am i gonna need a new drive shaft??

[savagek5diesel]

hey guys,
i'm doing a 3/4 ton axle swap onto my jimmy and i just wanted to know if i'm going to need a lengthened/ shortened driveshaft for the rear 14b sf? i have a 6 inch lift with a 208 tcase. I've searched through old threads and couldn't find this one detail. the donor axle's are from a 78 i believe, or a 77 pickup.

 

[75-K5]

I don't believe you'll have to do anything to the length of your driveshaft if you only swapped axles. You will need conversion u-joints to mate the 1/2 ton shaft to the 3/4 ton axle though.

 

[jekquistk5]

You shouldn't need to lengthen the driveshafts. I just did a 14ff swap and I was fine.

 

[dyeager535]

It was hard to measure exactly, but looks like the 14SF is "longer" by about 1.5" than a 10 bolt. I suspect the 12 bolt is pretty similar.

I'm not certain that all of this length is at the pinion, there is probably at least some of the length related to the back side of the case to cover the larger ring gear.

 

[jekquistk5]

I'd grab a 2x4 and stick it on the pinion. Make sure its level, and measure to your perches because that is the length that matters. Do that on both axles If they differ you might want a new shaftl.

 

[savagek5diesel]

i'm not worried about the 14b pinion being longer, that would benefit me because the slip shaft out of my 208 is hanging out close to 5 inches. thank you all for you info and looks like i'll be doing this swap for cheaper than what i expected

 

[dirtwarrior17]

swap in the 14sf... hook up your driveshaft. if it doesn't vibrate you'll be fine.

 

[Hossbaby50]

It should benefit you in the length area and put some more of the slipyoke back in the case. It will hurt you on your driveline angles though. It wil make the angle a little steeper then it was before and may cause more vibration.

Also with a 6" lift and a stock shaft you are probably to a point that you can bind the ujoints in the driveshaft. I picked the a$$ end of my truck up and let the axle travel all the way down with 6" TC EZ Ride springs and my driveshaft binds near the bottom.

It only binds if both the tires have the ability to have alot of downtravel at the same time like if you got high centered badly. If you did this and it bound the driveshaft you will most likely break the driveshaft.

I had to add a limiting bar in on my rear suspension to stop this from possibly happening. Keep this in mind if you don't have a limiter in the rear suspension if you are offroad. To check and see if your shaft will bind pick the truck up off the ground with a jack and support it with tall jackstands on the frame. Then lower the jack under the axle and slowly move the tires with the tranny in neutral. If the tires won't spin the driveshaft is probably bound up.

The only answer is a CV driveshaft or to shim the pinion up which will probably cause driveline vibs. So basically what I am saying is yes your driveshaft will work but you are at its very limits and be careful with it.

Harley

 

[savagek5diesel]

thanks harley, your write up was perfect. i was thinking about limiting straps until i could afford to buy a nice cv/telescoping drive shaft. but all your info hit the dot.

 

[dirtwarrior17]

it usually does.....

 

[short sub]

hey man- i bought a 90 k5 bone stock. i eventually lifted it 6" and ran it like that for a while, one day the gov lock blew and took the entire 10 bolt with it and i opted for the 14 sb swap. put the axle in and the driveshaft was perfect. no unusual vibrations at all except for the 35" sx's.