Twisted Front Driveshaft

[Jesse B.]

I tried asking this question on bb and got one (mildly helpful)response, so I thought I would try it here. I have a 1975 Scout II with a stock 304 and rebuilt 727. Dana 20 transfer case. 3.54 gears and 32x11.50 tires. It has a rancho 2.5 lift, which is acutally closer to a 4 inch lift. I just completed a reverse shackle (IHOnly) and had to have the stock front driveshaft lengthened. The tube diameter of the stock shaft was 1.25". I got the driveshaft back several weeks ago and they used 1.25 tube with .120 wall. I took the truck out a couple weeks ago for its first 4wd test. Once I got on a good trail I locked the hubs, put in it 4-lo and promptly climbed up a fairly steep dirt motorcycle trail. No jumping, no bouncing. Once I got back off the trail and satisifed that everything worked, I popped it out of 4-lo into 2wd, but left the hubs locked in. At about 20mph, I got a vibration and loud rattle. I crawled underneath and did not notice anything immediately wrong, I was in a hurry, so I just unlocked the hubs and figured I would take a closer look later. I finally got a chance to crawl under and really take a good look and noticed that when I spun the front driveshaft by hand it wobbled about 1/2 inch up and down. All the paint at each weld was also missing and you could see the stress twist in the metal. When I took the driveshaft off, it was about 1/4 turn out of phase (from the twisting). Now the question is, has anyone had this problem? If so, what did you do to correct it? I can't believe it was anything I did, or didn't do, because if that driveshaft twisted with what little I put it through, I don't know how it could stand up to trail use. I know 1.25 was stock, and many people are using them that size, but I don't know what could have caused the twist.

I've looked through the web and some people say I should not go with a larger tube because it May hit my automatic pan. What about a heavier wall, say .188? Does anyone know if the stock shaft was .188 wall to begin with and I got ripped when they put in .120? How much stronger will .188 wall be than .120? Thanks in advance, Jesse

 

[Craig]

Jeff is out of town, so that the reason no responses.

Going by memory as I lost a lot of pictures from a hard drive failure. I thought the upper end of a stock front drive shaft was solid or almost solid. I believe there was a change from the early years to the later years too. ( I'm sure I wil stand corrected)

anyway you need to stay with the stock 1310 joint as a 1350 or 1310 cv will hit the 727 pan, even with grinding you May still have issues.
Stick with a small dia drive shaft. Under 2" I took my stock shaft and cut off both ends and made a sq drive shaft. ( low tech) but I need something right away and I have other drive train changes on the way.
I used 1.5"x.188 for the upper tube and 2 x .250 for the lower tube. Anti seeize for lube
plus with all my lift I used a Tom wood super flex joint at the t-case and one of Jeff's u-bolt yokes at the pumpkin as they are a 1/4" longer allowing the shaft to turn and the drive shaft yoke now does not hit the pinion yoke nut when fully drooped.

 

[Jesse B.]

Fyi

this weekend I pulled a front driveshaft out of a Scout that was parting out, took the shaft home, cut it in half, and measured the wall. Stock Scout front driveshafts are 1.25" in diameter and have a 3/16 (.188) thick wall.

 

[Craig]

I have my profile setup correctly, but never get e-mails on post.
I would ask for the shop to fix it, if you paid good money to have it done. What did they think you had a samurai