I took my automatic transmission apart!

[Tom Colitt]

I pulled the transmission apart today and found that the fluid was absolutely clean after 2 years of use. That was a relief as it seems to be no catastrophic failure or extreme wear. I checked the front primary pump o-ring as suggested by Dan and Joe, but although the front of the transmission was dirty it did not appear to be wet as though that seal was leaking. Also the hydraulic clutch is not of the rivetted variety, so no leaks there. I'm beginning to worry that ther could be another cause for the slipping at lower speeds. Another worry is that the BBB says that the broonze bushing in the primary pump can not be replaced separately as suggested. Was this part only available later on and does anyone have a part number for a 12/1969 USmodel 280Sl? If I can't get this part from MB, can I get it elsewhere? The bushing doesn't look worn, but I haven't taken it out yet to check its play in relation to the torque converter.

Another guy that worked on a lot of these transmissions told me today that the cause is most likely not the o-ring seal because that one doesn't seal off the high pressure. Is that true? It seems that the o-ring must have something to do with sealing the high pressure generated by the primary pump, though. But why isn't the front cover wet?
This guy suggested taking a look at the brake bands as they often break? I took a priliminary glance and they appear okay with about 0.8 to 1mm friction lining (There are two brake bands, right?)
If nothing else shows up tomorrow, I probably won't dig any further, but I'm worried about throwing it back together without finding any smoking gun? That transmission isn't a cake walk to remove in a tiny garage under jack stands. The whole thing literally feel down on me today, but only about 12". I'm glad I didn't break anything!...those parts can be hard to find :-)

Regards, Tom Colitt

Tom Colitt

[ja17]

Hello Tom,
That unit is quite a bit heavier than the standards. Didn't you say you were losing quite a bit of fluid? The leak should be somewhat obvious. Don't forget to check the modulator diaphragm. Also see if the valve body bolts are tight. Sometimes the gasket between the valve body and transmission will blow if the bolts become loose.  I have a dealer transmission parts book. It does not list the bushing separately. I used to buy them somewhere. Maybe Will Samples, Dan or Tom Hanson might have a source now. I will try to get the part number for you this evening and possibly a source.
The reverse gear band adjustment on the outside of the transmission does work it's way loose often (22mm lock down nut with 10mm adjustment bolt). This adjustment is on the left side lower. If your transmission ever hesitates to go into reverse check this. It should be tightened up just snug then backed off One and a half turns (check me on this , working from memory).



Joe Alexander
Blacklick, Ohio

[Tom Colitt]

Hi Joe

Yes, I was losing fluid, how heavy depended on the usage. It was very little in city traffic. At 70mph I was losing about 1 quart every 300 mls which would evebtually lead to the slippage due to low fluid level.

Recently the problem suddenly got much worse. The fluid loss in city traffic got a little heavier, but still only drops, not a real flow of ATF. However, the transmission slips in all forward gears (maybe reverse too), even when cold and even though the fluid level was high. If I forced the engine to rev up and slowly gained speed, the transmission would eventually engage completly and transmit power without slipping.

Joe, basically I'm just worried about missing something seeing as the leak at the front of the transmission isn't very obvious. However, there appears to be no other place the leak can come from other than the pump o-ring or the torque converter radial seal.

Seeing as I am very unfamiliar with automatic transmissions, I guess I was just expecting to find something a lot more obvoius or severe than what I'm finding to cause this kind of slipping. Please excuse my nervousness about this. And as always thanks for your generous help.

quote:Originally posted by ja17

Hello Tom,
That unit is quite a bit heavier than the standards. Didn't you say you were losing quite a bit of fluid? The leak should be somewhat obvious. Don't forget to check the modulator diaphragm. Also see if the valve body bolts are tight. Sometimes the gasket between the valve body and transmission will blow if the bolts become loose.  I have a dealer transmission parts book. It does not list the bushing separately. I used to buy them somewhere. Maybe Will Samples, Dan or Tom Hanson might have a source now. I will try to get the part number for you this evening and possibly a source.
The reverse gear band adjustment on the outside of the transmission does work it's way loose often (22mm lock down nut with 10mm adjustment bolt). This adjustment is on the left side lower. If your transmission ever hesitates to go into reverse check this. It should be tightened up just snug then backed off One and a half turns (check me on this , working from memory).



Joe Alexander
Blacklick, Ohio

Tom Colitt