350 or 400 most bullet proof

In you opinion/experience is the GM 350 or 400 transmission most bullet proof.

The application is for driver car that gets driven on real roads. Mostly driven in normal conditions within the legal posted speeds(OK, maybe stomp the pedal sometimes) Engine 350 to 400hp range.

The goal is buy it right the 1st time and be reliable.

Please include technical rational if you have any you base your comments on.

The 400 is hands down the winner, built right it will handle 2 to 3 times the torque the 350 can handle.

I ran one in drag car for 5 years between rebuilds and it was still good to go only needed fresh ATF and replaced the rear thrust washer with a torrington roller bearing.

For a street car... I prefer a 700R4. They may be a lil more expensive but if you drive very much you'll save the diff on gas! Just my .02!

BoB

Here ya go...

BlueNorther said:

The 400 is hands down the winner, built right it will handle 2 to 3 times the torque the 350 can handle.

I ran one in drag car for 5 years between rebuilds and it was still good to go only needed fresh ATF and replaced the rear thrust washer with a torrington roller bearing.

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I have a TH400 in my 3/4 ton Chevy truck that has never really worked right. We dropped the pan this morning and found shavings and actual chunks, so a friend called his buddy, a retired transmission shop owner and builder who is going to rebuild it for us. He said the chunk is a sprag, without even seeing it, and, "You don't want to go down (to the 350), only up (4l60), maybe, but honestly, that 400 will take anything you throw at it and last longer and be more reliable and bullet-proof." That's good enough for me!

There's a reason why most of the drag crowd uses them, and they can be hard to find.

The 400 is stronger and heavier. really have to think about what you are going to do with your rod, then make the choice. Tobby

Ran 11.40's in my wagon with a TH350 for 3 years. When pulled it down to refresh you could still read the writing on the clutches.

I prefer a good 700r4. It has a much lower 1st gear and is OD. You can get a stall converter that can be made to lock up. It will hadle 400hp easy.

tmgant said:

…."really have to think about what you are going to do with your rod, then make the choice. Tobby

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I am thinking about it, that's why I asked the question.

Tripper and RPM are right, the 700R is the way to go on a street driven car. That is what I plan on using in my 46 if I go with Chevy power. If I go with the 351 Ford engine I have I will run an AOD.

That extra gear really pays for itself and makes expressway cruising a pleasure.

Don

A T400 is much stronger, it is also much heavier and takes more power to run it.......If its a lightweight car, a T350 or an OD trans would be fine

RPM said:

I prefer a good 700r4. It has a much lower 1st gear and is OD. You can get a stall converter that can be made to lock up. It will hadle 400hp easy.

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That is the 2nd part of my thought process actually driving the car and living with today's gas co$t. But, that's another thread.

RPM said:

I prefer a good 700r4. It has a much lower 1st gear and is OD. You can get a stall converter that can be made to lock up. It will hadle 400hp easy.

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I love the low 1st gear in a 700 & the high 4th. I switched out a fairly new 350 in the Nova to a 700 after driving my Chevelle with a 700. I kept waiting for the 350 to shift to 4th gear. The Nova, my real daily, now gets 20mpg if I keep it under 70mph! The Nova has abut 300hp & the Chevelle has 625hp & reliability has never been a problem. I use Phoenix Transmissions here in Tejas!

http://www.phoenixtrans.com/

BoB

TH350 has a 2:53 1st gear ratio and a 1:52 second...
It makes the gear change from 1st to second by reversing the drum?
So at a 3000 rpm launch the drum is rotating at 7590 rpm in one direction and has to reverse direction to 4560 rpm in the opposite direction to make the 1-2 shift
That is an acceleration of 12,150 rpm that occurs in the time span of that shift.
Shortening the shift time by adding a shift kit compounds the stress

The TH400 uses a different flow path by adding more parts to make the 1-2 shift which is what makes it significantly stronger.
The 400 has a little more parasitic drag and eats up a little more inertia due to it having more parts and heavier parts.

The th350 I read was rated for somewhere under 300hp. I think 250 was what was published.
Alot of guys will sell you a "race built" th350 that is nothing more than a stock th350 with aftermarket clutches and a shift kit and maybe a performance converter.
That does nothing to make the tranny stronger.
To beef up the th350 for serious racing mandates replacing just about everything in it.
it is considerably more expensive to build a TH350 than it is to build a TH400 to handle similar power.
The big reason guys spend that kind of money is to get at those precious fractions of ET in serious racing where they can drop their et's by reducing inertia loss and parasitic drag.
Same reason they go with a 12 bolt. 9" is as strong or stronger but a 12 bolt has less drag due to the way the ring and pinions mesh. Both are Hypoid gears but the 12 bolt is closer to a bevel gear (driveshaft higher- closer to the axle centerline) while the 9" is closer to a worm gear (driveshaft lower- closer to tangent to the worm gear).

The power flow through a C6 I think is the same as the TH350 but it is made with bulkier parts for strength. Some ford racers run a th400 which has a strength advantage over the C6 due to that difference in the 1-2 shift

Quote:"It makes the gear change from 1st to second by reversing the drum?
So at a 3000 rpm launch the drum is rotating at 7590 rpm in one direction and has to reverse direction to 4560 rpm in the opposite direction to make the 1-2 shift
That is an acceleration of 12,150 rpm that occurs in the time span of that shift." Unquote.

under normal circumstances, no drums will rotate in the reverse direction of crank rotation, except when the trans is manually shifted into reverse.

the only time that can occur is, if there is a catastrophic failure of the secondary sprag which prevents the secondary drum from rotating backwards, and then the drum will accelerate from zero RPM to 1.5 x the crank RPM, no where near the 15,000 rpm burst rating of the TH350 secondary drum.