Push-start with automatic transmission
Push-start with automatic transmission
(OP)
Hey guys,
An idea crossed my mind the other day, and I was wondering if somebody could poke some holes in it (the idea, not my mind)...
Typically one cannot push-start a car with an automatic transmission, because the tranny can spin freely when the engine isn't running. (Torque converter slip % would be close to 100%, but the trans input shaft doesn't spin anyway)
Are there automatic transmissions where the tranny input shaft will spin when torque is input to the output shaft, even when the engine isn't running (and thus the trans fluid pump isn't pumping)? If such a tranny exists, are they common? Further, if such a tranny exists, and was coupled to a torque converter with electronic lockup, could one rig a cheater switch to goose the lockup while attempting to push-start the vehicle?
Thanks for any info
Isaac
An idea crossed my mind the other day, and I was wondering if somebody could poke some holes in it (the idea, not my mind)...
Typically one cannot push-start a car with an automatic transmission, because the tranny can spin freely when the engine isn't running. (Torque converter slip % would be close to 100%, but the trans input shaft doesn't spin anyway)
Are there automatic transmissions where the tranny input shaft will spin when torque is input to the output shaft, even when the engine isn't running (and thus the trans fluid pump isn't pumping)? If such a tranny exists, are they common? Further, if such a tranny exists, and was coupled to a torque converter with electronic lockup, could one rig a cheater switch to goose the lockup while attempting to push-start the vehicle?
Thanks for any info
Isaac
RE: Push-start with automatic transmission
The main problem is that to get the bands to engage you need oil pressure, and it would be a brave designer who put the oil pump anywhere but on the input side of things.
You could design a box in which the default position was, say, direct drive, but I think it would not be common, for safety reasons.
Cheers
Greg Locock
RE: Push-start with automatic transmission
Chumley
RE: Push-start with automatic transmission
The early Dynaflows had as many upshifts in reverse as forward. We use to get that old Buick up to about 60+ in REVERSE!!! Great fun???
Rod
RE: Push-start with automatic transmission
RE: Push-start with automatic transmission
Rod
RE: Push-start with automatic transmission
Rod
PS---Re the current IVT and CVT with their 'simulated' gears. It is hard to change the publics perception of what is "better".
RE: Push-start with automatic transmission
That makes more sense... I was starting to worry about whether I really knew a thing about auto trannies. I can state confidently that the THM400 used in at least one 1978 Jeep Cherokee had no rear pump, but that would be about the limit of my first-hand experience with auto trannies (rebuilt one under careful supervision).
RE: Push-start with automatic transmission
I suspect a towing situation would generate the same "objection" except that you might not see it if your in the tow vehicle. That could be a problem.
Chumley
RE: Push-start with automatic transmission
RE: Push-start with automatic transmission
Blacksmith
RE: Push-start with automatic transmission
RE: Push-start with automatic transmission