Overdrive Question

The measurement of .677 taken from the case to the top of the planetary gear. (Fig. 5) Per the instructions.

My question is. Is there a special gasket thickness needed for the Overdrive to case?

 

I use the gasket in the seal kit offered by Advance Adaptors. It is just a paper gasket, so not very thick. Are you having a problem with the measurement tolerance ?

 

I was wondering if a thick or thin gasket would make a difference. I've had issues with the overdrive not staying in direct drive.
I modified the shift fork to get full engagement. I had a .030 shim behind the planetary gear. (.712 measurement.) It stays engaged.
So, with a .010 shim. The measurement is .682. I know they want .677. I think it's close enough. I'll need to try to see if it stays engaged.

 

Scott can you give any details as to how you modified your shift fork? I have one of Herms rare 30% OD units and it will not stay in Direct unless I hold the stick. Adam (Herms son? emp?) told me I needed to add some shims. Which I did but then screwed up and also used a much thicker gasket between the D-18 and OD negating much of the shim. I will first try to correct the problem with a thinner gasket before adding more shims. If this doesn't work I would like to see what your modified shift fork might due for me.

 

Adam is one of Herm’s sons.

 

Herm told me the same, just add shims. The .677 measurement is so the syncros will work properly.
I removed the roll pin from the shift fork and slipped the fork down the shift fork shaft. (Away from detent ball end.) Then I bottomed the shaft and fork in the case. This makes the fork and shaft at full travel. I then measured where the fork sits on the shaft. I then calculated and drilled a new hole in the shift fork for the roll pin. Mine was off about 1/8"