The Troubles of a Lift

I just put a new 2.5" BDS suspension lift and .5" Performance Accessories shackles on my '72. I ended up getting about 4-5 inches of lift since my old springs were sitting kinda flat (I should have measured before and after! But I will take and post pictures to compare). Anyways, now I have a slight vibration at road speeds. Its not terrible, but my drivetrain felt surprisingly smooth before so its bothering me! From what I understand this is most likely driveshaft vibration. It was not at all present before the lift kit install.

A quick look underneath reveals the rear driveshaft will need to be lengthened about 1" since it backed out a ways now that the axle is a few inches further from the frame . The rear drive shaft obviously sits at a steeper angle than before but exhibits no binding of the u-joints so i think its ok. The rear axle pinion angle is still parallel to the floor as is the transfer case rear output, so from what I understand about these things (and I'm no expert) there shouldn't be a problem with vibration there. Correct me if I'm wrong.

The front driveshaft on the other hand has 2 different angles. The transfer case output is parallel to the floor as it should be, but the front axle pinion angle is noticeably turned up. If I understood everything I've read correctly, this inequality in angles produces the vibration.

So what would be the best way to fix this? Instead of spending the money on a double cardan drive shaft, could I just install lockers on the front axle? That would eliminate any driveshaft vibration on the road, and i probably won't be driving fast enough while offroading in 4wd to really get any vibration. I appreciate any suggestions.

 

I would put warn hub lockouts on regardless, I can't believe the Jeep has made it 40 years without someone already doing that.

 

I'd do what is suggested. Also check the rear ujoint angle with an angle finder. A ujoint can vibrate due to excessive angle but not bind. Also check your front caster angle as that can co tribute to steering instability. I prefer 5-7* positive on these Jeeps. Definitely not more than 7*.


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Staffords , I think nickmil is correct. However, I would want to know exectly what the problem is.

I would pull the rear drive shaft and drive it in four wheel drive. If the vibration improves, then the rear shaft/axle is at least part of the problem. I would then reinstall it and pull the front drive shaft. If the vibration is less or gone, then the front shaft/axle is at least part of the problem. Of course while you have them out, you should inspect them for bad u-joints and splines. All this because they may both be part of the problem. I hate replacing parts that are just fine, because I THINK the are the problem.

I also would install lock out hubs in any case. They will pay for themselves in fuel milage and less needed maintenance. Read wear and tear on the front drive train while in two wheel drive. IHTH, Matt W.

 

Thanks everyone for the help. I ordered some locking hubs but I haven't had time to pull the driveshafts. I'm pretty sure the front is at least part of the problem because of the uneven angles, and the hubs are a lot cheaper than the double cardan shaft. Meanwhile, here's picture of the rear driveshaft to see if you guys think the angle is too steep. You can see where the driveshaft has backed out some because of the lift and should be lengthened. I'd rather not lengthen this one if I'm going to have to replace it to get rid of the vibration though.

The jeep actually handles pretty well. Stable at highway speeds and no wandering. Steering characteristics have not changed, but just had it aligned and my front caster angle is -3*!

 

Might be time for a CV in the rear at the t-case and point the pinion at the t-case or down maybe 1*.. I can't believe it doesn't have lock outs on the front. Do that first.

 

wow thats approaching shopping cart angle...

 

Just measured it. 25°!

So double cardan in the rear should handle that better, right?

 

I am running a 2.5" lift. i changed the tranny and transfer case and was able to use the original driveshaft. i did drop my transfer case an inch or so. I also have a 25 degree angle on my driveshaft and i do not have any vibration at all. I am planning on tilting the rear end and getting a double cardan shaft in the future but will continue to drive it for now.

 

Dropping the transfer case and tilting the pinion up will shorten the driveshaft also.

 

You swapped in a different tranny and transfer case? Or are you saying you changed the angle?

I should have some lockers for the front to put on by Monday. If the rear driveshaft proves to be the problem I will be having a double cardan shaft made. I'm also hoping as the new leaf springs break in and settle down the driveshaft angle will decrease. I mean I got quite a bit more than 2 inches of lift from this kit.

 

If I'm going to be tilting up the pinion angle I guess I might as well go all in for the double cardan shaft instead of lowering my t-case and sacrificing some of the ground clearance which I went through all of this trouble to get. And I think tilting the t-case would create more problems for my front driveshaft since the pinion output on the front axle is already angled upwards after the installation of the lift.

 

Yes, I swaped in a difereent trans and t case. I had a t 15/dana 20 and now i have a t 18/scout dana 300. T.his combo is longer so it allowed me to use the original driveshaft. the extra length offset the extra height. I also dropped the trans/transfer case about 1" with homemade spacers between skidplate and frame.

 

Yeah I just did 2 inch yj springs with soa, we set pinion angles correctly and dropped the transfer case 1inch(homemade as well) with Tom woods driveshafts and cv rear. I also have a driveline noise but I think mine is something in the transfer case because I have a little play in the output shaft. Have not heard of cardan shafts but Tom woods was a great company they were extremely nice and I had my front and rear shafts built and on my door step in 5 days and the cost for front and rear with new straps and u joints with cv rear and new t case spline adapter for the cv was 640 and the also grinded on the cv housing for extra clearance.
Here is the photo of the rear against my old rear

 

The single u-joint shown in your pic is a single cardan joint. The part with two u-joints is a double cardan joint. Contrary to popular misuse of the term, it is not a cv or constant velocity joint.

 

Which I think you need anyway because it looks to me like your drive shaft is about to pull apart at the slip.
This is the exact problem my “too hard core for me” brother in law had with his Wrangler, too much lift for his driveline. His rear drive shaft u-joints were at about the same angle, with the slip yoke just about to pull out of the transfer case, and his rig would roll down the road just fine but as soon as he took it off road and that rear axle drooped it’d put the u-joint yokes in a bind and break something. His step father and I both tried to tell him that’s where the problem was but he was “too hard core” to listen to us.