I just picked up an '84 F700 that jumps out of reverse under load sometimes - esp. when backing uphill. Mounts seem good but I haven't checked them thoroughly. The two speed rear made some loud grinding noises when I tried to shift into high range. It seemed to catch and then let go and make nasty noises and kind of free wheel but did shift back into low where it has remained. The guy I got it from told me about both issues so it wasn't a surprise. He just used it on site but I'd like to at least use it for short runs to the gravel pit. I'll post the VIN for more info buts it's a 370 gasoline motor. Any thoughts are greatly appreciated.

 

Jumping out of reverse could be caused by a bent shifting fork, broken detent spring or a bad bearing. Also if its slipped out under load very many times, the gear teeth will get twisted, and will need to be replaced. As for the rear end, you will have to inspect the elec shifter for worn parts, not good to have them make that noise.

 

Thanks for the reply. Sounds like whatever is wrong with the transmission will require removing it. How obvious will twisted teeth be? How plentiful are good used trans. for this model?

 

Doubt a tranny gear will bend it's teeth, they usually break first. Hardened steel doesn't "twist" unless it's been overheated and softened.

Jumping out of any gear under load is unusual, there's definitely something wrong inside that needs to be looked at.

Check the diff for metal.

 

Since the OP failed to mention if his truck has A/T or M/T, the problem may have nothing to do with the trans...if it has an A/T with a column shift.

 

Good point Bill, a bad tranny mount would explain a lot if it was an AT.

 

OP has a two speed rear axle.

Worn or worn out MT I reckon...

 

Having a two speed does not rule out a automatic, Ford used a two speed rear end behind certain automatic equipped trucks, mainly to gain enough gears when a customer selected the cheap C6 automatic rather than the Allison.


It was recommended that you only shifted from low range to high though when moving. A limitation imposed upon this auto / two speed rear combination. Pretty much used it as a "overdrive" once the C6 was in third gear, not to split shifts.


I would hazard to bet that this truck is a manual though, and that it was towed rear wheels down with the driveshaft still connected, that can certainly damage the transmission, depending upon speed and distance.


But that is just a guess, based upon my experiences when I used to run nothing but manual transmissions (I learned my lesson on manuals though - I have had one shoulder surgery and will live the rest of my life in pain for this misguided loyalty!)


David

 

Column shift A/T's have a detent mounted to the bottom of the upper flange that the tab on the shift lever fits against. When the detent wears, the shift lever can pop out of park into reverse.