trans recommendations - Impala Tech
Transmission & Driveline Transmissions & Differentials

 
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post #1 of 11 (permalink) Old 02-13-2020, 03:13 PM Thread Starter
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trans recommendations

My th400 is needing replaced. Looking for recommendations on a good replacement. Definitely want to go back with a th400 but just wondering if I should buy a TCI or are some other rebuilds better? TCI only has a 90 day warranty. I've seen others with 3 year (Monster trans).

are local rebuilders a good source?

Any thoughts?
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post #2 of 11 (permalink) Old 02-13-2020, 03:43 PM
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TH400 will handle a lot of HP. I had a local, reputable shop quote $800 to rebuild the one I previously had and it would handle "pretty much anything I could throw at it on the street". New ones were $1800+ if I remember correctly.

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post #3 of 11 (permalink) Old 02-13-2020, 05:09 PM
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I personally feel that the top names out there are all of good standing as far as I know. Monster and TCI which you mentioned, and I'd probably also add in Bowler Transmissions.

In my own paranoid, bad experiences behind me, head, I always have a bad gut feeling that *some* local shops won't have the aftermarket HD parts on-hand and you get stock stuff where they just increase pressure.
I'd want to know with some level of confidence that I got HD sprags, clutches, etc. Don't forget to get a new torque convertor too! (I'm good like that with OPM)

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post #4 of 11 (permalink) Old 02-13-2020, 08:30 PM
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A local shop is probably your best bet (excluding AAMCO). Especially if you go there and things appear to be slow and the owner is an old geezer ready to retire. He will have the experience and time to build it right and if you buy HD parts he will cheerfully install them.

I rebuild my own, but at the time of my last rebuild I also had a shop with trained Chevrolet techs working with me that taught me how to do it correctly. It is not as difficult as a manual tranny which I had rebuilt a number of them in past times prior to my first automatic rebuild because I though it would be to complex. Just need a few hand tools and a few specialty tools. I recommend TransGo REDclutches and a new Torque converter.

As to stall speed, take your clue from the cam you use in your engine. Stock cam uses a stock (1,800 RPM) converter. Mild cam nothing more than a 2,400 RPM converter, anything more radical your cam company will tell you if the motor needs high compression pistons, a steeper rear gear and a recommendation of stall speed. Unless it lives on a trailer you won't be needing a 5,600 RPM or above stall converter.

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post #5 of 11 (permalink) Old 02-13-2020, 09:59 PM
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Rebuild what you have. That way, you know exactly what you're going to get, and how it's been treated. Also, you only need to replace the parts that are worn out or need upgrading. For a trans guy, a TH400 is an easy side job. A powerglide is just about the only easier one out there.

Two doors, four doors, wagons, and ragtops.
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post #6 of 11 (permalink) Old 02-14-2020, 10:17 AM
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I guess my first question is what is the transmission being fed from and what rear end is it feeding? What is your intention for the transmission? (hard launches and burn outs or just cruising) Do you have plans for an engine swap later to something bigger and badder?

The TH-400 transmission is a stout transmission in its stock form and you can spend a lot of money making it even more stout, but do you really need a transmission and the cost that goes with it that can handle 1500 HP or is something that can handle 600 HP going to be more than enough?
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post #7 of 11 (permalink) Old 02-14-2020, 06:11 PM
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First thing is horsepower doesn't break anything; torque does. The factory torque rating for the TH400 (3L80) is 80 which is just about as high as it gets There is a 90 rating in the 6L90 out of the new supercharged Corvette 427 model, and on Alison transmissions used behind a diesel engine in trucks and buses.

In stock form it will handle a BBC easily (even a potent one that will break a Muncie four speed). People complain in posts that the TH400 has a lot more internal friction (parasitic drag) but this isn't strictly speaking true. When in direct gear it has no more parasitic drag than the TH350 (now called a 3L60) or the 4L60.

Where the you can say it is sucking up power is in shifting.

All automatics bring the internal components to a dead stop and reverse the direction of rotation on up shifting. That is a matter of a lot of energy lost to inertia. The more massive the part being reversed the more energy it takes to stop it and getting it moving again in the opposite direction. This is where the TH350 has an advantage. It is made of weak but light weight aluminum. The TH400 is made of physically bigger parts than those used in the TH350, made out of cast iron that takes a lot more energy to shift.

Knowing how heavy the TH400 is, just think of the work (horsepower) is being done to stop the internals from rotating, and then to bring them back up to speed in the opposite direction upon a shift at 5,200 RPM from first to second in a drag race. It is because the parts are made out of cast iron that it has the strength that it does.

What you are replacing on a high performance rebuild is the drums (shells) that stop the rotation. These HD shells have stronger splines at the top of the shell. The four gear input carrier is replaced with a five or six gear input carrier, stronger springs to increase line pressure (clamping force on clutches and drums), solid aluminum spacers to replace the governor shift piston, and improved friction material on the clutch discs and the drum bands, and a shift kit or reverse pattern valve body. If you really want to throw money at it for a blown BBC application you replace the case, and the gears to match your power band.

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post #8 of 11 (permalink) Old 02-17-2020, 03:54 PM Thread Starter
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Thanks for all the valuable input.

I guess to answer some of the questions, it is behind a rebuilt 454, pretty stock engine. Nothing special except hei. In fact the car came with the rebuilt engine and old trans. The trans didn't work good from the beginning and was cracked and re-welded so I don't want to rebuild this one. Its not original anyway, it was from a '69 truck I think.

I found a trusted local shop and he said around $850 without a core and it includes a reman torque converter. And he's been around a long time. I'm sure he'd let me choose heavy duty parts or a new higher stall converter if I want.

I am kind of after a stock ride/drive. I may just go w/ the stock 1800 stall. I'll ask about the Transgo red clutches, but I imagine he has his favorite stuff as well.
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post #9 of 11 (permalink) Old 02-17-2020, 06:37 PM
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Can't be out of a 1960 truck (at least if it was, it wasn't a factory install) because the TH400 was introduced in 1965 along with the big block Chevy. The transmission was designed with the BBC in mind and had a torque rating twice as high as the torque out put of a 396.

With a cracked and welded case I agree with you. There are too many good TH400 still left in bone yards to reuse that case. I wouldn't throw it away though as the one you find in the salvage yard may also need parts that are still good in the one you have now. Particularly applicable to the steels found between the clutch discs. If run dry or with low line pressure the paper friction material will be toast and steel on steel destroys both clutch discs and steel (drums don't like running with low pressure either).

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post #10 of 11 (permalink) Old Yesterday, 09:16 PM
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He said it was from a 1969.


I agree, with a cracked case, time for a different one. Take the local guy up on the offer, you'll get good local work, and it will get built the way you want. Plus, you won't have to ship it if there are issues.

Two doors, four doors, wagons, and ragtops.
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post #11 of 11 (permalink) Old Today, 01:31 AM
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Sorry about the 1960. Eyes get blurry late at night; even with glasses.

One issue with a truck transmission versus the car transmission is the tail shaft length. To keep the drive shaft length down to a manageable level (or drive shafts with a carrier bearing or two in the drive shafts on some medium duty long wheel base medium duty trucks and buses) the truck version of the TH400 has a longer tail shaft length.

There are three different tail shaft lengths depending upon application, Long used in trucks, medium used in light trucks and 4x4 transmissions and a short shaft for cars.


As far as that goes GM made three different torque rated transmissions that used the same format of the TH400, TH450 and the TH475. Bigger number denoted heavier duty (that matched increasing GVW rating of vehicle). The TH400 was put in allot of civilian vehicles military vehicles as well as farm equipment. But like I said you might have to swap parts (tail shaft housing and out put shaft length)to get a 32,000 pound RV tranny to fit physically in your car. There are more BOP cases around (Buick, Olds Pontiac bell housing bolt pattern also used on the Cadillac), than Chevy cases. So if you need good internals and have a good Chevy case all of the parts interchange to build yourself a custom tranny.

If you have a long tail shaft now and some one cut down your stock drive shaft to get it to work you will need another truck transmission for a good case (since you can not stretch a drive shaft only bob it and reweld on the old ends again). So be sure to verity what you have now (or have someone else do it) when buying a replacement core to rebuild (get rid of the cracked case).

A cracked case that has been heliarced to cover the crack is just a band aid for a serious problem. There is nothing wrong with welding aluminum to patch it, it is the fact that the case is highly machined with many complex passages and surfaces inside that never get welded to totally fix the crack problem (it is always cheaper to replace the case than to weld it up and then send it to a machine shop to be remachined).

Big Dave
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