Front driveshaft w\6-7" lift?

What, if anything has to be done to my front driveshaft now that I'm at 6.5" of lift. Does it need to be changed in anyway, longer or shorter? I've got a droneing kinda vibe from the front after about 60 mph. When I remove the shaft the vibe goes away. I already put a new u-joint in. It's a short arm lift and since I added spacers to my 4.5" lift the vibe showed up and I haven't gotten an alignment yet either. At the same time I also put in 4.56s and a tru-trac. I've heard of people having to get a longer shaft, and a friend with a MJ said he had to shorten his. Other then the vibe it's great no DWs. TIA

check your slip spline, that was the cause of my front vibes, which ended up taking out my front pinion bearing.

you should be good with the stock shaft, I have a stock shaft in mine and I'm at 10"

Should the pinoin yoke and driveshaft be inline with eachother?

Rudy said:

Should the pinoin yoke and driveshaft be inline with eachother?

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In an ideal world that is true but unless you like to drive the twitchiest SOB on the road you should not do this - reason being the pinion angle is fixed in relation the the inner knuckles which set the caster.

Add to one angle and you must subtract form the other - I would highly recommend you stay above 5 degrees of caster for road manners...

The other solution is to get offset ball joints or grind and spin the inner knuckle to reset the pinion angle

Enjoy

Matt

PS - just scratch build an axle and you can have the best of everything!

When I was running short arms and 6" of lift, I had to shorten my front shaft about 1/2". When the jeep was on the lift and the front axle was hanging, the front drive shaft would bottom out. I didn't want to punch the shaft through the transfer case.

jalehman said:

When I was running short arms and 6" of lift, I had to shorten my front shaft about 1/2". When the jeep was on the lift and the front axle was hanging, the front drive shaft would bottom out. I didn't want to punch the shaft through the transfer case.

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HUH

I'd think that drooping the axle (like on a chassis lift or over a jump) would strech the shaft. I could see the double cardan joint or the joint at the pinion getting together. Having the slip spline come uncoupled might be extra-obcene. It's when fully stuffed (landing from that jump or bottoming out otherwise under load ) when things could compress & damage the case :explosion: In either case, limiting straps & bumpstops can help. The slip of the DS has to exceed those limits of extension & compression.

One way to spot potential problems is to mark the suspect areas with white-out or a dab of paint...then rotate the assemblies at their max operating angles. Look & listen for contact, then 'clearance' the areas that touch with a dremel and/or adjust the suspension until they don't.

I dunno if Rudy has a T case drop or a SYE...a tc drop will kick the front drive output upwards (not helping angles) while it kicks downward out back.

With short arms, the axle drooped so far that it basically swung down and underneath the rig and compressed the driveshaft till it bottomed out. With the long arms, the axle moves more up and down instead of down and back.

Yep on the bottoming out!Thats just one of the reasons Im gonna build long arms for mine.

Yeah, I shortened my front shaft by an inch. With 8" of lift a lot of droop, the axle moves rearward when drooping and actually compressed the driveline.

Any driveline vibration normally comes from the angle of the u-joint at the pinion. The XJ has a double carden joint at the top of the front shaft, so the driveline needs to have virtually no angle at the pinion. You need to adjust the castor to change the u-joint angle, either with the factory shims or adjustable control arms. One of the negatives of not having locking hubs in the front is that as your lift gets higher, castor needs to be lessened to maintain a proper u-joint angle to avoid driveline vibrations. Too little castor will make the steering feel loose or quirky. With locking hubs, or with no locker and a disconnect front axle, this isn't an issue because the front driveline doesn't turn when in 2wd.