Ive heard quotes from 500-550 hp. anyone have one fail, or know someone who had one fail? how much power did you have? i know there are other factors that dictate when a trans will fail (stall, rear gear, weight, etc), so if you had one fail, what was the setup?

 

I ran a 70 Chevelle with a 427 pushing 525 hp with a turbo 350. I rebuilt the tranny and put a B&M shift kit in it. It handled it fine. I did not race the car and usually got on it while the car was under way. I suppose it depends on how you plan to drive it. Certainly a Turbo 400 can handle pretty much anything you throw at it.

 

I had the 350 trans behind a 396 in a 65 chevy truck,450 lbs. of torque. I broke it getting on the interstate kicking in the passing gear. It popped like a rubberband and I ended up walking home. It also had a shift kit.

 

I have known numerous people with 500+ hp cars that had no trouble with a TH350.
I have broken the output shaft on one with about 350 hp.
I also know a guy that went through 3 TH400s that were professionally built for street/strip use, with about 500 hp on street tires.
I think luck is involved sometimes.

 

We run a TH350 in a 700-horse bracket car with slicks. The 350 has been built by a good tranny builder and has good parts in it - it holds up great.
Lars

 

Lars is that a lite car? I did the nearly full blown th350 kit short of a transbrake in my original 79 Vette. it was 355 ci and shifting at 7200 rpm with 3500 stall 8 inch TC 9X26 goodyear slicks. The th350 lasted a couple of years,100's of 1/4, and street driving. Then one fateful day doing the friday night street drags it went crunch big time. I limped home and pulled the pan and it had lots busted chunks of steel in it. with aluminum flake and clutch black sediment. I was changing the fluid every couple of months to verify the trannies health. It was the end of that TH350.

IMO - the 350 saves power over the th400 and they are relatively cheap to run or replace so it is not a big deal Just do a quality hop up and run it till it blows and not worry about it.

 

I've heard that from most of the guys I've asked about this. kinda surprised me. Oh well, screw it. I'll run it till it blows.

 

I did have the NHRA aluminum blast shields around it and SFI flex plate!

 

It's in a 3200 lb '69 Camaro with slicks and excellent hookup - using a trans brake. Engine dyno'd out at 700 hp and the car gets run every weekend during race season.

The tranny lasted 3 years before blowing the direct drive drum and sprag. After updating to a HD drum and the TH400 sprag (with good clutches) it has held up perfectly. Valve body is a TCI with pretty high line pressures - If I remember right, it does not vary line pressure like a stock unit but keeps the pressure up around 300 psi to make the clutches survive.

Lars

 

I prefer the th350 actually. I broke and output shaft as well along time ago with probably 400-450hp on a stock trans. I have a TCI built one these days and it sees 600hp at the track every week like Lars said and cruising on the streets during the summer. No problems all last year.

I also agree they have less loss that the th400 and are lighter, I think.

 

Having had to rebuild a few after failure - here's what I've found:
1. The intermediate sprag (overrun roller) race is brittle, but even with the "heavy duty" races (black color), they will brinnell from the force of the rollers when shifting to second under high loads. I now use Coan's Extreme duty sprag race without problem.
2. The direct clutch has often worn out. I now always add an additional clutch to the stock four clutches in the direct drum by using a thinner piston to accommodate the 5th clutch. Also, a stiffer regulator spring to run higher line pressure helps too.
3. I stay away from very grippy trans fluids such as the B&M Trick Shift and Ford fluids because the shock loads increase considerably compared to the Dexron fluid. I do add 1 or 2 quarts of Ford fluid to get the right feel, but I want to avoid shocking the drivetrain too much.

One time when I used the "Trick Shift" fluid, the 1-2 shift was so hard that it blew the overrun clutch to bits. Although I had a "heavy duty" sprag race (not the Extreme duty Coan piece) which survived, but the ground up bits of the overrun roller clutch cage looked like they'd been through a metal shredder!
4. I prefer the TransGo 350-2 Shift Kit.

__________________
1978 Corvette
406 SBC AFR heads Lunati roller Quadrajet TH-350 3.08
11.59 sec / 118.9 mph 1/4 mile

 

I had a stock th350 behind an earth turning 455 Oldsmobile. It held up with stock BFG 60 rubber. I have heard the yoke or u joint let loose before the trans

 

LarryWalk,
I don't want to hyjack this thread but, I always wondered about different fluids. So the Ford fluids get more grip? Have you tried the TCI stuff? It might be the same as the Trick Shift/

 

I was using Ford ATF for the additional amount of friction modifiers. It was the old trick before trick shift..... came along.

It makes the clutches grab compared to Dextron

 

No, I don't know; I haven't tried TCI stuff.

 

i have a B&M Th350 with 3000 stall behind a 420 hp motor 355 gears and 295 tires. it now has the heavy duty sprag and i have been flogging it as hard as i can for 2 years. has not broke yet.