View Full Version : layshaft interchangeability.

07-19-2012, 8:35 AM
soooooo. I have a complete 1971 4 speed t120 transmission. but I want to run a tranny driven speedo since my project has GSXR wheels. The bossman I'm an apprentice for says if I use a pre 65 layshaft and the rest of my 71 gears, the transmission will bind and not function.

First question - is this true? I know the later trannys are beefier so I understand this could be possible, but the layshaft gear pressed on has very similar teeth except they're cut a little different.

second question - could I just press off the layshaft gear and swap it so I have all the same gears, but just a different layshaft?

I know somebody on here has the answer for me (the bossman hates running speedos and if I press him any more on the issue I think he's going to kill me - so I've turned to the internets)


oh - and I already have the pre-65 tranny cover.

07-19-2012, 9:05 AM
you already have all the parts needed, the early lay shafts will interchange and the 65 inner cover will work fine, but make sure you loose the 71-72 leaf spring shift cam indexer and go back to the bottom style piston spring indexer.

the bad news...the trans mounted speedo drives often leak.

07-19-2012, 11:47 AM
the bad news...the trans mounted speedo drives often leak.

everyone says this, and in 47 years there hasn't been a solution? I put a new rubber on the brass insert - maybe some gasket goo for good measure, too?

07-19-2012, 2:34 PM
it leaks into the cable and drips out

07-19-2012, 2:39 PM
you're the best. thanks for knowing everything (not sarcastic - it really is handy)