4x4 Hum and Vibration at 45-50 mph and up

[mr98z71]

I checked my U joints, they don't have any play in them, They are probably the originals so I will be changing them this weekend for good measure. Tires are brand new and have been aligned, brand new gear oil. Only makes noise going 50 mph and higher in 4 hi, I can't say if it would in 4 low.

Check for wear in the splines on the front drive shaft. I have no idea why they wear out because they don't move in or out in normal use but i have seen several worn completely out and jumping rope.

Ok, I'll check that out while I'm Under there, thanks.

 

[mr98z71]

If it only makes the noise in 4wd then its something up front. if it does it all the time, its probably in the back. Im also going to have to request that you post pics of your truck… It looks bada$$ in your sig, need to see bigger pics of it!

Here's a couple pics, a lot changed since then (4 months lol) but here they are:

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Next to a stock Z71

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[SkyHighColorado]

I'm running 6" pro comp and 4:56 . To sure about your year or brand of lift, but my pro comp manual says if you get the noise and vibration you are experiencing to try flipping the front drive shaft 180* if the problem doesn't get better then you need a custom shaft made. I'll try and find the section for you.

 

[mr98z71]

Humm, that's interesting, I wonder how that would make a difference? Anyways, It's worth a shot, mines a 1998 with a 6'' RCX, The driveshaft angle is very slight, like 10-15 degrees downwards, that's it.

 

[SkyHighColorado]

Ok, it says "note: manually turn drive shaft and check the u-joints for binding. If u-joints do bind flip drive shaft 180 degrees with slip yoke now facing front of truck."

I guess it might be worth a try.

 

[mr98z71]

I'll give that a shot tomorrow, thanks!

 

[ShadowRejects]

Yea i would say its probably the driveshaft up front as well. could vibrate at high speeds. idk if mine is an autotrac or not but it fit fine with the lift kit, and sometimes i feel a very small vibration when im at high RPMS haulin @$$.

 

[SkyHighColorado]

Shadow...your not auto trac that's for newer trucks iirc correctly.
Found some more info in the pro comp manual.
"Front end noise and vibration may occur on '94-'95 vehicles equipped with new downsized spicer type u-unit front drive shafts and operated in 4wd on even surfaces such as pavement. It is recommend not to exceed 20 mph in these conditions or replace to a CV style (early model) front driveshaft may be required."

 

[mr98z71]

What I thought would be a 2h u-joint job ended up turning into a nightmare! I took off the cap straps at both the t-case and diff but could not compress the drive shaft for the life of me. I ended up cutting the u-joint at the diff to slip the driveshaft from underneath the truck. At the end of the day, I had the driveshaft in between my two oak trees, 2 chains and a load binder trying to pull the 2 halves apart, didn't work and I used lots of pb lol! Has anybody ran into the same situation that I am faced with?

 

[TylerZ281500]

Check for wear in the splines on the front drive shaft. I have no idea why they wear out because they don't move in or out in normal use but i have seen several worn completely out and jumping rope.

thats exactly why they wear out they dont move and GM didnt use glidecoat on them. they sit in whatever leaks in between them and rust and then get loose.

back to topic the hum is your gears the vibration is likeyl your driveshaft.