I've got a 74a D6 that's in pretty good overall shape, I bought it from a small construction company about 4 years ago. S/N is around 1300, the plate on the dash is gone and the winch covers the one on the rear. My issue is it is jumping out of forward and reverse. I've found that gear one through three make no difference, as far as staying in the selected direction, never have any use to run 4th, unless I'm walking across the farm. Sometimes the problem is more prevalent than others. I've got a parts manual and a reproduction service manual. I'm guessing start with the interlock, but I'm asking before assuming. Any and all help is appreciated.

Hi 74A6C,
welcome to the BB.
From my Specs book we are given a centre to centre distance for the Interlock Linkage Rod as :- 15.22"
This dimension can be correct but lost motion--worn linkage etc.-- can allow the Interlock inner mechanism to be short of its intended position to fully lock the shifter rails in place.
Worn gear shaft bearings within the Trans. can overload the linkage too by allowing the gear teeth to run at angle and so cause end thrust on the gear shifter levers etc.

The Fwd. Rev. mechanism is the most used linkage and so wear is your enemy in high hour poorly maintained units.

Others may be able to contribute more as I do not recall any of these DD units in our area so have no experience of them.

Hope this helps.
Cheers,
Eddie B.

Thank you for the reply Eddie. I've measured that and came up with 15.25 and really didn't find any signs of slop in the linkage. The shifter itself makes a pretty solid engagment, but still has a lot of travel back and forth. It will nearly lean back to neutral while in forward.

You need to get the cover off the interlock plunger compartment and see what's going on. Maybe a broken plunger.

Hi Team,
now you have confirmed the Factory setting OM has covered the next step for you.

The Fwd/Rev lever is usually used more than any of the others so the interlock plunger and slider rod groove that the plunger engages and that the shift fork is mounted to is the next likely area to inspect as OM says.
Cheers,
Eddie B.

Thank you for the advice. I'll see what I can find.

There must be a problem in the transmission interlock .I have a 74 A and the forward and reverse bar has a lot of slop in the linkage ,and never jumps out of gear when the forward and reverse bar engages the gear

Interlock can be a touchy adjustment and subject to wear and plungers have been known to fail.

"74A6C" wrote:

Thank you for the advice. I'll see what I can find.

Good luck and update us on what you found out.

I had a problem for a time. Pulled the side cover with the interlock plungers,cleaned with solvent and air. Sprayed with lube and it worked without any more trouble. I was surprised as there was nothing I could see or feel. I was expecting a weak spring or rust.


It was one of the mounts of success I generally only dream about. So who knows if it will work for you.