my rebuild kit will be here friday! Can you walk me through it!! I have the MB cd and it talks about a special clamping tool?

You will need to reuse the old o-rings, otherwise you'll drive yourself mad trying to figure out why the rebuild didn't work.

The pump is really simple to rebuild. This page pretty much contains everything you need to know. You can mount the pump on a board with a small wooden block under the rocker arm in lieu of the clamping tool.

I'm not sure that it is really necessary to remove the piston rod assembly if you're rebuilding because of a vacuum loss situation and not a mechanical failure. Do inspect the rocker arm bearings and movement carefully for wear, though. Removing it just isn't very likely to tell you much more.

The rebuild kit doesn't include a new pump-to-engine block gasket. I assumed it would (before finding the above link), and ended up buying one at the dealer for ~$6.00. It is part no. 616 011 03 80 in case you still need to order it.

Good luck!

Tom

[warrenp]

Maybe I should start a new thread? I'm new as of 24MAY2005

The vacuum pump is a cam-roller diaphram style. I found it easy enough to remove and disassemble with one exception. I do not see how to separate the two aluminum castings between which resides the diaphram(s ?). I removed the anti-rotation yoke. I looked for a snap ring or similar to disassemble the rod with a roller / bearing on one end and I presume a head on the other. Do I simply compress the spring and move it sideways? I would like to see an exploded sketch showing what moves where. I'll post this and then go out to the shop and give it another try. I can take a photo if it helps.
Warren Powers 97071-3602

[d.delano]

OK- could anyone tell me why in the hell they package the wrong thickness o-rings with the rebuild kit? Is it just me or are 'they' simply remiss and beyond frickin stupid for doing this?

[James L]

I bought my rebuild kit from ********** and the new o-rings worked perfect and the same thickness as the old ones. Do not forget to order the gasket as it does not come with the kit.

[Wes Bender]

OK, James L got the correct O-rings when he bought his kit from **********.

A question for those of you that got the wrong O-rings in your kit(s):

Where did you buy your rebuild kit?

We need to boycott the suppliers of incorrect parts and patronize the ones who supply the correct ones.

(rant off...)

Wes

[franklyspeaking]

I recently bought a kit from Performance Products. O-rings fit okay...pump works great.

[dieselgeek]

Sorry to resurrect this thread but if anyone wants to know I recently bought an EFFBE repair kit for my 617 vacuum pump. It had the thin check vlave o-rings which didn't work. I replaced them per this thread with the original thick o-rings and fixed the problem. The original failure was due to a check valve diaphragm which cracked.

Do not use the EFFBE repair kits...

Jim
'82 300SD

[dannym]

I used Autohauzas too and didn't have any problems.

Danny