TH350 or TH400
 

Im gonna be pulling the 307ci and powerglide out of my 68 and putting in a new crate 350 and trans.

I know nothing about the above transmissions or what the differences are. From what Ive read there really is no difference unless I'm missing something.

Which would you more knowledgeable folks choose?

Thanks

Re: TH350 or TH400
 

You mean between the t350 and t400.
Output splines are different.
Kick downs are different.
Sometimes length is different.
T400 uses more horse power to run.
Gear ratios are different.
Which crate 350 determines which one you want.
T400 is stronger.

Re: TH350 or TH400
 

It all depends on what you are going to do with it. The 400 is stouter but uses more power & larger & heavier. The 359 is more compact & is plenty strong for normal use behind a stock 350 engine. Have you thought about a 700 R4. It is similar to the 350 & has o-drive.
George

Re: TH350 or TH400
 

I think the correct abbreviation for the two is TH for Turbo Hydramatic but yes Im talking about the turbo 350 and 400

Right now im looking at a crate 355ci 310hp/360tq.

It'll be strictly a street truck, local cruises maybe a show here and there, something me and my two young sons can cruise in. No plans to make it a daily driver or put a ton of highway miles on it and gas mileage is really of no concern to me. I breezed by a 700r4 but haven't really looked into them. Im trying to stick with a budget lol and saw the 350/400 was significantly cheaper.

Also I'll be buying new. Im not looking to source a trans from a junk yard or second hand.

Thanks

Re: TH350 or TH400
 

The 400 will outlive the truck behind a mild 350...
What rear end ratio do you have? I'm thinking a 3:73 or 3:42.

But keep in mind, if later you are driving down the road at 3200 RPM doing 75 MPH - wishing you had installed a 700r4, and hear that re-gearing the rear end to a 3:07 will help get the RPM down at highway speeds (which it does), that is $1000 alone.

Factor that into your decision.

I personally have a 350/350 with 3:07 rear gears and cruise at 2500 RPM at 80 with 31" rear tires. Im happy.
I lost the pinion gear on my 3:73 and had to rebuild the rear end anyways, and the 350 works great, so that dictated my decisions. I scored a low mile ring/pinion and carrier - which never happens.

Re: TH350 or TH400
 

Who’s crate engine are you gonna use?
Who’s tranny are you looking at?
Depending on your choices we could save you some grief on what you buy.

Re: TH350 or TH400
 

lots of debates over this from one end of the internet to the other :lol:

I'm not exactly sure what all is required to convert to either from a glide, but assuming both require modifications, I'd go with the TH400..

the only two minor drawbacks I can see are the minimal hp loss and conversion costs [if any more than a TH350]

performance wise, speaking in terms of truck applications, the TH400 beats the TH350 handsomely..

gear ratio differences in 1st and 2nd are slight, but even a modest HP crate motor will make no fuss over it..

even if towing, burnouts, etc. is only occasional, the TH400 will outlive the TH350 given the same abuse [you did mention two young sons ;)]

something else to consider, GM installed many TH400s behind small block V8s in the factory, must have been some logic to their choice..

and both can be had outright from places like Summit and Jegs for near the same initial costs [less conversion items]

for most folks going through the trouble to convert something, I think the TH400 would be the most common choice..

for a lot of folks like me working with factory installed TH350s, we settle for the convenience and beef them up as much as possible..

google the thread title and browse other forums for different opinions and you may find more relevant arguments to support your specific needs..

good luck!

Re: TH350 or TH400
 

From the OP's description he could get by with rebuilding the 'Glide.

Re: TH350 or TH400
 

Advantage of the TH350 is it is same length as Powerglide and would use same driveshaft.

But if I was spending $1000 on a TH350 I'd go ahead and spend $2000 on a TH700R4.

The one single part of a car that has changed vehicle performance more than anything else are overdrive transmissions. Lower first gear combined with overdrive give better acceleration and better cruise RPM.

What gears are in the truck now? 3.73 I'm guessing? Let's assume you have a 'Glide with the 1.76 first as found behind the V8's. With 3.73 that gives you a 6.56 overall first gear and a 1:1 on the highway. Figuring 28 inch tall tires that puts you about 67 mph at 3000 rpm but call it 64 with converter slip.

But with the TH700R4 you have a 11.4 overall first gear and at 64 mph (lock up converter, so no slip!) you are only turning 2000 rpm.

Remember, torque can be multiplied. So lets assume your crate motor makes 400lb/ft of torque. With the 'glide that means 400x6.56 is 2,624 foot pounds of torque to the rear wheels. But with the TH700R4 you get 11.4x400 or 4,560 lb ft at the back tires. That's 73% more power to the wheels in first gear!

So, 73% more power to the wheels, 30% reduction in RPM at highway speeds, and $1000 more money. Cheapest performance gain you can make when you look at it that way.

Re: TH350 or TH400
 

Looking at a couple of GM options and a motor from Blueprint. Trans I don't have one in particular. TCI, B&M, Performance Auto etc. Whatever is the best deal

Good post

Pass. I got a drag racing buddy that already said he'd buy it off me

Your math checks out lol. Thanks good post

Re: TH350 or TH400
 

I just have to say thank you MikeC for that lesson. I'm impressed.

Re: TH350 or TH400
 

I see you're in Dallas, I'm just outside of Abilene. If you want to drive 3 hours this way, you can have for free the working TH400 I recently took out of our '69 to swap in a 700R4.

I have no idea of the miles on it, but I opened it up awhile back, the pan looked nice (very little of the usual gunk on the bottom).

I installed the Trans-Go 1-2 kit, it shifted nicely - nice and quick, but not harsh at all. We drove it for about a year before swapping it out, now it's sitting on my garage floor taking up space.

It has the short tail housing, iirc and if it matters.

Re: TH350 or TH400
 

If it were me, I would be taking a road trip to meet up with jamyers and secure that TH400....maybe he even has the original driveshaft he could let you have...

700R4 are good...but ya cant beat free anytime it comes up...

Wondering why no one mentioned TH200R4 ...same length as a 350...and ya get overdrive as well....

Anyhoo...give jamyers a VM and get moving...thats an incredible deal...

:chevy::chevy::chevy:

Re: TH350 or TH400
 

I’ll take ya up on that offer. That’s a smokin deal.

Re: TH350 or TH400
 

PM sent

Re: TH350 or TH400
 

Smokin' deal on a pull-out working 400 tranny. Holy smokes!

This place is great.

-klb

Re: TH350 or TH400
 

Ive made my claim to it so I guess a turbo 400 is what Im going with. Thanks again Jamyers

Re: TH350 or TH400
 

You won't be disappointed! Also the simplicity of the swap over having to set up a TV cable like with a 700 or 200 is huge as well. Plus you can't beat that price!

Re: TH350 or TH400
 

agreed! I didn't mention it for fear of an argument, but I know a couple personally and read about several that have trouble with that.. not fully understanding the function and adjustment is usually catastrophic to the trans..

Jacoby, like I mentioned, the conversion you're going for was a common factory combo, just saw this yesterday..

https://fargo.craigslist.org/cto/d/1...717605765.html

I agree with above, I think you will be very pleased with performance and durability of your choice, good luck!

jamyers, very generous of you to help someone out like that!

Re: TH350 or TH400
 

All hail JAMYERS!

JAMYERS !!!:metal:

JAMYERS !!!:ennyd:

JAYMERS !!!:clap:

I don't guess you have a hood laying around gettin' in your way, maybe ready for paint? just kidding!

Re: TH350 or TH400
 

Not much talk about the 200-4R. It's the same length as the power glide & 350 turbo, therefore uses same length driveshaft. Not as sturdy as the 700-R4 but could be depending which one you get or build. They installed these in the Monte Carlo SS, 442, GTO, etc. I'm in the process of removing my 250 with 350 tranny and installing a 292 with the 200-4R. Just another option to consider.

Re: TH350 or TH400
 

After all the help I've received from board members here, it's the least I can do!

See above... :) No hoods, sorry. If I did, I can't imagine the shipping... :lol:


I agree, the 200-4R is a good trans that doesn't get the publicity or respect it deserves - I know several turbo Regal and Grand National guys who beat on them regularly with few problems. Sadly, finding a decent one or getting one rebuilt properly is getting harder and harder...

Re: TH350 or TH400
 

Not so much hard as expensive.... I have decided a TH200 4R will be the trans behind the L36 427 in my short step. Extreme Automatics will be the dealer based on my buddy's experience with his '73 'vette. But it will cost more than I paid for the truck...