Jonota

So I'm working my way to decent mileage, hopefully the next check will put me over 25mpg for my commute. As happy as I am with that progress (I started off around 18mpg), I know there's still a bit more in it. The thing that I am noticing now is I have a vibration somewhere. Having had relatively little experience wittling down vibration issues, I thought I would start by asking what kind of vibration issues people have successfully dealt with.

I'll start with my own: the only thing I've dealt with so far was an unbalanced driveshaft in my 95 TA. $40 balance at a local driveline shop and it was good to go.

Anyone else?

Also - anyone that has some sort of procedure for ruling out various components would be super helpful!

Jon

wssix99

iTrader: (5)

When does it happen and under what conditions does it change? You can tell a lot about where a vibration is coming from with that information.

Jonota

My current issue happens at all times. It is noticeably worse at cold startup, appears to vary directly with speed (so not engine/trans related), is bad enough you can visibly see the passenger seat vibrating. No change with braking, more or less throttle, wet or dry. It has a sound, but it is hard to verbalize, but sounds very similar to me to when I had a bent input shaft on a T-56 (long story), making me think a bearing might be the cause (woo wooo woooo wooooo wooooo?). I recently closed the Borla open side off completely to see how it affected my mileage, and now at low engine speeds the "noise" is louder than the engine (which admittedly is pretty quiet).

wssix99

iTrader: (5)

So it happens at start up before the car is even moving?

Jonota

Wow... that's an obvious one I should have mentioned.

No, it only happens when the car is moving, it is just noticeably worse if the car was just pulled out for the day than if it is warmed up (or looking at it the other way it gets better as whatever it is heats up).

wssix99

iTrader: (5)

Well, if it doesn't vibrate at a standstill or revving the car in neutral, its likely something unsprung or behind the engine.

Odd that a vibration would improve with heat? Have you checked the fluids in your diff and transmission?

Another thing to eliminate would be the brakes. I wonder if the problem goes away with use instead of heat? Does applying the brakes stop it?

Jonota

I don't actually "know" that it is heat that improves it, just that it is worse when I start driving to work than halfway there. If it is something greased or a poor clearance, heating up can change the dynamic, but that is entirely speculation.
I have not checked fluids yet, but it is on the to-do list for today or tomorrow. After that will be the attempt at recreating the vibration while on the lift. If still there I will be checking the u-joints, then removing the rear wheels and seeing if that makes a difference, then pulling the driveshaft and trying again.

wssix99

iTrader: (5)

Yea. That's why I asked the question about brakes. If the vibration goes away while you are under braking that may be telling and might point to something dragging.

Jonota

I'm fairly certain that the brakes are irrelevant to the vibration, and I know the noise doesn't go away. I've actually had those apart inspecting them recently (due to a squeak) and everything looked good.

dailydriver

When you check the u joints, check to see if they have zerk grease fittings,

IF they do, put some high quality, washout proof, high dropping point, preferably synthetic grease into them!

Jonota

We'll see if actually posting works this time (3rd try). Much typing wasted.

Trans and diff full, good fluid.

No audible vibration on the lift, up to 50 mph (obvious at any speed on road). No marks on driveshaft. No zerks on u-joints, no play in rear u-joint, front had play but didn't seem to be u-joint seemed to be splined section of shaft wiggling.

Might be front wheel bearing. I could spin driver's front as hard as I could, walk over to passenger's side, spin it as hard as I could, and the passenger's side would stop well before the drivers side did. Didn't sound any different than the other side, could just be a pad wear issue. Car doesn't pull to either side driving.

Oy.

wssix99

iTrader: (5)

Sounding more like the problem is unsprung.

If you take the wheel, brake caliper, and rotor off and spin the bearings by hand they should be smooth as glass. If not, that would indicate bad things.

IMO - If you have more than 100K on the bearings, you don't have a whole lot to loose by changing them. They won't last too much longer, anyway, if they prove not to be the issue.

Speedy1990

It may be a good idea to check your tire pressures and do a tire rotation and wheel balance if you haven't already done so. I've had some strange issues with three different vehicles of mine (two of them F-bodies) where I've experienced some similar symptoms as you that turned out to be tire-related, due to age, irregular wear, etc. My '02 Z28, for example, has a set of 275/40/ZR17 Pirelli P-Zeros that are very sensitive to tire pressure; anything below about 30-32 psi cold, and they tend to have a more noticeable "thump" to them while I'm driving, which causes more vibration (almost as if they are more out of balance; this condition is also more noticeable when I'm just getting it out for the day). If the pressures are between about 32-37 cold, they roll a bit smoother and there is very little, if any, vibrations. Above 37 or so, however, and they start thumping again. In any case, though, the more I drive the car (usually about 100 miles a day when school's in), they get smoother throughout the day as the tires soften up.

If nothing else, it would be good to check them out just so they can be eliminated from your list of potential problems.

Speedy1990

I also don't think I'd be too concerned about the fact that one wheel spins longer than the other when you have them in the air; both my '94 and my '02 do this, and although it did drive me nuts wondering why, I never had any driveability problems because of it. I guess that's one of the many examples of "character" that these cars seem to have lol.