VACUUM PUMP FAILURE! Are you neglecting yours??
 

Déjà Vu! Lately there has been yet another spate of Vacuum Pump horror stories and angst that could so easily be avoided. Vacuum Pump failures are invariably caused by failure of the cam follower bearings – the cages wear through and disintegrate releasing the balls, surely not too surprising after over 30 years of continuous service?

I copy below a post I first posted here 10 years ago, my 2nd or 3rd I believe? Surprisingly after all the countless threads here on vacuum pump failures I am not aware of a single poster, apart from myself, having replaced the pump bearings or even suggested it.

For an investment of about 2 hours work and around $30 you can install new bearings and thereby buy yourself another 10 years peace of mind! Surely a worthwhile insurance against incurring the expense and ordeal of an engine rebuild? For many here it would appear not.:confused:

For the first time in over 50 years I am no longer running an MB Diesel. My faithful 1982 300D has been retired after 934,000km on the original engine and it has never once let me down. I have treated myself to a new car with a little more style and comfort, not an MB or even a diesel – a German brand I would never dare mention here!;)

Since this will be my final post here may I wish you all the best with your MB Diesels. Adios:)

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VACUUM PUMP FAILURE! - Are you neglecting yours??

The Vacuum Pump is a vital component of your braking system and its sudden failure will lose you about 70% of your braking efficiency instantly. Rambo should cope but your wife or daughter certainly would not - your life can depend on it. It is naïve to expect this important mechanical device to perform reliably for over 30 years without any servicing or inspection.

There are three types of vac pump fitted to the 123 series diesels – the diaphragm type, pre 1979, has two pipe connections and exhausts into the air filter housing. The piston type fitted to later models has only one connection and exhausts directly into the crankcase behind the pump through a pair of plate valves. Both types are interchangeable, piston type for diaphragm and vice versa. They have a check valve incorporated in the vac line pipe fitting after the suction plate valve.

A twin lobed cam on the fuel pump timer reciprocates the piston (or diaphragm) via a rocker mechanism with a roller cam follower. The forward stroke exhausts air while the double spring return stroke draws the vacuum. The mechanism and piston sleeve are oil-spray lubricated from the timing chain. When >25” is reached the vacuum parks the piston forward against the springs keeping the rocker roller almost clear of the cam apex. As vacuum falls (e.g. at braking) the roller once again moves back to contact the cam and restore vacuum.

Thus the vac pump should operate for less than 5% of the time that the engine is running, 15 sec at idle to 25” at start up (i.e. FSM spec.) and less than 10 sec to top up after braking IF you have no leaks in the vacuum circuit and the plate valves are sealing perfectly! Any leaks in the system will cause the pump to run continuously and it is not designed to do so. It’s no surprise then that those pumps are going to wear out, fail prematurely, and cause excessive wear to the thrust face of the fuel pump timer bronze bushing. If you have any leaks in your lock system isolate it until fixed as this will cause the pump to work continuously and also reduce braking efficiency.

The most common failure is the rocker arm bearings – the bearing cage wears out and disintegrates releasing the balls (dirty oil is a factor here!) N.B. - Visual inspection of the bearings will not reveal whether the cages are paper-thin and about to fall apart! Balls and debris get caught in the chain and crushed through it pushing off the end plates and/or skipping teeth on sprockets.

By the time that you hear mechanical noise from the vac pump at least one of the bearings have already failed. While the pump may continue to function for a short time the cam is now rubbing on the rocker arm instead of the roller, tipping and jamming the piston. and the mechanism will soon disintegrate. The chain breaks followed by the camshaft and from there on it’s a train crash.:eek:

Servicing and Rebuilding

Several kits are still available from MB Agent or ex-Stuttgart. (* Prices correct @ June 2012) .

1) Complete Piston Pump:- MA 000 230 13 65 $580*
2) Diaphragm Kit:- MA 000 586 41 43 $45 ?
3) Piston Seal kit (with piston):- MA 000 586 17 23 $187*
4) Rocker Complete with Brg's:- MA 000 586 08 43 $300*
5) Plate Valve Kit:- MA 000 586 40 43 $127*

The vacuum pump is a very simple device that can be stripped cleaned and rebuilt by any average DIY’er. Replacement of the bearings and plate valves can restore your pump for around $30. You will have little or no warning if your pump fails and I would suggest anyone running the original pump, regardless of whether you have a problem now, should consider a rebuild. Just two to three hours work will reward you with at least another 10 years piece of mind! You will be astonished at how much better your brakes are. A good pump will restores vacuum to the booster as you are braking.

Piston Seal
The current price of the piston seal kit is $171 (June 2012). If the seal is slightly scored or worn you can turn the Teflon band inside-out and restore to a pristine seal. It is important to replace the seal with the same edge to the inside of the piston as the seal band is very slightly coned by the O-Ring pressure. The last time I changed the bearings on mine I did this and it worked perfectly!

Rocker Roller Brg's Replacement
The rocker roller bearings are available from any specialist bearing store and are easily replaced.(choose a reputable brand! SKF FAG NTN INA. usually they will have to order). Plate valves too are standard and available from pneumatics stores cheaper if you are prepared to search. The rocker and bearings are identical on both types of pump. They are a standard # 626 "Precision" deep groove journal bearing 19mmØ x 6 x 6 (6 balls) @ about $10 each. A parallel 6mm pin is a press fit through the bearings and roller and can be pressed (preferably) or driven out with a punch.

N.B. Use ONLY an open SIX ball "Precision" 626 (i.e. Grade 50 or better) without metal dust covers even if they have been removed. Grade G50 is a benchmark for reputable brands but make sure that name is stamped on Brg! "Precision" bearings never have metal dust covers. The eight ball 626 is a light duty utility (junk) bearing and is intended for use in draw sliders casters etc. Care is needed to avoid damage to the new bearings when installing – support and do not side load the ball races when fitting!

Have a nice day - Beagle

As compared to the thorough post made by the OP, I will maybe oversimplify.

All you have to do is listen to the vacuum pump. When the roller gets loose you will hear it easily. When the roller starts rattling, pull the pump and replace it or replace the pump.

Bye bye Beagle

I for one will miss you.

Mine's all taken care of :)

http://img826.imageshack.us/img826/5186/sanden1.jpg

THANKS Beagle!!!

Thus the vac pump should operate for less than 5% of the time that the engine is running, 15 sec at idle to 25” at start up (i.e. FSM spec.) and less than 10 sec to top up after braking IF you have no leaks in the vacuum circuit and the plate valves are sealing perfectly! Any leaks in the system will cause the pump to run continuously and it is not designed to do so. It’s no surprise then that those pumps are going to wear out, fail prematurely, and cause excessive wear to the thrust face of the fuel pump timer bronze bushing. If you have any leaks in your lock system isolate it until fixed as this will cause the pump to work continuously and also reduce braking efficiency.

this is extremely important, and most often neglected information I was unaware of!

ALL MY CARS will now be subjected to pristine vacuum service!!!

Beagle, Happy motoring, thanks for your help over the years.

Thanks for all of your invaluable contributions. Personally, I'll miss your very knowledgeable and detailed information on all related components for the IP system.

Maybe you'll stop back periodically...........???

This is a good argument in favor of a vacuum gauge which could serve as an indicator of how much the pump is working.

First the Tappet Bros and now Beagle. Another ikon .

Beagle, before you leave can you post your "top ten" contributions so I can look them up.

There's this, the clutch hydraulics...what else was I sleeping through?

Would you happen to have a more precise part number? Almost every 626 bearing that I have located is either shielded or sealed.

I have a question about the vacuum pump.
I do not trust my pump atm, i have a metallic noise around 1500 rpm.

Can i remove the pump and run the car without pump to see if the sound is gone?
its an OM602.911 from 1986
The is my engine running: http://www.youtube.com/watch?v=92A5gLom_ug&feature=plcp
start at 0.25 mark

i would not.

the first thing I'd do is remove the belt, then start the car and see if the noise is gone.
if so, then your tensioner arm is failing.

to check the pump, I'd just remove it, and look it over. if it's showing signs of wear on the face of the ramp on the IP drive, or if either of the plastic cages are missing from the bearing, I'd replace the pump.

X2 :)))

thanks Beagle !!
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Excellent post Beagle. If you do decide to leave you will be missed!

This is incredibly timely for me, and a bit sad. Even though I don't know you Beagle, it is a loss, and I thank you for this and the other info you have shared.