Hey Guys, newbie member on the forum. Ive been a lurker of the forum for many years now, but have hit a roadblock and need some insight from the other experts on the site.

Ive been a Benz fanatic ever since I was a kid, and a die hard car enthusiast ever since. Ive thankfully had the opportunities to collect the cars ive always sought after, and my old 420sel winter DD, is part of it.

Ive always been my own mechanic on all my cars, its one of the main reasons I can afford some awesome rides, and a good reason to buy more tools, something most folks could agree with. Anyways back on track. With winter here up in central Ontario kickin away ive been driving my 1990 420 sel. Its currently got 386,000km, and it was a bit of a basket case when I first got it (with the sole intention of a winter DD), ive been slowly working out the kinks and its been a wonderful, comfortable, quiet car to drive to and back from work each day; without the pain of the salt chewing away at a more expensive ride (sorry for sayin that guys)

Anyways, the transmission has been getting a bit weak, reverse is getting a bit sluggish, after doing some research and getting all the rebuild manuals (ATSG, and BENZ) I know what im in for when I tackle it for a rebuild. (ive rebuilt a few 4L80E's to keep as spares for one of my other vehicles, so transmission work isn't too voodoo for me.

With the weather getting cold, and a bit a free time in the evenings, I decided to pick up a core 722.355 to rebuild, and have on hand if and when the original trans gets too tired.
Luck has it that the core I picked up looks like it just had been rebuild. There wasn't any history on it, but it had been freshly painted, and looked like it was installed. Probably for only a few 100 km's.

Tonight I started to dig into it, and sure enough, all new parts thru out. New bands, spick and span valve body, all new seals. New B2 seals, new governor, new looking governor shaft. (ill be inspecting the B1 assembly once I get a chance to fab up a cover compression tool.

I didn't dig into it too much, but after buttoning up the pan, I heard a whisper in my head to check out the B3 seals, and pull the front pump assembly off to check and see how everything was doing.

Before I pulled the pump off I noticed that the front input shaft (center shaft) had a tad of play in it. But if it is like other transmissions, the torque converter should have internal bearings to center the shaft and provide support.

So 10 bolts, I pull the front pump off, and Ah HA!, I find the culprit.

Heres where I need some insight.

It looks to me that the K1 drum has some sort of slop, and chewed away at the seals on the pump assembly. It scored the pump assembly a bit, and also slightly gouged the inside surface of the K1 drum.

What would of caused this. Is there a bearing surface that supports the K1 drum assembly? does the B1 band have any vertical/horizontal centering adjustment that would cause the K1 drum to shift to a side when applied? and rub against the sealing surface on the pump assembly?

Could this be caused by not applying lube on the shaft during assembly, and damaged during the first few revs until the pump primes itself?


Sorry for the non-pro pics, all I had with me in the shop was my phone.

If you need more pics, I can get them to show you the assembly

Any tips would be great!


Pump assembly with B3 cage




B1 inner drum

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