Vacuum Pump / Timebomb Advice - PeachParts Mercedes-Benz Forum

Bob Albrecht · #1 05-10-2011, 12:46 PM

My '91 350 SD has 120,000 miles and an old style vacuum pump.

There is no sign of vacuum pump failure, but from what I read here the thing is a ticking time bomb.

I wish it wasn't so expensive to replace, but it is a lot cheaper than killing the whole engine.

I want to order my new vacuum pump now, but I want to get the best quality so I don't have to do this job again.

In the parts universe I see Hella and Pierburg vacuum pumps. Which is better? Are there any other brands worth considering?

Does anyone have advice on doing this job?

vstech · #2 05-10-2011, 07:39 PM

first thing I did with my 87 wagon was park the car, pull the vacuum pump, and the belt tensioner...

Bob Albrecht · #3 05-10-2011, 09:16 PM

OK, but what brand of Vacuum pump should I get?

babymog · #4 05-10-2011, 09:30 PM

All of my original vacuum pumps have lasted well over 200,000 miles, and I have replaced them between 200k and 250k miles because of horror stories.

However, I've been reading about a lot of late-version Pierburg/M-B pumps failing at very low miles, so I've decided to inspect my pump annually and keep it in there to 250,000 miles like my others had.

We'll see if it is a fail, but I'm thinking it'll be fine. I pulled both of mine this winter at 237k and 205k and both looked great.

Bob Albrecht · #5 05-10-2011, 10:33 PM

The other threads on this forum say that the old style pumps are a ticking time bomb that can shoot ball bearings inside your engine when they fail with no warning.

It sounds kind of scary to me.

So, what do you mean by "anually inspect" the vacuum pump? Do you remove the pump and look at it?

If the Pierburg pumps have short lives, are the Hella ones any better?

When I look at the "Hella" pump on Fastlane the pump in the picture says Pierburg on it. Which is it?

Diesel911 · #6 05-11-2011, 12:29 AM

Different Engine and Vacuum Pump but I have removed and inspected the Arms and Bearings on my Vacuum Pump 2 times in what in the about 4 years I have owned the Car.

I have not read anything on the later models than mine where Hella or Pierburg quality was different.

I believe that is simply because few have replaced their Vacuum Pumps with the Hella ones and the other reason is the newly installed VPs have not been on the Engines long enough to tell which one is made better than the other.

So there may not be an answer yet.

ah-kay · #7 05-11-2011, 01:49 AM

I have 4 cars with the 'time bomb' vacuum pump, SDLs and the 190D. The mileage are 220K, 290K, 280K and 340K miles, none of them is spring chicken. 2 have stack of service history from newish and 2 have none. I never look at the history so I do not know what had been done.

3 are daily drivers and 1 is a drivable no-op spare. I drive them everywhere, up and down No and SoCal now and then. I never worry about them, why should I? There are more things in life to worry about than the pump. My attitude is if it ain't broke, don't touch it. If I were you I would not worry about it, especially at 120K miles. Bending a rod is more of a clear and present danger with your car.

JohnS · #8 05-11-2011, 10:11 AM

Hi, I bought a new pierberg off e-bay for under $300. I've had it in for about 10K miles with no problem. I cannot comment on the pierberg/hella relative quality; the pierberg is definitely well made.

FYI, you will probably get a little notice of failure, I did; you will notice locks get a little suggish and you lose power assist in your brakes. You will not notice any particular noise from a failing pump.

One word of advice I can give is stay away from the Chinese pumps, if it's less than $200, it's Chinese. A good used new style pump may be an alternative if you are looking for a bargain.

vstech · #9 05-11-2011, 10:16 AM

on the 3 87's I have, only one had any issues with the vacuum pump. 168K on the clock, and the pump when I pulled it, had all 12 balls still in there, but the plastic cage on one side was gone. I feel like I caught that one JUST in time.
annual inspection would require a new gasket, and cleaning the surface of the mounting, and the pump, and looking over the bearing cage on both sides for signs of the plastic retainer failing or missing.

ashedd · #10 05-11-2011, 10:23 AM

This is what I would do.

Buy one of these
http://www.grainger.com/Grainger/SPOTCHECK-Dye-Penetrant-Kit-3WU63

Inspect your old style pump annually/30k miles. Maybe even every 60k miles. If/when cracks start to appear, you will see them before it fails.

EDIT:
Look at the bearings too, obviously

Diesel911 · #11 05-11-2011, 10:40 AM

One thing about Mercedes seems to be that if you hear a abnormal noise you need to identify that the noise is not coming from the Vacuum Pump or another critical part as best you can.

There has been more than a few Threads by People who have ignored noise or other warning signs and continued to drive and the results of that.

Bob Albrecht · #12 05-11-2011, 11:09 AM

My car has updated rods, so I want the engine to last.

The vacuum pump is the most likely cause of major engine damage at this point.

jt20 · #13 05-11-2011, 11:47 AM

Ultimately, you need piece of mind when you are driving, or the car is a source of stress. If you at least take a look at the working parts of pump, you may ease this fear.

Pierburg is the OE supplier. I know that much. But who knows if what other companies just rebrand the OE stuff and repackage these days?

babymog · #14 05-11-2011, 10:01 PM

The pump bearing/arm was re-designed to IIRC have a single bearing inside of the roller and fixed axle instead of the older design that had two bearings on either end of the axle fixed to the roller. The bearings in the original design were caged, and the cages do wear out dumping plastic bits and eventually without the cage the bearings can bunch up on one side of the axle and allow enough clearance for the bearings to start escaping into the timing chain cavity. This can happen without damage to the engine, seems that it does some times as people find bits in their oil pan that work through the oil pump screen after many miles, when they bought the car with an updated pump (indicating that a previous owner had an uncontained failure of these bearings without damaging the engine, replaced the pump).

The newer design seems to fatigue at the arms and fail, which destroys the timing device, but AFAIK there haven't been any cases of parts dropping into the chain and destroying the engine. Part of the reason for this I would guess, is that the pump stops working at this point and is replaced where the early style might rattle from the increased clearance due to the partially missing cage, but still produces vacuum and therefore the car continues to be driven.

Anyway, I look at the bearings and casting, if the cages are in good condition and there is no damage I consider it a good pump. Whether this will prove to be a good choice we will see, but it doesn't seem that the cage will fail suddenly and without signs of wear/fatigue. The R&R isn't a simple matter completely, the serp-belt at least must be removed IIRC, and likely the fan and shroud also. I didn't use any gasket sealer on mine so it should come off clean and a new gasket fitted easily enough.

It is clearly a gamble, but so is the new design IMO, and the vacuum pump is just one of many possible failure items as my '91 had a piston squirting jet come loose and be crushed by the crank, somehow the ball and bolt didn't make it into the oil pump, some have had the oil pump bolt back out, the early windage tray ('90-??) on the .97x engines is noted in the FSM to not re-install but to replace with the updated design (reason??), some have had windage-tray bolts come out, ... I'm taking a calculated risk.

ashedd · #15 05-12-2011, 12:13 AM

I think I remember seeing some engine damage on GSXR's website.

Seems like the general consensus is to remove the pump and take a look.