Hello,


My 1985 C6-transmission F250 won't move when I put it in Drive after it has sat for a while, say a week or so. The engine revs and the truck makes as though it wants to move - but doesn't actually do so. If I move the transmission to R, 1 or 2 then to D, it will engage just fine and then shift fine.


This is a consistent problem. How do I remedy it?


The shift lever moves the transmission into gear for every other gear and, once the wheels have turned, the Drive has no apparent problems.


Any thoughts out there?


Any help is appreciated.


Thanks.

 

Sounds like seal shrinkage, to me.
I used to back out of a parking space and hold up traffic, until it would get enough pressure to move forward. This only happened when I didn't drive it regularly.
That was my guess, anyway.

 

First thing to do is to check the level of the tranny fluid. And while doing that, take a good look at the color of the fluid. Maybe even wipe the dip stick with a clean white paper towel to see the color. If it isn't pink then it probably hasn't been changed in quite some time.

Tranny fluid has a number of additives in it that wear out. One of those sweets the seals slightly. Another modifies the friction so the tranny shifts correctly. So my recommendation whenever people have problems is to change the fluid - including that in the torque converter. But, if your truck sat for any length of time without being driven there may be gum in it. Sometimes that comes out with lots of driving, but something like Sea Foam's tranny cleaner will speed that up. Then you could change fluid. Or, change and add Sea Foam to that.

 

Thanks for the replies.


Well, I actually changed the transmission fluid a few months back and I added Lucas Transmission repair fluid at that time. The fluid now is fine.


I am not sure if this is related but I have posted another problem regarding the truck not going into 4-low with the engine running. Coincidence?


I am not opposed to adding seal-fixing fluid or the Seafoam Transmission cleaner. I'll give one a go this weekend. Which to try first, and if one does nothing, can I then add the other?


Thanks again.

 

Coincidence. And you can use both additives at the same time. The cleaner is pretty thin and evaporates quickly.