Gene writes;
>Good into on the tranny shifting. I am going more and more to pulling
>it down to second at 2000 and back up at almost 3000. I wish it would
>do this by its' self but does not shift like that. Also find I have to
>hold it down into second on on ramps or it lugs the motor too hard
>getting up to speed.
It is possible to compel the transmission to HOLD second gear very very late
in 'Drive' but it is tricky trying to get them to kick BACK 3-2 in most
cases. At ~10" Hg acceleration, you should see a 2-3 shift occur pretty
close to 45 mph - at ~7"Hg perhaps 55mph or so with a standard 3.07 axle. At
nearly closed throttle it will occur about 20-25 mph ideally.
Modification to encourage part throtle delay in upshifts and detent touch
downshifts is pretty easy, is there interest in a parts list of springs and
transfer plate modifications to achieve this? I was compelled to make this
sort of modification to a 455 Pontiac I use for towing that is handicapped
with a 2.56 axle. It is now able to 'sense' loads and hills MUCH better and
delays upshifts accordingly. I also use a Switch Pitch converter in this car
so that I have not really needed to get it to do 3-2 downshifts until quite
heavy throttle. 70,000 miles of towing a 7500 lbs car trailer has been
pretty good with this combination- it still has its hands full at ~55mph
into a headwind, but for the most part it works fine. Total all up weight is
about 13,000 lbs, and I see roughly 10-13 mpg US at lowish highways speeds
with it (55-58 mph). Solo the car gets about 17-18.
I am fairly sure that parts to make the THM425 shift a little later and
remain civilized would be availible off the shelf at GM still, as it's
largely a question of matching up complimetary springs from stock. I used a
few parts from the six cylinder truck THM 400 in mine to get a more
responsive shift schedule for mine, among other things.
What would you like the THM 425 to be doing that it does not?
Brent
>Good into on the tranny shifting. I am going more and more to pulling
>it down to second at 2000 and back up at almost 3000. I wish it would
>do this by its' self but does not shift like that. Also find I have to
>hold it down into second on on ramps or it lugs the motor too hard
>getting up to speed.
It is possible to compel the transmission to HOLD second gear very very late
in 'Drive' but it is tricky trying to get them to kick BACK 3-2 in most
cases. At ~10" Hg acceleration, you should see a 2-3 shift occur pretty
close to 45 mph - at ~7"Hg perhaps 55mph or so with a standard 3.07 axle. At
nearly closed throttle it will occur about 20-25 mph ideally.
Modification to encourage part throtle delay in upshifts and detent touch
downshifts is pretty easy, is there interest in a parts list of springs and
transfer plate modifications to achieve this? I was compelled to make this
sort of modification to a 455 Pontiac I use for towing that is handicapped
with a 2.56 axle. It is now able to 'sense' loads and hills MUCH better and
delays upshifts accordingly. I also use a Switch Pitch converter in this car
so that I have not really needed to get it to do 3-2 downshifts until quite
heavy throttle. 70,000 miles of towing a 7500 lbs car trailer has been
pretty good with this combination- it still has its hands full at ~55mph
into a headwind, but for the most part it works fine. Total all up weight is
about 13,000 lbs, and I see roughly 10-13 mpg US at lowish highways speeds
with it (55-58 mph). Solo the car gets about 17-18.
I am fairly sure that parts to make the THM425 shift a little later and
remain civilized would be availible off the shelf at GM still, as it's
largely a question of matching up complimetary springs from stock. I used a
few parts from the six cylinder truck THM 400 in mine to get a more
responsive shift schedule for mine, among other things.
What would you like the THM 425 to be doing that it does not?
Brent
