Drive train clocking and driveshaft measurement

[j10builder]

I finally got back to work on my '81 J20/10 project. Got the NP 208 in after realizing I built the wrong TC because the T-18 has a different spline count. DOAH! That was a moment of ...reality. Still had the other 208 so I disassembled and reassembled and am now good to go.

I know there have been threads about this stuff but I'm lousy with the search bar and I'm not doing something right to find the info.

I know doodley squat about transmission, and front and rear axle clocking. I know the axles should have similar angles but I'm not sure what the angles should be or how much tolerance wiggle room there is.

This rig has the J20 Dana 44 up front and Dana 60 in the back with the T-18 and NP208. Skyjacker 4" lift springs all the way around. Front drive shaft is good but not a lot of clearance on the transmission cross member (roughly an 1"). Is that enough?
I'll have to have the rear shaft cut and shortened but don't know how to measure properly for THAT and I'd like to avoid the banghead emoji again. I've got the J10 and J20 rear shafts and imagine I should use the J20 drive shaft unless there's some physics thing I'm unaware of.

I travel for a living and I'm heading out for a couple weeks. That puts me in research mode which is why I'm asking. I can gather knowledge and order parts and tools and such and dive in when I get home.

[tgreese]

The search bar is a waste of time. Use Google or Bing or your favorite search engine.

https://www.bing.com/search?q=site%3Afs ... e+clocking

Limit the search to this forum, or you can do the same with IFSJA.org - then vary the search terms.

[tgreese]

There is clocking for the transfer case and clocking for the axles. I presume you only mean the axles. You can clock the transfer case to rotate the outputs up and down. This can be done by redrilling the adapter or transfer case, or with an adapter.

I think the best reference for axle clocking is the Tom Woods site. They have articles discussing the issues you mention, ie how to measure the driveshaft when changing the length, and how to split the u-joint angle between the transfer case and the axle. This mostly applies to the rear axle, since the angle at the front axle is fixed by the welded spring pads and needed caster. With part-time, you don't care about the front so much since it carries less load than the rear, and typically is used only at low speed.

https://4xshaft.com/

[j10builder]

Thanks, I was noodling around trying to figure out what the transmission mount shim was all about and read that you could change the angle of transmission and transfer case by stacking shims. Then my mind started going "Well what's the right angle for the trans in the first place? How critical is this?" Ha! I'd never even considered that could be a thing before.
Anyway, I'll check out the site. Much appreciated.

[akguy09]

To measure the driveshaft length I think Tom Woods has the correct way to do it on their website.

[devildog80]

Just for reference, here are the trans mount shims on my '81 CJ5, which has about a 4" lift. PO had these installed when I got it, and work well, so leaving them as they are.
Just 2 brass bars about 1-1/2" wide on each side, with holes to bolt through with the normal skid mount location. You can use steel too, just stay away from aluminum.
Yes it is much shorter wheelbase, but you get the idea.
DRIVERS SIDE2 by Scott Weckerly, on Flickr

Thanks, I was noodling around trying to figure out what the transmission mount shim was all about and read that you could change the angle of transmission and transfer case by stacking shims. Then my mind started going "Well what's the right angle for the trans in the first place? How critical is this?" Ha! I'd never even considered that could be a thing before.
Anyway, I'll check out the site. Much appreciated.

[j10builder]

Thanks Devildog80, that's a good idea and easily doable.