I've got a 76 F-250 4x4 C6 and the transmission has been kind of quirky since I've owned it. I'm starting to tow with it occasionally and I'd like to get this sorted out. It only has issues cold. After 5 minutes at most its good to go, probably more like 2-3 minutes. After that it works 100% as it should.
When cold, reverse is really weak. If I fire it up cold and go for reverse it will hardly move. If I put it in neutral and run it at 2000rpm for about 30 seconds it will pull but still weak. And after getting out on the road 1st and 2nd are great but 3rd gear is basically non-existant, all slip. I just hold it in 2nd for a few minutes then its fine. There are absolutely no issues when it warms up. I was towing my Bronco with it and abosolutely no slippage at all. I'm dealing with it for now. Don't back up when cold and hold it in 2nd for a bit when cold only. That or rev it before reverse etc.
I have adjusted the band. I have never changed the fluid. I did buy new fluid for it but have not done it. Who knows that kind of fluid is even in it. The fluid is a little dark but its really not that bad and doesn't smell burnt.
Any suggestions here or is this thing on its way out? I'm in the market for a 4 door super duty so I might just have to limp it along until then.

 

Third and reverse share the same drum to work, the direct drum. It sounds like the drum might have a sealing problem when cold like from worn or hard rubber seals. If this is the case the only way to fix it would be to remove the trans and rebuild it, or at least replace the seals in the direct drum.

 

^5 .

 

Thats what I figured. I'm not real familiar with C6s so I was hoping for a possible valve body issue. Thanks!