Difference between power steering pumps

[Berggreen]

Hello all

I am somewhat confused and almost in tears about the different versions of power steering pumps (servo-pumps) used on the w113 and other Mercedes models of the era.

I can see that there seems to be pumps which at a glance look identical apart from one having a conical and the other a cylindrical axle. But there also seem to be two different working pressures 65 and 82 bars. Furthermore, as you can read from my horror-story below, maybe there are also other physical differences in relation to mounting them in a 230/250/280SL.

So my initial question is, if both versions (65/82 bar) work in a 1971 280SL in relation to the power steering house?

MY HORROR POWER STEERING STORY:

I had a nightmare of a servo-pump incident recently, where my original power steering pump unfortunately was damaged beyond repair, when my mechanic tried to remove it from the engine to do some other work on the engine - he could not get the nut off the pully as it was rusted stuck, and he therefore had to use heating to loosen it, and in that process he unfortunately pulled the entire axle and bushing out of the pump. 

I found a nice looking and (according to the seller) renovated pump online with 82 bar working pressure like my original pump. But when we tried to vent it, it turned out to be impossible using normal venting procedures which I found on the forum - no oil at all came out of the pump. Only way he could get oil through it was by pushing oil through the pump using compressed air. Now the pump gave pressure, but only at rpms over 1000 rpm when the oil got warm. So he gave up, and the conclusion he gave was that it must have been put together wrong during the renovation. Unfortunately, my mechanic does not have insight into how to renovate these pumps, and we had to get the car out of his shop, as it was stuck there.

But I had another power steering pump at the shelf, however of the older type (probably 65 bar but model plate was gone) with the cylindrical axle with a matching pully. And as the pumps to me looked identical at a glance apart from the axle, I told him to mount this older pump instead of the "renovated". However, he came back to me and told me that it did not fit into the holder - so stuck again!! 

So in the end, in order to get the car out of the workshop, he took the front part of the "renovated" pump, and merged it with the rear part of the older pump with the straight axle, having then created a hybrid pump! He said it was the front part of the cylindrical axle pump which did not fit into the holder. He vented the hybrid pump and it seemed to work. Unfortunately, when I drove the the car back home on the highway, then I noticed that after driving at high rpms and then exiting the highway with the rpms dropping instantly, the power steering was suddenly lost. But after 10-15 seconds at idle or low rpms the power steering returns. Daaaaaaamnnnn....I was almost in tears and cursed these stupid power steering pumps!!! 

So now I bought a new renovated power steering pump from a company in Holland. However, even though it has the conical axle, then it seems to be a 65 bar pump I have been sent - model plate is painted over, so I cannot be certain, but the shape of the plate is the larger square one, compared to the original and "renovated", which both have the elongated one. But therefore my initial question above.

However, I would highly appreciate your help with some advice and input here to help me understand what is going on with these power steering pumps. 

Best wishes and I look forward to hear what you think, thanks!

Christian

[WRe]

Hi,
afaik is the construction of the servo pumps all the same. The pressure relief valve determines the pressure and can have 65/90 bar as required for different cars or trucks.
Appanrently there have been two different drive shafts: cylindrical or conical.
If you look at this web side you'll find both in the same models but the conical only in 280SL: https://www.mercedesscheune.de/webshop/navi.php?qs=Dichtsatz+Servopumpe+Vickers&search=.
...WRe

[MikeSimon]

You cannot use a 65 bar pump in a system that requires an 82 bar pump. If you do, the pump "goes into relief" , i.e.: "blows off" before you reach the maximum wheel turn.
Somewhere buried deep in my records, I have a Daimler Benz power steering pump application list.
Unfortunately, the original Vickers nameplates of that era did not show the maximum pressure of the pump.
Here is a picture of the one on my pump, December 1970 280SL

[Berggreen]

Thank you very much for your feedback! 

I managed to remove the paint from the model plate of the new renovated power steering pump, which I bought in Holland. See picture attached.

Can you see from the model numbers on the plate, if this is a 65 or 82 bar pump?

Also, will it fit into my 1971 280SL?

Cheers and thanks,

Christian 

[MikeSimon]

This early Vickers tag does not show the relief pressure. Probably because at that time, there were no differences. I am assuming from here, that it is correct for a 1971 280SL.
In a different thread it shows the 82 bar pump to be a different model, the later VT49.
Without finding my old Vickers data sheets, I cannot confirm any of this.
I just know, that when DB decided to make the p/s standard equipment, they added a second supplier - ZF. The pumps were interchangeable and looked very much the same. The design was significantly different. It was an aluminum cast housing with an integral reservoir. Vickers installed a complete new transfer manufacturing line for this product and slowly phased out the cast iron pumps as it is not a good idea to machine cast iron and aluminum on the same floor.