Lift kit frustration........need some advice

[tiger9297]

Have a '90 K5. Just installed 3" TC front springs and 4" blocks. Now I have 2 vibration problems.

1) At very slow speeds 10-20 mph I get a "shake" (not so much a high frequency vibration). It feels like when you go slow in a truck with VERY aggressive knobby tires. It does this when you accelerate and decelerate.

2) I get a high frequency vibration that is present at higher speeds. The funny thing is that if I take my foot off the accelerator it will stop. Press the gas again and there it is?????? This "vibration" resonates throughout the truck.

So far I have changed both U-joints on rear driveshaft, and installed new front brakes (one member told me could be a brake problem). I also have had new tires (only 3,000 miles on them) REbalanced. Nothing has made any change at all.

Questions:

1) Could this be a driveline angle problem? If so, should I just have a longer driveshaft made?

2) I was told yesterday to shim the rear end with angled shims to rotate it so it's facing up towards the transfer case which would reduce the angles. However, I have never seen any shims like this. Would this work, and if so where do I buy them? Also, I would rather not go the route of dropping the transfer case.

3) Since this problem seems to stop when I take my foot off the gas does that eliminate a driveline angle problem seeing as how everything is still turning even though I'm essentially coasting?

4) This truck has 256,000 miles on original engine and tranny. I don't want to overlook the fact that it could be something engine or tranny related. Could this be it???

5) Some have said it could be axle wrap. I am not really familiar with what this feels like but it seems from what I have heard the this is present during hard acceleration. Am I correct on this? If so I just don't think this is my problem considering what I've stated above. The "shaking" is present during acceleration AND deceleration, and it does it during very slow acceleration.

I have tried to be as descriptive as possible. If I need to provide any other information please let me know. I am ready to get my truck RIGHT. I can't stand it when something is wrong with it. It is NO fun to drive right now. Thanks in advance for the help.

 

[divorced]

A starting point would be to get a magnetic angle finder (about $7 at HomeDepot) and check your u-joint angles. They should be within 3 degrees of each other.

 

[bangedup]

Your blocks should have an angle on them make sure it is in the correct direction to rotate our axle housing up. I had to drop the T case down ½ an inch to fully remove my vibrations. I simply used the bolt spacers on the cross member support and moved them down between the frame and member. This works ok but you now snag everything that’s on the trail. The only way to fully resolve this is to rotate your rear spring perches.

 

[blackblazer717]

dido check the pinion angle and than as a last resort lower case, its going to happen eventually. and i had the same problem in my k-5 it shook only on the gas, dropped case and it was gone.!
LUKE

 

[tiger9297]

Ok. I understand that I can drop the rear of the transfer case and decrease the rear driveline angle, BUT if I were to get a longer driveshaft wouldn't this do the same thing?

 

[divorced]

A longer driveshaft will do little to change the u-joint angle. The reason the t-case drop sometimes works is becasue the rear end pinion points more "staight" at the t-case after a lift, and by dropping the t-case you will take angle "out" of the t-case end joint to make it straighter like the axle end. Look at the angle of your u-joints, and the t-case end should have the same angle that the axle end does, just opposite directions. If your rear end angle is closer to straight than the t-case end you can have vibrations.

I advise against lowering a t-case because it will increase the angle on an already "over angled" cv joint on your front shaft.


This link may help a bit http://www.4xshaft.com/index.html click on "tech info" then "geometry 101"









.

 

[tiger9297]

What should I do then.

A longer driveshaft will do little to change the u-joint angle. The reason the t-case drop sometimes works is becasue the rear end pinion points more "staight" at the t-case after a lift, and by dropping the t-case you will take angle "out" of the t-case end joint to make it straighter like the axle end. Look at the angle of your u-joints, and the t-case end should have the same angle that the axle end does, just opposite directions. If your rear end angle is closer to straight than the t-case end you can have vibrations.

I advise against lowering a t-case because it will increase the angle on an already "over angled" cv joint on your front shaft.



I see what you are saying and I really do not want to drop the T-case if I can keep from it. However, I don't know that I understand what you are advising me to do. If I'm correct, you are saying that dropping the T-case will help but you advise against it????? What should I do then??? I am open to anything.

 

[divorced]

*If* your rear u-joint angles are more than 3 degrees different I would fix the problem with a degree shim or by welding new spring perches on the axle at the correct angle. The shims are easier of course.

If I'm correct, you are saying that dropping the T-case will help but you advise against it?????

It will help with the rear drive shaft angle, but hurt the front drive shaft angle.

 

[divorced]

This pic may help describe what is meant by the "same" angles. It isn't exactly like yours, so just use it for reference. You can see how the u-joint on the left is operating with almost no angle at all beacause it comes straight out of the differential and points at the t-case, and the u-joint on the right has quite a bit of angle? These two need to be operating at the same angles so there is no vibrations. The red lines show the different angles, and they need to look the same instead of one straight and one bent.

 

[tiger9297]

My problem is basically the same as the picture above. The angle coming out of the rear end is minimal. However, the angle coming out of the T-case is much greater. So.... how do I correct that angle without dropping the T-case? A longer driveshaft would decrease it some, but would it be enough? Thanks again for all of the advice.

 

[kyser_soze]

Degree shims

Here you go
http://www.truckperformance.com/pro...sion+~~+Chassis/mode_change/sf4_Degree+Shims/

 

[divorced]

You can use some shims to turn the pinion down toward the ground. They are available in different degrees depending on how much correction you need. You would install the thick end toward the front of the vehicle to shim the pinion down. Don't buy aluminum shims because the can break easily, be sure to find steel shims. http://www.wfoconcepts.com/CustomParts/steelleaf.html

 

[smalltruckbigcid]

I'm doing almost the same thing in a couple of weeks and have a question or two. I'll be using Sky mfg shackle flips for the rear, is there a way to measure pinion angle before the lift to see what shim I might need. It would be handy to have it on hand when doing the work. I have a magnetic angle gauge already, so could I pull the driveshaft and measure the angle? TIA
George
Sorry for the hijack

 

[divorced]

I'm doing almost the same thing in a couple of weeks and have a question or two. I'll be using Sky mfg shackle flips for the rear, is there a way to measure pinion angle before the lift to see what shim I might need. It would be handy to have it on hand when doing the work. I have a magnetic angle gauge already, so could I pull the driveshaft and measure the angle? TIA
George
Sorry for the hijack

You can measure off of anything that is parallel to the pinion or 90 degrees off from the pinion. On my 14 bolt I just put the angle finder on the bolts that hold on the pinion housing next to the u-joint. You could also put it somewhere on the rear of the housing as long as it is 90 degrees off compared to the pinion. I don't know of a good way to pre-determine what shim you may need. Maybe someone else good make a guess?