C6 Shifting at 4000 RPM.
 

Why does my C6 shift at 4000 RPM when the throttle is open? My motor produces peak torque at 5000 RPM, and peak HP at 6500 RPM.

I would like to have the lower gear until I exceed the peak torque at least.

Have you tried adjusting your vacuum modulator? Follow your vacuum line from your intake manifold to the modulator valve on the back of the transmission. Pull the hose off of the modulator valve and you will see an adjustment screw in there. If you turn that in, clockwise, it will raise the rpm at which your tranny shifts. If you back it out, counterclockwise, it will lower your shifting rpm. Assuming you want to raise your shifting point, you would want to turn it in, clockwise. If you have done all of this already, go to your parts store and see what other modulator valves they have. There are a couple different ones out there that should work. Also, if you pull the hose off of the modulator and there is tranny fluid in it, then it needs replaced, it is no good. Hope this helps.

Fatfender,

I'll try to adjust it. I think that it is OK.


BTW, when it shifts from 2nd to 3rd, it breaks the 295R50x15s loose through a 3.25:1 posi 9" rear at 70 mph.

If you have an adjustable modulator, they are designed to be adjusted for your performance engine, nothing wrong with having to adjust them.

Mine breaks the tires too. I have heard this is common when running shift kits, I have a stage-2 shift kit. I have the 285/70x15s with 3.50 gears in a 9 inch :) We're close on our setups, but I know you have me beat with the horsepower and torque :)

If you still aren't satisfied, you can go one step further and run a manual/automatic valve body and do your own shifting or let it shift automatic. I have this type of valve body as well.

danlee, there are also 3 different modulator valves for the C6. you want the purple stripe. this is the sea level valve . the green stripe is high altitude, and the black stripe is for race cars.

What does a White Stripe indicate?

I adjusted the screw clockwise, it took several turns. I didn't seat it, but it was beginning to stiffen. I'll take it out today and give it a try.

i just read your forum, and i am quite interested to see what you came up with, because i have had similar problems with my C6 in my Dually 4X4

I had the truck out, but was not able to get a good run on it so I could determine the shift point. It did feel better.

I'll try it again during the week.

Does anyone know what a White Stripe indicates?

I don't know what the white stripe indicates, but it could be some aftermarket one such as TCI, I'm not really sure. Be careful not to seat the screw all the way in on the adjustment. Seems like I have read where if the transmission is run with it all the way seated it can cause problems. If it seats, I would back it out at least 1/2 to 1 turn. There is quite a bit of adjustability there with these modulators. I was noticing significant changes with just 1/2 turns. Keep us posted.

i have a C6 in my F350 4x4, and i would like to adjust the shift points. does that screw just adjust wat RPM's the tranny shifts at? because i have never heard of that.

.. Anybody got any further info to share on this subject/thread? I'm planning to build up the 351M/400 with C6 in my F150... DiMora is already at the C6 point...

I am currently using an E4OD controlled by a Bauman Opti-Shift Controller. The controller is programmable, and lets you select your shift points and line pressure.