Strong Vibration at Steady Speeds

[Bobith]

I have a 95 firebird with a strange problem.

When i get into 3rd gear the car mostly the rear vibrates badly at 1600-2000rpm if i accelerate it stops but i cant keep a steady speed from 45-60. I half to accelerate and just take my foot of the gas or the car felas like the backs going to fall off.

Any ideas what could be causeing this?

[Philo]

Originally Posted by Bobith

I have a 95 firebird with a strange problem.

When i get into 3rd gear the car mostly the rear vibrates badly at 1600-2000rpm if i accelerate it stops but i cant keep a steady speed from 45-60. I half to accelerate and just take my foot of the gas or the car felas like the backs going to fall off.

Any ideas what could be causeing this?

Was any maintenance done on the car just before this problem started?
Does it shake in first and second gear at the same RPM? Does the shaking stop as soon as you apply more throttle, or after you pass the 2000 RPM mark?

[dwalmop]

check to see that the drive shaft is properly balanced. Since it's easier, though, bring the rear tires to a shop and have them road-force test them to make sure they're not out of round, if that doesn't clear it up, I'll be it's your driveshaft you're feeling.

[Hypsi87]

Originally Posted by Bobith

I have a 95 firebird with a strange problem.

When i get into 3rd gear the car mostly the rear vibrates badly at 1600-2000rpm if i accelerate it stops but i cant keep a steady speed from 45-60. I half to accelerate and just take my foot of the gas or the car felas like the backs going to fall off.

Any ideas what could be causeing this?

I would put good money that you have control arm bushings that are shot. Or a control arm bolt loose. My GN did that when I got it out. it would be steady even under hard acceleration but, when you took your foot off the gas, the whole rear end just wobbeled around like there was no tommrow. After that happend I was driving it back to the shop to check it out (I lived about 3 miles away from the shop at the time) and the bolt that holds the passenger side lower control arm to the frame fell out and it was an interesting ride to the shop with only three links in a four link suspension. I could only go about 5 MPH and when you hit the brakes... Hold on for the ride of your life. THIS IS A VERY DANGROUS SITUATION, FIX IMMEADATLY!!! I would of hated to have that happen going down the track at 100+ MPH.

[Bobith]

Originally Posted by Philo

Was any maintenance done on the car just before this problem started?
Does it shake in first and second gear at the same RPM? Does the shaking stop as soon as you apply more throttle, or after you pass the 2000 RPM mark?

Only 3rd and alittle higher havent had time to do alot of interstare driveing to try it out. But its fine in first and second. Yes it stops shakeing as soon as i pass 2000 rpm.

Im not sure wat mantance was done before it started it was a long time ago it was my roomates car.

Talking with some people at work one had the idea of rear universal joint. Could it be going or gone bad?

[Philo]

Originally Posted by Bobith

Only 3rd and alittle higher havent had time to do alot of interstare driveing to try it out. But its fine in first and second. Yes it stops shakeing as soon as i pass 2000 rpm.

Im not sure wat mantance was done before it started it was a long time ago it was my roomates car.

Talking with some people at work one had the idea of rear universal joint. Could it be going or gone bad?

I agree with Dwalmop, do the cheapest things first. You could save some money by swapping the front and rear tires yourself and retesting for a change in vibrations. Then I also would look at the driveshaft.
If you go into a garage to have them look at the tires, maybe you can sneak a quick look at the rear undercarriage to see if anything is loose. Or if the tires are OK, ask them to take a quick look while it is on the lift.
If all OK, change the rear U-Joint. Then the front U-Joint.

[Bobith]

Wouldnt the driveshaft cause vibration nomatter what speed i went? Not just dureing steady speed 45+?

[FormulaLT1]

A damaged driveshaft could do either. If one of the weights or something fell off it could cause vibration at a certain speed or if it had more serious damage or a damaged U-joint it could cause a varaition at any rpm range. From the way your describing it though I would tend to agree with Hypsi that it would most likely be a bushing. Good luck and keep us posted. Also welcome to the Forum.
John

[Bobith]

Thx I will keep all of you posted.

Im planing to take it into a shop next week. Till i get it fixed i can just use my unkillable 1980 monte carlo. Looks like crap but it not going to die any time soon.

Here is some of the things im going to have looked at when i take it in.


TuneUp-Since i dont know when last one was done.
Replace driverside window motor-Its dead
Check Engine Mounts-Just so i feal beter
New Drive Belt- current one just looks a bit warn just make me feal better.
Radiator Flush-I noticed alot of crud built up when i checked it.

If you have any sugestions on things i should have looked at. i welcome any sugestions.

[Hypsi87]

Bushings!!!!!

[Kurtdg19]

Yes, if the vibration occures at the same engine speed reguardless of which gear the transmission is in, the driveshaft shouldn't be the issue.

Since you said it only occurs in third then you may have a faulty driveshaft since the speed of the driveshaft varies in different gears at the same rpm. I would do a visual check of your driveshaft and make sure there isn't any built up dirt or any type of foreign undercoating on it that can affect the balance. If you see any dents in the in then I would definately get it checked out. Missing weights could also cause the vibration. Worn u-joints bearings is also a possibility.