Riddle me this

[Lumpy Grits]

I did lower the skid plate but it made it worse. I got longer bolts to make sure I had plenty of threads. The tires have been balance recently as well but thisbisna totally different feel from tires. I may have to give up and get professional help, and an expert mechanics too.

Just because they were recently balanced-Doesn't mean you have not lost a balance weight. BTDT
Are you absolutely positive, the d'shaft is balanced and phased correctly?
How much rotational & side to side play do you have in the slip-spline?
LG

 

[b3uhbp]

Well, now you know what does not work. So, you might as well put that skid plate back up. Other possibilities could be rotating the pinion angle, although there might be an issue with the motor mounts as this could affect the driveline angle. Searching the internet for "Jeep CJ driveline angle" or something similar might provide some good info.

Edit: "Tom Woods Driveline 101" provides some good info, but like I said it does get complicated.

Thanks man. I did put the skid plate back up and I will definitely take a look at the site. So far my research indicates the angles should be the same which makes me wonder why diffs are pointed up toward the t-fer case on lifted jeeps, which insures that the angles will be different since the t-fer case will always be close to horizontal. ? ? ?

 

[Lumpy Grits]

Yes-VERY GOOD info.
Tom Wood's Custom Drive Shafts - Driveline 101

OP-You have never answered the question about the condition of your engine mounts. OR, how old they are.

LG

 

[b3uhbp]

Yes-VERY GOOD info.
Tom Wood's Custom Drive Shafts - Driveline 101

OP-You have never answered the question about the condition of your engine mounts. OR, how old they are.

LG

Well, the engine mounts LOOK pretty good. A few small cracks. Not sure of the age but I think they only have approx 45k on them. Haven't ruled them out but the drive line is a better possibility.

 

[Lumpy Grits]

If the engine mounts have cracked and split. You may well have metal on metal contact inside of them, that will transmit 'vibes' from the engine. BTDT
LG

 

[Torxhead]

Thanks man. I did put the skid plate back up and I will definitely take a look at the site. So far my research indicates the angles should be the same which makes me wonder why diffs are pointed up toward the t-fer case on lifted jeeps, which insures that the angles will be different since the t-fer case will always be close to horizontal. ? ? ?

Those steep pinion angles you see on lifted Jeeps have a lot more lift than you do plus a constant velocity u-joint and have the pinion angle the same as the driveshaft does. The Transfer Case drops down about five or so degrees. I am thinking that you might have to increase the pinion angle and check the play in those driveshaft u-joints. Check the amount of lift your engine has when you rev it up while under the hood.

 

[b3uhbp]

Those steep pinion angles you see on lifted Jeeps have a lot more lift than you do plus a constant velocity u-joint and have the pinion angle the same as the driveshaft does. The Transfer Case drops down about five or so degrees. I am thinking that you might have to increase the pinion angle and check the play in those driveshaft u-joints. Check the amount of lift your engine has when you rev it up while under the hood.

I read the article. Good stuff and double cardon/CV style u-joints explains a lot for big lifts. I didn't learn anything new with regard to standard two u-joint shafts but it prompted me to go measure the yoke angle on my t-fer case and diff. Well guess what? They are about 16 to 18 degrees apart from each other. They should be the same. When the lift was installed they put what looks like 4 degree shims on the rear axle to aim the diff toward the t-fer case. That's where almost all of the deviation is. I'm thinking that if I remove the shims the differential center line will return to stock and be nearly horizontal. That should fix it. Anything wrong with my logic? My jeep only has a 2.5" lift so the shaft angle is only 17* or 8.5* angles at the joints, if I did the math right. What do u think?

 

[Lumpy Grits]

Please confirm that the shim's thick side is towards the middle of the jeep on both axles

LG

 

[b3uhbp]

How much in degrees did you rotate the pinions up?
Please confirm that the shim's thick side is towards the middle of the jeep on both axles

LG

The shaft was already toast. The PO or the lift installer shimed the axle to rotate the pinion up. That's precisely the problem in my opinion. The angle at the diff and t-fer case should be the same.

 

[Torxhead]

It might even be too much pinion angle. As I recall when I installed my 2.5" lift, I did not install those shims and did fine until I changed to 4" springs. Then I got vibration! So maybe removing those springs might be worth a try. What size tires are you using?
edit#1: Wow! there are 7 members viewing this thread!

 

[Lumpy Grits]

I have seen more than one installer put the shims in the wrong way.
Just strange, that all this started after a t'mount change. Can you post a picture of your tranny mount set up, as it is now?
LG

 

[b3uhbp]

I have seen more than one installer put the shims in the wrong way.
Just strange, that all this started after a t'mount change. Can you post a picture of your tranny mount set up, as it is now?
LG

Yes, the tranny mount is the only change and that really messes with my head too because it wouldn't have changed the angle of the t-fer case even a degree. That said, the new tranny mount could have just manifested a problem already present. I still don't understand why lift installers add a shim at all on a modest lift. Why not leave the diff horizontal so the center lines of the diff and t-fer case will be parallel?

 

[b3uhbp]

It might even be too much pinion angle. As I recall when I installed my 2.5" lift, I did not install those shims and did fine until I changed to 4" springs. Then I got vibration! So maybe removing those springs might be worth a try. What size tires are you using?
edit#1: Wow! there are 7 members viewing this thread!

I think you meant remove the shims which I plan to do. My tires are 32/11.5.

 

[b3uhbp]

Please confirm that the shim's thick side is towards the middle of the jeep on both axles

LG

They are.

 

[b3uhbp]

Just because they were recently balanced-Doesn't mean you have not lost a balance weight. BTDT
Are you absolutely positive, the d'shaft is balanced and phased correctly?
How much rotational & side to side play do you have in the slip-spline?
LG

Brand new shaft built by a very reputable company. New yokes, new spline, new u-joints. That's all I know.

 

[Lumpy Grits]

At this point-I also say pull the shims.
LG

 

[Posi]

I have seen more than one installer put the shims in the wrong way.

You mean like the shims that were installed by Kong 4x4 in Phoenix Az on my 42 MB before I purchased it........

DS rear tire, before


After

 

[Lumpy Grits]

"Kong" somedangbody really named their business that.
Guess they lived up to the name..........
LG

 

[Posi]

Kong's 4x4 Off Road Center | Phoenix, AZ 85021 | DexKnows.com

back on topic.....

 

[JR74CJ5]

Went through all this before OP - numerous times because I kept changing things...

1st, yes changing the mounts probably just let you feel a problem that was already occuring before. Not 100% without feeling it myself but driveline vibrations are pretty noticable when you've got one...

With the tire size and lift you are running, you shouldn't "need" a Couble Cardon style driveshaft, but angles are funny, and with my 33" tires and
2-1/2" lift and the amount I flex when wheeling I figured I did...

What I ended up doing is bringing my jeep to the local driveshaft builder. They crawled under, measured angles, shims I had, and sold me 2 new shims that corrected my angles. They knew their stuff. THey were also who I bought my shaft from, and I liked that better than ordering online even with the reputation TOm Woods has - which is great.

If you're battling with the math, it will help. I measured, read, thought I understood, and tried myself multiple times before and got close but just that little bit screwed me up. Although I did get the CV style driveshaft so completly changed my pinon angles including removing and rewelding my spring perches etc after I got it right with their help... I'm pretty sharp with math too...

Just a thought, I love turning my own wrench, but sometimes the pros can teach you a few things to really make your life easy. I'd have bought the shims from them either way as they were good quality shims, and I was not ready to re-weld the perches yet, so their knowledge was just a added bonus.