Does a 2" rear shackle drop require a pinion angle correction? Ever since I did it I have a vibration. at around 40mph it feels like one of the wheels is out of round. I don't think it's the pinion angle, but I'm not sure. anyone else have this? Thanks

 

For me to says yes, could be a lie. It really depends on where the pinion angle was set at before you dropped it with the 2" shackles.
I know how to measure this stuff! I'm still trying to correct the ****!
A pinion angle dial gauge goes a long way in helping you find out if your pinion angle if off or not.
When you lowered it with the 2" shckles you put your pinion angle down a little. Meaning it went a little more negative, but not meaning it is still not a positive pinion angle.
This stuff can get confusing, but after more than a week of hands on and reading a lot of useful info, I know what I need to do.
My pinion angle went to a -0.5* when I did just the 2" shackles. That threw it way off. I thought a set of 2* shims (fat side facing back) would fix it, but was wrong. For me to get my pinion angle perfect, I would need a 5* shim, but that's not counting what axle twist will do. A 4* or 4.5* shim will get my pinion angle back to where it needs to be. A 4.5* shim would be perfect, but there's no such thing. I wish there was.
I can help you if your willing to be helped.
A $11 dollar Craftsman angle finder. It reads in 1* increments. Though you can still see half degrees. Don't get the cheap one that only reads in 5* increments. I know personally, it sucks!
The only other money spent will be for shims, but they are cheap too.
Lets first start at me knowing if you have a 1-piece DS or 2-piece DS?

Jim

 

To clear up you counting out the wheel being out-of-round, if this began right after you lowered the rear of the truck with the shackles, then it's the driveline angle, not the wheels or a balancing issue.

Jim

 

Thanks Jim, I have a 2 piece d/s. I have angle finders that will do 1* or less. Comparators that will cut 1* into 100. But What am I comparing? is it the incoming driveshaft angle compared to the front vertical face of the rear Diff? What do I want it to be? I'll get some shims and cut them to what ever angle you want if you need some. I have access to some goooood Machinery. Thanks Again

 

Wow, you sound like the man to know!
Well here it is, first make sure truck is setting on somewhat level ground (it really isn't too much of a factor) Though everytime the truck is moved, all angles will have to be remeasured. Make sure the suspension is settled and if possible, place a full tank of fuel in truck.
Get under truck and measure the propeller shaft angle coming out of the carrier bearing (if there is enough shaft coming through this will be easy, but if not, make sure that particualar propeller shaft's u-joing is facing down. Then measure off of that flat sureface.) . It should be somewhere between 3-5* "negative" if your truck is on level ground.
Then measure the axle's pinion angle. This can be tricky. You need to measure at the yoke u-joing coming out of the diff. Some find it really easy if you remove the driveshaft.
Your pinion angle should be at a positve angle of degree.
Example: propeller shaft coming out of carrier bearing measures 4* negative.
You will then need to set the pinion angle to 3.5 or 4* positive.
This makes them equal, but at the same time opposite. Basically your making two parallel lines.
Depending on what you do with your truck will depend on where you will want to set the pinion angle at. You want to set the initial pinion angle a bit lower than the propeeler shaft because of acceleration torque on the differential. The torque will want to twist the diff in an upward manner. Therefor, by setting the axle pinion angle to 3 to 3.5 *, it will not go beyond 4* under accelleration.
Once these are set, you need to measure your U-joint angles where the front DS and rear driveshaft connect and the u-joint angle where the final DS section and the diff connect. The maximum working angle a u-joint is allowed is 4* and the minimum allowed is 1*. I'd keep them around 2-3* if possible.
The only way to change these will be with a carrier bearing relocator backet or some shim changes to the diff.
The tranny output shaft angle and the propeller shaft angle coming out the carrier bearing are supposed to be within a 1/2* of each other.
Confussing?? I was at first.
If you PM me your e-mail address, I can also forward you a 6 page sheet of info on setting your driveline angle properly.
Let me know.

Jim

 

Quick question. Does it feel like a vibration or more of a small bouce? I've had 3 trucks, all different, all with suspension mods(up & down), all with different rim & tire packages, and all 3 had a slight bouce at about 42 mph. It's the weirdest thing. No one ever pinpointed the cause, and yes the pinion angles were correct. It might just be something you'll have to live with. Best of luck.

 

8MC, Yes, Thats it to the T. I'm going to check all my angles so I can rule that out. I know it's not tire balance. I have had 3 sets of tires on 2 sets of rims. It's starting to **** me off. My wife's like, wtf is that, It wouldn't do that if you didn't screw with it, and I'm like stf-up and ride in your own car, and she's like why's your truck so loud, it wasn't like that new, and I said new it wouldn't do this, I stomped it, pitched it sideways comin up my long *** driveway, off into the grass, slid sideways up to the front door, she was white as hell, eyes like golf *****, all she could say was MFer. Hah



Life is NOW, Live It!!!!!

 

So will adding a 2" shackle drop combined with a 2" lift block removal tend to make this pinion angle problem worse? I have an ecsb and was interested as well.

 

well i havnt even put my 2" shackle kit and my damn truck does that. EXACTLY at 42 mph just like 8MC... weird

 

All I can say is this, if a specific truck drove smooth and vibration free prior to lowering or raising it, and the results give a vibration or abnormal ride, then the driveline is out of specs.
I'll tell you this, GM is by far not perfect in any means when these trucks are assembled at the plants. The driveline angles could be off from the beginning.
Even Belltech said, when you see the drive axle off further to one side or the other, it is effecting the driveline angles. Meaning the tranny, drive shaft, and rear axle are not lined up in a straight line.
Belltech told me they have seen new trucks with the axle off center up to 1-1/2 inches. They offer an adjustable kit to fix these issues.
If there is a slight vibration at a certain speed, I would put the balancing concerns to the side and focus on measuring your driveline angles to make sure there where they need to be.

Jim