92 4x4 rumble strip type noise

[Levi1a]

A little background info on the truck. Getrag is freshly rebuilt, new clutch, frontend has been completely gone through, new rear brakes and hub seals so the rear wheel bearings were checked at that time, rear carrier had spun a bearing but the carrier was pulled re shimmed to proper backlash and a new bearing installed with the carrier staked and locktite sleeve retainer used. Basically I have been through this truck top to bottom. The noise just started and it started after the addition of one of 2 things, but could just be coincidence. I just put on a set of treadwright guard dogs, and also just put new bushings in the leaf springs and threw in an add a leaf in all four packs. I ended up with about 1.5 lift total. Anyway the noise always seems to come in 5 gear running at about 1900 rpm around 65mph. Once the noise starts if I let off the throttle, or accelerate more the noise will stop , but if I maintain that speed, rpm , and throttle position the noise continues and it sounds just like you are hitting the rumble strip. When the noise started I checked for play in the u joints , but they feel tight. The only thing I found was a slop in the rear output of the 205, which I corrected with a new bearing, but still have the noise. I considered driveline angles after the add a leaf causing problems but I cant imagine the add a leaf being enough where that could be an issue. I also pulled the cover on the rear diff. to double check my carrier bearing fix and make sure it had held and it has so I am at a loss. I am thinking ujoints, but I greased them recently and there is 0 play in them. Any ideas???? Thanks in advance for any replies!!

 

[RWherley]

I think you have the right idea with the drive line angles a change in ride hight will do that but not at all speeds, when I change my truck from a "D" to "W" I had the same issue in 4th gear around 35 to 40mph until I got the drive shaft carrier spaced down right.

 

[cerberusiam]

Can you replicate the noise in any other gear at the same rpm?

Torsional harmonics can be hard to trace and at 1900 rpms you are right there where it could be fading in an out.

Since you did lift the truck a bit the ujoints may have been worn in for the angle they were at and now are causing a harmonic. Might have to chnage u-joints to see if that helps.

 

[Levi1a]

Yeah gonna throw a set of U joints at the rig and see what happens. Why not everything else is new... Will report back after I get them installed.

 

[DVolk]

Could be slip yoke slop in the dive line you might need to do a re balance

 

[Levi1a]

Well crawled under the truck the other day and it looked like the trans mount bushings were a little crappy so today I threw a set of bushings at it and it actually seemed to help with the noise. Gonna give it a few days of run time before I call it fixed but so far so good. May go ahead and throw a set of U joints at it anyway here in the next week or so.

 

[S.Morris]

Measure the angle of the ujoints at each end . The angle of the front and rear joint on same shaft should be running at same angle. The slip of the driveshaft could also be worn and not allowing unbinded slip of the joint as it moves because of change in driveshaft running length.