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27 spline TH400???

1-tonmudder

1-tonmudder

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I picked up a core 4wd TH400 with the tall CUCV style 208 adapter.The output shaft looked small to me but I loaded it up anyway.Now that it's home and I've had a better chance to look it over it has a 27 spline output.I have counted the splines twice and a 27 spline drivesleeve fits right on.So how is it possible to have a 27 spline TH400,does somebody make a shaft for this or does the TH350 and 700R4 shafts fit the Th400.One other thing is that the adapter looks different than all the other tall adapters I've had,looks to be alum but didnt have a magnet handy to check.
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well 400 and 208 or 241 would be male female

and i am betting on aftermarket adaptor to some other tcase combo other than factory.

i just linked a 27 spline shaft sale to 76zimmer for his dubbler kit build. so yes thay were made.

dont know if he got it tho. but drop him a line he might buy it from you . http://coloradok5.com/forums/member.php?u=27517
 
sweetk30 said:
well 400 and 208 or 241 would be male female

and i am betting on aftermarket adaptor to some other tcase combo other than factory.

i just linked a 27 spline shaft sale to zimmer for his dubbler kit build. so yes thay were made.
Click to expand...



I betting on something aftermarket as well but it would have to be for a 27 spline 208.Thats all that has the round pattern and 27 splines.So they DO make a 27 spline 400 output????? That's kinda dumb aint it????

Edit-Do you have a link for the shaft????
 
Yep, aftermarket. Those shafts were pretty common back in the 80's when guys had the 27 spline t-cases and were upgrading to 400's.
B&M and TCI are two companies I know right off the bat that make/sell them.
 
I'm going to put a 27 spline shaft in my 400 instead of getting a different 205
 
The 400 turbo I put in my truck has a aftermarket 27 spline output that some one installed before I got it.
 
sweetk30 said:
well 400 and 208 or 241 would be male female

and i am betting on aftermarket adaptor to some other tcase combo other than factory.

i just linked a 27 spline shaft sale to 76zimmer for his dubbler kit build. so yes thay were made.

dont know if he got it tho. but drop him a line he might buy it from you . http://coloradok5.com/forums/member.php?u=27517
Click to expand...
yes I did buy it....paid 105 Didn't know they were a produced part.
anyhow full speed ahead on the doubler.
 
I dont know if anyone else thinks this is big but i do! I need to find one of these shafts!
 
IIRC the TH375 had the 27 spline shaft and other than that looks identical to a TH400 (basically a light duty TH400). I don't know however if there were ever any factory TH375 4WD trans ever made. If not then it would be an aftermarket shaft for sure. There are also TH475 trans which are a heavy duty TH400 with straight cut gears rather than helical cut like the TH400.

EDIT: Found this on a website.

THM375B - This trans is identical to the THM350, but is considered a heavier duty transmission.
THM375 - This transmission is a derivative of the THM400 sharing the external appearance of the 400. It'll be marked 375-THM on the bottom of the tailshaft housing. It's a light duty version of the THM400, has ABSOLUTELY NO RELATION to the THM375B, and was found in 1972 to 1976 full-size cars. The Turbo 375 was modified to accept the Turbo 350 driveshaft yoke.
 
1-tonmudder said:
Yeah but you will have to bore the case to accept the bigger input bearing.
Click to expand...

Or completely tear down a TH400 to replace an output shaft? Having the 205 case bored isn't real expensive, and I'll bet by the time you buy a conversion kit for the TH400, and have it installed, you would be saving money by converting the 205.

I'm not saying that if you stumble across one as you have, not to use it, but going out and buying a new conversion kit doesn't make much sense to me, when one of the reasons to use a TH400 is for the strength.
 
I'm concerned some about the strength factor of the 400 w/27 spline behind a 540tq BBC, and 38" tires....should I be? The 27spline is about 1/4" smaller diameter than the 400's 32 spline.
 
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bigredblazer said:
You can just upgrade the 205 input to a 32 spline, instead of decreasing the strength of the TH400 by going with a 27 spline output.
Click to expand...

The tranny guy is probably 20 yards from my shop and he gives me a great deal. It was recently rebuilt also so it should be cheap.

76zimmer said:
I'm concerned some about the strength factor of the 400 w/27 spline behind a 540tq BBC, and 38" tires....should I be? The 27spline is about 3/8" smaller diameter than the 400's 32 spline.
Click to expand...

It should be strong enough, people get away with a lot of power and 10 spline manual setups.

I should have around that amount of torque and 42" tires when I put my 400 in.
 
I broke a 27 spl conversion shaft in my K5 a couple years ago. It worked hard for a few years but ended up in 2 pieces in a crappy spot to recover the truck from.

Given a choice of taking a 400 apart or taking a 205 apart, the 205 wins every day, the 205 is just way easier.

Cost wise, to convert a 205 to 32 spline runs $190 for the conversion kit and typically $60-70 to machine it.

Not sure you can take a trans apart and re-seal it for a lot less than that, definitely not if you're paying for labor.

Strength wise, not only is the 27 spline shaft smaller but conversion shafts are often weaker by construction than a factory shaft.

You also have to consider potential adapter issues, a 400/205 adapter housing isn't going to work with a 27 spl. input gear in the 205 so you have to use a 6 hole to 4 hole adapter on the back of the TH400 and then use a 350/205 adapter housing and drivesleeve.
Compare this to using a 32 spl output that plugs directly into the input gear of the 205 and a single adapter, overall a more robust system.

That said, if you have a 27 spl. shaft keeping it may work for you but I wouldn't spend money to go backward with it, especially if you have an application where you really need the strength of the TH400.
 
My frirst thought is "are you SURE it's a 400?"

Then "aftermarket shaft?"



I want to know what numbers are on under the tailhousing.

This is good info to cram into the back of my head.
 
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