Jon,
yeah if park works, thats not it.
Always keep a spare air compressor around as a wheel chock!
________________________________
From: Gmclist on behalf of Richard H Staples via Gmclist
Sent: Tuesday, July 14, 2020 9:56 PM
To: gmclist
Cc: Richard H Staples
Subject: Re: [GMCnet] Cooked my tranny
Keith V wrote: " One of the people
that know that type very well told me that I should change the trans lube from either Ford or GM to the other and that would fix it. It did."
I'd guess you changed from Type A/Dexron to Type F (older Fords). IIRC, the difference involves the coefficient of friction (film strength?) under
pressure. The GM Dexron fluid requires a bit more physical pressure before a friction element (clutch or band) locks up. This is great for smooth,
gentle shifts, a GM hallmark. Trannies designed for Dexron are calibrated for its characteristics (I assume filling servos and clutches faster, to a
higher pressure, etc).
OTOH, Type F fluid is "grabbier", locking up more quickly at a bit less pressure. This allowed Ford to use lower hydraulic pressures, ostensibly to
save energy and lighten components.
The conventional wisdom used to be that using Dexron in a Ford would cause slippage and burned out clutches, while using Type F in a GM would cause
very harsh shifts with (possible) transmission/driveline damage.
However, some (many) years ago in this forum there was a member who used his GMC to tow his race car, I think it was a drag racer. I'm sorry, I can't
recall his name.
He stated that since they used Type F in the race car, they just used it in the GMC, figuring it would help prevent slippage under the stress of
towing,etc. Said it worked fine.
So, I started using it in my GMC, some 20-odd years ago. I don't put a lot of miles per year on The Dancing Bear, especially recently due to some
health problems. So far, so good. It DOES shift a bit harshly, especially under wide-open throttle. I did a forced kickdown at 65mph once on the
Interstate. I try to avoid that now, shifting down manually when necessary. Changed fluid an filter recently, and the pan was clean.
JWID, YMMV
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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