Have a problem on my 01 Alty and was wondering if anyone has experienced it themselves.

It is a bad vibration. Bad enough you can see (or hear things) shaking inside the cabin starting around 50, 55 mph. The odd thing is it only occurs under load and varies according to the load. Give it a little bit of gas, it shakes a little. Give it a lot of gas, it shakes a lot. But as soon as you left off the gas, it's gone. Completely.

It started right after I replaced a slew of parts, all new, all aftermarket, all in the same shared_session. All four struts, front strut mounts, front rotors and pads and the driveshafts (new aftermarket, not reman aftermarket). I did notice a slight vibration around 50 then but did not take it above those speeds before I did a second round of repairs (all new): all belts, both idler pulleys, passenger's top motor mount, plugs, air filter, oil change. Again I can't say for sure when the massive vibration started but there was some noticeable vibration there at least after the first round of repair.

I've had the wheels balanced, rotated several times, alignment done twice and it's still there. Before I did the first round of repairs there was no vibration at all. Not only is this really annoying, I'm afraid as bad as it shakes something it going to shake somethin loose. What has me perpelexed is why is it only under load?

One thing I did notice multiple times when I went on vacation in the mountains is that when I was going up a big banked curve (can't remember which way, possibly when the curve went to the right), even under load, the vibration lessened considerably.

Has anyone else experienced this? If so how did you resolve it?

Thanks!
Sg

 

check to make sure everything is tight but it sounds like engine mounts to me....

 

that's what I was say... since it is only under load, gotta be a mount

maybe you had some vibration after the first round due to things not being balanced. Then, the second round caused a whole new vibration. you had that mount replaced, Why? Maybe it isn't tight. I can't remember for sure, but don't you have to remove one of the mounts to replace the belts? maybe that one got damaged and or isn't tight...

 

Slow,

Yeah I made sure everything was tight. Both my friend and myself. Knock out the easy stuff first.

Empire,

Yes the passenger's top mount has to be removed to replace the pulleys and belts. I noticed a tear in the mount so I went ahead and replaced it. Made sure it was tight as it supports the engine. Good point on it being two separate vibrations. Hadn't thought about that.

One thing I forgot to mention (and updated original post): I did notice multiple times when I went on vacation in the mountains is that when I was going up a big banked curve (can't remember which way, possibly when the curve went to the right), even under load, the vibration lessened considerably.

Since you both have mentioned motor mounts I've been looking on other boards about the mounts and it doesn't seem like the other two aren't too difficult to replace. So maybe I'll do that just to eliminate that variable.

So trying to reason this through, why would bad engine mount(s) cause it to vibrate under load? Because they are no longer a solid connection like designed and the rubber in the mount is actually moving back and forth, allowing the engine and driveshafts to move more than they should?

 

simply put, yeah.
part of what the motor mount does is absorb vibration. Think of it kinda like a strut. when that strut goes bad, you feel a lot more vibrations from the road. It is the same vibrations that have always been there, but now there is nothing to dampen/absorb them. same basic idea with the motor mount.

being front wheel drive, when you turn, some of that force gets transferred from the axels up through the block and to the mounts. So if that mount was bad, that added amount of pressure would make the vibrations change.

now, of course, it could have nothing to do with the mounts. not being able to see, hear, or ride in the car, it is hard to tell. But typically, if the vibration goes up with increase in load, it would be mount related

 

Exactly what I would have said ^ It could be possible when you changed out that mount and if you lowered the engine on that side when replacing the mount or other parts it could have put more stress on the other mounts.. if that mount was bad the others could have been ripped and only cause it to rip more which could give you the vibration.. Id say before going and spending anymore money replacing parts that may not be needed. Take a day and check the mounts, pull them off and see which one is bad or not bad.. it is a shot in the dark with not seeing the issues ourselves instead just information provided over the internet. Good luck and let us know what you find out..

 

Thanks again guys. I'll take a look at the mounts, check them out and post my findings here. Probably be after the weekend though.

I agree with the bits about not being able to properly diagnose since it just text you have to access to (versus the actual irl car) but appreciate your help and input very much.

 

re-check your strut install. When under load, weight transfer changes allowing the part you installed wrong (or is faulty) to vibrate, when you let off the weight transfers back and binds whatever is loose. The same thing is happening when you're rounding corners.

Check the suspension again and you will find the problem. 98% sure.

LMK if I'm wrong.

 

is it strictly under load? or RPM related? Recently my friend had started to ruin his driveshaft and would only do it at a certain rshared_pm but not at a certain speed.
Replaced the driveshaft and all is fine.

 

It was indeed the driveshaft(s). Brand new and they were out of balance. I wasn't even considering them being the problem since they were new. Replaced them and all is well. Just goes to show you that just because something is new doesn't mean it is right.