byrdman454

I am in the middle of changing the oil pump gaskets on the '91 auto transmission that I plan to install in my '88. I took the pump housing off the front of the transmission and flipped it over and noticed some nicks in the housing. It looks as if the drum (disc carrier) has been hitting this housing (piston) while spinning. The first pic shows the housing or piston (that is what PET calls it) turned over with the nicks. The second picture is from PET. The piston is find number 13. The third picture is also from PET and shows the drum or disc carrier and is find number 4. I think this is what was running into the piston and causing the nicks.

The metal nicks are not from the factory. You can see some small shavings in the area from the two parts colliding. The drum looks OK, just a little shiny from where it wore on the piston. I can clean the nicks up and re-assemble, but I am worried about what would cause this. I can't image this would be normal. I am hoping Steve Catteneo can shed some light on this subject and let me know if I should check or replace anything else. Is something else about to go out? The transmission has not been dis-assembled by anyone else that I know of.

Mrmerlin

was there any metal in the pan??

borland

That's your B3 piston hitting the K2 clutch pack because there is not enough clearance between the two. It's likely your reverse (Clutch pack for B3) friction and steel stackup is too short. You can adjust this with either new reverse frictions, steels, and shims or a combination of these.

The WSM Vol 3, page 37-156, shows how to measure the play 'L', and 'e' distances using a caliper and subtract the two for the play measurement.

Now's a good time to take that clutch pack out to see what they look like. They are probably decomposing, which according to Steve is common.

byrdman454

I did notice some trash in the pan, but it was very little and very fine. I was not sure if it was normal or not. The transmission was out of a '91 and it supposidly had about 80,000 miles on it. I did not notice any big chunks or anything. All of the stuff I found was in the filter when I cut it open. I did not see anything of significance in the pan itself.

Is the stackup too short due to normal clutch wear? It did not appear the pump had ever been apart from the factory, so I do not think the stack or anything else has been messed with. What do I have to do to get the clutch pack out? What am I looking for?

borland

Yes, too short due to excessive wear/decomposition of the frictions.

You need to follow the WSM procedure for assembly, but in reverse order. The WSM disassembly procedure might be confusing for your only partial dissembly. First removing the clutch K1, and band B1 to expose the B3 clutch pack.

It's been awhile since I did the overhaul on my 90' S4, so I'm not too clear. But it's pretty well explained in the WSM.

Steve Cattaneo

Those marks on the B3 piston are made by the K1 drum, caused by worn B3 (Reverse) clutches, allowing excessive B3 piston moment. I have seen broken pistons and damaged pumps, that’s minimal wear, Change the clutches and check B3 clearances. I am working on a PDF with the cause and fix.

Mrmerlin

dont forget to put some lubricant on the broze bushing thats just inside the front radial seal that the torque converter slides into, Vaseline has been recommended by Steve C. If you dont then there will be a chance that the bushing will seize onto the T/C and then it will ruin the front pump. Goodluck with the rebuild

byrdman454

Thanks for all the inputs. I will review the WSM on this clutch change. Are these clutches readily available, or are they a backorder item?

Steve, please let me know when you get the .pdf finished. This would be a great help. Is this something that will be finished soon, or will it be later when you get more time?

Good point Mrmerlin. I have been reading old threads and have been making sure I use all the tips/tricks.

Thanks

borland

Parts are readily available for MB dealer or other MB parts suppliers. Genuine MB parts, OEM, or aftermarket. Big three most likely won't have them in stock.

Part numbers in the PET are MB part numbers.

byrdman454

Does anyone know of any good MB suppliers like the big three that have good prices?

byrdman454

Are the clutches I need to change in the PET pics I posted above or are tehy deeper in the transmission?

If so, do I need to replace just the fibers (find number 14), or both the fibers and steels (find number 13)?

borland

Not shown above. They are the larger diameter frictions and steels.

You need to take it apart to see what needs replacing. Most likely you need new frictions. The steels and frictions are not that expensive individually, but parts do add up. You might also need to buy a different size shim, so the one currently installed might not work with your caliper measured stack dimensions.

Do a web search for "genuine mercedes parts". You should find someone that discounts.

byrdman454

So does everything have to come out the front in order to get to these larger diameter friction and steels?

Borland, I know you have rebuilt one of these before, is this a DIY or not? Is there anything to be changed WYAIT if I have to go deep in the transmission to get to these clutches?

borland

Not everything. Just the K1 clutch assembly, the B1 piston, and B1 band. With these removed, you can fish out the frictions and steels with your fingers.

Like I said, you need to follow the WSM reassembly, but in reverse. You may have to jump to the B1 piston section. I don't think you need to remove the B1 pressure unit, but may be that its easier to remove that instead of the B1 piston. The normal WSM disassembly involves removing the planetary gear set which requires disassembly of the rear portions first.

The B1 piston is the most difficult of all the pistions to compress and reassemble. That may give you some trouble when it goes back in. I had the valve body already removed when I put that piston back together and was able to use a long screw clamp from the bottom. WSM shows a compression special tool.

WYAIT, why don't you do a complete teardown? Then you could see how many parts you have. You'll be amazed at how they got all those parts in such a small package. The automatic transmission is an amazing piece of machinery.

byrdman454

Borland,
What other parts should be replaced if I did a complete teardown? Do you still have the tools you made when you did your rebuild? Can I rent them from you?