Deleted (double post) - see below post

 

The following problem I am having is with a 1986 F-350 Chassis Cab dually factory 4 speed 4 wheel drive truck with the 6.9 liter diesel. I just got this truck and the previous owner said the truck was working fine when it was parked one year ago. So it is possible that the issue may have arisen from sitting, but who knows...

This transmission issue is really odd and is pretty hard for me to believe but here it goes:
I step on the clutch, start the truck, put the truck in first gear, I let off the clutch, the truck doesn’t move and even with my foot off the clutch I can shift through any of the gears (it acts just like the clutch is pressed in or if the engine is off) It’s like the transmission isn’t engaged with the engine at all, at any time. So essentially, when in any gear, the truck doesn’t move and I can shift through all of them with the truck running. I also tried shifting the transfer case but the truck still won’t move. What does this sound like it could be?
Thanks

 

It sounds as if the center of the clutch plate has torn out (although you would still expect enough drive to feel something when selecting the non-synchro low or reverse gears).............otherwise probably the transmission input shaft is broken.

 

When you shift it into first, can you feel it go into gear? Is it hard to get into first, or does it slide in easily?

 

Two separate threads on the same topic merged.

 

I do not feel the gears like you would normally if the truck was running, I don't have to force it into gear. The truck shifts the same way with the engine off as it does with the engine running, so basically it feels like the transmission is completely disconnected from the engine. Now... the guy I bought it from said the truck was supposedly driving fine before he parked it a year ago. Wouldn't I hear some noise with a broken input shaft and can that even happen? I would assume it would take a lot to break one in a heavy duty F-350 like this. The truck only has 148k miles on it.

Thanks

 

Usually if the input shaft is broken, you'll hear something. Same for anything clutch/flywheel related. When the truck is off and in gear, does it roll? It sounds like a something related to the shifter or shift fork not engaging. Is the driveshaft still connected?

 

I'm gonna go with a bad clutch disc. If the center hub has broken out of the disc, it will act this way. Same goes for if all the friction material has disintegrated on the disc (quite possible after sitting unused for a while). The pilot bushing/bearing rarely has enough resistance to spin the input shaft, so even with the engine running, it's very likely to be able to shift into any gear without releasing the (non existant) clutch, as if the engine was not running but a properly functioning clutch was depressed.
A broken input shaft is another possibility, but as mentioned, this condition is *usually* accompanied by odd sounds, though not always.
Either way, plan to drop the transfer case and transmission in order to get to the root of the issue and return the truck to a driveable condition.

 

Oh yeah, I sorta doubt the seller was being totally honest. I'm willing to bet it was driving down the road like normal, and suddenly lost the ability to send power to the wheels, which then prompted it's dormant period.

 

Rogue you're right about the clutch, but usually there's some noise associated with that as well. Maybe it's not as easy to notice behind that clattering diesel. I broke the clutch hub in an RX7 Turbo I had, it made some serious racket.

 

Yeah, the 6.9L is a bit noiser than a 13BT. However, a buddy of mine broke the center hub out of the clutch on his 100% stock 79 RX7 12A, and no noise could be heard, that is until after the clutch was replaced. That was when the knocking from a spun rotor bearing began to be audible....... I think the engine locked up, clutch hub broke just as the bearing spun, allowing the engine to continue to run, but no power get to the rear wheels.
I tried to tell him to install an oil pressure guage, since Mazda didn't bother to do so. O-ring on the front cover was pinched when the engine was freshened up, and no OP guage caused it to go undetected until too late......

 

What was the owners response when you took delivery & it wouldn't move?

 

Very true! Of course my clutch came apart while launching on slicks at about 4000rpm, building 12psi on a 2-step controller in a 475rwhp car, so that's why it grenaded. That car was self destructing every time I hit the drag strip.

Anyhow, oldblue, best bet it to pull the trans and give it a look.

 

I will let you all know what happens. I guess when I get it home in a few days I will also check the hydraulic fluid in the clutch reservoir (if the 86 also had a hydraulic clutch). If that isn't it I'll drop the trans and transfer case. I have a 94 7.3 diesel F-250 4x4 with a ZF-5 speed so I guess if the 4 speed is toast I may just swap in the 5 speed. Does anyone know if the clutches are the same in both trucks? Will the transfer case in the 86 F-350 work with the 1994 ZF-5? I feel like going from the four to five speed could also require a different length drive shaft. You all are right about me possibly not being able to hear it, the truck had dual straight pipe exhaust that exited behind the cab.

Thanks

 

I really doubt it's a hydraulic issue, this would present itself as an inability to put the transmission into gear and difficulty pulling it out, not to mention the pedal would most likely hang up at the bottom of its travel.