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

[mr98z71]

I have recently re geared my rear and front diffs to 4.88's and put a 6" lift kit on my truck. I am very happy on how they turned out (patterns, backlash and preloads were to spec). Now that winter hit, I have been using 4x4 quite a bit. I noticed this very weird hum and vibration which is only there while in 4x4 going above 45 mph and when I let off the throttle. Any suggestions on what this may be? I sure hope it's only a u-joint but I'm starting to lean more towards the front diff since it is only apparent while letting off the gas. If anybody has any suggestions on what it may be or any tips, that would be greatly appreciated!

 

[IOWNJUNK]

Before I jumped to front diff, I would suspect u-joints, then maybe cv shafts.

 

[mr98z71]

My Angles are very steep (Bars are cranked), that could be a possibility I guess?

 

[IOWNJUNK]

Most certainly can!

 

[Hezsus]

check your u-joints for any play.
Is the noise coming from front or rear of truck?
your front cv's are always spinning and usually make more noise when turning so I would rule them out. along with anything else from the diff beyond.
are your tires severely wore on the back and new on the front or vice versa?
check the colour of your gear oil (front and back)
hum in 4low at all?

 

[oohunter04oo]

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!

 

[98slv]

I wouldn't go that fast in 4w4 unless your truck is equipped with auto trac. If it has auto trac every lift manufacture specifically states a new driveshaft is required.



To answer your question a little better though, I would suspect a u-joint. Their number one call sign is noise after letting off the gas and cruising. Another thing is you are probably listening much more to how the truck sounds now, since you just did a bunch of work to it. Atleast thats the way I am. I'd check your joints for any of them being loose and if they are ok, I'd sit tight for a bit and see how it does in a couple months.

 

[98_k1500]

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.

 

[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.

 

[mr98z71]

I wouldn't go that fast in 4w4 unless your truck is equipped with auto trac. If it has auto trac every lift manufacture specifically states a new driveshaft is required.



To answer your question a little better though, I would suspect a u-joint. Their number one call sign is noise after letting off the gas and cruising. Another thing is you are probably listening much more to how the truck sounds now, since you just did a bunch of work to it. Atleast thats the way I am. I'd check your joints for any of them being loose and if they are ok, I'd sit tight for a bit and see how it does in a couple months.

Yeah, good point about listening for noises since I changed a bunch of stuff. I am going to try and change the U-joints this weekend and see if it helps. While I was driving yesterday, I took a turn then heard a huge "Bang" in my front end, I pulled over; Cv shaft bolts all fell out and the last 2 sheared, Took out my sway bar link. I took 2 bolts off the passenger side CV ( they were all there ), drove home then installed 12 brand new bolts (6 per shaft). What I don't get is why the drivers side bolts all fell out but not the passenger side, they were all torqued to spec (58 Ft. LBs). Anyways, the same sound is present after bolting the CV back so I will be changing the Ujoints.