hey guys ,
New here and don't know much and also understand this is a ford forum but seem to have a lot of good advice so I figured I would ask.....I have a 1986 GMC c60 with a 2 speed rear. Cannot figure this out as well as many mechanics I have tried. the truck wont always grab when shifted into gear but it will sometimes. it also gives out once I hit about 30 mph just completely nothing. can hold pedal to the floor and don't even get a rev out of it. this problem has also affected the pto? I have replaced the electric motor of the switch but have not a clue what else to do. if anyone can give me any ideas I would really greatly appreciate it. very close to going to the junk yard with it

 

Possibly, The O-pipe blocking the muffler bearing flutter?

 

I’m having trouble connecting the symptoms to your two speed axle. Overall it sounds like fuel starvation maybe. If you were having two speed axle issues I’d think you’d have shifting problems, like maybe electric or vacuum gremlins in the axle shift mechanism. But don’t see how that would create the overall problem you describe.

The guys at the Stovebolt.com site might be good ones to check in with on your GM truck, even though they focus on earlier era trucks like here. Stu

https://www.stovebolt.com/ubbthreads/

 

any oïl in transmission! i seen a guy seize a transmission ,there was more water than oïl in it.

 

2 speed is electric, probably has points. Some of those vintage just have a plastic cover and gravel will break it letting water into where the points are. Pull that cover off and have a look, it isn't a mars rover. If your "mechanics" can't figure it out, I'd find new ones.

 

thanks everyone! ya all mechanics were recommended but useless I'm not sure havnt checked the oil I will do so. ya I cant seem to figure out anything I do have touble with the shifting its only catches sometimes if that makes sence? and other times truck just wont move I don't get it

 

not sure what you mean "points" sorry not very familiar with this stuff

 

I'm assuming its prob more then one issues here but I wasn't sure what possible to affect the shifting/driving as well as the pto the trans or the rear or maybe even clutch?

 

this is the truck please disreguard the mess of storage in the back lol

 

Maybe these guys can help you out:

Chevrolet truck gear shifting ques... - Yesterday's Tractors

 

Gas or diesel motor?


Not being able to rev the motor could cause an issue of the rear not going into gear and maybe even shifting.
Some of the trucks of that size have rev limiters so you could not over rev the motor. Could this be an issue?


Yes do check the oil level in the trany, PTO & rear axle and top up as needed.
I think the rear is electric with the switch button on the side of the shifter handle. I think power is sent to the button then to the rear to move the elect. motor to shift hi or low range. Could power to this be failing at times?


I have found on more than 1 car/truck if they sit for a wile the fuses get a film and don't make good contact all the time. Pull them all and clean the fuse ends & holders as that may fix both the rev & rear 2sp shift issues.
Dave ----