<VV> Problem with 1961 Powerglide shifting into reverse

[Brent Covey]

> The first problem was that when shifted into reverse, nothing
> happened for  about 20 seconds and then it started reversing.

Sounds like everythings been put together OK- If you want to double check
the cable installation thats covered over on the Corvair Forum site, look
about halfway down here;

http://corvaircenter.com/phorum/read.php?1,25613,page=1

Early Powerglides use that 'lip seal' on the reverse clutch which is usually
preferable, it provides instant and soft engagement of reverse.

GM is aware that 98% of shifts to reverse are on a cold engine leaving the
driveway for work in the morning with the choke fast idle going so they
actually have a name like 'garage engagement' (I forget the actual term) to
describe the smash into reverse an automatic transmission car with a cold
engine does under these circumstances. Lots of energy goes into making
reverse engage gently on all GM automatics, thats why the big Hydramatics
before 1965 used cone clutches and other lines have various provisions to
ease or delay the reverse clutch engagement on a cold engine running fast-
hopefully to preclude whiplash and a couple streaks of rubber down the
driveway in the mornings.

Anyhow, on the Corvair the reverse clutch with the lip seal extends the
piston fast at low pressure from the excellent sealing of the lip type seal
and then seats itself and has a rapid rise in pressure to engage. This is a
very nice arrangement, and I usually use lip seals in Powerglides when I am
rebuilding them for a car that gets driven on a regular basis. Reverse seems
instant, and then theres a soft nudge that indicates its ready to go, no
thump.

Somewhere around 1963-'64 the seals were changed to a square cut ring that
does not seal anywhere near as good but is far less susceptible to nicks,
distortion from long disuse putting a flat spot on them, or grinding damage
from wearing as the pistons moves thru its stroke This is a very durable
seal and rarely gives trouble but it also can leak, harden, shrink or tear
and seal poorly. I bought a 1967 with 22,000 miles that took three minutes
to engage reverse after 20 years standing idle the first time it was started
up, but it worked progressively better as the day went on and was fine
within a week without attention.

The square cut seal is fine and good to use and slightly more durable but it
isnt quite as refined on that first shift into reverse in the mornings,
although its not awful. I would imagine the seal kits from the vendors are
supplying square seals in every case by now. The lip seal is more vulnerable
to heat and friction damage but few are overheated and the wear is seldom
enough to effect operation even at very high mileage, it should last the
life of the car.

Usually what happens is the seal gets a little wrinkle or flat spot on it
from being shut off nice and warm and flexible and left sitting a long time
(like a month or more) and takes a slight set with a distortion from
wherever its touching anything and the cold disuse that needs a couple days
to iron itself back out. You have probably a 95%+ chance this seal will sort
itself out once you're using it a little again. Warm fluid really works
wonders on seals.

I think the product Larry Claypool suggests is 'Forte' transmission
conditioner. It comes in a small pop top can similar to what tomato sauce or
STP comes in. There are a few brands of similar products. These products
contain compounds that swell and soften the seals and get them limbered up.
Automatic transmission fluid contains compounds like this also. It wouldnt
hurt anything to try something like that in your Powerglide and see if it
has any beneficial effect. I would not suggest a product like this for a new
transmission.

Something that also occasionally happens is the reverse clutch discs wear
out and the piston is trying to overextend itself because they arent a tall
enough stack to stop the piston in the normal range of travel- it travels
too far and the piston hits the snapring that retains it. There is sometimes
enough pressure to have the piston blow off and this creates a transmission
failure that requires a few new parts, however given your experience it
doesnt sound like thats likely.

So, it should start working again on its own after a day or two and a few
cycles warming up and being used, failing that try the can of seal
conditioner and see how that goes. If it doesnt resume normal operation in a
few more days you might want to throw a seal kit in the Powerglide, which is
not very hard to do once its out of the car.

Here is a link to some quite good online illustrations of Corvair Powerglide
parts;

http://charlietranny.com/CorvairPGparts.htm

I think that we're discussing what probably will turn out to be a
self-healing situation in a 45 year old transmission is a good indication of
the tremendous reliability of Corvair Powerglide.

Good luck!
Brent Covey
Vancouver BC