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Old 02-08-2016, 12:13 AM   #11
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GM Turbo 400 Transmission Stock Up to 450HP | eBay

Not a bad price with converter. Shipping might be a bit depending on where you are. If you can pull the transmission and install yourself it's hard to beat the above price.

I don't know much about th400's but I sure hope they have lockup converters. Save you a ton on fuel and reduce transmission heat tremendously.
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Old 02-08-2016, 03:38 PM   #12
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Originally Posted by uhlhazard View Post
GM Turbo 400 Transmission Stock Up to 450HP | eBay

Not a bad price with converter. Shipping might be a bit depending on where you are. If you can pull the transmission and install yourself it's hard to beat the above price.

I don't know much about th400's but I sure hope they have lockup converters. Save you a ton on fuel and reduce transmission heat tremendously.
I thought lock up converters are overdrives and create heat. I'm not a tranny guy but this makes good learning conversation.
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Old 02-08-2016, 05:05 PM   #13
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Originally Posted by leadsled01 View Post
I thought lock up converters are overdrives and create heat. I'm not a tranny guy but this makes good learning conversation.
From wikipedia:

"Lock-up torque converters

As described above, impelling losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the impeller and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and virtually no power loss."


Overdrive comes from the internal transmission gearing. The best a torque converter could give is a 1:1 drive ratio.
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Old 02-08-2016, 05:12 PM   #14
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The usage of the term "overdrive" for gm transmissions means any ratio below 1:1. On the 4l60e /700r4 4th gear is .7:1 where 3rd gear is 1:1.

On the turbo 400 which only has 3 speeds, 3rd gear is 1:1 there is no overdrive. From what Ive read theres also no lockup option available either.

It is however a very stout transmission but shes showing her age.
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Old 02-09-2016, 12:11 PM   #15
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After looking on Craigslist in Colorado I found a few rebuilt TH400 trans for $350 to $400....Looks like some great deals here....Denver is around a 5 hour drive for me but can't beat these deals...


Is the fact that the trans that I have now doesn't always catch in reverse a sign that I really should change the trans before I take my trip back to Pa from Co? I have no way to know how many miles is on the trans that it has now..
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Old 02-09-2016, 03:16 PM   #16
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Transmissions have a multitude of challenges in a bus. First, age. Seals deteriorate and the th400 is a tank of a transmission.

Its probably been around since the early 90s carrying a bunch of sticky kids on stop and go trips in all weather conditions.

If maintenance at your place was anything like mine, then shes likely rocking vintage 1991 model year fluid. When a transmission sits up the fluid settles low leaving exposed iron parts to atmosphere and condensation. This means rust. A lot or a little doesnt really matter.

When the clutches sit long enough and the rust hits them it can delaminate the clutch material in chunks. Fluid has both a mileage and a time interval to change.

Thermal cycling breaks mechanical parts down. Car parts getting hot and cooling down is like quenching a sword on every use. The problem is, you arent a samurai. The parts shift at a molecular level and temperature changes accelerate this phenomonon. Perfectly flat disks become warped, drum surfaces irregular etc.

You are rocking a by-gone era transmission. Techs today dont know how to use a vacuum gauge to troubleshoot, they need a computer to diagnose the problem for them. Finding someone who can troubleshoot your bus is likely more effort than its worth and since its such a critical part I myself would have it rebuilt or replaced based on the information you have shared.

Now, if you find a reman trans for 500 bucks (which might be an awesome price) make sure to remember you need an application specific torque converter as well. You absolutely do not want to reuse your existing converter. They go from 100-200 bucks a piece for a decent quality daaco brand.

And finally depending on trans failure it might have dumped a ton of contaminants into your transmission cooler system which can include your radiator side tank trans cooler , any rubber lines joining hard lines, and the transmission cooler actual.

My apologies for posting here with such verbosity. I thought I was replying to the original poster.
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Old 02-09-2016, 06:44 PM   #17
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No problem, man. Good information to have. I've never been inside an automatic transmission.
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Old 02-09-2016, 09:15 PM   #18
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Since it is a 1991 model I would lean more towards a 4L60(E) or a 3L80HD rather than a TH400 or TH700R4.

It will cost somewhere in the neighborhood of $3K to R&R the transmission.

Personally, if I had doubts about the transmission, I think I would take it to a local shop that has a good rep and have it taken care of before I went anywhere. I would spend the extra $$$ to get it with a nationwide warranty.
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Old 02-09-2016, 10:51 PM   #19
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There is no such thing as a 4l60e until 1993 in any gm platform.

Best way op can ID the trans is to post up a picture of his rpo sticker. Mine was under the passenger visor stuck to the headliner. They are usually found in the glove box, followed by the body near the door striker on the drivers side.
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Old 02-10-2016, 09:43 AM   #20
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If you get any trans, make sure it's for the bus. Things like converter stall, governor weight, and maybe even the clutches might be different depending on usage. So I doubt any old 400 of craigslist will work for you.
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