Hot Rods turbo 400 output shaft

I have a SP400 and bought a Doug Nash overdrive a couple years ago. I verified the input case was the TH400 but when I got around to installing the adapter gear it fit a 1-1/8" 28 tooth while mine is a 1.4" 32 spline. So does it fit something or did I get a mix and no parts available anymore?

 

I'm not fully versed on the Doug Nash trans but I've heard there are "early" and "later" mfg. I suppose that could have something to do with it.
And yes, many parts for the early ones are not being made.

 

There were a few 400s made with the small output shaft, I think they were called 375, but they were medium length, not short like most 400s. I wonder if your adapter gear is for a Th350 DN unit, instead of a 400?

 

IIRC the TH375 output is 27-spline.

Can you post a picture of what the transmission-side of the overdrive looks like?

 

Yeah if I remember correctly BOP used a 375-400 trans on the light duty stuff like 2 barrel big engines. The 4 barrel and/or high compression (premium gas) motors along with performance models got the true 400.

I'd bet the kit fits the light duty 375 turbo 400 trans.

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It should look like this:

 

If it is a 27-spline input, but has the TH400 output housing pattern, it will need a TH375 output shaft.

They are out there for sale. The appear to have the same toothed flange as a TH400 output, but I have no idea about shaft lengths, or if there are different ones.

For example: https://www.ebay.com/itm/143865535795?hash=item217f0ddd33:g:p0gAAOSwojBdMgtg

That one was an odd-duck, and I have never had one across the bench.

Doug Nash, and later on when the design was sold to US Gear, had different length adapter housings to accommodate different output shaft lengths, in addition to the input gears.

A TH350 and a TH375 input gear would be the same part, but the intermediate adapter housing would be different.

 

The TH375 output shaft is about 15 inches long, 6 inches longer than a short shaft T400.That would have a pretty long adapter housing.Like gimpy said check the adapter housing bolt pattern to verify it is for a T400.might be for a PG

 

Here's the US Gear version of the manual. Keep in mind that they made both overdrive and underdrive versions of this unit.

 

The eBay pictures do portray a crazy-long shaft.

 

Like I said before, the 375 is a medium length output shaft...not as long as the early Caddies, but quite a bit longer than the normal Chevy transmissions. I have one of the shafts and housings still, I think...they were used in some full size cars around 1970.

Pictures are oh so helpful.

 

Imagine that: Two torque converter pitches, and a dual-range box on a 3-speed!

Twelve outcomes, not including reverse!

 

I have a TH400 out of a Buick and it has a larger output shaft with more splines. It also has the short tail housing. When I had my driveshaft made I specified that the trans was out of a Buick. Instead of checking the driveshaft guy found there were 2 slip yokes available and ordered the one that most applications used. Of course it was the smaller one and wouldn't fit.

 

I used to run a Switch Pitch 400 with a Gear Vendors overdrive in my Studebaker. A really great setup.

 

Yeah, we're gonna need some pictures of both the transmission and dual-range box.

 

I have that setup in my Chevy II, it works pretty well...lots of 10.0 time slips, and lots of miles cruising at 70....

 

The depth of knowledge here still blows my mind.

 

What does that make a 27 speed, 3 cubed? 3 speeds on the trans, Switch Pitch on and off each gear, and a Gear Vendors OD in each gear ?
Wild stuff.

 

Mine is more like a 5 speed....high stall in low gear, then switch to low stall, then 2nd, then 3rd, then OD.

When I'm racing, its just a 3 speed with a high stall converter. I leave the switch in high, and shift 1-2-3, never use OD.

 

I built the Stude to be a true street performer with the ability to go land speed racing. I knew I'd have a pretty healthy cam in it, but I didn't want a real loose converter. The switch pitch gives the best of both worlds with, in my case, 3500 stall or 1300 at the flip of a switch. I use a 3.23:1 rear gear so it's pretty quick out of the hole, but combined with the Gear Vendors its a final drive of 2.52:1 which let me reach 205 MPH in the mile at about 6,500 RPM with my Hemi. All this without crawling under the car and swapping gears or converters. Oh yeah, and with the first motor I had in it, (454, 6-71), it went 181 MPH, I got 13 MPG on Powertour.

 

May just have to drive a dual quad 455 with 4:11 gears

 

I'd start by taking the adapter off the overdrive, and see what the coupler looks like.

btw the dual quad 455 will probably run great with 4.11 gears

 

Can you post a side shot that shows the adapter housing that couples the transmission and dual range box together?

I want to compare it to the TH400 one, to see if it is different in length.

 

adapter is 5 " long

 

5-inches is the correct length for a TH400, without a Cadillac output shaft.

It would appear that your input gear is incorrect for the dual-range box.

 

I cannot figure the 28-spline count. I think that was Ford passenger car, like C4, etc.

I can only find two part numbers for GM and two for Ford input sun gears. One each is for overdrive, and the other underdrive. That gives me the impression that these were on the TH400 and the C6, only.

 

Inside of an Doug Nash 4+3, found in the Corvette, there is also an input sun gear.


Not sure if that would inadvertently fit the sun-side of the dual-range box, or what spline it is.

There was a T-10, which was the 4 ahead of the +3 in the 4+3 arrangement, and there did exist T10's with a 27-spline output. That would make for a 27-spline input sun gear there. The gear you pictured might be a 4+3 part.

Are you sure that you counted to 28 correctly? On female splines, you would want to count the valleys, not the peaks, to get the spline count for the shaft that goes into it.

 

Sorry, my coffee just kicked in:

That input spline shell is just randomly stuck in the housing. That is not where it goes.

Take the adapter housing off, and you will (should) see the proper one sticking out of the dual-range case.

This is the stick out of the typical TH400 shaft:


Contrast that to where that splined part is, in your picture. That splined part, whatever it is, would be hitting the speedometer drive gear, and would be past the TH400 splines.

The end of the TH400 output shaft would go directly into the input sun gear on the dual-range box, roughly 5-inches past where it attaches to the TH400.

 

Here is a picture of one with no adapter on it:

That thing pointing down is where the end of the TH400 output shaft goes, not at the very beginning of the adapter, but almost at the end.

Have a look in there and see if you count 32-splines (as in the valleys).

 

@34Phil did you pull the adapter housing off?