View Full Version : thm 425 strength
fuzzy dice
02-06-2008, 03:12 PM
anyone know which front wheel drive transmissions are the strongest or best built in stock form? do any have limited slip diffs? also what about factory gearing? thanks
Mr. P-Body
02-07-2008, 10:27 AM
TH425 is a TH400 "sideways". Tough stuff. They came in cars with TONS of low-end torque. I can't speak about the gear ratios.
Jim
They are the same as 400's
1. 2.48:1
2. 1.48:1
3. 1:1
There was no differential in 425's, 325's or 325-4L's, it is a seperate bolt-on iron housing. Those where not transverse mounted if that's what you are looking for.
4T80E's will take a good bit of power, are transverse mounted and I believe have an available posi but am not sure.
Oooops, old post.
stevep
02-23-2008, 10:33 AM
GM Used the 425 in their front wheel drive motorhomes in the 70's.
Just the fact that a 70 Eldo had a 500 motor with 400 horsepower should say it's a tough trans.
FIREFOX
03-23-2008, 08:46 AM
The 425's came in 2 versions : '66-67 switch pitch convertor and 3.21:1 diff with a planetary carrier , '68-78 normal convertor and 3.07:1 diff with bevel gear carrier.
No "posi" was offered but the planetary acted much like a torsen diff.
The switch pitch could go from 1800 to 2500 rpm stall speed by the movement of
the stator.
engineer
03-23-2008, 07:37 PM
if 425 were front wheel drive, there could be no posi, which is a locking rear drive. what am I missing?
stevep
03-24-2008, 05:39 PM
if 425 were front wheel drive, there could be no posi, which is a locking rear drive. what am I missing?
The differential is bolted to the trans, so is is a transmission, not a transaxle.
smittyseng
04-19-2008, 08:49 AM
th-425's also used 6 clutches in the direct (3rd gear/reverse drum) instead of 5 like most 400's,Smitty
Cammer-6
04-19-2008, 06:07 PM
from what I remember the old system of ID the trans sort of relates the torque rating.
TH350 is 350 ft lb,400 is 400ft lbs etc.
Primitive Artist
04-22-2008, 03:41 PM
anyone know which front wheel drive transmissions are the strongest or best built in stock form? do any have limited slip diffs? also what about factory gearing? thanksMy Starfire had the same basic engine as the Tornado. But with 10 horsepower less and 10 horsepower more than all other high-compression full-sized Olds models. There's nothing to worry about these THD not doing their job reliably, as was the case otherwise with 4 speed Hydro heaps prior to '65 which spent almost as much time in the trannie shops as on the owner's driveway.
Since the Tornado-Eldorado-'s engine weight sat in front of the differential, there was really no need of positraction. Only on rearwheel driven models where there wasn't enough weight to apply enough pressure to both wheels.
Why?
What do you intend on doing?