Rear Drive Shaft Length

[cbturf]

OK here's my deal. I am having a 700r4 put in the CUCV. My problem is that the drive shaft that is bent from forklift damage so it must be replaced. It is barely bent at all BUT it seems way to short. The one I am having built will be 1.5 inches longer (I told my wife it was 6 inches longer for consistency) just to make it fit up into the yoke properly. (Double Entendre not intended!) Has anyone else had the problem of their driveshaft being way to short. I am starting to wonder if I should wait on getting the driveshaft built until I get a proper measurement rather that just using the original and adding additional length to make up the difference. Let me know your opinions. My situation is that if I wait I probably won't have the truck back by Friday afternoon when I need it to pull the boat to the duck blind Saturday morning.

 

[Iceman3005]

I have done a lot of these swaps, the front and rear drive shafts should not have to be changed if the turbo 400 had an np208, the drives hafts are the same length. If it has an NP205 then the rear will have to be lengthened and the front shortened.

 

[cbturf]

The one in it was to short to begin with even with the 400, only about three inches on the yoke tube was on the shaft, over half of the tube was not. I was asking why it would have been to short. Forklift damage? or just the wrong one to start.

 

[roveroverme]

What is the length of the M1008 driveshaft, anyway? The data plate says the wheelbase is 131.5" and the driveshaft ~51,5" to 52" (weld to weld). I have a Np205

 

[roveroverme]

The one in it was to short to begin with even with the 400, only about three inches on the yoke tube was on the shaft, over half of the tube was not. I was asking why it would have been to short. Forklift damage? or just the wrong one to start.

Was the truck lifted? Maybe it's that way for suspension travel?

 

[cbturf]

The truck has not been lifted. That was the first thing the driveshaft guy asked me too. Should have mentioned that already but forgot. The only thing I have done to the truck is put 2 inches on the front to level it up and install 255/85-16 KM2 tires on it. Now that the r4 is going in it I plan to add AC and a turbo after duck season but I can't have it out of commission any more till the end of season. Tired of having to ask my buddies to come pick up the boat when we hunt.

 

[Iceman3005]

I have done a lot of these swaps, the front and rear drive shafts should not have to be changed if the turbo 400 had an np208, the drives hafts are the same length. If it has an NP205 then the rear will have to be lengthened and the front shortened.

I have the info wrong here, if you have an NP205 with a fixed yoke and your installing an NP208 then the drive shaft will have to be shortened and a slip yoke added, if you have an NP205 with a slip yoke tail and your installing an NP208 then the drive shaft should be the same length. If your truck came with an NP208 and your installing a 700r4 with an NP208 then the shafts are the same, the 700r4 is about 1 inch longer than a turbo 400.

A bent shaft should not effect the length that much, when I got my trucks home both of them had severely bent shafts, they where almost touching the bed and they didn't seem to hang out much more than they do now.

 

[cbturf]

Ice that was what I thought. I told the driveshaft guy to go ahead and add the 1.5 inches to the shaft length and I'm certain I'll be fine. I do not off road the truck at all so suspension action is not an issue at all. I did not change the TC stuck with the 208. Since the only 4x4 my truck sees is a 6 inch deep mud hole on the way to the duck blind I don't need all of the heave duty stuff. If it turns out I guessed wrong on the length I'll have an excuse for that lift and 37s I think look so cool on these trucks!

 

[porkysplace]

A good driveshaft builder should be able to make the correct length with measurements from yoke to yoke.

 

[cbturf]

Yes he is a good driveshaft builder but the transmission is not in yet so I cannot sit the truck down and measure it so we are using the bent shaft as our template to build the new one. The bend is almost unperceptable so it would not affect our process. I wouldn't bet my house on it but maybe half the back yard that the shaft had been replaced with one to short while the truck was still in service.

 

[porkysplace]

Yes he is a good driveshaft builder but the transmission is not in yet so I cannot sit the truck down and measure it so we are using the bent shaft as our template to build the new one. The bend is almost unperceptable so it would not affect our process. I wouldn't bet my house on it but maybe half the back yard that the shaft had been replaced with one to short while the truck was still in service.

Kinda putting the cart in front of the horse . If it is too long a busted transfer case or transfer case to transmission connector is the likely result .

 

[roveroverme]

A good driveshaft builder should be able to make the correct length with measurements from yoke to yoke.

a good driveshaft shop will charge above $300 for a new driveshaft.

 

[Warthog]

For the OP, you never did say which CUCV you have. That does make a difference in the meassurements.

M1009? M1008 or the CUCV-II that you won in Alaska?

 

[roveroverme]

For the OP, you never did say which CUCV you have. That does make a difference in the meassurements.

That's what I was trying to get at with my initial post thank you.

 

[cbturf]

Sorry for the CUCV confusion. I have been talking with Iceman so he knows what I have and the others were left out. I have an M1008. The 6.5 Blazer does not exist, no need for an r4 in it anyway since she had an L80E. I have been relying heavily on Iceman's knowledge of the 400-r4 swap since he has done so many of them. He knows that the driveshafts do not need to be changed. Problem is my driveshaft was clearly way to short and although it probably could have been fixed since the bend is more like a dent, I have to have the new one made. Actually not a new shaft just a new shaft tube and while it's out we are putting in new U-joints too. Also putting in a new rear main and oil pan gasket. I just want to make sure that everything that needs done now or may need done in the near future is taken care of while the transmission is out of the truck.

 

[MarcusOReallyus]

There is another thread on here about a short drive shaft. Looked like an incorrect one was put in by somebody along the line. Might be your problem, too.

 

[Csm Davis]

The one in it was to short to begin with even with the 400, only about three inches on the yoke tube was on the shaft, over half of the tube was not. I was asking why it would have been to short. Forklift damage? or just the wrong one to start.

If you add 1.5" to the shaft you will end up busting your transfer case. Here is why you said your slip was in 3" now add 1" for 700r4 plus 1.5 that you are adding to the shaft, that's 5.5" into the transfer case. I have not measured one but if memory serves the slip yolk is only 6" the stock setup only moves around 2", one inch in and one out roughly but if you stuff that yolk that far in it will break something. I worked building drive shafts for a few years.

 

[porkysplace]

a good driveshaft shop will charge above $300 for a new driveshaft.

Cheaper than a new transfer case and adapter and still have to get the driveshaft to the correct length.

 

[cbturf]

I have considered all of the options and even done a few calculations and I am almost certain (over 90%) that I will be fine. I do not want to sound like a geometry or calculus teacher but we have to consider that just by lengthening the driveshaft a certain amount does it change the position of the U-joint and yoke the same amount. Look at the driveshaft ends as one side of a triangle and the height of the transfer case shaft above the rear end input shaft another side and then a straight line from the transfer case output to a spot directly above the rear end as the third.

Then, although not exactly the same, remember the 3,4,5 or larger triangle rules (Pythagorean Theorem) to estimate that adding 1 inch to the output shaft, which is a direct measurement, and then 1.5 inches to the (hypotenuse) of out triangle and we actually add less than two inches to the engagement of the slip home to the TC shaft. I had thought through all of this before posting but I wanted other opinions and input, mainly to see if anyone else had the same issues. My slip yoke is quite a bit longer than 6 inches. As it was installed in the truck the worn part of the yoke was less than half way down the outside of the shaft.