Tandem Power Steering Pump Rebuild - PeachParts Mercedes-Benz Forum

stephenson · #1 02-18-2007, 09:02 PM

Rebuilding the Tandem Power Steering Pump
1991 350 SDL with ASD

Will attach photos in succession. I probably used some incorrect terminology, but didn't have a full schematic handy.
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Power steering fluid leakage noticeable by: fluid on the serpentine accessory drive belt, backside of the drive pulley wet, hood pad showing thin line where it was slung upwards by the pulley, and body work beside the drive pulley.

Reviewed all the posts I could find on the topic and then ordered pump kit. While waiting for it to arrive I removed the front part of the pump and took it apart (one post recommended this – I believe the application was a V-8), photographing bits as I removed them.

Removal and Disassembly
- remove pulley bolts while serpentine belt still under tension (note fluid inside of pulley)
- remove the reservoir top, spring loaded plastic sleeve, and filter
- remove fluid lines and let drain into small container set below the fittings; cover or seal all lines to prevent contamination
- remove four short pump bolts and two long mounting bolts
- either remove front portion of pump or back off two other bolts and remove entire pump (if only doing the front, be careful to not drop any blades/vanes)
- move everything to bench/clean area and start disassembling the pump
- WARNING – as you pull the pressure chamber apart, ensure you don’t lose any of the blades (vanes) that slide back and forth in the rotor. They are polished and slightly rounded on the outside edge that fits towards the wall of the chamber and square on the end facing the shaft – this may be related more to wear than a design factor, but it does allow the reassembly with certainty on direction
- pull off the back plates which are held aligned by two pins
- remove the “c” clip that holds the rotor on the shaft; likely you will need to bend it a bit to spread – my rebuild kit had one of these included, but it too will need to be spread and then re-bent once in place (unless you have a special tool for such a process); I could have reused the original, but, as one of the photos shows, the thickness is quite a bit different, probably caused by wear
- slide rotor off shaft (don’t lose the vanes)
- drive aluminum carrier assembly pin from casing with correct diameter drift (this will release the drive shaft from the casing)
- remove the four cover plugs and their respective pins and springs
- remove shaft from the casing towards the front, sliding it through the aft seal
- drive the pin through the eccentric cam; it is same diameter as the longer pin and much easier to remove
- remove both driveshaft seals; both were incredibly brittle and difficult to remove – neither could be driven out from the back and had to be pried out – I did mess up some of the aluminum in both locations, but tried to smooth it up some with emery cloth - I could not tell which direction they were facing (this became an issue on reassembly)
- remove the three torx bolts holding the reservoir to the rear pump assembly
- all o-rings were so brittle they also broke on removal

Reassembly and Reinstallation
- the pump and components were very clean inside with no pieces of any kind of material, fiber or metal - I tank cleaned all components then blew out all the fitting with compressed air then lubed them up with new hydraulic fluid (MB version for power steering systems)
- rebuild kit arrived and was clearly not the correct kit for my application – tandem pump has two shaft seals (vice one), and many more o-rings for various purposes. So I started looking again, finding a 400% price differential across various supplier options – I bought cheapest, figuring that o-rings shouldn’t cost $5 apiece!
- install new o-rings in appropriate locations
- due to the poor condition of the seals, I was unable to clearly determine which direction they faced; I asked via this forum and got general consensus that both faced toward the front of the pump (manufacturer markings are the front face) so I lubed them up and drove both of them into their respective positions
- reinstall the rear seal keeper washer
- I used some 1000 grit wet and dry paper on the drive shaft to remove the very, very slight rough areas where the seals had rested
- reinstall the aluminum carrier and the eccentric assembly with washer on the shaft
- reinstall the eccentric locking pin into place
- slide the reassembled shaft into the casing and through the casing seal, aligning the aluminum carrier pin slot with the casing pin slot
- install the aluminum carrier locking pin
- reinstall the rotor and install new shaft end clip
- reinstall blades/vanes, pins, plates
- reinstall reservoir to rear casing
- reinstall entire front assembly into the rear casing
- bolt up the four shorter bolts and pump is mechanically sealed
- reinstall pump onto engine with two long bolts
- reinstall pump pulley
- reinstall serpentine belt and tensioner assembly
- tighten the pulley bolts
- connect up all the fluid lines
- install new filter, plastic support/marker and nut
- add fluid to reservoir (I went about half way to top

Fired up the world’s most famous rod bender and after a few moments got pump pressure. Seems to be working OK, but only a few thousand miles will confirm.

stephenson · #2 02-18-2007, 09:04 PM

Photos 5-8

stephenson · #3 02-18-2007, 09:04 PM

Photos 9-12

stephenson · #4 02-18-2007, 09:08 PM

Photos 13-16

stephenson · #5 02-18-2007, 09:09 PM

Photos 17-20

stephenson · #6 02-18-2007, 09:12 PM

Photos 21-24

stephenson · #7 02-18-2007, 09:13 PM

Photos 25-28

stephenson · #8 02-18-2007, 09:14 PM

Photos 29-33
End

moakesr · #9 11-23-2007, 07:52 AM

Thank you for a superb thread, its very useful.

I am right in concluding you overhauled the ASD part of the tandem pump as well?

I have a suspected failure in of that part of my tandem pump, lots of fluid in the reservoir but no pressure in the system or return flow, and I wondered if it just needed bleeding, or was perhaps internally damaged?

Did you have to bleed that part when you re-installed, or was it self priming?

stephenson · #10 11-23-2007, 09:53 AM

hmmm ... I think I just cracked the lines on the pump after reinstalling - my ASD has been down since I bought the car - electrical switch on the brake system, so can't comment.

Power steering function came back immediately and have not had any leaks or issues with it ...

One day I'll get around to replacing the ASD switch to see if it works.

obwielnls · #11 11-23-2007, 10:18 AM

I am getting ready to do this EXACT job next weekend.. Was that a Vickers pump? How long did it take?

moakesr · #12 11-23-2007, 12:18 PM

My pump is a Vickers, so I will wait with interest to see how you get on

I will attempt to bleed mine this weekend, the PO had the PS pump overhauled a couple of months back, and I suspect they might not have bled the suspension pump, mind you if it's run dry for so long, it's probably busted

moakesr · #13 11-26-2007, 05:58 AM

I am a very lucky man, it has turned out that mine didn't need rebuilding.

The PO hadn't bled the pump or the SLS system, a few hours work on my part and its all working again

Richard

mbzak · #14 08-07-2012, 02:29 PM

This is a shot in the dark because i have an older 87 version of this pump which is apparently identical EXCEPT for the inner oil seal. What i need to determine is if i could use the seal washer from this pump in mine and have it work, second if i could find one of those seal washers as pictured in #22 above to convert it.

That seal is 1mm larger in the new version than the old. As in this version above the seal has a washer that fits around it. In my 87 pump it's an actual bushing that the seal fits inside. Finding the right seal would seem to be impossible as they are specifically designed in the kits.

I have the workshop manual CD for the 87 model and it appears to show the same seal washer that is above in the 91- not the one that i have. Mine does not have the larger thrust washer which the manual notes earlier models do not.

Bottom line the seal that comes in the FIBI kit is 24mm. The bushing i have is a 22.5mm tolerance which would need a 23mm seal. Believe me i had 2 of these seals and destroyed one trying to get it into the bushing.

pwogaman · #15 01-03-2013, 07:34 AM

These are great pictures. I found another set from a fellow in Japan with a 300TE 4MATIC that I follow. He provides pictures on bleeding the 4MATIC system at the read differential, which is what you need for bleeding an ASR system.

S124”õ–Y˜^

Being in Japanese make a little harder to navigate through the frames, but after some trial and error I managed to get through it. The direct link to the tandem power steering pump is here:

ƒ^ƒ“ƒfƒ€ƒ|ƒ“ƒvC— ¥¥¥ ('12”N 11ŒŽ)

If you click on the pictures you get the larger version.

Note that if you use an automated translator some of the pictures might not appear.