New Driveshaft and pinion angle (check to see if my math is correct)

[nbrown2500]

This is my first post and I need some advice. I have a 1990 full size Blazer with a 6” Pro Comp Lift that the PO installed. It has a 241c T Case and a 3/4 ton SF 14 bolt rear. The PO installed a small lowing kit for the T Case. I was getting a growling noise coming from under the blazer from the middle and rear. I thought I needed to replace the U-joints so I did. While I had the driveshaft off I noticed that most of the U-joint caps were spinning in the eyes of the yokes. So I figured something wasn’t right. I took some measurements of the driveshaft, pinion, and T Case slops. Could you guys give these diagrams a look over to see if my thought process is correct. After seeing that my driveshaft is toast I’m thinking about getting a CV Driveshaft with a slip yoke. I don’t really want to spend the extra money on an SYE kit. This rig is only going to be used for camping and hunting. I am not cheap, it is just that I have had it almost a year and things that I thought were OK have turned out not to be. I don’t want to spend money on things I don’t need. The rear blocks have a 5 degree slope built into them. I think I need a pair of 5 degree shims to bring the pinion up more in line with the proposed CV Driveshaft I want. Please look at the following diagrams.



Diagram 1 is the current configuration. There is a 5.5 degree difference in the working angles of the U-joints. I think this is why I have the noise and the yoke eyes are out of round and the U-joint caps spin in the yokes.



Diagram 2 shows the approximate geometry of the proposed CV Driveshaft shown by the pink line. With my current axle location I need to rotate the axle up 7 degrees to be in-line with the proposed driveshaft. I need to account for axle wrap and from what I have read that is 2 degrees. So I think I need a pair of 5 degree shims.



Diagram 3 shows the proposed axle location and the CV joint with a working angle of 12.9 degrees. Is that good or bad and have I covered all my bases.

 

[jekquistk5]

Shimming or rewelding your perches are going to be your best bet. The general rule of thumb is the rear axle yoke, and the tcase output match. So if the output of the Tcase is at 5 degrees down, you match the axle yoke to be 5 degrees up. If it has a block in the back, this is a good chance to get a shackle flip, as it will most likely correct your pinion angle.

 

[rebelgregory]

Shimming or rewelding your perches are going to be your best bet. The general rule of thumb is the rear axle yoke, and the tcase output match. So if the output of the Tcase is at 5 degrees down, you match the axle yoke to be 5 degrees up. If it has a block in the back, this is a good chance to get a shackle flip, as it will most likely correct your pinion angle.

True for single cardan, but I believe the OP was asking about CV shaft. OP, your measurements are as good as they can be on paper. You may have some final shimming after you install the CV shaft. That said, ditto on getting a shackle flip, and ditto on re-welding perches for the best solution, but shims would be ok.

If it was me - skip the SYE, get CV, and shackle flip, ditch the blocks, then either cut and weld the spring perches or do a final shim. In my case, with a 4" lift, CV shaft, and a shackle flip, the angles came out perfect.

 

[nbrown2500]

This is my first lifted truck and my first 4x4 so I really don't know what I want. I intend the blazer to be my hunting and camping rig. I would also like to make it my second DD if needed. It also needs to tow firewood. Its not going to be heavily wheeled. Its just nice to have 4 wheel drive when your on the Oregon Coast. I'm tired of getting stuck in my 2wd Dodge. That being said I want it to be mechanically sound and safe. The rear lift consists of a 4" block and an add a leaf. The 4" block is sloped 5*, would it be safe to add a shim to the leaf pack with the block? Another option I'm looking at is going with 6" lift springs to replace the blocks and just shim to the right angle. Really don't want to have to grind and beat rivets out for the shackle flip. I also don't want to have to weld the perches. I guess I'm just looking for the easiest and safest method to fix the problem.

 

[skunked]

The easiest solution would be a block with the correct slope built in along with the CV shaft.

If it was my truck I would do the shackle flip and reweld perches as mentioned above, that's the correct way IMO.

 

[nbrown2500]

The easiest solution would be a block with the correct slope built in along with the CV shaft.

If it was my truck I would do the shackle flip and reweld perches as mentioned above, that's the correct way IMO.

What parts would I need to do a shackle flip to get a 6" lift?

 

[K85 Octane]

Can you run the block backwards to get the angle right? Or even run a block with no degree. Sorry, Im not very good at diagrams, more hands on.

If you aren't apposed to spending a little more, call up Tuff Country and get a complete 4" spring lift and tell them you plan to run a CV. It will ride better than a 6" spring. If you need a little more, EZinch will give you more plus you can have a degree cut into those. My fronts are 5*. All bolt in, no ruvets or welding, and no Tcase drop

 

[skunked]

What parts would I need to do a shackle flip to get a 6" lift?

if you have an add-a-leaf in there you should be able to get away with the flip and a EZ-Inch. Add a shim to straighten out your pinion angle and you should be good.

 

[nbrown2500]

My friend has a guy that can reweld the perches and set the pinion angle. For now I'm going to leave the blocks and have the perches welded. When funds permit I'm going to get a set of BDS 6" rear springs. With the new perch angles and springs all I should have to do is shim to the right angle. Don't have the money for everything right now and I just want to drive it. Was thinking about ordering the cv driveshaft from Tom woods driveshaft. Does he do good work?

 

[jekquistk5]

My friend has a guy that can reweld the perches and set the pinion angle. For now I'm going to leave the blocks and have the perches welded. When funds permit I'm going to get a set of BDS 6" rear springs. With the new perch angles and springs all I should have to do is shim to the right angle. Don't have the money for everything right now and I just want to drive it. Was thinking about ordering the cv driveshaft from Tom woods driveshaft. Does he do good work?

If you get the same length springs and don't flip you should t have to shim if you get the perches re welded. Ideally the axle will be riding in the same place if it's a 6" lift spring. Or a stock spring with a block.
My Tom woods shaft has taken a beating. No problems

 

[K85 Octane]

Yeah, my TW shafts are doing fine.
If you set your perches to work with your degree'd blocks, the perches will be wrong when the new springs come in. Probably a considerable amount of shimming would be necessary.

 

[nbrown2500]

Yeah, my TW shafts are doing fine.
If you set your perches to work with your degree'd blocks, the perches will be wrong when the new springs come in. Probably a considerable amount of shimming would be necessary.

That is true. The blocks have a 5* slope. I need another 5* to set the pinion the the correct angle for the cv driveshaft. I can set the perches to correct the pinion angle with the blocks installed. Later when I get the springs and remove the blocks I should only have to shim the axle 5 or so degrees to compensate for the removeal of the blocks. That shouldn't be that bad should it? I could buy everything now but I don't want to spend a grand at this time. I have other projects I'd like to do on the blazer.

 

[K85 Octane]

I suppose not, I've got 5* cut on my ZeroRate for my fronts.

 

[nbrown2500]

Well just wanted to fill you guys in. Getting back a good tax refund and have some money to spend on the Blazer. I'm going to order an SYE kit with a 1350 flange and a local shop is going to make me up a new drive shaft. I also found a guy through a friend that will cut and re weld the perches. I wanted to order a set of tuff country 6" lift springs but the wife said no, so the lift blocks are going to have to work for now. Do any of you guys have any used 6" rear lift springs?

 

[blazinzuk]

If I could find some 63s and other crap would stop breaking lol.

I will keep you in mind