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Old 02-28-2002, 07:51 PM   #1 (permalink)
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How weak is a Turbo 400??

I ran into an article in a magazine claiming the Turbo 400 has a weakness related to the gears.

Basically, it said the heli-cut gears used could destroy the Turbo 400 under servere load/power.

The fix was replacing the heli-cut gears with some factory available straight-cut gears(cost approximately $1000 from factory)

Has anyone heard of this? How durable is a Turbo 400?

I'm a bit curious on this as I've always heard the Turbo 400 is the beefiest auto
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Old 02-28-2002, 07:57 PM   #2 (permalink)
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Wow this is a first as big motorhomes and just about every racer wants one with the only down side being that it has higher drag then other auto's causing it to draw or use more ponies but is one stout tranny that can take a beating....
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Old 02-28-2002, 08:08 PM   #3 (permalink)
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Actually, the article points out that a good portion of motor homes use the "suped-up" Turbo 400.... I think they called it a Turbo 475 A standard Turbo 400 used heli-cut planetary gears while the Turbo 475 used straight cut planetary gears.

The $1k I mentioned above is for brand new parts... they did say you could get a motor home version and swap the gears over.

Unfortunately, they said there was no physical way to tell a 400 vs a 475 externally

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Old 02-28-2002, 08:31 PM   #4 (permalink)
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The words "weak" and "TH400" are generally used in the same sentence by jealous stick guys. J/K

The TH475 is what your talking about, it is somewhat stronger, and it is generally found in some heavier trucks (1.5-2.5 tons) or Motor homes. About the only way to spot one is if you see the parking brake on the tail shaft, AFAIK, the TH400 never came with that.

That said, the word "weakness" is a relative thing. The TH400 is way more than strong enough for any sane application. As long as you don't let it run low on fluid, with water in the fluid, or severely over heat it, it will last forever even in hellish applications. The only time the planetary gears become a weak point is when it's expected to consistently pull 20k+ or swallow ungodly amounts of HP/TQ.

Disclaimer: I love TH400s and I've run them totally stock in modified Vettes, drag raced a full bodied GTO with a built 455, various "working class" trucks (including a 2 car hauler for my body shop/salvage yard and a C30 camper hauler doing duty at my fathers camper sales), etc. I've never had a problem with one that wasn't caused by my screwing up. However, I do not claim to be an expert on TH400s or autos in general. The only problem (in my mind) is the size, weight, and parasitic loss. "Weakness" doesn't even enter my mind with regard to a TH400.
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Old 02-28-2002, 08:31 PM   #5 (permalink)
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Quote:
Originally posted by Lil'John
Coyote:
Actually, the article points out that a good portion of motor homes use the "suped-up" Turbo 400.... I think they called it a Turbo 475 A standard Turbo 400 used heli-cut planetary gears while the Turbo 475 used straight cut planetary gears.

The $1k I mentioned above is for brand new parts... they did say you could get a motor home version and swap the gears over.

Unfortunately, they said there was no physical way to tell a 400 vs a 475 externally
makes me wonder if the military cuccv 1 1/4 tons used the 475 behind thier diesels?
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Old 02-28-2002, 08:35 PM   #6 (permalink)
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makes me wonder if the military cuccv 1 1/4 tons used the 475 behind thier diesels?
Nope.
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Old 02-28-2002, 08:48 PM   #7 (permalink)
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Quote:
Originally posted by BadDog


Nope.
oh well i can dream can't i? i got the th400 i am running from a cuccv. that's why i was wondering.
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Old 02-28-2002, 10:38 PM   #8 (permalink)
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The 475 will not always have the stright cut gears. But they are easy to find, will have a deep pan, and a bolt on rear yoke.
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Old 02-28-2002, 11:18 PM   #9 (permalink)
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IF I ever grenade my TH400 I will going with the TH475 set-up. My TH400 has 0 miles on it right now and I am going to be running with Amsoil synthetic fluid, an Allison torque converter, a deep sump pan, and an external cooler with an additional external filter. The temp guage will be for show only. Okay, it sounds a little overkill, okay, its way overkill !! BUT I don't think I'll have any problems with it. Do you?!?
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Old 03-01-2002, 04:39 AM   #10 (permalink)
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Quote:
Originally posted by BadDog
The words "weak" and "TH400" are generally used in the same sentence by jealous stick guys. J/K
...Or those who sell $1000 planetary sets.
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Old 03-01-2002, 05:18 AM   #11 (permalink)
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I ran a TH400 in my cruza for years. It was a non-rebuilt boneyard tranny, just pulled and installed. When I was switching to a manual (out of boredom) I tried to abuse it....shifting from forward to reverse at high RPM....did not phase it.

The best is when I was driving back from a trail ride late at night in the rain and my german shepard jumped to the front seat and knocked it reverse while going 55 mph forward. The rear tires locked up! (3 speed tcase ). FYI, the dog was fine.

We have several guys run them, almost all non-rebuilt units. The only failure we had is a guy who did not put an extended breather and sucked in grime = ruined slushbox.

If I were to set up a heavy rig again with a slushbox I would only chose a TH400.

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Old 03-01-2002, 12:35 PM   #12 (permalink)
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Thanks for the replies. Good info

I wasn't trying to say a 400 was "so weak" that a small engine would blow it up. I was more curious about the validity of the claim that the heli-cut gears were weak.

BTW, I already knew about the rules of "heat=dead auto", "no atf=dead auto", and "poluted aft=dead auto"
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Old 03-01-2002, 02:44 PM   #13 (permalink)
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Originally posted by emsoffroad
The 475 will not always have the stright cut gears. But they are easy to find, will have a deep pan, and a bolt on rear yoke.
...........But, not ALL bolt-on rear yoke TH400's will be TH475's
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Old 03-01-2002, 03:12 PM   #14 (permalink)
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Quote:
Originally posted by Lil'John
Thanks for the replies. Good info

I wasn't trying to say a 400 was "so weak" that a small engine would blow it up. I was more curious about the validity of the claim that the heli-cut gears were weak.
heli-cut gears WEAK You ever look into the tranny's that are in todays BIG RIGS: Kenworth-Freightliner-Volvo-Ect. They all have these gears in them.

Grave Digger STILL runs these trannies in some of the trucks and they are putting out 800-1800 HP (Depending on truck)!! They have been "beefed" up also.....extra Clutches/Sprags/Case Savers/Ect......
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Old 03-01-2002, 07:53 PM   #15 (permalink)
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Yes some are the 475 but not any that I've had...all were stock 400's and just nneded to be kept cool...around 225 or less....had it in a old farm truck that pulled for 200k plus miles and then installed in my drag car without anything...not a heavy vehicle put put out 575lbft of torque and went from stallll to go at 4500 rpm....would ripple the tires something nasty and leave soe good marks!
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Old 03-01-2002, 09:46 PM   #16 (permalink)
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the person doing the tech for that magazine article is Craig Caukins(sp?) owner of CRC trans in thousand oaks,ca. i should say that's him if this article was a few years ago and had a big black chevy fot the article shoot. That is his truck,he runs a 502,th475,3/4 ton truck running 37" tires and pulls a BIG ASS aprox 36' weekend warior 5th wheel with his bad ass buggie and banshie. nice guy has built most of the tranies in my friends tow rigs.
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Old 03-01-2002, 09:48 PM   #17 (permalink)
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sorry forgot to add any normal person would not hurt a 400 and the 475 is overkill.
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