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4'' Lift Excessive Pinion Angle?

MAX89K5

MAX89K5

1/2 ton status
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Hey guys I just finished up a 4" lift on my 89 K5. Tuff Country EZ rides in front with a DIY4x Shackle flip in the rear with 4.5'' shackles. I have a vibration from around 20-60mph under throttle and off throttle. Above 60 it is minimal.

I have measured my angles and have 2* at T-case output and 14* at pinion. Overall driveshaft angle is 17*. The K5 has a 700R4/241 with a 10 bolt rear end and a stock single joint rear shaft. I have spoken with Kert and we both think 14* pinion angle is high.

Has anyone else run into this problem with the shackle flip or am I the only one? Since there is no way I can shim my diff enough to cancel vibes, what is my next best option? I do not have the resources to move perches and shock mounts. I'm guessing CV shaft.... I was hoping I wouldn't have to worry about vibration issues since I only went with a 4''. Thanks for any input!
 
You wouldn't have to move the shock mounts, just rotate the spring perches, but since that option is out.

Without the CV shaft, I believe you want the angle of the pinion and tcase to be parallel (ideally). DIY4x sells 4, 6, 8, and 10*. You could try shimming the pinion with the 8 or 10 and that may keep you from having to get a CV driveshaft.

With the CV driveshaft, you are going to want your pinion pointed directly at the tcase output (or 2-3 degrees below).

Here is a some good info

http://www.4xshaft.com

look under the technical information and then geometry 101
 
Thanks, I have read throught that information recently. Should I try a 10* shim before deciding on a new shaft? Kert calculated a 17* shim for my application which is of course out of the question. This truck will see minimal off road use so is there an option out there for a stock cv shaft that would fit the blazer? Would I still have to shim my diff if I was to use a cv shaft, or is it a fix all? The diff is pointing at the t case more or less.
 
I don't know about stock CV drivelines that might fit.

You shouldn't have to shim the axle if your driveline is pointed at the tcase output and you decide to go CV. A local driveline shop can build a CV driveshaft. Ballpark $500 +/-

Can you post a picture?
 
This should give you an idea of overall angle, is the diff pointing at t-case enough for a cv shaft to operate well without shimming? :dunno:




driveline_zps5fdd8899.jpg.html
 
No, that didn't show up right. When you are on the photo on photobucket, there are 4 links on the right side of it, simply click once in the 4th link, it should say "copied" when you do that. Then come into ck5 and just paste it.

From everything you are saying, there are probably two things at play here making the vibs. One, is what has already been said. Ideally with a normal 2 joint shaft (like what you have) you want the output of the tcase and the pinion of the axle to be parallel with each other. This is how each joint cancels each other out to make it smooth. With a CV shaft, you want the pinion of the axle to be pointed directly at the output of the tcase. So you are most likely getting vibs from that.

Also, what a lot of people don't think about, is that even with just a 4" lift, you most likely have pulled that slip yoke out far enough that you don't have enough spline engagement and are getting vibs too. Your best bet is to try and take your shaft down to a shop and get a CV with a longer slip put on it. Or places like Tom Woods or High angle can build you one for pretty close to the same price. I was getting a lot of vibs before getting a CV the right length, now it is like butter :D

P.S. Sorry for the long reply
 
The slip is engaged plenty, there is approximately 2" out of the extension housing. With the pinion angle I have currently, do y'all think I could get by with a CV shaft without shimming?
 
i think a you have a good setup for the CV, it will work without extra shims.

Are you sure the vibration is from the driveshaft?
 
Nearly positive. Brand new u joints, all new spring bushings, new tires. Felt for grinding in axle bearings and they are smooth as well as the pinion bearing. I don't know what else it could be. I wouldn't mind paying for a new shaft as long as I don't have to shim the diff, seems like a band aid to me and when I'm spending 400-500 on a shaft, I want it right.
uhynarat.jpg
Here's the finished product besides wheels and tires, now if I can get it driving as well as it looks!
 
Thanks man she's getting there! Do you have any recommendations as to where I should have my cv shaft made? My wallet can only handle 4-500, I'm a broke ass college student lmao
 
Have them build a complete new shaft or just modify original with a double cardan joint? This blazer will see minimal off road use and there is no need for a 1 ton driveshaft like most are running.
 
a double cardan shaft is the best way to fix the problem. If you had that type of shaft your angles are pretty much perfect.

Hopefully I have a driveshaft for you. Got quite a few at the shop.
 
72blazerguy said:
You will get the best deal if you can find a local driveline shop...
Click to expand...

This is true sometimes. When I went to get a CV shaft made with a flange to bolt to my SYE 241, I contacted a couple local shops, and after taxes, it was more expensive then just ordering up a shaft from Tom Woods (even after shipping).

Yeah, a CV shaft would be perfect for you with those angles. And it does look like you have enough spline engagement too, so once you get a CV shaft on there, it should be really smooth!! :waytogo:
 
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