Rear End Vibe

[78Bu88SS]

Well I narrowed down a vibration at speeds over 55+ in m '87 1/2 ton 4wd. It seems to be coming from the back of the truck somewhere as I can duplicate it on jackstands.

So far, I have swapped the rear rims/tires, had a entirely new driveshaft made and balanced (old one was bent), and I just pulled the rear apart to check it over. All the bearings look fine. It seemed both axle shafts had some excessive runnout so I replaced those as well. I'd have to say after all that there is little to no change in th vibration.

What else can it be? The only things I havent physically touched is the actual rear end housing and tailshaft bushing in the transfer case. I'm going to swap pinion yokes today just to rule it out.

Any thoughts? I'm getting tired of putting money into it w/o any changes.

Truck is stock height with an extra leaf out back.

 

[Goob]

Brake drums?

 

[monzaz]

transmission mount...check that too. Since the drive shaft was bent it could have tortured the rubber mount to Hell. Do check the drums...They are a ballanced item.

Bearings in the rear MAY look fine BUT you will never be able to tell .... You should remove the bearing caps and yank the carrier out by pulling on the ring gear outward. IF you can pull it out by hand YOUR BERINGS ARE WARN OUT! This means at higher engine speeds your carrier will start to float and will resinate vibration. This may or may not AGAIN be your vibration problem...BUT I am trying to help. Weak shock making the tire bounce???? Another thought.... Please keep us informed cause alot of people seems to have these vibration problems . Good luck and i wish you the best. Vibrations are almost as bad as electrical problems.

Jim

 

[388bu]

Did the vibration change at all when you replaced the driveshaft? And how confident are you in the shop that made your driveshaft?

Reason I ask is I was trying to nail down a vibration for the longest time. Turns out the original guy I used to get my shafts from just made a crappy driveshaft. Went with a new guy and havent had issues since.

 

[monzaz]

WOW...That would SUCK! Trying to track a problem that you tought you fixed....NOT GOOD.

Yes did the vibration change at all after ANY of the changes...You always need to feel for that. Worse or better. Jim


DO only one change at a time too. Jim

 

[LS6 Tommy]

If the drive shaft is bent, I'll bet the output bushing on the trannie's a goner, too. That caused a Lulu of a vibration in my 87 Monte...

Tommy

 

[78Bu88SS]

transmission mount...check that too. Since the drive shaft was bent it could have tortured the rubber mount to ####. Do check the drums...They are a ballanced item.

Bearings in the rear MAY look fine BUT you will never be able to tell .... You should remove the bearing caps and yank the carrier out by pulling on the ring gear outward. IF you can pull it out by hand YOUR BERINGS ARE WARN OUT! This means at higher engine speeds your carrier will start to float and will resinate vibration. This may or may not AGAIN be your vibration problem...BUT I am trying to help. Weak shock making the tire bounce???? Another thought.... Please keep us informed cause alot of people seems to have these vibration problems . Good luck and i wish you the best. Vibrations are almost as bad as electrical problems.

Jim

transmission mount looks ok but I may pick up a new one. I actually replaced the drums as the old ones looked awful. The vibe is just about gone but I have a little nagging shimmy I need to get rid of. Could be mostly tire related.

Now when I pulled the carrier out, it did infact come out by hand. Backlash was a tad on the loose side at 0.012". Looked like original GM shims but you never know. I can replace the bearings, not a big deal. Would I have a problem tightening up the backlash to say 0.008 or should I leave it be?

The tailshaft bushing actually looked great. Running at speed, the driveshaft did not vibrate.

The driveshaft came out real nice and did infact help it some. I trust the maker of the driveshaft, he actually takes pride in his work.

I think I'll look into the transmount and carrier bearings, other then that I'm gonna say its tire related as the ones on there gotta be 7-8yrs old at least.

 

[Goob]

Run it on the stands without the wheels. Process of elimination.

 

[monzaz]

If you think or know the rear has never been f-ed with then the carrier bearings are getting pretty sloppy. When you put new ones on the shims will be tough to get in. They will need to be tapped into each side. It will not be fun SO please do not blame me for this if you change them...lol. I do this all the time and even for me I get angry at some builds...lol. Jim

Change one thing at a time again I can not stress enough...... This way you know what the cause was. or multiple causes were. Jim

 

[Damon]

I know you had the wheels and tires balanced, but did you have them check the runout (i.e. are they really ROUND)? You can balance a bent wheel or egged-out tire, but that doesn't mean it'll run smooth.

Had a highway shimmy in my '05 Magnum (company car) that couldn't be balanced out by the crappy shops our leasing company sanctions. I took it to my GOOD shop and in 5 minutes they diagnosed TWO bent wheels. TWO! I got them replaced and it was smooth as a baby's butt up to...... well, the speed limit, obviously. They were probably damaged during transportation by the factory since the problem had existed since the day I drove it off the lot with 2 miles on the clicker.