th400 to much for a 350?

[pphatbasstard]

I have a th400 behind my 350 and I was told that that transmission was to much for a 350 to get "moving" I guess. I guess I belive this person because as soon as I take my foot off the gas my truck slows reallly realllly quick doesnt coast for anything. They said I need a th350. Would I be better off with that?

thanks cool dudes

[1969 GMC]

well, the TH400 came factory behind the 283, 327, and the sixes...i heard it takes somewhere around 40 hp to spin the tranny alone, but its the strongest light duty auto out there. i guess its up to you...

[lukecp]

One of my friends had a TH400 behind a stock '87 up 4bbl 305. The truck ran suprsingly well for a 305, and with the TH400 it would shift HARD into second gear. Leave it in 1st and floor it and that truck would lay down a 4' long strip of rubber when it hit 2nd gear.

[pphatbasstard]

Sooo I guess I was missinformed?

[lukecp]

Well they do take more power to run, but they are just about indestructable. If you are going to swap trannies you would be better off swapping to an OD tranny like a 700R4 or 200R4 so you can have that nice 4th gear for crusing down the highway.
IMO, swapping a TH400 to a TH350 wouldn't be too productive since you would only be picking up a few poinies (not sure on the exact number, from what i've heard maybe 15 would be freed up), and the TH350 is a weaker tranny, although plenty strong for a stock/mild small block.

[too much stuff]

I have an 87 305 fuel injected 2wd 1/2 ton with a turbo 400 factory. not good mpg and has the power of a 305...no problems though.

[72C203503ONTHETREE]

The biggest drawback to a 400 is the weight, they are HEAVY. A turbo 350 is an excellent trans also, many people use them in race cars and have little trouble. They are popular due to less weight and less parasitic loss. Thats the biggest reason the powerglides are even more popular for racing. For all out strength for everyday driving or abuse, a well built 400 will last almost forever. If your truck slows down that much, your torque convertor may have a way low stall speed or be defective. Any automatic should coast pretty good once you get off the gas, unless you are in too low a gear. If you get a 700R4, make sure you get a mid 80's and up Corvette or Z28 trans, they are the strongest. The 200R4 is ok but unless its built it will die sooner than any of the other trans. They arent as strong as the 350 or 400 and even worse than the 700. The 700 is a long tranny to, you will need to fabricate a trans mount and sgorten the driveshaft. The 350 is slightly shorter so you may need to find another driveshaft or have yours lengthened. The 200R4 and 700 will also need a way to engage the torque convertor clutch unless you get an aftermarket convertor that gets rid of that. B&M and TCI make a wiring kit that will allow you to use the convertor clutch which will give you better mileage. Do not use the convertor clutch without the wiring kit, it will burn your trans up without it working.

[Yellow Cheyenne]

You don't say what speed you are coasting down from and also no mention of rear end ratio. If you have a a ratio in the 4's and are slowing or "coasting" down from 70 MPH, it doesn't matter which tranny you have, it will try to slow you down when you let off the gas pedal.

Randy

[SWEET7T]

I have a 327/th350/3.08 rearend. When I'm doing ~75 down the road turning nearly 3000rpm, and I let off the gas, I slow down pretty quick too. My rpm drops about 300 when I do this, but remember that the torque convertor isn't just going to 'let go' and coast like you pushed in a clutch. When I am going slower like 45 or so, I don't slow down nearly as fast. If it is shifting fine, and your happy with it so far, don't worry about it.

The 400 is an excellent tranny. If I had one, I would keep it in there just because it isn't worth it to swap in a th350. The only swap I would do is a 700R4, and only for the overdrive.

[junkyardjohn]

THE T-400 IS PROBABLY THE STRONGEST AUTOMATIC TRANS. IN EXHISTANSE IN STOCK FORM. I DID GO WITH A T-350 IN PREFERANCE ONCE THOUGH, WHEN I WAS BUILDING A 67 CAMARO RACE CAR WITH A 400 SBC ON NITROUS, & THE EXTRA 70 LBS MATTERED QUITE A BIT TO ME. WHOEVER TOLD YOU THAT A T-400 WAS TOO MUCH TRANS. FOR SMALL BLOCK WAS MISTAKEN. JOHN

[crazy longhorn]

I would keep the 400 T, as aready said, it does take about 15-20 more ponies to run, & is heavy......but its 1 damn tough pc!

[rage'nrat638]

here's my coan converter.......TOAST......

TH400 STILL TICKING.....850 H.P.

[inline6Bill]

My shop truck, a '69 CST 20, had a 307 and TH 400. The only thing wrong with the TH 400 is that it is heavy. I have had my TH 400 rebuilt twice in 300,000 miles; at 125,000 and new seals at 250,000, but I worked the tranny hard, pulling an 8000# travel trailer up and down hills in the Cascades of Oregon when the tranny started to give up !!!

The TH 400 is one tough tranny to beat, in fact, I NEVER will change to any other in my shop truck, only added a Gear Vendors overdrive when I had the trans rebuilt last time; best thing I ever did.

Whoever gave you that info about TH 400s is wrong.

[72gord]

I had a TH400 behind a 350 in a 72 Chevelle...did the leave it in low, floor it, and let it shift into 2nd....motor and trans were fine but my driveshaft twisted off and became a 2 piece unit

[67cst]

ive got a 327 with a th400 behind it, we got it off a friend who pulled it out of a donor car, i think it was a late 60s impala..not too sure though, the motor is a low miler, has never been rebuilt and the tranny shifts great! i cant wait to get it on the road and smoke the tires

[RON WOODGEARD]

No doubts, The 400 is stronger, but everyone has failed to state that the 350 has a lower first gear. IE: better acceleration. Maybe that'
s what the guy was refering to????

I have a 350 in mine, It's been there for about 12 years,Behind a mellow built 350 HP ( approx.) 350. Some heavy duty off roading. It has a shift kit and an RV/Off road torque converter.

[lukecp]

Originally posted by RON WOODGEARD
No doubts, The 400 is stronger, but everyone has failed to state that the 350 has a lower first gear. IE: better acceleration. Maybe that'
s what the guy was refering to????

There's not much of a difference, 2.52 for the TH350 and 2.48 for the TH400......

[RON WOODGEARD]

Originally posted by yellow72custom


There's not much of a difference, 2.52 for the TH350 and 2.48 for the TH400......

OK, Now take that and the lighter internal turning weight....

[trukman1]

Thought this was about "slowing too fast" when letting off the gas! If it slows too much, the first gear ratio isn't enough to 'cause it and the weight shouldn't slow the truck enough to notice. If your power band is so low that the extra few ponies the TH400 takes is a problem then I'd be checking that. As is, I'd make sure you don't have a converter problem or brake/e-brake problems first. Normal operating tranny won't cause you to slow down that fast. Good luck. Bye!