Q for Muncie Experts / Rebuilders

[Wayne M.]

While dismantling two transmissions I acquired, was surprised to find these shims between the front bearing (of which both are OEM and maybe even the originals [New Departure 41307B]) and the input gear (clutch gear) face.

The M22 on the left is from an April '69 Camaro; "660" maincase, and the M21 on the right is from an early March '66 "010" maincase. The M22 has the oil slinger (added by factory in 1968, with intro. of 660 case ?) and someone has also added a 0.037" (or 37 thou) shim (probably from a GM differential rear pinion kit). The slinger itself is 20 thou, for a total of 0.057" between rear of front bearing inner race and the face of the gear.

The M21 had a bronze (?) spacer of 0.048" at the same location. In all my books on these trannys, I've never seen extra spacers added here. What is the purpose ? The result is that the gear teeth are positioned that distance further back towards the rear of the trans. Is this an old hot-rod trick ? Should I use them when re-assembling ?

[Michael M.]

Re: Q for Muncie Experts / Rebuilders

I do not have an answer for you, but you may want to post this on the Corvette Forum. Paul Cangialosi is a Muncie expert and frequents the CF. His handle is "5speeds", I believe.

[William H.]

Re: Q for Muncie Experts / Rebuilders

I belive this is a fix to keep the trans from jumping out of fourth gear.
Bill

[Jim Mitchell]

Re: Q for Muncie Experts / Rebuilders

This fix was commonly used by by drag racers in the NHRA Stock and Super Stock classes. The objective of the shimming was to move the input shaft deep enough into the transmission so that there was approximately .010 inches endplay between the input and mainshafts. As far as I can remember, it originated in the early '70s and served two purposes. First, by moving the input shaft deeper into the transmission, it allowed the mainshaft to have more bearing contact with the input shaft rollers, thereby aiding in mainshaft and input shaft stability. The second benefit was a crisper shift into fourth gear and better fourth gear retention.

I've used this fix on all the Muncies and T-10s I've rebuilt over the last 35 years and have experienced excellent results.

[Patrick H.]

Re: Q for Muncie Experts / Rebuilders

Jim,

What do you use for the shims?

Patrick

[Jim Mitchell]

Re: Q for Muncie Experts / Rebuilders

I've used pinion shims for either 10-bolt or 12-bolt 1964-1972 Chevelle/Camaro differentials.

[Wayne M.]

Thanks to all ( & addendum)

Jim -- makes sense what you've described. Strangely, the only other reference I've come across is in The Petersen series "Basic Clutches and Transmissions"; Hot Rodding Standard Transmissions; article showing one "Pepe Estrada" of Paramount CA installing a flat washer (looks at least 70 thou thickness in the picture) on the tip of the mainshaft, in front of the bearing cage; quote "... to maintain proper distance between the main shaft and main drive gear ... result is easier shifting from 3rd to 4th".

Putting a spacer / washer in this location seems to run counter to what you've described and to what I have seen in the 2 trans that I dismantled.

[Jim Mitchell]

Re: Thanks to all ( & addendum)

Wayne,

If you look at the pictures you posted in your original message, you will see that the spacers are installed exactly as I described.