TH 400 automatic trans question

[fastglass95]

Turbo-Hydramatic 400 transmission question:

1) On the drivers side of the case, about 1" above the pan flange, there is a wire harness type thing that plugs into the side of the case. What is it connected to? (wires) and What is it called? Mine is loose and appears to be contributing to a fluid leak, I assume these seal with some sort of "O"-ring?
I am replacing pan gasket and filter and noticed this, may want to repair the leak now, while pan is off. Looks like a plastic piece that pushes in and locks with locking tabs inside the case. From there, it has a white wire that goes to ?? and a brown wire that goes to a box only 1" away (inside case)

2) How do you correct the speedometer gears on a TH-400? Mine is out of a donor vehicle and reads about 7mph HIGH at 60 mph. Can this be done with the tranny in the car?

Haynes manual is of no help on this.

Thanks for any help.
Tom

 

[Tom Bryant]

Hi Tom,

Downshifts on a Turbo 400 are controled electrically. That part is the connector for the downshift control solonoid. You are right that it seals with an o-ring.

As for the speedometer reading to high (fast) you need to slow the cable down. That requires a bigger "driven" gear with more teeth count. The "drive" gear is the one actually on the output shaft.

Disconnect your speedo cable at the trans. Remove the bolt and Y shaped retainer that holds the speedo driven gear sleeve into the trans case. Now you can slip out the sleeve and driven gear. Count the teeth. This is your starting point.

Origional Turbo 400 gears ranged from 34 teeth up to 45 teeth depending on rear end ratio and tire size. They were also color coded but they discolor badly over time. You may not be able to go by what color your gear appears to be now.

I still have the parts books with the speedo gear charts in them. If you give me your rear end ratio and tire size I can probably get you real close to where you want to be. You may still have to go up or down a tooth or 2 to dial it. It seems like we used to say 1 1/2 mph per tooth but it has been a lot of years since I was in GM parts.

GM dealers that stock a lot of Turbo 400 parts are rare anymore but the bigs ones still might have speedo gears. You may have to go to a speedo shop or trans shop to find what you need.

Tom