TH400 Talk
 

Thought there was a "drive train" section, evidently not.

So, couple of questions after my first test drives.

Is an original OEM modulator adjustable for shift point? Mine seems to be shifting a few hundred rpm early. Like almost immediately after you leave from a stop it shifts to 2nd. I have to slow down to a dead stop to get it to start back off in 1st.

Manually it works great, shifts firm but not harsh. I rebuilt the whole trans using a Trans-go kit, nothing outlandish, basically stock. Converter is the Hughs 30SP(?) "Tow" model. 068 cam, Q-jet, engine has outstanding vacuum.

I'd like to use the OEM modulator if it's adjustable. I'll be honest, I don't even know if it's working properly ... sat in a box for 40 years, was a bit sticky till I freed it up.

And .... while checking out the diff I noticed if I rotate the driveshaft one direction the trans makes a quiet whistling sound, like drawing a squeegee across glass, you'd never hear it except in a very quiet shop. Sounds internal to the trans, up front somewhere ... don't think it's the speedo cable or tailshaft seal. Doesn't do it if I turn the driveshaft in the other direction.

Hate to bother folks with this kind of stuff, but it's been 40 years since I drove the car so I long ago forgot how it should behave and sound ... heck 40 years ago I would have jumped in and smoked the tires no matter what sound it was making :)

Check your governor 1st

I thought the Governor only controls the rpm of where the shifts take place at full throttle and no vacuum?

This ^^^

Governor control the early roll shifts (only a little with a selection of Stock
Govs #s 11-33); use stock outer weights with holes in them for a wee later shift from a roll. Inner weights; use stock lighter weights and flimsy springs for higher rpm WOT upshift.

Stock big can Mods might have the adj-screw brazed so it cannot be turned. Try and see if turning screw in can occur, and how the shifts are delayed. If screw locked then get the small single-red strip Modulator and adjust away. Keep the big can modulator on the shelf,as they might have value to some folks.

The bigass modulators "can" be adjusted, IF (big IF) you're successful in breaking the spot-weld that secures the screw. I don't remember seeing the screw brazed, but who know how many variations GM had.

Unlike the cheap aftermarket mini-modulators, the bigass ones compensate for altitude.

Trans squeal when turning driveshaft is totally normal. You're hearing the one-way clutch turn opposite to it's lock-up direction. Maybe some band-drag.

Thank you gentlemen, you've both put my mind at ease and provided me with useful information.