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I recently acquired an 83 f350 with a 460 and c6 tranny. The truck looks awesome and runs great, supposedly the motor was rebuilt about 15k ago...but...When I put it in D it won't move and sounds like it's not fully engaging, kinda like a gnashing sound not quite grinding. R 2nd and L all work fine. If I put it in 2nd or L and start out then put it in D it shifts through and goes fine...until I get below maybe 15mph or stop then it slips and starts the gnashing sound. I checked and readjusted the linkage and the fluid level is good. Looks like the PO changed the fluid it's like new. I'm not a tranny guy so hoping someone here can help...
It sounds like the low sprag has failed, it must hold for drive first gear. It overruns and is not used for second gear and in manual low the low clutches come on and hold the drum that the sprag is in, so it does the same thing the sprag would do. Thats why its a good idea to select manual low when pulling something heavy to take all the load off the sprag.
The sprag is in the bottom of the case and the transmission will have to be completely torn down, might as well rebuild it.
Thanks for your input. I was hoping for an easy fix but should know better....
I've never rebuilt a tranny before but I'm very mechanically inclined, is this a DIY kinda project? Any good references online or any words of wisdom before I undertake this?
Its one of the easiest ones to rebuild, I think you should try it, I am sure you can do it there is plenty of info out there and we can always answer any questions you have here.
Decided to go for it, did some research and it looks pretty straight forward. I'll be ordering the sprag and rebuild kit in the next few days and will have the tranny on the bench when they arrive!
Thanks for the help and encouragement!!