Truck will not go into reverse. It'll just grind, I'll try and hold it in reverse as hard as I can, but it won't work. All other gears work just fine. Just grinds in reverse. Thinking low oil or something, but haven't checked it yet. Anyone have an idea?

 

Check your clutch and everything from the pedal to the clutch.
If it won't disengage fully(say, low fluid or something), you'll have this problem.

Also, forcing it won't help, but you can try putting it in neutral, letting out the clutch, putting it back in, then shift to reverse.
Alternately, try putting it into first, then reverse.

My own has worn synchros(which seems to be very common), and I have to sort of 'wiggle' it into gear most of the time -- going from neutral to reverse a couple of times until it *clunks* properly. I've sometimes had luck holding it in reverse, and pulling out on the clutch just slightly until the gears slip a little and mesh together.

 

I did notice that the clutch was a bit touchy. Sometimes it felt like it was all the way down, but it wasn't because the truck wouldn't start. Then you had to push that little extra and you could feel it go then it'd work. But I tried all kinda of things trying to get it into reverse, played with the clutch a lot too, also put it in every other gear and put it back into reverse. I can't even feel it begin to grab anything. Just some good grinding. I think I did hear some vibratey sounds I guess you could say coming from the tranny when driving in other gears. I'll check the fluid when I get home and see if it's low.

I've read about the synchros but I'd think that'd affect more then one gear?

 

The reverse synchro problem is common in ZFs, the T19 that should be in your 85 is pretty stout and not really known for problems.

Unless someone put a ZF in at some time, it is a 5 speed? If so, ZF, if 4 it's a T19.

Check the firewall around the clutch master cylinder, there's a common problem of cracking around it and it allows the slave to flex and cause engagement problems.

 

It is a 5 speed, and I've seen silicone gasket around the tranny like it's been replaced or repaired once.

I will get around to checking that later tonight or tomorrow afternoon.

 

It was replaced then, the 5 speed wasn't available until '87, someone swapped that in there like I did my '85.

Unfortunately that's the weak point to the ZF, the synchros go out and usually it's the reverse. Then it's rebuild time, the whole thing has to come apart to get to the reverse synchros.

Mine is in the beginnings of this issue and from what I've read it only gets worse until you lose reverse altogether.

Some have reported some success with sliding the shifter into OD or first before stabbing reverse. I think going to OD first has helped with mine, but it may just be in my head. As Macrobb said, no amount of grinding or forcing will get it in reverse, it's either in or not so as soon as you hear those gears back out and try it again. Repeat until it goes in.

 

Oh I've also noticed my tachometer was not working for a short period of time. And my tachometer sensor might be bad, it does look a little iffy, and there is oil leaking from it.

 

Cracked open the hood last night and took a look at the master cylinder. Noticed it had some nasty looking fluid in it. Planning on taking it off and cleaning it all out. Or just cleaning it out, not sure how to do it exactly. But am I going to have to bleed it after I clean it out? Also, couldn't find a dip stick for the tranny fluid. Not sure how to check that either. Any help on this would be nice. Would like to take out all possibilities before having to replace the synchros.

 

To remove the clutch fluid use an evacuation hand pump. Like a mighty vac. You can find them at Harbor freight cheap enough. Suck out the old fluid the refill with new. Then flush the system by using the mighty vac to suck out the fluid at the bleeder. Just like if you were doing the brakes.

To check the fluid level you need to remove the fill plug on the trans. The fluid should be level with the fill plug. If it is the ZF-5 trans it requires ATF fluid. Good luck, it's fairly simple to do.

Edited: to make better sense. Auto correct can be a pain.

 

Thank you very much!

 

This should help explain it better. I know it's on a bike and doing the brake system but it's the same concept.

 

Where would the bleeder be located? By the master cylinder? Or close to the tranny? New to this engine, still trying to figure everything out.

 

Does it go into reverse okay with the engine not running? Try putting it in reverse with the engine off, then starting it, and see if the truck creeps at all.

Another clutch disengagement issue with the '80-'86 cabs is the firewall flex. You push the pedal, and the firewall moves instead of the pushrod pushing the master piston. Pedal box bushings and the bushing where the pedal arm engages the pushrod are also weak points. If the wear on that last bushing is so bad that it's ovalized (egged out) the pushrod eyelet, you'll never "get good pedal". This might also be a result of trying to use the original old-school hydraulics with the ZF5 transplant.

 

Haven't tried it with the engine off, will give it a whirl later.

I took a look at the firewall this afternoon, didn't really notice anything bad. The whole thing moved, but the pushrod went moved just fine as far as I could tell.

Been hard to find time to work on the truck.

 

If the firewall is flexing, the pushrod is probably not moving far enough to fully disengage the clutch.