jbtvt

Just bought a new '98 GS400, 111k miles, dealer maintained, no codes, runs and shifts strong. Body has some scratches and hail damage so I got what I hope turns out to be a good price. It has a pretty severe vibration at high speeds, get noticeable maybe around 50 and by 80 I'm shaking in my seat. It seems load dependent - stronger under accel and decel than cruising. Mounts and CVs seem OK, the vibration damper is a little cracked and I'll probably replace now but doesn't seem terrible



The center support bearing seems to allow quite a bit of play but the rubber is solid and shows no signs of cracking anywhere, so I assume its supposed to behave like this? When I wiggle the front shaft though I hear a noise which seems to be the splines moving around. It looks like a sort of compression fitting to me, anyone know if that's the case? If so, should I try to tighten it up a bit or better to leave it loose so it slides? Here's a video of what's going on there.

badblackgs

iTrader: (1)

replace the u joints in the drive shaft and the vibration will likely go away.

jbtvt

No discernable play in the u joint when twisting each side of the shaft against each other as hard as I can or spinning it.

kevin3344

Just went through this myself (actually, it's a common occurrence on the 2GS) and it turned out to be warped rotors. I had a vibration at 60mph that would go away around 72mph while cruising. Nothing around 45mph. Get your rotors turned / wheels balanced and see if that helps. I also had a bent rim once that contributed to the shake.

jbtvt

Thanks for the reply, did you also have a shake when braking? The rears did look pretty well worn but I get no vibration from braking at all on this car. I've run into a driving vibe from rotors before but was thinking otherwise here.

kevin3344

Yeah, same here...no vibration during braking. But if you're at 60mph and you can see the passenger seat head rest shake that's a sign. Btw, usually the shop would say the front rotors are the culprit.

jbtvt

Sweet, that'd be nice. Headed to Harbor Freight to grab a runout dial now...

I wish I had a chance to test drive it longer, it really seemed like it was worse accelerating or decelerating which wouldn't make sense if it wasn't in the drivetrain. Hope I'm wrong.

jbtvt

.003" runout on both front and rear drivers side, same with variation in plate thickness, both within standard spec. I don't think it's a rotor issue.

Anyone out there yanked on their driveshaft that can say if I appear to have more give to it than I should, or if that spline connection should be tightened??

bruceb58

Not rotors if there is no vibration during braking.

I would first take your spare and run it in all positions to see if its a tire before going further.

badblackgs

iTrader: (1)

the problem is coming from the driveshaft. inspect further. pull it out if you have to and double check the u joint in the middle. plus you need to pull the splined section out all the way and clean out all that rust and buy the specific grease thats made for drive shaft splines, than reassemble with new u joint and attach a new clip to keep that boot on securely.

jbtvt

Thanks for all the replies, after some convincing I swapped the tires and rims from my 99 LS I'm parting out onto it, and the vibration is almost gone. They all looked good visually except a small amount of dry rot on the rears too.

One of my CVs has noticeable runout which measures roughly .040" in the middle which is not ideal, between that and the various other things in the drivetrain which are nearing the end of their lifespan that's probably the remaining bit of driveline vibration I'm feeling. After all the reading the last few days I now know how to replace every chassis component on the vehicle, so there's that anyway. Love it when it's an easy fix.

badblackgs

iTrader: (1)

But you said that it only does it accelerating or decelerating. out of round tires would always vibrate. just sayin'

bruceb58

Doesn't have to be out of round to cause a vibration and a vibration can be accentuated if it hits some harmonic frequency.

I had my doubts about the driveshaft.

jbtvt

Had it on a lift and there was a harmonic spot where it got bad between 28-33 mph, then better, then worse again around 50 and steadily worse the faster it went from there.

Hey, I thought the same thing which is why I was spending so much time looking at the driveline. Check this video, you can see the chassis bouncing hard when it's decelerating and then less as it accelerates/coasts. If I had to guess at an explanation it's that the slight rotation in the diff as it gets torque was tightening up some of the mounts back there and making the vibration less noticeable.

badblackgs

iTrader: (1)

holy hell!!! there is something seriously wrong with your subframe mounts and lower control arm spherical bearings. notice how in the beginning of the video while making it happen your entire wheel vibrates out of round. and also the rear lower control arm where it mounts to the subframe is also vibrating and moving? yikes.