Mike, I have a 1974 Chevy Nova with a 355 small block, 13:1 compression, Brodix heads and intake, Lunati roller .600-.609 lift. The car is about 3150 lbs. It has a TH400 trans with ATI guts and manual valve body, 8-inch 4500 stall converter and 4:10 gears. My problem is this trans slows down on each pass down the track. Normally it goes 11:20s at 120 mph, then drops down to 11:50s at 117 mph.

We’ve gone through the trans twice with the same results and upon teardown we find the high gear clutches to be burned badly. Am I just wasting time and money on this trans setup or what?

I hate to think of the expense of changing over to a glide. Is there any hope for the old 400? Any help would be greatly appreciated.



Tim, Even though your 400 package has all the ATI components, it may need some finishing touches to make it into a good working unit.

A few things I could suggest: main line pressure should be between 180 and 210; teflon seating rings need to be used; you need a 1/16 bleed hole in the drum, it may be trying to apply high gear clutch in the top of low gear. That’s why we use a bleed hole in the drum.

For the same reason, we usually don’t peak out the motor in low gear. In other words - short shift. At least on the 1-2. This is also why most trans brake manufacturers use stiff springs in the direct drum.

Clutch pack clearance in the high clutch should be .050-.070. Also, normally the ATI aluminum drum (if that is what you have) won’t accept very many clutches. It needs 5 or 6 in the forward and direct packs.

Try these tips and see if they get more life out of your 400.




To contact Mike Stewart email trannytech@dragracingonline.com


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Tranny Tech — 4/8/04
Mike Stewart Can Cure Your Automatic or Powerglide Problems

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