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Discussion Starter #1
I'm still debating whether or not to go TH350 or TH400. With a NP203/NP205 doubler setup, I don't want my transmission to be the weak link. I often hear of people breaking their TH350s, but I never hear the details. I wanted to post this thread to hear how and why they are breaking their TH350s. Here are some questions I'd like answered. If you have broken your TH350, please spend the time to answer these questions so I can make a decision. This only applies to people who have actually broken theirs. Don't post "Yeah I saw a guy break his in half, it was cool." unless you know detailed specs of his rig and why it broke.

1. First off if you broke your TH350, what are the specs of your rig and specs on teh transmission. Ex. K case, 2WD with divorced t-case, etc.
2. What did you break? Internals, input/output, case, mounts, etc.
3. Were you running any bracing? For example, the girdle piece that goes near the bottom, also any support bars similar to what the Chevy trucks come with stock. The ones that go from the bellhousing area back.


I thank anyone who takes the time to answer these questions in advance. I'm getting flooded by TH350/NP203s for free or under $100, but can't find any TH400s. I dont' really want to spend the time finding and buying one unless I really need it.
 

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I broke the housing on mine, all the way around the tail area.

454 engine, 205 transfer case, no bracing, 40" tires, 3.73 (!) gears. I also broke losts of drivelines and transfercase adapters. I broke the adapter so bad once the the transfer case ended up in the mud behind me. That sucked so bad that I:

- Went to 5:13 gears to help unload the drivetrain
- Installed an "L" bracket from the 205 to the frame.
- Changed out all the mounts to new ones.
- Lost about a 1,000 pounds of weight.

I think my problems were a combination of a heavily loaded drivetrain and an unbraced transfercase. Thats a lot of weight to hang off the end of that adapter.

Since the above changes, I have had no problems at all.
 

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Build it once and build it right. Go with a 400. I've seen TH400/203 combos sale for around 250.00. You need to look around. There was one for sale in Corpus about 1 year ago for 250.00.
 

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I've broke countless Turbo 350's in my street cars. Always break internally probably because I like to set them up with very firm upshifts on full and part throttle and when you have soft compound road race tires something has to give!!!
My Mom probably broke at least 3 or 4 350 transmissions in the 20 years or so she drove a pumped small block Buick street car and she drives fairly conservative so the constant banging of part throttle tire barking shifts did these in I'm guessing and when you finally do a 6000 RPM upshift like after I do a tune up and I test drive it--KABOOMM!!! Broke my Art Carr Turbo 350 in my Supercharged 350 K20 tow rig withstock 65000 miles...I built a 355 with 12 psi boost and after surviving at the 330 HP+ level I proceeded to break in my new 450 HP motor and broke it on the first full throttle 1-2 shift. Not sure what broke as I never rebuilt it and put in a 700 R4. It would lock up in 2nd gear so I had to drive the rest of the way to work in 1st gear and back home in 1st gear! Oh yeah before I was Supercharged I broke a case at Pismo in the whoops at the bottom of Comp Hill (back in the day when it was the hill on the left which is now almost flat) and coasted to the top! That I believe was from the weight of the heavy 200 lb unsupported NP203 case hanging off the back of the transmission. I don't believe I was running the optional skid plate with the extra rear crossmember as back then it was all about performance--so less weight is better...
I don't know if the skid plate would have helped as it does not directly support the rear of the transfercase--it only touches the bottom of the case if your rubber transmission mounts are oily and soft. This truck did not come with any K case or front to back bars or the side mount--I know because my Dad bought this truck new off the dealer lot. I have three Turbo 400's, two in full size 4x4's and I finally put in my Mom's Buick and never had a problem since. I love the reliability which so far has been 100%--knock on wood...

Jason
 

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Discussion Starter #6
fj40charles said:
Build it once and build it right. Go with a 400. I've seen TH400/203 combos sale for around 250.00. You need to look around. There was one for sale in Corpus about 1 year ago for 250.00.

Yeah, that was the one a buddy and I had when we parted out a old GMC dually. I thought to myself "man, i'll never need that" so we sold it. The thing that sucked is I could of had that one for free.

:(
 

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1st break was all around the housing at the front pump. Pulled against a Semi. He lost the pull off. I lost the tranny. :D 2nd one was in Moab. Broke off the rear of the housing where it bolts to the t-case adapter. Failure was because I lost the bracket that bolts the t-case to the frame. Had the tranny housing welded up and continued to wheel.
In both breaks the trannys continued to work. Just spilled fluid. I build them up with a TCI high HP kit you can get from Summit for $200.00. Never any clutch slippage.
6-71 blown 427 BBC, 2,500 stall, t350, 205 t-case, 5:13s and 39.5 boggers. :cool2:
 

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4.3/TH350/Toyota Tcase in a 3200 lb buggy. 2WD case with a 4WD output shaft, no braces.

Broke the tail area three seperate times, with changes to the mounting between each one. I finally got it to stop breaking the case, but then mysteriously lost reverse...turns out I stripped the "teeth" out of the case where the reverse clutch keys in--my tranny guy told me it's from the forward-->reverse shifting under power. :D (gotta do that sometimes to save rolls....)

No trans breakage since the swap to the D300. (though I have broken the Tcase :rolleyes:)
 

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Is the case of a TH400 really that much stronger?
 

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Broken cases are usually due to mounting issues and there is really not much difference in case strength between a TH350 and a TH400. Broken internals are usually due to a combination of torque and driving style. What kind of motor are you running and how do you intend to drive it?
 

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Discussion Starter #11
Black Dog said:
What kind of motor are you running and how do you intend to drive it?

Cadillac 472 rebuilt to stock. They came with TH400s in the cars.

I think I'm going to spend a few months building the motor. Hopefully by then I'll find a combo for free or very cheap. It sounds like I could get away with using a TH350, but I'd rather find a TH400 and not have to worry about it so much. Instead I'll just be worrying about front axles.....
 

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Dont piss around with a 350 if you can get a 400. The 400 will be much cheaper in the long run. All it takes is having to rebuilt the 350 once and you just bought a 400.
 

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TexasBlake said:
Cadillac 472 rebuilt to stock. They came with TH400s in the cars.

I think I'm going to spend a few months building the motor. Hopefully by then I'll find a combo for free or very cheap. It sounds like I could get away with using a TH350, but I'd rather find a TH400 and not have to worry about it so much. Instead I'll just be worrying about front axles.....
If you're running a Caddy motor, BOP th400's are dime a dozen, easy to find. You just need a chevy 4x4 output shaft,adapter, and TC.
 

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Discussion Starter #15
70~K5 said:
If you're running a Caddy motor, BOP th400's are dime a dozen, easy to find. You just need a chevy 4x4 output shaft,adapter, and TC.
I have access to a BOP TH400 adapter. I work with lots of tranny people, shops, etc so I get the line on good stuff. That's how I havn't had to pay jack for any of my 472ci, NP203s, NP205s, TH350s, etc.

I found a TH400 that needs a rebuild for $15 and when I pick up the motor, the guy has the matching 2wd TH400. I found a 4x4 output shaft for $20 used at a tranny shop, so I think I'll convert it to a 4x4 transmission if I can find an adapter and NP203 input.

Soudns like y'all convinced me, I really hate to spend time on a weaker part if I can upgrade for relatively cheap and not ever really have to worry about it.
 

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79 chevy, 406 sbc, th400/np203. 3/4 ton truck with 1 piece rear shaft and slip yoke, no carrier bearing.

The 406 is fairly healthy with Dart heads and everything else. Probably around 350 hp maybe and tons of torque.

No tranny problems but I couldnt keep u-joints in it. I dropped a rear ujoint doing 80 on the freeway. the lower joint went and the shaft slipped out leaving the slip yoke still bolted to the tcase. It flung around hard enough to crack my th400 housing allthe way around the mounting surface of the transfercase adapter, about an inch forward of the mounting surface. when they pulled it out of the truck the trans fell into two pieces. because I had basically twisted the mounting surface off the trans.

It wobbled SO hard before the slipyoke broke off that it threw my 4x4 shifter ball off the lever and stripped all the threads off.

This is a catastrophic event and had this not happend, that th400 would still be alive today so I'd go with a 400.
 

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TexasBlake said:
I have access to a BOP TH400 adapter. I work with lots of tranny people, shops, etc so I get the line on good stuff. That's how I havn't had to pay jack for any of my 472ci, NP203s, NP205s, TH350s, etc.

I found a TH400 that needs a rebuild for $15 and when I pick up the motor, the guy has the matching 2wd TH400. I found a 4x4 output shaft for $20 used at a tranny shop, so I think I'll convert it to a 4x4 transmission if I can find an adapter and NP203 input.

Soudns like y'all convinced me, I really hate to spend time on a weaker part if I can upgrade for relatively cheap and not ever really have to worry about it.
If you want to run a NP203 you need the Extra short trans output shaft if you're using stock parts. The TH400/NP203 uses a shorter output shaft than a TH400/NP205 does. Check ORD's webpage they have the info there.
 

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TH400 to NP203 output shaft is 6.5" long. This is the shortest output shaft you can can get.
 

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fj40charles said:
TH400 to NP203 output shaft is 6.5" long. This is the shortest output shaft you can can get.
Yep which is shorter than the TH400/NP205 figuire eight adapter output shaft.
 
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