Two questions.

1) Is not the brake booster suppose to hold vacuum? Mine doesn't. It is a slow leak, but if I pump it to 15 and come back in 3 or 4 minutes, it'll be down to 10. Is this something that I can rebuild? I don't see the parts on FastLane -- maybe I'm looking in wrong place?

2) The vacuum pump -- I put my Mity Vac on it and I get nothing but my vac needle jumping from 0-5-0-5-0-5... so I'm guessing the pump needs to be rebuilt.
a) Can this be removed without pulling the radiator etc.? (I see some posts say yes, and some say no. Anyone who actually did it? Thanks!
b) Which kit would I need, the "valve" or the "rocker arm" one? Or do I need to pull it first?

Thanks,
GD

Gotta,

When you are pulling a vacuum on the vacuum pump, you are moving the air in the opposite direction so the pump valves are opening and releasing the vacuum. This is not the way to test the pump.

The test of a vacuum pump is how much vacuum it will pull when operating and how long it will hold that vacuum when shut off.

P E H

Not that much of newb... I didn't pump the pump when I tested the vac. I only hooked it up to use the guage.

Don't bother rebuilding the booster cause you don't get what goes bad regarding holding vacuum in the rebuild kit. Only the dealer has the booster rebuild. They cost under $10 and are stocked in Germany since no one here seems to rebuild them. Go to a wrecking yard with your Mityvac and test one there and see that it holds steady for a while. You'll get real tired pumping down the rbooster but it's better to do that before removing/installing and...after that remove the master cylinder to check that it was not to badly contaminated with brake fluid. Once approved crawl under the driver side dash, and fumble around with the booster bolts (it's a real pain to unbolt but it goes pretty quick). Should cost $50 or less.

You can rebuild the vacuum pump with parts from Fastlane but a new pump is a better guarantee and you need to build a simple wood jig if you rebuild it yourself. Don't need a new rocker unless yours is bad (need to remove the pump to view). It could be a disaster for your engine if the rocker broke apart in there though. Don't forget to order a mounting gasket if you decide to rebuild. The mounting gasket holds in place with a little grease.

No need to remove the radiator. But do slip in a piece of cardboard to protect it while yoiu are removing the fan. Remove the screws from the fan with a ratcheting box wrench (no room for a socket) or spend 15-20 minutes slowly removing with a plain box wrench. Don't remove the last screw, just loosen it.

Good luck

__________________
1972 450SL
1982 300D Turbo

Can you explain the wood jig?

Also, once I remove the pump, if I take it apart, will I be able to see if a rebuild kit will fix it (i.e. see a worn part and know that the rebuild kit will deal with it?)

Thanx

GottaDiesel,

You'll find the answer to your question and more here:
rebuilding vacuum pump

I doubt you can tell by inspection that you need or not the "valve" rebuild kit cause it's hard to see when the check valve and pison ring leak. You get 3 check valves, the piston sealing ring, etc in the kit.

Before you go spending $ on the pump you've got to test it by taking the leaking brake booster out of the equation. With the booster leaking you can't test the pump until you do the following: Disconnect the pump to booster hose at the booster and put your thumb over the hose end. There are two small nipples on the hose for the vacuum controlled accesories and transmission. One you'll disconnect to attach the Mityvac and the other you need to plug off. This way you've isolated the vacuum pump. Now measure the vacuum you develop at the pump with the engine running and your thumb plugging the big hose end at the booster end of the hose. If you are getting a lot less than 18-20"HG then you need to also fix/replace the pump. The way you described your problem maybe it's just the booster that needs replacing.

Oh yeah, make sure your pump to booster hose isn't cracked/leaking else you'll waste a lot of money fixing everything around it that may actually be OK. They crack at the nipples pretty easily.

You really need the assembly plate ( i called it a jig) to rebuild the pump. Hard to explain why until you try. Without the assembly plate you'll wrestle with the pump and probably end up scoring the piston cylinder and damage the new seal that came with the rebuild kit. Not too hard to rebuild but the results are better with a new pump in my opinion.

The rebuild kit w/out the rocker costs about $55 plus $3 for the gasket and your time. The new pump is about $200 and comes with the mounting gasket i believe. If you need the rocker, the kit costs about $150 at which point don't even bother rebuilding. You wont know if you need a new rocker until you've taken the pump off of the car.

The problems with the vacuum system just get more fun from here. i bet you've got some bad vacuum elements for doors, climate control, etc. But first make sure the pump, booster and big pump to booster hose are good before moving on.

good luck,
Elliot

BTW, i'm paying a fortune in property taxes here in LA. Any tips on your website for my problem? i doubt there's anything to do about that.

__________________
1972 450SL
1982 300D Turbo

Oh...

I tested the pump by removing the the booster hose and testing it right at the line coming out of the vac pump. That is where I got the jumping vac needle 0-5-0-5-0-5... are you sating that I did it wrong? I have a brand new booster hose since the one on the car was broken.

The property tax situation in LA is very hard, but not totally impossible to deal with. Have you tried to seek any relief in the traditional ways? (rate card request, etc.)? Even with surging property values, you would be surprised at what can still be done!

Thanks for the help.

OK, sounds looks like you tested the pump with it isolated so you need to fix/replace it. I guess you have a big enough test hose and adapter to connect the Mityvac right at the pump. I don't so that's why i suggested connecting the Mityvac at a nipple and blocking off the big hose at the booster with your thumb.

Your booster reads like it's leaking as well so you'll want to replace it. It has a relatively large vacuum chamber so if you see a leak over a short period of time (3-4min) the leak is not insignificaqnt.

Once you've got the booster replaced and the vac pump rebuilt or replaced you'll need to move on to the accesoroies operated by the vacuum. there are a lot scattered over the car for locks, climate control, etc and I would guess there are some bad ones in your 20year old car. we can deal with that when you're ready as there are techniques and tricks for troubleshooting them as well as replacing them.

Regarding LA prop tax: I am paying about 1.25% based on my purchase cost of the house (bought 8/99). this is the norm. I recently refinanced and value is up over 50% with no major home improvements. In fact all the properties in the area have, so comps will not help my case. Is there a risk that I'll end up paying higher property taxes if I try lowering it by traditional means. sorry abpout this non MB issue. i'll cool it off after this.

__________________
1972 450SL
1982 300D Turbo

erubin,

Thanks for the tips on the pump. I just removed everything... I'll start a new post for that when I have my pics and questions. (so get ready!)

As for the tax issue -- yeah, let's not take this off topic. Go to my site and post... heck, you'll be the only one. I started that site when work was slow... needless to say, work isn't slow anymore, so I've kinda let it go. Which kinds sucks because people email me all the time with questions. I'm never going to get a "forum" started if I don't endorse posting. so go, and post.

Thanks again,
Pete