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Discussion Starter · #1 ·
I am considering a Duramax / Allison transplant into a 79 Chevy. Can I hook it to the existing 205 transfer case? What is in there now is a 400 transmission with the big one ton shaft. I know this because I have not quite finished the 350 to 400 transmission swap, and I had to send out the transfer case to get the larger one ton shaft put into it. Thoughts?
 

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Other than that truck is CLEAN and to have a duramax in it would be SWEET:cool:
 

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I am considering a Duramax / Allison transplant into a 79 Chevy. Can I hook it to the existing 205 transfer case? What is in there now is a 400 transmission with the big one ton shaft. I know this because I have not quite finished the 350 to 400 transmission swap, and I had to send out the transfer case to get the larger one ton shaft put into it. Thoughts?
I'm Assuming it can be done but at what cost? The folks at Extreme 4x4 mated a 32 spline NP203 to an Allison in their project suburban gorilla (87ish suburban, with hummer body mod, Twin Turbo Dmax, Allison, and Offroaddesigns 203/205 doubler t-cases). They bought a stub shaft to convert the allison's male 29 spline to a 32 spline female to mate the male 32 spline on the 203. They made up the space by using a clocking ring and spacer.

Here is the quote from Ian himself
***
The real issue was the spline count on the Allison. 29 Spline, then we had to make up the length of the shaft with adapters. To do it again, I would have had the output of Allison Re-Splined when it was being rebuilt to a 32 spline output. That would have been the best way, but since we were the first people doing this anywhere, we kind of had to go blind. It did work out though.

Ian
***

This was taken from another site I belong to.
http://coloradok5.com/forums/showthread.php?t=160975

I don't know where they got their adapter shaft but I'm sure it wasn't cheap. A good machinist should be able to make an adapter to mate to the NP205 and then to the Allison.

Another question is what NP205 do you have. I'm assuming you have an older one with the figure 8 mounting pattern as opposed to the round 6 bolt circular (I think the round bolt circular only came with the large input, so if you had to have yours enlarged I'm assuming it's the old style). That being said, there was a short input shaft and a long input shaft 32 spline (large bearing). You can see/read the differences here
http://www.offroaddesign.com/NP205tech.htm

Ideally you would want the short input.
I also prefer the round bolt pattern (newer 205) cases as the adapters are less prone to breaking (ask me how I know)...

Let us know if you decide to do this and how you proceed. I'm very interested.

Good Luck.
 

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Might check with advanced adaptors, they make a lot of adaptors for everything and may have something already.

May check to see how the 4wd kodiaks work. IIRC they are SFA and maybe utilize a 205 or 208 or something that could be used in your application.

Finally, you may wanna contact the guy on this site that built the puller with an 87 CC w/ Duramax. I know he went with a NV4500 but I would think he could be a VERY valuable asset to your entire process. His name is nick04dmax or wayne04dmax (or something similar to those).

Good luck. I hope you find out something positive with this as my dream build is exactly what you are considering. (maybe a 72 instead, but still virtually the same)
 

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Hey about xtreme 4x4...

Did anybody ever see that truck move?

Just to let them know, it won't move :)

The Allison with 4x4 is programmed with a 2.72:1 ratio T-case. When you throw the ORD doubler in there it screws up the output speed reading..Since the output speed sensor is located behind the t-case.



I'd like to hear IAN's comments on this.
 

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Discussion Starter · #6 ·
Thanks for the encouragement. I have spent a long time on the truck to get it the way it is, but have lost interest since my 03 is soooo much fun! I will keep on digging and keep everyone informed on the progress.

Mark
 

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if you need a hand mark, let me know!

brayden, thats funny!
 

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Hey about xtreme 4x4...

Did anybody ever see that truck move?

Just to let them know, it won't move :)

The Allison with 4x4 is programmed with a 2.72:1 ratio T-case. When you throw the ORD doubler in there it screws up the output speed reading..Since the output speed sensor is located behind the t-case.



I'd like to hear IAN's comments on this.
As far as I know (and have heard) it's an easy fix when using an aftermarket controller (which they are). In 2WD/4WD high it is 1:1, so not different than the stock t-case. As for when in low range or "double low", it is the same as installing a real deep set of gears in the rear end, or a really small diameter tire (frisbee sized), there is a changeable parameter in the tranny controller.

NOTE: I have not tried this nor attempted it first hand, this is only the what I have heard.
 

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Leadfoot.. It's nothing like changing to deeper gears in the rear end.

The problem lies with the doubler. The output speed sensor is after the T-case. It is looking for a 2.72:1 reduction ratio from the factory t-case. Since the ORD doubler that they used (NP203/NP205) is two 2:1 t-cases together Low range will always be the wrong ratio.

IF the speed sensor was on the back of the trans like on a 2wd, it would be just fine.. The trans wouldn't care if you had a 100:1 gearbox behind it.

BUT since they used the factory 6 bolt standard NVG/NP t-case flange that the allison utilizes, they don't have an output speed sensor on the trans itself.. There's no location for one.

Aftermarket controller.. :) Ha.... I bet. What is this.. Year 6 of the aftermarket controller joke?
 

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Leadfoot.. It's nothing like changing to deeper gears in the rear end.

The problem lies with the doubler. The output speed sensor is after the T-case. It is looking for a 2.72:1 reduction ratio from the factory t-case. Since the ORD doubler that they used (NP203/NP205) is two 2:1 t-cases together Low range will always be the wrong ratio.

IF the speed sensor was on the back of the trans like on a 2wd, it would be just fine.. The trans wouldn't care if you had a 100:1 gearbox behind it.

BUT since they used the factory 6 bolt standard NVG/NP t-case flange that the allison utilizes, they don't have an output speed sensor on the trans itself.. There's no location for one.

Aftermarket controller.. :) Ha.... I bet. What is this.. Year 6 of the aftermarket controller joke?
Not that I believe everything on the net...but:
http://www.atsdiesel.com/atswebsite/ProductsGM/Control.asp

I believe there are other units (basically one-offs) that have been utilized as well.

I'm not saying you are wrong, as I am not sure I am right. But I do know some things to be true:

I don't claim to know how the Ally works but I know changing rearend gears increases/decreases the output shaft (transmission and t-case) vs. a given MPH. This affects your output sensor on the tranny/t-case and is the reason you need to update your TCM/ECM when you change gearing or increase/decrease tire size to keep your speedometer accurate (back in the days it was corrected by a different tooth count speedometer drive located on the transmission tailshaft of a 2wd truck or transfer case tailshaft on a 4wd truck). If this signal is used for shifting it will cause erratic shifts if the rear end gears are changed or the transfer case ratio is different than expected (that was what I was alluding to).

The TCM/ECM expects to see a specific transmission output shaft speed vs. a given input shaft speed when the torque converter is locked, if it sees a difference it assumes slip. I'm assuming this is integral to the tranny (not t-case). Meaning the sensors are on the input and output shaft of the tranny (probably internally) and not in the t-case (regardless of 2/4WD).

I'm assuming, again I am no expert, but the sensor (you speak of) on the tailshaft of the tranny is only for 2wd speed sensors and is moved to the t-case for 4wd vehicles as they have done for years (even back in the mechanical speedometer drive days).

This is done for simplicity. A given transfercase output RPM equals a specific MPH (assuming the rearend gear ratio and tire height are known). This sensor does not care if the transmission is in first gear or high gear or whether the t-case is in hi or low range.

Back in the days, a transmission shifted when certain conditions were met (based upon governor setting, output rpms, and vacuum signal). I do not know how they shift now in the days of electronic controls, and I conceed that there MAY BE a shift algorithm based upon the stock 2.72:1 ratio and having a 4:1 reduction will produce awkward or incorrectly timed shifts, but that should ONLY be in low range.

Again, I'm not disagreeing with you per se, I'm just trying to furthur my understanding. Hopefully somebody that knows ALOT more than I can help.

I don't think they would build that rig without taking that into consideration............
 

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I'm your man..

The Ally speed sensors are external, and there are three of them.

Input, turbine, and output.

The output speed sensor in 4wd trim is on the T-case...

NOW, when the trans is shifted into low range, it will throw all kinds of ratio codes. It's designed to see a certain ratio and output speed in any given range.

The trans will set codes, and give you range inhibits.

Brayden
 

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Discussion Starter · #14 ·
I really want to do this project. It will come down to if I can find reasonably priced donor truck. I want a 02 or newer LB7 automatic. The prices around here seem to be a little high. Anyone have a lightly rolled truck? Watching Extreme 4x4 today gave me some good ideas. Thanks for the help!
 

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I'm your man..

The Ally speed sensors are external, and there are three of them.

Input, turbine, and output.

The output speed sensor in 4wd trim is on the T-case...

NOW, when the trans is shifted into low range, it will throw all kinds of ratio codes. It's designed to see a certain ratio and output speed in any given range.

The trans will set codes, and give you range inhibits.

Brayden
:thankyou2


That is some great info. When you say "It's designed to see a certain ratio...", what does the "It" refer too (the TCM)?
 

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Yeah.. It's looking for the 40 pulse signal from the tone wheel on the T-case.. 40 is pretty standard across the board for GM's.

Logically, it then multiplies the pulse/rev times the ratio's to "know where it's at" as far as speed is concerned.

If you throw another gearbox in the mix, or change t-case ratio's it skews all the signals.
 

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Currently putting Allison on 5.9

I am currently putting Allison on 5.9 Cummins w/205. If you use input shaft for 89-93 Dodge man. trans. which is 29 spline & coupler will match up. Built my own adapter. I didn't know about speed sensor being on trans. case. I'm going to try to contact Brayden to see what he says on a fix for that.
 

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That's why I ran a divorced NP205 w/ a 2wd trans on mine.

I do have the 29 spline input gear for the NP205, but then how do you get a reading for output speed when you don't have the correct tone wheel.

There's where the problem lies.

Send me an email/PM.
 

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I believe it's a matter of getting the nv4500/205 spacer and mounting it up.We had my ZF6 apart the other day for a clutch and it appeared to have the same pattern an my NV4500. It will require a round pattern 205 though.85-91 version. I'd like to see it when done.Then you could swap a D-Max/ZF6 into my 67' :D .
 
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