Rumble/Vibration when letting off the throttle at high speed (2 Viewers)

[SamMontana]

1994 80. Stock grocery getter with normally worn tires. No lockers. Recently had front bearings greased and replaced. Went on a hunting trip in which I had to use low gear quite a bit and fjord a river twice a day for 7 days (pushing water with bumper) had to go through a nasty muddy swamp hole a few times at a high velocity to get through. Since this little trip a month ago now when I get up around 60 on the highway and let off the gas it sounds like I am driving over a highway rumble strip. Only does it at that higher speed. Doesn't matter if I am in 4th or 3rd gear so doesn't appear to be tranny related. I had fluids swapped in everything btw in case water got in anywhere. Ideas where to start looking for the problem or what the most likely culprit would be? Could it be as simple as a wheel weight being thrown off?

 

[Gabriel 71]

I would check u joints,I had a truck sound like that few years back.replaced the u joints in the drive shaft and wow what a difference

 

[inkpot]

If you don't feel wear in the joints, you can grease them one at a time to see which one changes/improves with grease.

 

[Tools R Us]

Check the knuckle moly grease level, if low/empty will make the noise you describe.

 

[bajaphile]

Seems like this question is asked weekly... common problem with these trucks it seems. Rear u-joint needing grease seems to "fix" the sound/rumble.

 

[SamMontana]

So...upon further investigation...if I was a betting man I would say that my rearmost universal could use replacing. However as I scoot under the front of the Yoda I notice she is bleeding profusely from where the driveshaft goes into the front bell. I assume a seal has gone out recently. As I grab that driveshaft there is a lot of play as I twist it...should there be play? The rear has none.

 

[inkpot]

Sounds like you have wasted the pinion seal and lost the preload on the pinion bearings. Problem seems to be getting more common as all these rigs age.

 

[SamMontana]

So how many millions of dollars will this fix cost me?

 

[SamMontana]

Keep in mind I own a hammer and a chainsaw...I will be paying someone to do this, lol.

 

[SamMontana]

So I brought the 94 into my favorite mechanic (who is not a fan of cruisers, lol) and he found the universals to be good. He also found that all the bolts holding the front shaft were loose which is what my vibration was...to the point the shaft was ready to fall out. How did I not see that? He tightened her back up to spec and found there is a bit of play back and forth. He said I will need the bearings replaced as well as the seal on the pinion. He estimates $150 if he can just get away with replacing the front reachable bearings but over $1000 if he has to tear apart and replace the lower. The old girl has 216k miles. Opinions on what to do? Replace and run till the next catastrophe or is it time to say goodbye to the old girl and sell. I am torn.