How do you Change Shift Pattern on C-6

[sweetlou]

How do you change the shifting patterns on a C-6 Trans? It is coupled to a '72 390. I just want it to shift at some higher RPMs.

[Donnie]

Hi, the easiest way to gain a small increase in your shift pattern is to turn IN the screw in the end nipple of your modulator. Try 2 turns in, then another turn or two...keep track of where you are at , if this doesn't work, you may need to work with the governor or valve body if you are looking for distinct changes...What speed's are you shifting at now at moderate throttle?..What rear end gear set is in it ?
How much increase are you looking for...............Donnie

[sweetlou]

The shift is at around 12mph then again at 25 mph. The rear end gears are 3.7.

[Donnie]

Been away for a few day's.. Have you tried adjusting the mod? there are many ways to increase shift speed, from gov work, to valve body spring changes..to the easy way...try first: add 1/16 inch to your modulator pin.. you can make one from a 1/8 " welding/brazing rod...if this fails, take an old buss glass fuse break away the glass, just use the end cup.......drill a 1/16" hole in it & install it in the line going to the mod valve..
If none of these work, you will be going into the gov or valve body...4x4 gov is tough to reach+pull transfer case. 2x4 easy, pull tail shaft
The problem is : your gov signal is weak, e.g., your gov valves are stroking too soon..The gov pressure must over come the vacuum signal for the unit to shift....this is happening too soon.... There are other modulator valves with different values, but I can't recall in my mind which way to go........Does your mod have a stripe on it that you can see...purple, white, yellow, black?...post back & I will see if I can find my notes on this .
Donnie

[crazyhorse]

Mr Donnie, this is very helpful.
Thank you for the good information.
I'm saving it since I hope to build a c 6 some day just to see if I can.

[sweetlou]

Been away for a few day's.. Have you tried adjusting the mod? there are many ways to increase shift speed, from gov work, to valve body spring changes..to the easy way...try first: add 1/16 inch to your modulator pin.. you can make one from a 1/8 " welding/brazing rod...if this fails, take an old buss glass fuse break away the glass, just use the end cup.......drill a 1/16" hole in it & install it in the line going to the mod valve..
If none of these work, you will be going into the gov or valve body...4x4 gov is tough to reach+pull transfer case. 2x4 easy, pull tail shaft
The problem is : your gov signal is weak, e.g., your gov valves are stroking too soon..The gov pressure must over come the vacuum signal for the unit to shift....this is happening too soon.... There are other modulator valves with different values, but I can't recall in my mind which way to go........Does your mod have a stripe on it that you can see...purple, white, yellow, black?...post back & I will see if I can find my notes on this .
Donnie

Donnie, I will try the easy way first. May take me a few days. Got other hunny do stuff