M40 adjustments

**WILMASBOYL78** · #1 07-28-2009, 05:29 AM

The factory CW code TH400 trans was the unit that was installed in the L78 cars and the Z28. Hi-shift point with the large can style modulator...the adjustment screw is sealed on these units with a glue/wax type product. I have never tried to loosen the factory fitting...the aftermarket small gold colored units have an internal adjustment screw. Just remove the hose and turn it in to restrict vacuum and create a later and firmer shift. There are shift kits available for the TH400, but the factory hi-perf unit is pretty good "as is".

wilma

**RPOLS3** · #2 07-28-2009, 06:20 AM

You can also buy aftermarket kits with different weights - similar to distributor advance weights - that will alter shift points.

**John Brown** · #3 07-28-2009, 07:28 AM

[ QUOTE ]
You can also buy aftermarket kits with different weights - similar to distributor advance weights - that will alter shift points.

[/ QUOTE ]

I take it that you're talking about the weights in the governor assy.

**RPOLS3** · #4 07-28-2009, 05:35 PM

Correct - I have a "CD" coded low perf M40 in my 72. By adding a shift improver kit (not a full blown shift kit) and tweaking these weights I was able to get it to shift where and how I wanted it to. It is a little bit of a trial and error process but is not overly difficult. It has performed flawlessly behind a GM crate 454/425 for 8 years now.

**TimG** · #5 07-28-2009, 05:52 PM

Thank you for the information. It is the original CW transmission and it shifts very well now. If it is adjustable, I was going to play with it to see if I could make it bang a bit harder.

**Mr70** · #6 07-28-2009, 05:54 PM

Tim
Which posi rearend ratio are you running...3:73...4:10?

**TimG** · #7 07-28-2009, 06:04 PM

The original 4.10, it's kind of a beast.

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