How much spline engagement do I need?

[87Skier]

I'm working on mating a 6L90 to a np205. I have the short 29 spline transfer case input, and the shortest 4wd 6L90 output shaft. After I get done cutting everything to length, I'm probably going to have about 1.5" to 1.75" of engagement of the transmission into the transfer case. I haven't found anything out there whether this will be enough.

The truck won't see a lot of abuse and it won't be a high hp/tq build or anything, so I'm thinking it will be alright.

What do you guys think?

[sweetk30]

offroad design has a kit for that combo .

and when I checked a 203 input and a 205 input there was basicly 2" of spline on them . so I try and fill it all up the best possible.

I would say if you get 1.75 tho you should be fine . . . but I am no expert in this combo area .

[obijuan]

i dont understand what parts you have. you should be using a coupler if using the 29 spline dodge np205.

Do you have the aftermarket female 29 spline input?

[kwmech]

At the bare minimum you want to be engaged the diameter of the spline. So if the diameter is 1.5 that is your minimum

[87Skier]

Sorry for the confusion. The 4wd 6L90 has a 29 spline output shaft, so I believe when you order this kit AdvanceAdapters you get a female 29 spline dodge shaft for the 205.

I am going to try and keep as much splined together as possible, but I do need some clearance. I think it will be very close to 1.75".

[obijuan]

Call off-road design. I believe their spacer is shorter giving the most engagement possible.

[87Skier]

A shorter spacer/adapter makes the problem worse. The shaft is only splined about half way down, and there is only 2 7/8" of splines. Where everything is mounted right now, the transfer case is about 1" from mounting to the transmission.

Shortening the shaft by 1 7/8" means that there isn't room for the 2" of transfer case input shaft, so this will need to shortened as well.

This would be a lot more clear had I taken a few pictures, but I was annoyed that there was so much of a gap, so I took some measurements and called it a day. I can post pictures later this week.

[sweetk30]

http://offroaddesign.com/catalog/NP205%20Parts.htm

part way down this page is there stuff.

['63GENIII]

Ok, I gotta ask. What in the heck is a 6L90? Is it the same as an Allison? Are they put in the newer trucks?

[87Skier]

The 6L90 is a revised version of the 6L80. It is said to have been designed to replace the 4L80 (in form and function), and uses clutch-to-clutch shifting and does away with bands completely. The 80 and 90 share about half their parts. They have the same gear ratios:

1st - 4.027
2nd - 2.364
3rd - 1.532
4th - 1.152
5th - 0.852
6th - 0.667
R - 3.064

Production started around 2005, and are being pretty much replaced by the 8L90. Evidently, you can only get a 6L90 in a 1500 series new truck. All the rest have 8L90's. You can find them in Camaro's, Corvette's, vans, and trucks in both 4wd and 2wd versions mostly between 2006-2016.

These are not Allison transmissions.

They require a CAN bus to operate, so they came behind gen IV ls engine.

The 6L80 uses a 32 spline output that is the same spline as a 4L80.
The 6L90 received a 29 spline for 4wd applications and a 36 spline for 2wd applications.

['63GENIII]

Originally Posted by 87Skier

The 6L90 is a revised version of the 6L80. It is said to have been designed to replace the 4L80 (in form and function), and uses clutch-to-clutch shifting and does away with bands completely. The 80 and 90 share about half their parts. They have the same gear ratios:

1st - 4.027
2nd - 2.364
3rd - 1.532
4th - 1.152
5th - 0.852
6th - 0.667
R - 3.064

Production started around 2005, and are being pretty much replaced by the 8L90. Evidently, you can only get a 6L90 in a 1500 series new truck. All the rest have 8L90's. You can find them in Camaro's, Corvette's, vans, and trucks in both 4wd and 2wd versions mostly between 2006-2016.

These are not Allison transmissions.

They require a CAN bus to operate, so they came behind gen IV ls engine.

The 6L80 uses a 32 spline output that is the same spline as a 4L80.
The 6L90 received a 29 spline for 4wd applications and a 36 spline for 2wd applications.

Man, .66 OD? Thats pretty tall!

I did read your other thread with Clinebarger on it. Very impressive build. I wouldn't ever even think of doing more than removing the pan to change the fluid. Very cool upgrade!