Axle pressed out easily...Removed solid center wheel....Bearings pressed out with a socket on the outer race.....

New bearings went in easy just like Beagle said...Center axle pressed in without loading the races because the center wheel supports the center races as the axle is coming through.....(supporting the bottom center race as axle comes through)

Pulled in new bearings with a fine thread bolt and large flat washers....
Will see how long the new (Explorer SKF) bearings hold up....8 balls instead of 6)

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

I posted this several years ago – Don’t know what kits are still available and prices are no doubt out of date.

VACUUM PUMP - 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 two 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 and 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-mist lubricated from the timing chain. When >25 inch is reached this vacuum holds the piston forward against the springs keeping the rocker almost clear of the cam. 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 run for less than 5% of the time that the engine is running, 15 secs 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 system 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 - no surprise then that these pumps are going to wear out and fail prematurely. If you have leaks in your lock system isolate it until fixed as this will also reduce braking efficiency.

The most common failure is the rocker arm bearings – the bearing cage wears out releasing the balls (dirty oil is a factor here!) By the time that you hear mechanical noise from the vac pump at least one of the bearings or the piston 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 and the mechanism will soon disintegrate. Balls and other debris are caught in the sprockets breaking the timing chain and from there on it’s a train crash.

Servicing and Rebuilding

Several kits are/were available from MB. Prices are very approx.

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 $50

The vacuum pump is a simple devise that can be stripped cleaned and rebuilt by any average DIY’er. Replacement of the bearings and plate valves can restore your pump to new condition for around $50 and 4 or 5 hours work. 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 cosider a rebuild. You will be astonished at how much better your brakes are. A good pump will restore vacuum to the booster as you are braking.

The rocker roller bearings are available from any specialist bearing store (choose a reputable brand) and are easily replaced. 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 No 626 deep groove journal bearing 19mmØ x 6 x 6 (6 balls) @ about $7 each. Do not use a 626 with dust covers even if they have been removed. A parallel 6mm pin is a press fit through the bearings and roller and can be pressed or driven out with a punch. Care is needed here to avoid damage to the new bearings when installing – do not load the ball races when fitting!

Have a nice day

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Beagle

yellit and beagle, Thanks again for your very informative posts! I didn't get a chance to tear my pump off yet, WI whitetail deer hunting opener was this weekend. Hopefully with Thanksgiving break coming I can get some shop time. One nice thing about teaching for sure, I get time off when my kids do. Middle son is a mini me gearhead and can't wait to help get the Benz going.
Nick

6.9 formoco use a belt drive where 2 mount & where 2 get drive pulley power from is another hurdle 2 overcome . regards Butch

Over the years I've pulled the metal shields off of a few bearings where open bearings were specified and not readily available. It's one of those things that 'everyone does', the counter folks at bearing supply places suggest it when they don't have the non-shielded bearings in stock. I am not an expert of any sort in this area and so was hoping you could tell me the difference between a non-shielded bearing and a shielded bearing with the shield removed. To keep this on-topic I have not had much luck finding non-shielded 626 bearings locally.

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'82 300D - Light Ivory, 2nd Owner (Back in the wind April 2013!)

'95 E300D - White, grey interior. (Suffering from stuck/broken glow plugs)

Deuteronomy 22:4-
"Thou shalt not see thy brother's ass or his ox fall down by the way, and hide thyself from them: thou shalt surely help him to lift them up again."