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Pinion angle with new 8 inch lift?

D

Don Crawford

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Just installed a new 8 inch lift on my 84 k5. At about 50 mpH with deceleration I get a quick grind noise from rear end I think it had to do with my pinion angle with new lift. I first had the stock shims that came on new 4 inch rear leafs with the fat part pointed towards the rear this is when I first noticed the sound, and the drive shaft was almost straight on with rear diff. So I loosened u bolts and tapped the shims to fat towards the front and sound was a little better but still there. Any help would be much appreciated. Thank you.
 
might want to start with the type of driveshaft your using, that will dictate proper pinion angle (see below). Also, is it a slip yoke? With that much lift you may need to extend your driveshaft length.

cv_angle.gif

2joint_angle.gif
 
It is a slip yoke with the conventional 2 joint drive shaft. I guess my question is how to know if I should go with a cv style double cardan driveshaft or look at other options
 
Roger that, I was kinda going that direction was just looking at them online, I would like to know now what orientation for the shims on the leafs for proper alignment with a new cv style driveshaft
 
basically, you point the dif at the trans output.. down a degree or 2... usually the best way to achieve this is weld new spring perches to your axle.. as opposed to trying to shim it..


conceivable to get a standard shaft joint setup smooth with 8", but tough with the short wheelbase.. get one of these


6A511_AS02



and check your current front and rear angles to see how far off they are from each other..... you generally always want the axle pinion pointing down a degree or 2 in CV, or non, setups, to account for axle wrap...
 
Thank you for the info and the angles I would like to check would be in relation to the output shaft on the transfer case and the pinion yoke?
 
yup.. the lower diagram pictured above for your current , 2 joint setup... odds are, they aren't super close to even..
 
I dont think anyone makes shims large enough to rotate the axle up to that extent from stock perches. Even if they did i wouldnt run them. I just started with new perches and welded them on. Its pretty easy to do if you have a welder.
 
Don Crawford said:
Roger that, I was kinda going that direction was just looking at them online
Click to expand...

The problem you are going to run into with the 8" lift is the operating angle of the u-joints. They are made for a very small range of operating angle, which is why even at 4" of lift it becomes a potential issue. The short wheelbase of the K5 exacerbates the problem.

IMO probably zero reason to even bother checking the angles, you need a CV.

Bunch of reading here, but to make informed decisions one has to understand things: http://www.pirate4x4.com/tech/billavista/PR-shaft/index2.html

Of all the diagrams, this is one of the ones I like: http://www.pirate4x4.com/tech/billavista/PR-shaft/joint life vs angle.jpg The difference in life (stress) on a joint from a 2-4* angle is significant. Over 20% reduction in life for a 2* increase in operating angle.

Here is a video that clearly shows why you don't mess with the factory operating angles (dropping t-case, shimming spring perches, etc) UNLESS you have a CV joint

You won't believe how often this comes up, and how common misinformation is on this.
 
what's that cwazy big size that one dude was putting together in here? like 1680 or some chit.... :yikes: :haha:


just trying to save the guy some coin temporarily if need be.. sure, you'll be at the "beat the snot out of me till I'm screaming" limit of a 1310, but it HAS been done...
 
ryoken said:
what's that cwazy big size that one dude was putting together in here? like 1680 or some chit.... :yikes: :haha:


just trying to save the guy some coin temporarily if need be.. sure, you'll be at the "beat the snot out of me till I'm screaming" limit of a 1310, but it HAS been done...
Click to expand...

Or shatter the tailhousing, losing the driveshaft at 65MPH, etc.
 
I assume :rolleyes: means "yup, aluminum slip yoke tailhousings/transfercases DO come apart with improper lifts/bad u-joint angles/improper driveshaft lengths".

Also, nowhere do I see that driveshaft length was taken into account with the lift.
 
nope, you can assume it means "flaming intraweb nuns will come flying out of it"...

is it the best way, no.. have people gotten away with it, yup... worth dropping a $9 angle finder on it to see how far off it is currently...
 
All have been very helpful and the education off this site is great, lastly what is the actual noise at my higher speeds, is it the ring and pinion or a driveshaft sound. And should I be driving it, it only happens in 3rd gear and on acceleration and deceleration. Appreciate the schooling guys.
 
I would say noise, if I'm traveling at 55 and just let off of gas it happens just a quick noise almost a grind kinda as it goes to coast then if I give it gas again it will do it for a second as it speeds up, but goes away in both directions pretty quickly
 
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