Vibration between 25-30 mph

I just acquired a 1993 diesel crew cab dually. The truck has been lowered static 5/7. Got it that way. My question is that I get a lot of vibration between 25-30 mph but then goes away either when let off accelerator or I increase speeds.

Just got the truck last night drove it home 300 miles and haven't got under it yet.

I've been googling and what I've found is either carrier bearing or driveline related.

I'm not a complete noob, i owned a 93 ext cab chevy lowered 4/6 and I have a bagged 72 c-10. Just noob when it comes to duallies.

Any and all help/suggestions is greatly appreciated.

DZL1.

Something with the drive shafts. Bad bearing, U-Joint or out of balance problem. As its a 93 its may be time to change the U-Joints and drive shaft Bearings anyway,

i agree^^

Thanks for the replies. How can I tell if I need either of these or both? I will change both, I'm just curious.

DZL1.

To check the u joints the easiest way is put tranny in neutral then try to turn the driveshaft by hand if u can twist it back and forth a ujoint is bad keep twistin back and forth and look at them the one that has play is bad , for the carrier just try and move the driveshaft up and down if it moves a lot its also bad

if everything checks out, check the driveshaft angles.

Thanks for the info guys! I will check both.

DZL1.

This ^^^



A 2 piece shaft with carrier bearing of course changes this a little bit. Typically when you drop something with a 2 piece shaft you correct the angle by installing a carrier bearing spacer and a transmission mount spacer, along with correct shimming of the rear axle in its saddles.

The problem occurs because the driveline gets straightened out when you lower. Gotta restore the angle. When the driveline is straight, u-joints don't work correctly; they're not pivoting on their axis. Extreme wear happens pretty quickly...

Richard

Thats very good info. I will check that as well. Thanks for all the suggestions guys, I really appreciate it!

DZL1.

Well I changed the u joint and im glad i did. One of the end caps was broken/missing pieces. Carrier bearing is perfect, looks like it was recently replaced. No more vibration...woohoo! Thanks to everybody for all your info and help.

DZL1.