Powerglide Installation Question

[67stripper]

I am working on a 1967 Norwood convertible, L30 Powerglide, built 11B on November 11, 1966. The car is very original and has been in the family since 1978 when purchased with 62,000 miles. It now has 74,000 miles on it and has not been driven much since 1984.

During the late 1980s and early 1990s the car partially came apart for some bodywork and the engine and transmission were rebuilt by local shops. In the late 1990s the engine and transmission went back into the car and it was run a few times.

A couple of years ago I took the engine and transmission out again to fix bad oil leaks in the engine after driving it briefly. What I noticed when I disconnected the torque converter from the flexplate was that the flexplate was under tension against the torque converter and when the three bolts were out there was a 5/64 to 3/32 gap between the flexplate and the torque converter at all the converter pads. The base of the torque converter crankshaft pilot hub was completely up against the crankshaft and the converter would slide back the desired 1/8” +/- so that it was not bottoming out in the transmission pump gears. All seemed good except for the gap.

When the engine and transmission were rebuilt in the 1990s the only thing that was not original during the replacement was the torque converter as the transmission shop that did the rebuild suggested a replacement for a rebuilt transmission. This seemed like a good idea and I went along with it. Unfortunately I gave up my original torque converter for core credit. I would not give up my original parts again.

Unfortunately the torque converter shop that supplied the rebuilt converter in the 1990s is not longer in business although from my research they had a good reputation. So, I took the converter to a local converter shop and had them look at it. They advised that it looked like all the other Powerglide cores they had and didn’t see anything unusual about it and it was good to go. I then looked around for Powerglide converter specs and finally found some and measured what I could. All seems correct.

Further research online and with a couple of mechanics leads me to my quandary. The “B&M Torque Converter Installation Instructions for General Motors TH-350, TH-400, & Powerglide” states under Step 15:

“If your flexplate is new or in good condition the converter may not contact the flexplate before if bottoms out in the crankshaft. A 1/16 – 1/8” gap is normal. When the flexplate to converter bolts are tightened the flexplate will bow backwards slightly and hold the torque converter against the crankshaft.”

This makes sense to me because all the parts are original except the torque converter and it appears to be the correct part based on my discussions with the converter shop, the specs I found and the pictures I have seen online of Powerglide torque converters.

The mechanics say no way I should shim the gap so the flexplate is not under tension. This appears to be an accepted practice in racecars with modified torque converters but for a stock application with stock parts?

After all of this my question is: who is right? B&M’s explanation seems to make sense but so do the mechanics that say it should not be under tension.

Any help here is greatly appreciated as I’m getting ready to put this back together and don’t want to damage anything or have to take it apart again. If anyone would like more information or pictures let me know and I’ll do my best to get them for you.

It seem like I am not the only one who has had this problem. Here is a previous post from 2012 with virtually the same problem. There is some discussion about this but no resolution.

http://www.camaros.org/forum/index.php?topic=9988.msg73767#msg73767

[usa1ti]

Definitely should not be under tension. In some of my street cars I have used washers as spacers in the past. In the racecars I use matched machined and ground spacers. Some of the higher end race transmission builders sell the spacers. ATI, TCI, Abruzzi, FTI, BTE. I bottom the converter in the pump. Pull it out 1/8” to 1/4” and space as needed. Have ran a 68 L88 turbo 400 camaro to my 1150hp 175 mph super gas car this way.

[KevinW]

The nose of the torque converter should fit into the end of the crankshaft all the way to allow for the flywheel to match up without tension.  Sounds like the converter was not fully fitting into end of crank or nose of converter is too thick.   my .02

[67stripper]

Thanks for the replies. Much appreciated.

[olddragracer]

Was a reground crankshaft installed when the engine was rebuilt? The rear of the crankshaft on 1967 small block engines with manual transmission was machined differently than engines with automatic transmission. If the crankshaft has an old pilot bushing in it or has a bore that is correct to accept a pilot bushing the bore for the torque convertor may not be deep enough. In the automatic crankshaft the bore for the standard transmission pilot bushing is unfinished and is undersized for the OD of the pilot bushing. New GM replacement crankshafts have both bores finished correctly. I believe if the torque convertor centers in the crankshaft 3 washers of equal thickness can be used between the convertor and flex plate. Be sure there is there is rearward movement of the torque convertor from the washers into the front pump of at least 1/8 inch. Other problems I have seen are bent or dish shaped  flex plates.

[Everett#2390]

As suggested, use washers  as spacers between the T/conv & plate.