What in particular causes vacuum pump failure? - PeachParts Mercedes-Benz Forum

Diesel911 · #1 11-03-2007, 03:01 AM

1984 300D with 197,000 miles showing on the odometer.
After reading all the awful stories about Vacuum pump failures causing timing chain failures I decided to pull mine off and check it (197,000 miles). Everything looked normal and there was nothing that looked at all worn .
I was wondering if anyone could tell me which of the parts inside the Vacuum pump is prone to failure?
Or, is it always that by the time the damage is over with there is now way to tell what failed?

Jeremy5848 · #2 11-03-2007, 03:10 AM

There's a ball bearing that, in the earlier models, does not have a caged race. If the bearing comes apart, the balls and such can drop out and end up jammed in the timing chain, causing it to break. That stops the camshaft and leaves one or more valves open, which, since diesels are interference engines, causes one or more pistons to smash into the valves.

In the latest units, the ball bearing is sealed and should not be able to spill its guts into the engine. Apparently there's no way to tell when the bearing is ready to go.

Jeremy

Stevo · #3 11-03-2007, 12:14 PM

There is a bushing on intermediate shaft which will ware causing lateral movement of the timing device (2+mms in my case) which took out my V/P. The bearing if the V/P that rides on the little "roller coaster" track of the timing device, can fail also.

Diesel911 · #4 11-03-2007, 01:58 PM

Quote:

Originally Posted by Stevo

There is a bushing on intermediate shaft which will ware causing lateral movement of the timing device (2+mms in my case) which took out my V/P. The bearing if the V/P that rides on the little "roller coaster" track of the timing device, can fail also.

I am not sure which shaft you mean? I think there were 3 shafts:
1- The long bolt that goes through both sides of the housing and through the largest forked lever,
2- the shaft by the roller with tiny snap rings an
3-the shaft the roller rides on.
I looke but did not see any bushings. I will look closer the next time I remove it!
I forgot to say 84 300D turbo.
The only parts that looked delicate were those tiny snap rings.

Stevo · #5 11-03-2007, 02:12 PM

Quote:

Originally Posted by Diesel911

I am not sure which shaft you mean? I think there were 3 shafts:
1- The long bolt that goes through both sides of the housing and through the largest forked lever,
2- the shaft by the roller with tiny snap rings an
3-the shaft the roller rides on.
I looke but did not see any bushings. I will look closer the next time I remove it!
I forgot to say 84 300D turbo.
The only parts that looked delicate were those tiny snap rings.

The intermediate shaft is inside the timing device, you cant see it unless the T/D is removed. There is an exploded drawing in the Haynes manual that show the whole thin including the bushing which wears causing end play in the timing device, causing V/C failure. When the V/P is remover pull the timing device in and out to determan "end play"

Diesel911 · #6 11-04-2007, 11:46 AM

Quote:

Originally Posted by Stevo

The intermediate shaft is inside the timing device, you cant see it unless the T/D is removed. There is an exploded drawing in the Haynes manual that show the whole thin including the bushing which wears causing end play in the timing device, causing V/C failure. When the V/P is remover pull the timing device in and out to determan "end play"

Thanks. I got it the intermediate shaft is not in the vacuum pump. I have seen the pic in the manual.

Do you know what the Max. end play is?

Diesel911 · #7 02-06-2010, 12:44 PM

Quote:

Originally Posted by Stevo

There is a bushing on intermediate shaft which will ware causing lateral movement of the timing device (2+mms in my case) which took out my V/P. The bearing if the V/P that rides on the little "roller coaster" track of the timing device, can fail also.

Timer End Play
I went back and took a closer look at both the CD and book Service Manuals and found it listed as: End plan of intermediate sprocket shaft: 0.05-0.12mm.
In section 07.1-240 of the Service Manual.
I assume this measurement is take with the Timer installed on the Shaft and with no Timing Chain on it to interfere with the measurement.
Repeat broke new vacuum pump

Stevo · #8 02-06-2010, 04:00 PM

Quote:

Originally Posted by Diesel911

Timer End Play
I went back and took a closer look at both the CD and book Service Manuals and found it listed as: End plan of intermediate sprocket shaft: 0.05-0.12mm.
In section 07.1-240 of the Service Manual.
I assume this measurement is take with the Timer installed on the Shaft and with no Timing Chain on it to interfere with the measurement.
Repeat broke new vacuum pump

Good show, I dont think the timing chain would interfere the measurement, the intermediate shaft (and TD)will move with the chain on (at least several MMs). wouldn't it be like measuring how far to tighten the nut when doing wheel bearings?

Diesel911 · #9 11-03-2007, 01:43 PM

Quote:

Originally Posted by Jeremy5848

There's a ball bearing that, in the earlier models, does not have a caged race. If the bearing comes apart, the balls and such can drop out and end up jammed in the timing chain, causing it to break. That stops the camshaft and leaves one or more valves open, which, since diesels are interference engines, causes one or more pistons to smash into the valves.

In the latest units, the ball bearing is sealed and should not be able to spill its guts into the engine. Apparently there's no way to tell when the bearing is ready to go.

Jeremy

There is no side shields on the bearings in my Vacuum pump; you can see the ball bearings (car 1984).

nate300d · #10 04-22-2012, 01:59 PM

Quote:

Originally Posted by Jeremy5848

There's a ball bearing that, in the earlier models, does not have a caged race. If the bearing comes apart, the balls and such can drop out and end up jammed in the timing chain, causing it to break. That stops the camshaft and leaves one or more valves open, which, since diesels are interference engines, causes one or more pistons to smash into the valves.

In the latest units, the ball bearing is sealed and should not be able to spill its guts into the engine. Apparently there's no way to tell when the bearing is ready to go.

Jeremy

This happened to a friend on a 617, but the valve was not damaged. The finger operating the valve is softer metal so it bent. No head removal. He replaced the finger, reapaired the vac. pump and was back in business.

Diesel911 · #11 04-22-2012, 11:03 PM

Quote:

Originally Posted by nate300d

This happened to a friend on a 617, but the valve was not damaged. The finger operating the valve is softer metal so it bent. No head removal. He replaced the finger, reapaired the vac. pump and was back in business.

Unfortunately there is more than one way for the Vacuum Pump to be destroyed.

New Vacuum Pump Ruined due to too much Timer/Intermediate Shaft End Play (the title from my notes).
http://www.peachparts.com/shopforum/showthread.php?t=258062&highlight=vacuum

zeke · #12 11-03-2007, 12:21 PM

Is this a problem on all 61x engines, just the turbos, or just some years? Seems like I haven't seen people with older (pre-w123) or non-turbo models report this problem.

Jeremy5848 · #13 11-03-2007, 01:32 PM

Quote:

Originally Posted by zeke

Is this a problem on all 61x engines, just the turbos, or just some years? Seems like I haven't seen people with older (pre-w123) or non-turbo models report this problem.

My understanding is that it isn't so much the vacuum pump itself as the way the pump mates with the engine block and the casting holes in the latter that will allow parts to fall into the timing chain alley. The 603 appears to be most prone to this problem. I've hears of vacuum pumps failing on the 617 but apparently they are less likely to cause a failure of the engine itself. It's possible that the other 60x engines also have that risk -- but that is beyond my ability.

Jeremy

whunter · #14 11-04-2007, 12:56 PM

In order, the most common issues:

*****
#1. System vacuum leaks allowing dust and trash to enter the vacuum pump check valves.

*****
#2. Pump piston seal fails = allows engine oil to enter piston cylinder = oil coating check valves, system vacuum leaks allow dust and trash to build up on the oil coated check valves, eventually holding the valves open.

*****
#3. Incorrect rebuild, very common.

***
#4. System vacuum leaks allowing ABRASIVE dust and trash to enter the vacuum pump cylinder, scoring cylinder walls into junk = impossible to repair as a DIY = send in for rebuild or scrap it.

**
#5. Bearing or piston arm failure.

Have a great day.

dawsonj3 · #15 02-17-2008, 08:57 PM

I'm trying to track down the source of a light scratching sound coming from under the hood while the engine is running. I just replaced the alternator. I ruled out the ps pump by removing the belt. Does the vacuum pump make any type of sound when it begins to fail?