Vibration at 65

[spanky55amg]

Since I purchased this truck, it has had a vibration. Now, when it had the 22's, it happened at like 73 or 75 mph. I thought maybe it is was the big dumb wheels. I since put on a set of stockers with a 235/75 and it still has a vibration but now at 65.

Ok, I know this is now rotational to RPM. It happens at about 1800 rpm and is especially worse in OD. I felt something like this before and it was a poly trans mount in my 4th gen f body. So I replace the $11 transmission mount. That took away about 50% of vibration.

Now, I know these trucks are old and Im not expecting a smooth ride, but this pretty bad. The only other thing I could thing of is the engine mounts. Do y'all think that engine mounts would do that? I mean, it only starts to happen around 63-64 mph but its like a light switch that turns on at 65 mpg or ~ 1800 rpm in OD.

What do you think?

 

[1987 GMC Jimmy]

I’ve gotta ask the standard questions here. I’m going to assume that your tire balance was okay since the issue persisted on two different sets of wheels and tires. I don’t think steering and suspension would necessarily behave this way, but I’d still check for play if you haven’t already in your ball joints, tie rod ends, Pitman and idler arms just to be safe. Anything that clunks or has play when you move the wheel side to side or up and down is worth investigating. Not to mention shocks. U joints, too. Those could definitely start vibrating like that, but you’d have heard them by now if that was likely. What about torque converter shudder when it locks up? I’ve battled this issue, and it’s pretty bad, but it’ll usually kick on between 35-65 depending on if my speed is increasing marginally in the city or if I’m getting on the interstate and going through the gears quickly. If it does it the same in third gear as it would in overdrive, I wouldn’t suspect the TC so much.

 

[spanky55amg]

Well, I didnt think TC as it doesnt happen at lower speeds and it does happen at higher speeds without lock up.

I see where you are going with suspension, but that shouldnt change with speed and RPM.

 

[spanky55amg]

And the only time I have felt engine mounts were Mercedes Benz hydraulic filled mounts, and that happened at idle. So thats why I was curious about solid rubber mounts. Though, youd thunk I would have felt them other times.

And I did consider u-joints... buttttttttt once again, never felt a bad u-joint like this....

Though I did have a caliper once on a Caviler that did about same thing. I wondered if one of my calipers were sticking a little. Though I feel no brake issues.

 

[TIE_Fightertk06]

Check the drive line...
What is the truck? Out of balance driveshaft(s), carrier bearing, decoupling slip joints, maybe u joints?

Sagging leaf springs can throw off geometry and cause a vibration too.

 

[1987 GMC Jimmy]

A stuck caliper or bad brake hose should cause a pull in the direction opposite to the failure. Are your rotors within spec thickness and not warped?

 

[Honky Kong jr]

Umm bent wheel, broken cord in the tire, thrown wheel weight

 

[spanky55amg]

Check the drive line...
What is the truck? Out of balance driveshaft(s), carrier bearing, decoupling slip joints, maybe u joints?

Sagging leaf springs can throw off geometry and cause a vibration too.

84 C10, no carrier, slip joint is go (trust me, had other issues with it leaking and fixed it). So it could be driveshaft, as someone has replaced the TH350 for a 700r4. And it could be u-joint also...

Leaf springs seem to be good.

 

[spanky55amg]

Umm bent wheel, broken cord in the tire, thrown wheel weight

But I have a different set of wheels and brand new tires. But they are cheap ones.

And this feels like a butt in the seat vibration, not a front end or front tire vibration.

 

[Honky Kong jr]

But I have a different set of wheels and brand new tires. But they are cheap ones.

And this feels like a butt in the seat vibration, not a front end or front tire vibration.

Is the seat loose or just the nut behind the wheel maybe.

 

[spanky55amg]

A stuck caliper or bad brake hose should cause a pull in the direction opposite to the failure. Are your rotors within spec thickness and not warped?

That is a good question. I dont feel a warp (and I have in other cars before), that being said, it does pull like holy hell to a side stomping on the brakes. (that doesnt happen often as Im not riding anyones ass in this truck. haha. )

 

[spanky55amg]

Is the seat loose or just the nut behind the wheel maybe.

Actually... both. Seat is loose, thank you PO. And I am chaotic neutral.

That said, you can see and feel it in the steering wheel and the rest of the cab.

 

[Honky Kong jr]

That is a good question. I dont feel a warp (and I have in other cars before), that being said, it does pull like holy hell to a side stomping on the brakes. (that doesnt happen often as Im not riding anyones ass in this truck. haha. )

Sounds like calipers and hoses are in your near future.

 

[1987 GMC Jimmy]

That is a good question. I dont feel a warp (and I have in other cars before), that being said, it does pull like holy hell to a side stomping on the brakes. (that doesnt happen often as Im not riding anyones ass in this truck. haha. )

Yikes, I’d get that taken care of ASAP. I chugged along for two years with my brake pull, and a nasty panic brake made me take it home and take it apart so that wouldn’t happen anymore. It was a right pull, and it ended up being that the driver side hose was bad. I ended up replacing both hoses and calipers. The other hose looked worse, and both of my calipers were super rusty.

 

[1987 GMC Jimmy]

Hey, have you posted any pictures with the new wheels? That profile has been the same since you joined if memory serves.