1940-1947 transmission synchros installed in a 1939 Buick 40 series transmission

[buick looks fine for 39]

A while back I wrote a post regarding the use of 40-47 synchros in a 39 Buick Special transmission. There are 2 different part numbers for 38-39 synchros and 40-47 synchros. Many people believed the two different synchro types were not interchangeable. I posted the different part numbers were due to a synchro design  change. 38-39 synchros were spin poured in a steel shell like a babbitt connecting rod and the brass friction surface was machined into the synchro. 40-47 synchros had the brass friction surface press fitted into the steel shell. Years ago I found a Muncie (?) interchange manual  and it listed 38-47 as having the same part number. I believed 40-47 synchros were superior to 38-39s because the earlier synchros had a tendency to delaminate and shed brass fragments into the gear box. 

 

Today I made my maiden voyage in my 39 Buick 46c with 40-47 synchros and the transmission performed flawlessly. Finding 40-47 synchros are still like hen's teeth but It might give folks more flexibility who own 38s and 39s if 40-47s will work as well.

 

Thanks

Leif

[Bloo]

Good to know this works back to 38.

 

A year or two further back there was a change in cone angle, and a potential gotcha exists with synchros that look like they fit but don't function in use.

 

Edited March 7 by Bloo (see edit history)

[buick looks fine for 39]

Thanks for the input. A change in cone angle between 38-39 and 40-47 was the main concern regarding interchangeability. In my car it dosen't seem to be a problem.   

[Bloo]

There is a Buick service bulletin with a dire warning about the angle mismatch, and I have seen it in the last year or so, but I can't quite remember. It occurred at either 1936/1937 or 1937/1938.

 

It surprised me at the time. Until I saw that bulletin I had been thinking that the change occurred in the later 30s. Obviously not. This is for the 40 series transmission.

 

[buick looks fine for 39]

Thanks Gary, that sounds better.