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Old 06-19-2012, 05:51 PM   #1
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Reading through various posts, I keep seeing references to the TH475 transmission/ Turbo 400. Someone please educate me! I was under the impression that it's just a turbo 400. Is the 475 designation something thats motorhome specific?
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Old 06-19-2012, 05:57 PM   #2
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One has helical cut gears, the other has straight cut gears. There are some other more minor differences, as well.
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Old 06-19-2012, 06:08 PM   #3
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Ok, that makes sense. Straight cut gears are stronger but louder than helical cut gears. So mine must be a 475!
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Old 06-19-2012, 07:13 PM   #4
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The diesels take a "reprogrammed" 475 Turbo Hydra-Matic. No clue what they used in the gas coaches.
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Old 06-19-2012, 07:35 PM   #5
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Some would say helical cut gears are strong due to the increased surface area of tooth contact.
Planetary gear sets from what I have seen in automatic transmissions are helical.
But then again it all depends on the angle in which the teeth are cut on a helical gear, size of the gear in comparassion to the straight cut gear and the fact that helical gears are trying to force each other apart creating axial loading.
I think bottom line is if the gears are the same size and the straight cut gear isint hardened or made of some special alloy the helical gear would be stronger (and quieter) and as long ad the case can handle the deflection caused by the helical gear action.
I'm sure someone else will add onto or correct something I have typed.
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Old 09-05-2012, 02:07 PM   #6
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They're basically the same transmission, but the TH475, also nicknamed "the dump truck transmission", has the straight cut gears and sometimes a deeper pan. If you can look at the top of your transmission's tailshaft, it ought to have "HD" (heavy duty) brazed onto it if it's the 475.

By the way...the planetaries in the 475 are purportedly almost worth their weight in gold.

Change your fluid REGULARLY!

Cheers!
Slick
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Old 09-05-2012, 02:46 PM   #7
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IIRC the last 2 digits refer to a torque rating of the trans. These days its also the last 2 digits before the "E" for electronic...ie: 6L80E is a 6 speed, longitudinal (rear drive), torque rating of 80, electronic. A 6L90E is the same...except higher torque rating.
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Old 10-11-2012, 07:16 PM   #8
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Interesting.....
The TH-475 is also known as the 3L80HD....
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Old 10-11-2012, 07:56 PM   #9
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Seems like I learn something new every day
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Old 10-11-2012, 08:04 PM   #10
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Yup, LOL!

I have decided... from now on the transmission in our Airstreams shall be known as the 3L80HD...

Sounds much more Hi-Tech and expensive!
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Old 10-15-2012, 08:28 PM   #11
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A 3L80 by any other name will still be a big chunk of metal.

Luckily my neighbors have kindly helped out with my project, I can undo/install smaller stuff just fine, BUT manhandling transmissions or anything else heavy is a thing of the past for me. Good luck with your 3l80, it is one tough beast, just do not cook it. ( like I did mine)
All the best.
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Old 10-15-2012, 09:15 PM   #12
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I have to disagree with Mike on the question of all the diesels having the TH475. My 280 diesel has a TH400. It was rebuilt a couple of years ago with 4L80E clutches, bands, bushing, seals and other parts. The upgrades are doing well with over 40,000 miles on them.

The thing I wonder about concerning the straight cut verses helical cut gears is this, does anybody know of a TH400 failing because of the helical gears? Everyone I've ever heard of burnt up from overheating, or lack of fluid or a combination of both. If this is the case straight cut gears are not of much concern.

Cheers, Dan
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Old 10-18-2012, 07:09 PM   #13
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Become a believer.
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