Which vacuum pump bearings did you get? - PeachParts Mercedes-Benz Forum

cook · #1 11-15-2012, 09:01 AM

1984 300D
I am rebuilding my vacuum pump, including the bearings.

I am wondering what others have found when they tried to get the bearings. I have found it to be rather difficult to figure out all the different choices each catalog lists about their bearings.

My original SKF bearings were made about 30 years ago, and have "SKF 304991a Italy" etched on their side, but I don't see anything in Internet searches for that today. I figure that model number is no longer valid.

The other postings in this forum really gave me a good start (6 ball, high precision, 626, 19x6x6, etc.). They also recommend "grade 50" or better, yet I don't see that information listed in information from the manufacturer. But I do see ABEC ratings for bearings and now understand that ABEC-1 is the lowest rating.

To help others that might have asked the same questions, it might be good to list what others have found when they selected their bearing.

What brand?
What model?
Did it come with shielding?
What was it rated? (ABEC-1 or higher)
Where did you get it?
Approx cost?

For example, my local bearing place said this was the right replacement
Brand: MRC
Model: 36 steel/co/abec-1 051z
No shielding when they showed it to me, even though model said 1z.
About $14.00 each

What did you use when you replaced your bearings?

Junkman · #2 11-15-2012, 10:46 AM

Generally when dealing with any bearings, I go to the local industrial supply store & have them measure & match. That is difficult when I don't want to take the thing apart without knowing that the bearing is available. Always buy brand name bearings.

Measurements have always included inner & outer diameter and thickness. I'm partial to Timken but haven't bought any lately and don't know if they are still good quality.

vac pumps are on the warm weather list. Do you have more particulars?

cook · #3 11-15-2012, 12:16 PM

I am just rebuilding it as preventative maintenance. After 360K, I sure don't want it to drop a ball bearing and toast the timing chain/engine.

Is it safe to say that an MRC ABEC-1 is about the same quality that MB used in the original bearing?

Stretch · #4 11-15-2012, 12:50 PM

All you need to know and more can be found here =>

http://www.peachparts.com/shopforum/diesel-discussion/320095-vacuum-pump-failure-you-neglecting-yours.html !!!

(Apparently it is not just manufacturer but the precision to which they have been made that is important)

KAdams4458 · #5 11-15-2012, 01:13 PM

Having dealt with and becoming rather educated about bearings quite a bit in my vintage woodworking equipment ownership, I have a tough time believing that they would have specified anything beyond that. I have some bearings in my equipment that see over 10,000 rpm while suffering all kinds of axial and radial stress that a vacuum pump will never see, and personal safety is a lot more critical in my eyes than any amount of expensive equipment damage, so I do my homework each time a bearing needs replacing in anything that might remove my eyes or a limb! ABEC-1 is probably sufficient, and shouldn't break the bank, but there's more to a bearing.

With bearings, a reliable manufacturer is the key in my experience. Specs are only as good as the company providing them, and in the world of bearings, there are a ton of Chinese knock-offs, and they do regularly enter supply chains without being detected. It's a bit of a crap-shoot, especially at auto parts stores, due to their tendencies to re-box on a whim anything that might be on a shelf somewhere when suppliers are changed.

For me, I'd either hit the Mercedes parts counter for bearings, or I'd hit up a bearing supply.

cook · #6 11-15-2012, 01:49 PM

Good info KAdams4458. Thank you for posting it.

The bearing shop said the MRC brand is made by SKF. Mine say "Japan" on them, so I feel good about that.

I hope this info helps others that may be looking to get the bearings themselves.

Stevo · #7 11-15-2012, 03:34 PM

Bad bearings are not the only thing that will take out a vacuum pump. Lateral play in the intermediate shaft, causing the timing device to slam back and forth took mine out by driving the piston through the pump body. I always check the timing device for lateral play now when the VP is off, mine had 2.5mms.

qwerty · #8 11-15-2012, 03:45 PM

Quote:

Originally Posted by Stevo

Bad bearings are not the only thing that will take out a vacuum pump.

The issue isn't so much with the vacuum pump being "taken out." The problem is with what the dozen loose ball bearings "take out" after the vacuum pump fails.

Stevo · #9 11-15-2012, 03:58 PM

Quote:

Originally Posted by qwerty

The issue isn't so much with the vacuum pump being "taken out." The problem is with what the dozen loose ball bearings "take out" after the vacuum pump fails.

True, I should have said, "other ways for ball bearings to enter your engine's privet places and do nasty things" I caught mine before any balls got into the chain case, very lucky, for sure.

cook · #10 11-15-2012, 06:39 PM

Right you are.

I will definitely be checking the lateral play in the intermediate shaft when I'm in there.

Stevo · #11 11-15-2012, 06:54 PM

I dont know whats allowable but the ones I have checked, the play is barely detectable, dont know what that translates to in spics.

Brian Carlton · #12 11-15-2012, 08:08 PM

I thought about rebuilding the vacuum pump myself.

After weighing all the possibilities and the costs to do so, and the risk of a bad component getting introduced, and the cost of a failure, the $300. for a new one can be considered a bargain. I expect the SD to go another 100K miles and I don't want to be thinking of all the issues that can fail on a rebuilt pump.

Now, if I can just find the time to install it............

Stevo · #13 11-15-2012, 08:23 PM

I bought a new pump for my TD

Stretch · #14 11-16-2012, 03:10 AM

Quote:

Originally Posted by Brian Carlton

...

Now, if I can just find the time to install it............

Now that does sound familiar - all these good intentions!

Stretch · #15 11-16-2012, 03:13 AM

Quote:

Originally Posted by Stevo

Bad bearings are not the only thing that will take out a vacuum pump. Lateral play in the intermediate shaft, causing the timing device to slam back and forth took mine out by driving the piston through the pump body. I always check the timing device for lateral play now when the VP is off, mine had 2.5mms.

That is pretty impressive.

The only value I can find in the FSM is in the non-turbo part - chapter 07-240 right at the top of the first page =>

0.05 to 0.12 mm

You were over 20 times past that upper value matey!

EDIT - it is also in the turbo manual - same chapter 07-240...

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