I replaced the fuel shut-off valve yesterday in my 79 SD. The Vacuum pump appears to have failed in the process - no brake booster, no auto door locks... I have the Haynes manual, but it barely touches on the Vac. system. Can someone point me toward correct procedues for testing/repairing/rebuilding/replacing the pump? I am heading down a stinky river with no paddle and a vaccum pump appears to be my only salvation. Glug, glug...

On my '82 300D, the vacuum supply completely failed (in terms of supplying vaccum to the brake booster & other systems) when a piece of an upstream check valve went into the vacuum pump and lodged against a "button" style check valve inside the pump.

I was able to resolve this by taking the cover off the vacuum pump (had to remove the fan first) and taking out these three internal check valves. Behind the one internal check valve, I found a plastic part and a spring. The plastic part was just the size to block the operation of the internal check valve. While I had it apart I also cleaned the internal check valves with cleaner. Most advice I received here was that the upstream check valve was relatively ineffective and could be done without, so I simply removed its loose parts found in the pump.

This completely restored vacuum pump operation. Since your car model is different, your results may vary!

I think some of the models used a vacuum pump with a rubber diaphram that would eventually fail and need replacement.

Good luck, Ken300D

I just replaced the diaphram on my pump. About $8 and two hours. I suggest if you go through the trouble of pulling the pump go ahead and install the kit as the rubber is old and it's a cheap rebuild. There are two types of vacuum pumps on the older diesels. Diaphram and piston type pumps. I have never seen the piston type so I can not tell you the external difference. Have your VIN number handy when you order the kit. I had to pull my battery and large fuel filter to get at mine. My old diaphram was not ruptured but simply stretched and worn. upon replacement I almost doubled my vacuum.

Check to make sure you didn't dislodge a connection on the main vaccuum line, too -- I have a tendency to lean on things while working on the car (middle age catching up with me!) and it is possible to breack the hard plastic vaccuum line or one of the big check valves. Needless to say, that would eliminate vaccuum to the entire system. Pulling a small line off ususally won't.

Otherwise, I'd also suspect a pump failure.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Update. The vac. sys. worked perfectly for a spell today, then fritzed out again.

Mccan, couple of things:

First, if you are in your car for the long haul as a DIYer, the Haynes manual is woefully inadequate. Spring for a set of MB factory workshop manuals or buy the CD from FastLane that has them all on it -- justify it in your mind by not paying for just 2 hours of current flat rate times. And, particularly in the case of vacuum troubleshooting.

Second, if your pump failed in the process of replacing the shut-off valve, then it probably didn't fail at all. It is very likely that you knocked a line loose in the process -- they're all bundled up right near that general area. A quick test would be to remove *everything* from the source by disconnecting the line downstream of the pump near the cruise control actuator. Put a vacuum gauge on that line at that point and see what you have.

Bythe way, a good preventative maintenance "check" on the vacuum system is to put an in-line clear fuel filter in the take-off to the interior vacuum stuff near your firewall/brake booster (thanks, George Murphy). Monitor it and, that way, if your vacuum lines start getting oil in them, you will instantly know it -- before the oil starts causing serious problems with your vacuum elements and other things inside the car.

Finally, if your vacuum pump did indeed fail -- and it lost some hard parts in the process (very common) -- make sure that you remove your lower oil pan and clean it real good . . .

Richard Easley
Waco, Texas

Thanks for all the help. Where might I locate Fastlane for the CD?

Click on the fastlane button at the top of the page.
Welcome aboard RE.

__________________
Jim

This vac. sys. is a bugger. Working intermittently and some oil in hose from Fuel shut-off and main hose to pump. Oil probably from the bad Fuel Shut-Off Valve (just replaced). Ordering vac. sys. filter and service manual. Once I have details re: piston or diaphram pump, I can move ahead with diagnosis and repair. On to plugs; flashing GP ligh while idling...

GP light flashing at idle just after startup or all the time? Does it flash when pre-glowing?

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Only flashes after cranking and while idling. Preglow functions perfectly. I believe that the flashing indicates one or more inoperable plugs.

Exactly. Replace them all, save doing it one at a time!

Unless, of course, you have a loose wire shorting out on the ignition switch, intermitantly turning them on and off!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Where is the best place to get plugs? Priced them at NAPA last week at about $18 a pop. Want Bosch, but with the litany of work to be done on this tank I want to economize as where I can.

Right here on FastLane. Good price. And with your location you should have them in a few days. One good thing I can say about FastLane is that they truly are FAST.

When you get to the glow plugs in the selection menu, you will probably see Bosch and a few other brands that will be cheaper. However, the Bosch price is pretty darned good (a little under $11 I think) and I'd steer away from the others.

For my part I usually economize by collecting required items along with future routine maintenance items (filters, etc.) so that the shipping cost is spread out among more items.

So, we keep coming back to telling you about FastLane.



Ken300D

Went ahead and ordered them from the dealership - $15 each. Will install Sat.