1985 C10 Rear Differential Vibration.

[brlarl]

OK Guys I need some help!!! I have a vibration on the rear of my truck when I drive between 60 to 65 MPH anything before or after I don't feel it.  This is what I've done so far........At first I thought it was my wheels....I run a set of 15x10 Centerline Champ 500 on the rear and I had them checked and one of them was slightly out of round and I had it fixed.  Put them back on and the same issue.  I pulled the cover and visually checked the internals and all is well no wear on the gears and no shaving within the housing.  I resealed the diff. and added new lube and additive so that was fine.   I jacked up the rear of the truck...cranked her up and put her in gear to look at the wheels spin.....now this is where it gets weird, the wheels actually go up and down enough to where I could believe this is my cause of the vibration.  (Oh, I forgot to mention that I changed out the ujoints and driveshaft to a reworked unit.) Now I took the wheels off and did the samething, drums are moving in the same manner as the wheels leading me to believe my issue has nothing to do with the wheels.  Now this happens on both sides (the drums going up and down).  Keep in mind the truck sat on jack stands for about 2-3 years with the wheels on it.....What is the chance that my axles are bent?  Can the drums be bad to where they cause this issue?  I do not recall whether I had this vibration before the truck sat on the jack stands.  I remember that when I had the truck emission inspected and they ran it on the machine I noticed that back end of the truck was going up and down pretty bad.  Any input or suggestions would be great.

[Blue 82]

could be you pinion angle is out a few degrees

Got any fat friends?

Load 4 of em in the bed and run it up to speed and see if the vibration still exists

[Lt.Del]

I would believe your axle shafts may be bent. 
Was a load of gravel or sand or dirt or shingles or something dropped on the bed from a fork lift or bucket prior to the truck sitting for so long? 

Is there any play (up and down, in and out) on the shafts which means bad bearings?


YOu can remove the c clip  and pin in the differentials and remove the shafts and inspect them.

[brlarl]

No play at all coming from the axles other then the norm to remove the c-clips and no noises at all.  Logically speaking if the drums slide on the studs and the drums move in an out of round fashion then chances are the axle shafts are bent, correct?  Can the drums themselves be causing my issues?  Can you also tell me what causes a 700R4 not to go into drive as soon as you shift it first thing in the morning? Does the 700R4 have a pressure vent on it to be able to release fluid if over filled?  Thanks Guys

[Captkaos]

Check your U-joints.  If the axles were bent it would be doing this All the time.

[brlarl]

The u-joints have been replaced and driveshaft have been replaced with a rebalanced unit.  Correct the drums are spinning out of round (so they look).  My question again is if the axles are bent will this cause the drums to look as though they are spinning out of round?  With the wheel and tire mounted they bot look like they are out of round, spinning in the same exact manner.  Can the drums cause this or is there a possibility that the axles are bent?  The vibration is constant.  Other then taking the axles out and taking them to an axle shop is there a way to check the trueness of the axle at minimal cost?

[Captkaos]

In the beginning you said it only vibrates between 60-65, now you are saying it is constant.  Which one is it, as I am confused. 
Looking at the drums with the tire off isn't going to show you anything, ( your eyes will concentrate on hard edges for reference) due to the fact that it is spinning on the end of a shaft there will be the appearance that they are not true. 

If your axle was bent, you would know it as the rearend would jump off the ground.

[brlarl]

Constant meaning that the vibration is always there at the same speed. (sorry for the confusion).  I had the truck emissions tested a few weeks back and noticed while they ran it on the dyno the rear of the truck was bobbing up and down constantly of course worse the faster it was ran.  You wrote:  "Looking at the drums with the tire off isn't going to show you anything, ( your eyes will concentrate on hard edges for reference) due to the fact that it is spinning on the end of a shaft there will be the appearance that they are not true."  Why would the wheels move in the exact same fashion as the drums an I know the wheels are true? 

[Captkaos]

If the axle was bent, it would be constant from the time the tires started rolling until you came to a stop and with speed it would become more and more violent.

have you tried putting the front tires on the rear?  bouncing around sounds like the tires are out of balance, did you rebalance them with the wheels

Do you have a tach?  Find out if it is RPM specific, take the truck to the same rpm speed in 2nd gear.

Letting a truck sit any amount of time will not bend axles.

[VileZambonie]

Did you replace the driveshaft because of this vibration? Or are you just saying it's a new driveshaft? Is it a one piece driveshaft? The outside of the drum will not be true. It's the inside that needs to be true. I doubt you have bent axles from what you are describing. You can install a few hose clamps on the driveshaft to act as weight to see if it changes the vibration. How's your trans mount?