Transmission experts. Varification needed, please.

[Tim Smith]

I just put a second hand SIII transmission into the lightweight a few hundred miles ago. I had no verification on it's condition before hand, so this serves me right...

After completing a lumber run, pulling under 1000 pounds in a trailer for a few hours at highway speeds, I got off the highway and onto the side streets. That's when I noticed 1st gear was difficult to find. I did get it in eventually but then second gear makes a terrible racket on over-run or if I hold it tight in gear. The racket on over-run makes me think the 2nd-3rd distance piece has let go. The fact that 1st is difficult to select makes me think a fork has bent. If it's a fork then at least I can get at it without pulling the whole box again, but I'm not confident.

Does this sound familiar to any of the transmission experts out there?

This is a let down either way. I was going to drive this truck to Utah next week but not with a finicky transmission I'm not.

[Tim Smith]

Right, so I popped the top off and took a look. At this point, I don't see anything that is obvious. I pull the forks and that seemed to look okay. Nothing major going on. I put the back end of the truck on stands, engage the clutch and turn the output shaft by hand while going through the gears manually. Still nothing. Slightly frustrated, I started it up and try to go through the gears and I think I found it.

Sorry for the sloppy video work.

http://www.youtube.com/watch?v=IjcRTTmLF5E

Looks like the fork is actually pulling too far forward and allowing it to rub 2nd gear. If you look closely, you can see the intermediate gear lock out shaft is actually passing beyond the selector rod tunnel. How it didn't fall out and get run through the gear box, I'll never know.

I pulled out the forks again and compared my 1st/2nd fork with another one I have sitting around the shop which is also from a SIII. There is very big difference in the end of the fork where it attaches to the sliding gear.
6580

This looks manufactured but who knows if it was correct. Anyone know if there was a difference in the forks between suffixes? The box in my truck is Suffix A according to the top but the comparing fork does not have a designation on the top. The case has a C followed by an A, so I'm not sure.

I'm thinking there might have been a goof in manufacturing my current shift fork and that it is rubbing 2nd if you push it to far by hand and that on overrun, the gear is pushing the fork back into 2nd again. They do show the same part number on the forks though. Maybe I bent it when I had trouble getting it into gear?

By the way now, on very close inspection, I can now also see two dings in the fork where it has hit 2nd which it clearly hovers over when 2nd is engaged.

Otherwise they are comparably the same.
6581

Any thoughts on the fork ends being different between suffixes? Either way, I think I bent it so that will be an easy fix.

[SafeAirOne]

Are you sure both forks SIII forks? I'm wondering if SIII forks are different than earlier forks to accomodate the synchro mechanism. By the looks of the two shown, one holds the gear in a slightly more aft position than the other.

I wonder how much force one has to apply to the shift lever to bend a fork. Those forks are pretty sturdy. Are you sure it's bent (it isn't obvious in the picture if one of 'em is bent).

[Tim Smith]

Both are SIII forks so i think they should be the same. Not sure if there is a difference depending on suffix type though.

But as you said, other than the end that attaches to the sliding gear, they look pretty much the same. I can't really see that mine is bent either.

[Terrys]

Tim, You asking for transmission help is like Julia Childs asking how to make French Toast.

[Tim Smith]

Thank you for the compliment but not sure if that is deserved. Unfortunately I have been plagued with multiple transmission problems with this truck lately. My biggest problem has been identifying the correct suffix on whatever transmission du jour I've opened up to fix. Seems none of the top cases are original on my transmissions and that really grinds my gears.

Any way, with this box, I did find the selector shaft had an extended groove for the clamping bolt which holds the 1 & 2 fork on. That was a first for me. Guessing that I slid the fork on this groove, seemed to make sense with the way it went bad. So I swapped the fork and selector with another that did not have the extended groove but did have the elongated fork. Guess what, it was exactly the same. :(

I decided to run this box any way because there were no shards or shavings any where in the box and figured I would drive out west with my fingers crossed. Later today while highway testing some tires (for balance) that I had just mounted, the bloody transmission went right back to normal operation after fighting it for a while in that weird break down mode.

I can't explain it. Silly truck just fixed it's self despite my efforts.

My best guess at this point is that the shim post has come come out of the distance piece and I'm getting a misalignment with the syncros or the reverse gear (aka, the gear that the 1 & 2 selector fork applies). I'm not all too sure what the catastrophic failure will be but I've driven many transmissions with broken distance pieces and they never let me down till I opened them up to fix them... full circle.