Vibration While Accelerating

randynoguts · November 30, 2007

hello everyone. i got a '84 blazer a couple months ago. it has the 6.2 "j" code diesel. it had been sitting for a while when i got it. had to change a few seals and such that had either dried out or just because they were 23 years old i guess. i am having a vibration problem between 25mph and 45-50mph. only while acclerating and only in drive. it is smooth as heck while cruising at 65 or at 30. i looked back at other vibration posts and checked the things that were mentioned. found nothing wrong so far. what am i missing? what should i delve deaper into? if it was transmission related, would it not do it all the time while in gear? i can live with it, but i dont want to damage something else. now this vehicle is a ex military m1009. it is stripped of all interior sound deadining and carpets headliners , insulation etc... could this be a harmonic thing. i drove these in the airforce when they were new and dont remember having this happen so it cant be "normal" . just seems like an out of balance rotating object, but nothing is jumping out at me. any thoughts would be appreciated. randy

Wingnut · November 30, 2007

Every time I've had a very speed specific vibration like that, it's been the ujoints. Not saying that it couldn't be the transmission or something else...But ujoints are cheap and easy to replace.

Jacqson · December 3, 2007

Every time I've had a very speed specific vibration like that, it's been the ujoints. Not saying that it couldn't be the transmission or something else...But ujoints are cheap and easy to replace.

I have to agree with that, but I had a 1980 Pickup that was doing the same thing and it ended up being the rear end was toast. Funny thing was it only vibrated at certain speeds. It might be worth checking out.

Nytemare · December 3, 2007

Agreed. U-joints, or trans mount would be my first suspects.

If it were an out of balance rotating part I would figure it would vibrate all the time. This happens to you only under acceleration, Thats why I'm saying trans mount. Just grab the tail shaft or the drive shaft and shake the trans back and forth...if it has excessive movement, your mount is gone.

Also, drive around with your windows open and listen for a clunking sound during acceleration around the affected speeds.

randynoguts · December 4, 2007

thanks guys, will check the joints and mounts. as soon as the rain stops here in WA. so that would be about july5th. ha.

Nytemare · December 4, 2007

Tell me about it...I live in Victoria BC....

It's been rain or sloppy snow stright for the last couple weeks now. The sloppy snow isn't even good to have fun in.

It is sunny right now...for like the last hour....it will be rain again soon.

randynoguts · December 12, 2007

ok so heres the update. two differant places tell me its the harmonic balancer. that it has leaked some or all of its insides out. anyone ever have this happen? i mean i have owned 20+ vehicles in my 28 years of driving and i have never had a harmonic balancer die on me. now i could see it in a race application spinning so fast all the time but under normal use? although i guess if they did not fail they would not make replacemnets right? so if i do this, anyone suggest a brand? other than stock, the only one i can think of is fluidamper.

randynoguts · December 20, 2007

hello all, along with the vibration was a delayed shift between 2-3. never thought it could be related, had the shifting problem solved by replacing the vacuum pump and a switch. surprise, the vibration is 80% gone! WTF? . how in the world could this be related?

nhproxr · December 20, 2007

Harmonic balancers are a problem with 6.2s. Since these motors are externally balanced like a small block 400 it is important to have a good balancer on there. The stuff "leaking" out is the rubber sandwiched in there, must be dry rotted and chunking off.

Replace it asap. You could go with a fluidamper, but think they are like $500 for a 6.2.

randynoguts · December 21, 2007

thanks mike, i still plan on that but this vacuum pump and switch just set me back 600 clams. the dealer (thief) wants 300 for a balancer then 200 to put it on. i have seen some on the net for 70 but im too dang crippled up to do it myself anymore. so i will have to pay someone.

gmtech4 · December 24, 2007

Agreed. U-joints, or trans mount would be my first suspects.

If it were an out of balance rotating part I would figure it would vibrate all the time. This happens to you only under acceleration, Thats why I'm saying trans mount. Just grab the tail shaft or the drive shaft and shake the trans back and forth...if it has excessive movement, your mount is gone.

Also, drive around with your windows open and listen for a clunking sound during acceleration around the affected speeds.

saw the same complaint on another section of site,if the u-joint isn't fixed ,the vibration can and WILL break the t case adaptor,i know she's a old girl but fix it soon