Driveshaft vibration after RC 2.5 inch suspension

[cowboytwang]

Got this 95 YJ about a year ago, and it had the original factory shocks & springs. They were completely waisted, so I finally bought the Rough Country 2.5 inch lift suspension kit. After installing the leaf springs and shocks, I was getting a slight vibration in the drive shaft at around 30-40 mph, that wasn’t there on the stock suspension. So I did the 1.5 inch transfer case drop, now I have an even worse vibration between 35 and 45 mph.
So I’m thinking the shim on the RC Rear springs is to drastic and the pinon angle is to high, so doing the transfer case drop made it even worse.
I’m not sure what came on the RC, I haven’t been able to get an answer from them, but saw on a review someone mentioned it’s an 8° shim angle. Anyone have any experience with this? What degree shim will fix it?

 

[ytradio]

Got this 95 YJ about a year ago, and it had the original factory shocks & springs. They were completely waisted, so I finally bought the Rough Country 2.5 inch lift suspension kit. After installing the leaf springs and shocks, I was getting a slight vibration in the drive shaft at around 30-40 mph, that wasn’t there on the stock suspension. So I did the 1.5 inch transfer case drop, now I have an even worse vibration between 35 and 45 mph.
So I’m thinking the shim on the RC Rear springs is to drastic and the pinon angle is to high, so doing the transfer case drop made it even worse.
I’m not sure what came on the RC, I haven’t been able to get an answer from them, but saw on a review someone mentioned it’s an 8° shim angle. Anyone have any experience with this? What degree shim will fix it?View attachment 124099

The pinion is pointing up too high as it sits in photo. Go to Tom Woods drive shaft web sight, and it tells how to measure drive line angles and has a calculator that will give you the correct shim for your situation.

 

[machoheadgames]

Rough Country supplies a shim on the leaf packs that is more geared towards SYE and double cardan shaft usage in my experience. My 2.5" springs from years ago (purchased January 2014) came with a 6 degree shim and for a 4.0 5 speed that worked out perfectly for an SYE and DC shaft setup.

The stock shaft definitely doesn't work well with this setup, on mine with no t-case drop, I could only go like 40 mph and it was so bad that it was unbearable. I drove a few days like that while I waited for the t-case drop to come in. The RC t-case drop was the same 1.5" one you got, and it actually made mine drivable, I took it on a few 1-2 hour drives and it was mostly fine. A bit buzzy but much better than without the drop. It was weird though, when I installed the drop, I still had a weird buzz and then while driving a day or so later there was something like a pop and then all of a sudden things were fine. So I must have something not settled properly during the t-case drop install or something. No idea.

I still didn't love that setup with the t-case drop so I went the SYE route a few months later.

Looking at yours, your pinion definitely needs to be angled much lower. The stock pinion in my experience is about 10 degrees upwards. Remove the shims and see what happens. With the t-case drop, it might be about perfect. In stock form, the angles are already a bit weird and unconventional because the t-case angles down only 5 degrees and the axle points up 10 degrees. I am pretty sure that is why my now stock Jeep is still vibrating at highway speeds with a stock style shaft. I am considering even going back to an SYE on this stock setup, but I really don't want to.

It would be good to measure the t-case slope and pinion angle to see where things officially are right now also.

Also, watch out for your RC leaf spring bushings. They are utter crap and will fall apart in about a year or two.

 

[cowboytwang]

Rough Country supplies a shim on the leaf packs that is more geared towards SYE and double cardan shaft usage in my experience. My 2.5" springs from years ago (purchased January 2014) came with a 6 degree shim and for a 4.0 5 speed that worked out perfectly for an SYE and DC shaft setup.

The stock shaft definitely doesn't work well with this setup, on mine with no t-case drop, I could only go like 40 mph and it was so bad that it was unbearable. I drove a few days like that while I waited for the t-case drop to come in. The RC t-case drop was the same 1.5" one you got, and it actually made mine drivable, I took it on a few 1-2 hour drives and it was mostly fine. A bit buzzy but much better than without the drop. It was weird though, when I installed the drop, I still had a weird buzz and then while driving a day or so later there was something like a pop and then all of a sudden things were fine. So I must have something not settled properly during the t-case drop install or something. No idea.

I still didn't love that setup with the t-case drop so I went the SYE route a few months later.

Looking at yours, your pinion definitely needs to be angled much lower. The stock pinion in my experience is about 10 degrees upwards. Remove the shims and see what happens. With the t-case drop, it might be about perfect. In stock form, the angles are already a bit weird and unconventional because the t-case angles down only 5 degrees and the axle points up 10 degrees. I am pretty sure that is why my now stock Jeep is still vibrating at highway speeds with a stock style shaft. I am considering even going back to an SYE on this stock setup, but I really don't want to.

It would be good to measure the t-case slope and pinion angle to see where things officially are right now also.

Also, watch out for your RC leaf spring bushings. They are utter crap and will fall apart in about a year or two.

Thank you.. I ended up taking those shims off and put a set of 2 degree shims on, from Amazon overnight for $20, thinking I would also delete the t-case drop. Got the new shims in and took it around the block, and it’s perfect. No vibration at any speed, accelerating or coasting. It’s actually the best it’s ever driven since I’ve had it. So guess I’ll leave the transfer case drop on it, since it all seems to be working.
Sure wish Rough Country would give a little more detail in their description and instructions.