I'm having this problem with road vibration, it's so bad my dash vibrates! I know my tires are balanced, because I just got new rims and had them all mounted and balanced. It's really bad at around 40-50MPH and still very noticable at freeway speeds. I'm going to jack it up and see if it's in the rear axle, although it sure feels like it is. If it is, my question is, what is likely to be the problem? the axles themselves? the differential unit? I just want it to ride smooth. If it matters, I'm running 12.3" wide bias-ply tires in back and radial in front. Ok so, I'm aware that with glasspacks, headers, and sidepipes, my car will be loud . But is there anything I can do to cut down on the noise INSIDE the car? I mean, some is obviously going to come through my windows, but it comes from undernieth and through the doors really bad. What's the most effective/cheapest/eisiest way of dealling with that? (impossible to get all three I know, of the two, effective and easy are the most important by far) Thanks in advance guys!

Not sure how to quiet the car down but did you recently change the motor? I see you have a 400 in it, they are balanced different and require a different flexplate then the 350's.

could be bad u-joints. When you're under there grab the driveshaft and try to twist it. If they're good there should be no slack at all, cant hurt to do a close visual inspection on em too.

I did swap in a 400, but I had to use it's flexplate anyways since it was a different size then the one on my 305, and needed it's own to fit the starter for it. It doesn't feel like an engine vibration, it feels like a road vibration.

I'll check the u-joints today I wouldn't be suprised if they had gotten some slack in them, I'm putting alot more torque through them than they were designed for.

Thanks guys

Yes check the u joints. I really doubt its the rear diff. I know your tires were balanced (I would still recheck the balancing) but it could be that one or more of them has a separated belt(fronts because they are radials). I remember having some very nice looking tires but they made the car vibrate. I took it to have them rebalanced 3 times to no avail. Finally someone closely inspected the tires and found that the belts were separated on one of them. If it only does it at one speed(say 65-70 mph) then its definately a balancing problem. If it does it at all speeds, then its a tire issue(also could be a bent rim but I doubt that since yours are new). Let loose of your steering wheel while you are driving. Even at slow speeds you can see the steering wheel move if you have belt separating up front.
For the noise, I would take out the carpet and seats. Patch any and all holes if you have any. There is a prodauct called dynomat(many other brands) and it is used as a sound deadener for vibrating subwoofers. It also works for helping with some road noise and exhaust. Dont expect a miracle though with headers.

I hope this helps.

Only thing left that I can think of that hasn't be mentioned would be driveshaft. Don't know how in the world it could have went out of balance though.

I can't imagine the tires are bad, I've been running these fronts for a long time, and it's never vibrated this bad I don't think, and the steering wheel stays still, and the car tracks very straight. I'll check those u-joints today.

Thanks again

How many mile are on the tires. Sorry to beat a dead horse but one pothole could break a belt. Its really hard to diagnose without being there though. Good luck.

Well, probably alot, they were the front tires when I bought the car. I have some others that I could try. If it's relevent, one of those tires has a small leak that les shwab couldn't find, does that imply it's messed up? Thanks.

oh, and do bias-ply not break? Thanks.

They just get weathercracked and split. If they sat a while they could be flat spotted. I would say, if they have over 50 thousand on them, there is a good chance they have problems. I dont think a leak would be an issue as long as they were inflated properly during driving.

put some dynamat all around the inside of your car

Ok, so I jacked up the back, and put it in first so I could watch the tires/rims, and the rims seemed to move around SLIGHTLY, but the tires! They have pretty bad flat spots/bumps. I'm thinking the reason the vibrations come and go and change around is because the tires get in and out of sync. I knew they had flat spots after I bought them, because it was REALLY bad, but that seemed to go away after a few days. Obviously it didn't go all the way away. One thing though, I have them deflated to around 15PSI or so, so I get more ground contact, could that be causing flat spots?

That said, can anyone point me to some nice 295/50-15 tires? I don't need snow capability, but it has to handle rain fairly well. I need sticky though, the 400 puts out a rediculous amount of torque. Thanks.

if it's not your daily driver bias ply tires will get flat spots when they sit and they work there way out when you drive a bit.

Flat spots alone will cause the vibration.

it is my daily driver, but like I said, I drive them with low PSI for better take off. Would that be causing flat spots?

I'm not positive but if ya think about it bias ply by nature get flat spots so if you run lower pressure then the flat spots would be bigger causing more violent vibrations than if it had the right pressure in it , try putting the right air in them and see what happens not to mention it is very unsafe to drive on low pressure if it's to low you can break the bead and blow it out . Anyway back to the flat spots that"s one of the reasons they developed radial tires because they hold there shape and are stronger than bias ply.

get some rear control arm relocation brackets if you want to put the car out of the hole harder without spinning

I bought some, I havn't installed them yet. Is it really that big a difference? It doesn't seem to squat to bad, so Is it still a good thing? I've been wondering about this for some time. Thanks!

The problem with going radial, is I can't find any sticky radial tires. ET Street Radials look deadly to me (and also don't come in just the right size), and everything else is a "all weather tire" I don't want "all weather" just dry and rain. I'm NEVER driving this thing in the snow anyways! So I want a meatier tread.

There is a common problem with the steel driveshafts in these cars. Take it out and throw it in trash. Get a aluminum one, pretty easy to find out of a 4th gen and bolts directly in.
Car craft did an article on the steel shafts, and showed how they flex VERY badly when spinning, even if they are completly balanced. There is nothing you can do to fix stock line.
I fought my car for two years with an interstate BAD vibration before I found the article on the driveshaft. Changed it out and drives smooth as glass now.

do a search on the driveshafts if you want.....there are many threads about before and after on getting a new aluminum line.

Even if that's not totally the problem, it IS a cause of some of the vibration. If you would have seen that article and how much the shaft flexes and bows at speed, you'd never drive your car again with that steel line in it.....SCARY.

hope that helps some.

so are all 4th gen driveshafts aluminum?

i think so....i got mine for 100 bucks. ebay it...you'll find a lot. or should anyways. there were a couple thirdgens that got them but not many.

What about getting one out of a wrecking yard? there are a couple of 4th gens here at the local pick-a-part. Or am I likely to get an un-balanced one? Plus, do the u-joints work as replacements? So I could replace both at the same time? thanks.

get one from a ls1 car

it has a balancer

Ok, which years are LS1's? Thanks.

It doesn't matter what year 4th gen. I have never heard of a "balancer" on any of them, mine is out of a LS1 TA and it looks like a standard aluminum line.

Anyway, yeah go down and get one at your pick apart. The diameter of the line should be bigger than the one you have now....can't remember, like 3.5 inches for the aluminum on...
on balancing, it is NOT common for a line to be out of balance....but if you wanna make sure you could have that line balanced at a local shop that does that. I had mine done and it was right in spec. You do wanna change out the u joints and put new ones in just to be safe.

Thanks. How much did that cost you to have it balanced?

ummm, I think it was like $90 if they had to add or subtract weights, but since mine was good, I think he only charged my 50 or something.....it's been a few years since I did it. You'll need to find a driveline shop with a spin balancer. If you can't find one, I wouldn't worry about it, it MOST likely will be in spec. You don't balance that often.....think about how many times you've heard "you need your driveshaft balanced...." lol.

mine has a balancer

feels like a lexus

Ok, so I'll get an aluminum drive-shaft and replace the u-joints, that should help alot, plus I bought some of that sound-deadener from ebay (80Mil Zilla-mat) which should help with the noise.

But my tires still have those flat spots, So I want to go with radials in the long run, I just can't FIND any that look like they have good accel traction. I REALLY need some recomendations here guys. I'm looking for 295/50-15 or close. I can actually go a little wider, but I want the sidewall to stay the same or within an inch total. Thanks again.

try running a drag radial tire...like BFG drag radial TA or something.......those flat spots are probabaly some of the cause too.

I just put an aluminum driveshaft in mine today but it didn't help my vibtation problem. I have the same proble as you. I can fill the vibration at all speeds but it gets really bad around 50 mph and then smooths out a little, but it's still there. Here's a list of stuff I've done and it hasn't helped me yet.....

Switched all front and rear suspension bushings with energy suspension.

New moser axles and bearings.

Aluminum driveshaft with new u-joint's.

Front rotors and new wheel bearings.

Just installed yesterday, brand new wheels and tires. Had them balanced twice to be safe.

I've been trying to figure this problem out for over a year. I did notice when I had the driveshaft that the shaft coming out of the transmission tail seemed to have about a 1/4 inch of play. I don't know if there might be a bushing or bearing out or going out in the tranny. I thought maybe the torque converter could be going out, but I don't know what the signs are for that. Next weekend I'm going to take it to the tranny shop and have them take a look at that shaft. I'll let you know what I find out. Might want to check your if you have your driveshaft out and we can compare.

that's great, thanks! I'll let you know as I try stuff as well. I'm pretty sure most of mine is my tires, because it seems to come and go, and be worse when it's cold, and when I first start driving, which i've been told is what Bias-ply's are like.

Belted tires are prone to that.

I don't know how many shakes & rattles I've chased, only to find out I had multiple bad tires.

Like I said, I just can't FIND any tires that seem very sticky. I mean, even now, with mine, I still spin the tires from 0 ALL THE WAY to second gear if I floor it from a stop. am I missing something, I mean, I'm I "driving" my take-off's wrong, just not doing it right? Or am I really getting that bad of traction, will the LCA Brackets really make that much of a difference? Thanks. guys.