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Discussion Starter · #1 ·
I saw the thread on the TH350 and answer may be the same, but here it goes!
About 2 weeks ago a problem started with my TH400 transmission wouldn't shift up to 2nd or 3rd on it's own. I could manually shift it up. After it cools down and you drive it, everything is back to normal. This has now happened serveral times with the same senario. Drive it for serveral miles, slow down or even shut it off, go back or take off and it won't upshift. I drove it 100 miles Saturday coming back home from the Fred Gibb show in LaHarpe and it worked just fine, stopped for gas, and back on the road it wouldn't upshift automatically.

Have replaced vacuum line and changed the modulator where both times we thought we had it whipped. Fluid looks good and level is correct. I also have been experiencing a vibration around 55 to 65 mph around 3000 rpm's. When you back out of it the vibration occurs too. Speed up to 70 or 80 and it goes away. May or may not be related.
Any ideas before I go see the Tranny Doctor?
My 1970 SS is a 396 car. Your input is appreciated!
 

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Since your problem is heat related it is probably heat reducing the viscosity to the point were the governor spindle valve and vacuum modulator valve are leaking internally so neither can regulate the flow. You didn't mention your torque converter stall speed which is a generator of heat, making more heat the more it slips.

I would find the biggest external oil cooler I could find in the bone yard (look on pu-trucks and cop cars) or buy an aftermarket one to see if that fixes your problem.

Your vibration is a drive shaft out of phase most likely. Drop it and turn it 180 degrees to see if that helps. If not you have a pinion angle issue and need to raise or lower the rear of the tranny to match the angle of the pinion (same angle opposite direction).

Big Dave
 

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Discussion Starter · #3 ·
Thanks Big Dave!
Weird thing is that the car was fine before the restoration was done last fall, and that I drove to several shows and cruises since then and this only started 2 weeks ago.
Some more info: It does have a tranny cooler. This thing does have a shift kit in it and a stall convertor that were put in before I bought the car 4 years ago. I don't have the rear end jacked way up or anything unusual. We were going to send the drive shaft out to have the balance checked thinking maybe the cleaning and painting may be a factor. All new u-joints and the axle bearings, and pinion seal replaced and pinion torqued to spec.
Thanks again and if anymore ideas let me know!
 

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Check to see if it is clogged in some way. It should be around 210 to 230 degrees when you are driving around so the cooler will be red hot to the touch. If it isn't then no fluid is getting through and your bypass is open in the tranny.

The drive shaft is balanced as a unit, but the rear end was balanced with the drive shaft turning the rear end. It is possible to get minor vibrations if the prop shaft is installed 180 degrees out from the factory balance. Dropping it and turning over to reinstall some times fixes those small problems.

Pinion angles are a different issue. The angle formed by the transmission centerline to the drive shaft should be the same angle formed by the drive shaft and the pinion centerline. They are just opposite in sign (the front drops x degrees and the rear rises x degrees).

If the angles are not the same the natural vibration on the universal joint is not canceled out by the joint on the other end, you will get vibrations building up at the natural harmonic frequencies of the drive shaft. Since your pinion is welded in, it is easier to raise or lower the tail-shaft of your transmission with washers, and longer bolts.

Big Dave
 

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Discussion Starter · #5 ·
Big Dave!
Since you were kind enough to come back with some answers to my woes, I thought I would share what has happened. We pulled the pan off the tranny and removed the valve body and governor. Took them over to a really good shop and great guy, Fountain Transmissions in Iowa City. He said the governor was most likely the problem and handed me a perfectly good used on and swapped valve bodies with me.......all for free! Cooler lines seem to just fine. Drove it and got it good and hot and worked like a champ. Took the drive shaft out and took it to a shop to have the balance checked. They said it was twisted (I didn't see anything) with some 60% off, and re-tubed it. Vibration is now gone.
Thanks for your input!
 
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