Rear pinion angle, CV drive shaft length questions

[mvez]

I know some of these questions have been asked in other threads and other forums. I wanted to bring up my specific vehicle situation and see what the forum pros think. I'll do my best to not be too scatterbrained.

Shortly after I purchased my 95 YJ, manual, 4.0L, enough started going wrong with the transmission that I needed to have it rebuilt. one of the other things going on was that when letting off the clutch going to first from a stop, you would hear/feel stuff shacking underneath you and then see the shifter wiggly left to right until a little speed is picked up and clutch full engaged. It was bad. Here is a link to another forum thread that describes almost the exact same symptoms. I really felt that the transmission rebuild and SYE with CV DS would have fixed it.

https://Jeep Forum/threads/yj-shakes-when-pulling-out-of-1st-gear.1381940/

Let me explain what was on the jeep, what was removed, and what was added to combat the driveline issues I have been having. Then ill share my thoughts on what Id like to try, with some questions I could use help on.

At the time of purchase:

• Driveline all stock.
• Suspension appears to be a 4.5" lift kit. 33"x12.5" tires, this includes a ~1.5" T-case drop and extended shackles (I believe they are 6.5" bushing center to center) I do not know the brand because the PO painted over just about EVERYTHING with black paint under the vehicle. Lucky me now gets paint chips in the face everytime I'm underneath. There is no body lift.
• Track bars were still installed using provided brackets from lift kit.

Over the past year, the following has been done regarding the suspension and driveline. Mainly due to transmission failure and the vibrations I was feeling.

• new 33" tires.
• transmission rebuild by a jeep specialty shop. While he was doing this I also had them install an SYE and CV driveshaft. The T-case drop was not removed
• Engine and transmission mounts have been replaced
• I've recently removed both track bars while getting these measurements.

After the SYE and new driveshaft, the shaking of the shift lever going into first is still there. It's not as aggressive but still aggressive unless you REALLYY let off the clutch slow. slow to get honked at when the light turns green. You also hear the exhaust clinking on the rear shackle since the exhaust hangers are a little loose. But I am assuming the shaking is coming from the rear, causing what i have been describing. I have not had a chance to visually see what happens.

Okay so here are some pictures of my current setup. The rear end is still on jack stands as I'd like to have this sorted by this weekend if possible. I have not driven the jeep yet with the track bars off and Im really curious to see the chiropractor(my jeep) is not as rough on the road anymore.
I was told the pinon angle relative to the axle was not perfect but good enough. I'm not convinced and want more opinions.
It visually looks like the rear pinon is angled UP more than the driveshaft is. I through a digital angle finder on it to confirm. about 3* degrees. Can someone confirm i took these in the right spot? I'll retake if needed but visually you can see the difference, What should the correct angle be?

I feel like this would be a good place to start to help fix that vibration. I'm not convinced it cannot be fixed.

Here are my thoughts on having to tackle the angle change. before buying shims or shortening shackles to adjust rear pinion, I'd like to remove the T-case drop. I have an SYE, theoretically it should not be needed and this would bring the driveshaft angle UP and MAYBE pit it in line with the rear pinion. This brings up a question regarding the drive shaft. The CV driveshaft was ordered by the jeep shop to fit the current lift, SYE, and T-case drop combination. If I remove the T-case drop, will this extend the CV driveshaft too much? How do I know if my current driveshaft will still work?

I am starting here because id like to get rid of the t-case drop anyway. I will consider shorter shackles and shims if necessary but I don't want to waste money on this if I don't have to since I'm likely to completely replace ALL the old lift kit with a newer and better one. This was installed over 11 years ago. It still seems very solid, but maybe toooo solid.

I know it's not a car, it's a jeep. But this jeep could be smoother.

Thanks for any help that can be provided. I can get more photos as well if needed.

 

[machoheadgames]

Your pinion angle is too high for sure. Delete the tcase drop and reevaluate, it may work out just right. Otherwise, the axle needs to be about 3 degrees lower than the driveshaft so that the pinion can rise while driving under power.

It is not standard to keep the tcase drop, that should have been removed with the sye and double cardan swap, or at least usually it is. If you had extremely tall lift then it could help but usually anything 5-6" or less you're good without it on an SYE.

 

[mvez]

Your pinion angle is too high for sure. Delete the tcase drop and reevaluate, it may work out just right. Otherwise, the axle needs to be about 3 degrees lower than the driveshaft so that the pinion can rise while driving under power.

It is not standard to keep the tcase drop, that should have been removed with the sye and double cardan swap, or at least usually it is. If you had extremely tall lift then it could help but usually anything 5-6" or less you're good without it on an SYE.

Thanks. I was thinking the same thing with the tcase drop. The shop that did the transmission work and SYE said he thought we shouldnt mess with it. I'm starting to think because I asked after it was all assembled, that they just didnt want to put it back on the lift.

I'll remove the tcase drop and respond back with the result. based on the pictures do you think the driveshaft will still be long enough after? how will I know?

 

[machoheadgames]

Thanks. I was thinking the same thing with the tcase drop. The shop that did the transmission work and SYE said he thought we shouldnt mess with it. I'm starting to think because I asked after it was all assembled, that they just didnt want to put it back on the lift.

I'll remove the tcase drop and respond back with the result. based on the pictures do you think the driveshaft will still be long enough after? how will I know?

Hard to tell for the driveshaft length part as I don't know how much length you have left. usually the splines are showing and a blue section indicates where your length should be. I doubt the length change will really be that drastic though. If you change the short leg of a triangle, the hypotenuse does not shrink much relatively.

 

[mvez]

Tcase drop removed. Def effected the driveshaft angle more than I expected. I think the driveshaft itself still has splay left in it but I'll lift the frame next to test that.

I took measurements of the pinion and DS angle. I'm not sure it's the best spot to do it but maybe one of y'all can advise on that. My angle finder is now showing the pinion angle to be about 5-6 degrees lower than the DS, to but please let me know if I could be measuring this in a better place.
Anyway, So im now in the opposite situation than original post. Is this too much angle? I haven't drove the jeep yet but What issues could I run into when driving it? If it's too much would new axle shims be the best fix?
I've attached pictures

 

[machoheadgames]

Tcase drop removed. Def effected the driveshaft angle more than I expected. I think the driveshaft itself still has splay left in it but I'll lift the frame next to test that.

I took measurements of the pinion and DS angle. I'm not sure it's the best spot to do it but maybe one of y'all can advise on that. My angle finder is now showing the pinion angle to be about 5-6 degrees lower than the DS, to but please let me know if I could be measuring this in a better place.
Anyway, So im now in the opposite situation than original post. Is this too much angle? I haven't drove the jeep yet but What issues could I run into when driving it? If it's too much would new axle shims be the best fix?
I've attached pictures

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Your angle looks pretty good eyeballing it but that can be deceiving.

Your measurement spot on the driveshaft seems fine although you might want to move it a few inches over to the tube rather than the cap. At the axle, put it on the backside of the pumpkin, up against one of the cast circles on either side of
The diff cover. That is for sure a perpendicular surface from the pinion so it would give you the angle perfectly. It may or may not be the same angle as where you’re measuring it on the snout.

If you truly are 5-6° low, I’d figure out what pinion shims you have and get ones that are 1-2° thicker. But wait until you figure out the angles before doing that.

I’m surprised your tcase drop caused a change of 9° difference. That is surprising and I don’t think mine made that much difference but it’s also been a while so maybe I just forgot.

 

[machoheadgames]

You would probably be better off going back to stock shackles and installing a 1-1.5” body lift. That would get you back to a rough country 2.5-3” suspension lift. Rough country supplies those 6° shims (I can see them on your springs in one pic) and those are perfect for the 2.5-3” springs. That would solve the problem and then the body lift would solve the clearance for 33’s.

 

[mvez]

You would probably be better off going back to stock shackles and installing a 1-1.5” body lift. That would get you back to a rough country 2.5-3” suspension lift. Rough country supplies those 6° shims (I can see them on your springs in one pic) and those are perfect for the 2.5-3” springs. That would solve the problem and then the body lift would solve the clearance for 33’s.

How can you tell they are 2.5"-3" springs?
also I'm not a huge fan of the body lift look but not a hard pass. I was thinking about changing the springs and shocks out for new ones anyway. If i went with a 4" new lift this should come with the correct shims right?

 

[machoheadgames]

How can you tell they are 2.5"-3" springs?
also I'm not a huge fan of the body lift look but not a hard pass. I was thinking about changing the springs and shocks out for new ones anyway. If i went with a 4" new lift this should come with the correct shims right?

They look like typical rough country springs. Rough country 2.5” and 4” springs measure basically the same height oddly enough, I never have figured out why but they do. My 2.5” and my buddy’s 4” both measured about 3” and they both came with 6° shims. The 4.5” X series lift is basically the same thing but with 1.25” shackles.

They do have different part numbers for their 2.5” and 4” springs but I don’t know what the differences are since they end up sitting right at the same and come with the same shims.

4” lift is not a bad idea though there aren’t a bunch of great options on the market. I like the 2.5” old man emu stuff and when I wanted 33’s, the plan was the 1.25” body lift I installed to take care of it. I did that for a while but reverted on the 33’s idea so I removed the body lift and sold it. 1.25” did not really look bad at all to me. The benefit is you can do things like a tummy tuck and motor mount lift to add more clearance.