GerritD

Hi,

since there is no service kit available for the power steering pumps for the early 928 ( before 1981), I decided to
challenge myself and luckily it was a success .
Here the necessary parts and the cost :
bearing : SKF 6004/C3 : inner diameter = 20mm , outer diameter = 42 mm, width = 12mm 7,62€
retaining rings for bearing : A20 Stainless Steel - Din 7993 : inside diameter 17,7 mm 7,73€
oil seal ring : FREUDENBERG 20x42x7mm (72 NBR 902) 14,22€
oil O-ring seal1 : VITON 80 SHORE : inner diameter = 66 mm (outer diameter = 71 ), thickness 2,5 mm
oil O-ring seal2 : VITON 80 SHORE : inner diameter = 67,95 mm (outer diameter = 73), thickness 2,62 mm
25,4€

total = 54,97€ ( $61)

Hopefully it will help other 928 enthusiasts:-)
here some pics

karl ruiter

Awesome contribution. Thanks. Now we just need Roger to stock the parts!

docmirror

Motion industries will have all the parts you need as the OP has generously provided the specs for the bearings and seals. However, a kit with all of it together would be nice. Maybe even find the repl vanes for the pump hub.

interesting, it appears the pump is a rotary vane style. This is the first time I've seen that application on a production car. Extremely rare to see a positive disp style pump in a fluid media. Guessing there's some kind of buffering in the cooling system, but maybe not?

Hey_Allen

80's MB pumps are the same type, and look surprisingly similar to the Porsche pump shown here.

I used to own a couple of 300SD's and a 500SEC, all had a ZF pump, which were rotary vane pumps with a pressure relief plate (valve) in the pump.

islaTurbine

@GerritD
Thanks for taking my PM’s thus far and for creating this thread. I hadn’t previously seen it until today.

Can you tell me how to remove this top seal? I can’t tell if it’s a simple rubber seal or if it’s a shield on top of a bearing. Do I have to push out the shaft with a press?

GerritD

Seal is made of rubber so you need to remove it with a screwdriver. Just be careful not to scratch the axe or the housing of your pump in which the seal is set.
When you have removed it, it will look like this :

islaTurbine

Got it, though it wasn’t easy. There's a metal plate underneath the rubber which made it very difficult to remove without causing collateral damage. What are the two Vitron 80 Shore o-rings for? I currently only see one large o-ring for the back plate (which is held in with the spring clip).

GerritD

here is a picture with the location of the 2 O-rings :

islaTurbine

Excellent. I haven’t seen that second seal because I haven’t gotten that deep. Which leads me to my next question: how did you get this casing piece removed from inside the back? Does it simply pull out? I haven’t pulled on it too much yet and thought I’d check with you before I do.

GerritD

It should come out when you pull. But the O-ring will make it sit tight..

rg0115

Good stuff, thanks for sharing.

islaTurbine

Found the two Viton o-rings for those of us in the US:
https://www.oringsandmore.com/fkm-o-...minimum-2-pcs/

https://www.oringsandmore.com/fkm-o-...rice-for-1-pc/

$6.80 total after shipping.

GerritD

Great news! I envy you guys in the US because all car parts are much cheaper then in Europe😬

islaTurbine

This pump sure likes to fight me. Any suggestion on how to remove this other retention ring that sits on the shaft? I already got the outer snap ring out.

GerritD

Not this way. You first need to remove the whole ax (incl bearing) from the pump housing. Like this :



And then remove the retention ring to replace the bearing. The retention ring only serves to hold the bearing on its position on the ax.
Next you can put the whole ax back :


Ax with new bearing and retention ring