although I doubt a fluid change will fix a vibration. 
Vibration under load - '95 6-spd
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Vibration under load - '95 6-spd
I'm looking for suggestions on what to look for to help diagnose a vibration issue I've always had with my '95. Vibration starts getting pretty bad after about 55 mph. The vibration is only there when I'm on the accelerator. If I get off the gas, it goes away. Vibration is the same in 5th and 6th gear and it seems to be in rhythm with the exhaust drone. It seems to be coming from the back half of the car. Occassionally, I can feel it through the steering wheel, but I think that has more to do with the road I drive on.
Thus far I have replaced all 6 U-joints. I've replaced the rear hubs. I've had the tires balanced and had the front tie-rod ends replaced along with a 4-wheel alignment. None of these efforts have made a difference.
The car did sit in a barn for a couple of years before I bought it. The tires are about 8 yrs old (from the date codes). Any ideas/areas I need to look at next?
Thus far I have replaced all 6 U-joints. I've replaced the rear hubs. I've had the tires balanced and had the front tie-rod ends replaced along with a 4-wheel alignment. None of these efforts have made a difference.
The car did sit in a barn for a couple of years before I bought it. The tires are about 8 yrs old (from the date codes). Any ideas/areas I need to look at next?
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
The vibration is more vehicle MPH and load related. Vibration starts at the same mph in both 5th and 6th gear. Heavy vibration maintaining speed going uphill. Little vibration coasting at same speed downhill. That is why I originally assumed it was either drive shaft or half shaft u-joint related. All of the old u-joints were in good shape, but I went ahead and replaced them anyway. I put the shafts up against a straight edge, and they appeared to be straight.
Pro
Joined: Jan 2003
Posts: 706
Likes: 47
From: Denver Colorado
The vibration is more vehicle MPH and load related. Vibration starts at the same mph in both 5th and 6th gear. Heavy vibration maintaining speed going uphill. Little vibration coasting at same speed downhill. That is why I originally assumed it was either drive shaft or half shaft u-joint related. All of the old u-joints were in good shape, but I went ahead and replaced them anyway. I put the shafts up against a straight edge, and they appeared to be straight.
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Haven't tried it in 4th gear. I'll give that a try. I'm thinking drive train too, but the vibration going away when I get off the gas has me boggled.
Racer
Joined: Mar 2002
Posts: 498
Likes: 21
From: Maine
Check for excessive slop in the slip yoke.
I'm looking for suggestions on what to look for to help diagnose a vibration issue I've always had with my '95. Vibration starts getting pretty bad after about 55 mph. The vibration is only there when I'm on the accelerator. If I get off the gas, it goes away. Vibration is the same in 5th and 6th gear and it seems to be in rhythm with the exhaust drone. It seems to be coming from the back half of the car. Occassionally, I can feel it through the steering wheel, but I think that has more to do with the road I drive on.
Thus far I have replaced all 6 U-joints. I've replaced the rear hubs. I've had the tires balanced and had the front tie-rod ends replaced along with a 4-wheel alignment. None of these efforts have made a difference.
The car did sit in a barn for a couple of years before I bought it. The tires are about 8 yrs old (from the date codes). Any ideas/areas I need to look at next?
Thus far I have replaced all 6 U-joints. I've replaced the rear hubs. I've had the tires balanced and had the front tie-rod ends replaced along with a 4-wheel alignment. None of these efforts have made a difference.
The car did sit in a barn for a couple of years before I bought it. The tires are about 8 yrs old (from the date codes). Any ideas/areas I need to look at next?
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
The vibration under load only sure sounds like a differential problem. Has the diff fluid ever been changed?
Could be one of the clutch packs, worn ring/pinion gears, pinion bearing. I would start with a fluid change if it has not been changed in a long time.
Could be one of the clutch packs, worn ring/pinion gears, pinion bearing. I would start with a fluid change if it has not been changed in a long time.
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Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Thanks everyone. I will start with the slip yoke check and fluid change. I have a very good maintenance history on the car and can't find anything on differential fluid change. The car has 152k on it, so I can see the differential being a problem.
Last edited by csthews; Feb 22, 2015 at 10:22 PM.
Melting Slicks
Joined: Jan 2009
Posts: 3,181
Likes: 286
From: Puyallup Washington
I test drove a low mile Corvette that exhibited very similar symptoms. It was smooth as glass when doing a steady speed on a flat or when I had let off the gas, but when I stepped on the gas there was a vibration. The salesman tried to tell me it was a wheel out of balance or the car needed an alignment. I told him no way. The actual problem turned out to be the optispark. The dealer replaced it then the car was good all the time. I did not buy it.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I was going to suggest a misfire...what stopped me was this: That is not to say that the claim above is accurate, but if it is, it couldn't very well be a misfire. I'll be interested to hear what the OP finds.
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
Suggest rear wheels up with jack stands under the rear shock studs, run through the gears. If you can duplicate the vibes with the rear tires in the air there is a driveline issue. If you cannot duplicate the vibes the engine may be miss-firing under load or:
While under the car check the C beam bolts, bat wing & dog bone bushings. If anything is loose or worn the pinion angle will change when on/off throttle = vibes.
While under the car check the C beam bolts, bat wing & dog bone bushings. If anything is loose or worn the pinion angle will change when on/off throttle = vibes.
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Instructor
Joined: Sep 2014
Posts: 113
Likes: 6
I had a 6spd that I ran low 12's with and I can tell you those drive shafts can handle a lot , I doubt its the drive shaft. Have you had the tires dynamically balanced? I know I put a brand new set of tires on my truck and drove away and the issue didn't show up till I was going about 70, turns out one of my tires the tech had wrote the tire was "square" lol he balanced it out again and then I had no issues. Those are tough to find.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Thread Starter
Burning Brakes
Joined: Apr 2011
Posts: 917
Likes: 25
From: College Station Tx
Instructor
Joined: Jan 2014
Posts: 147
Likes: 10
From: Milwaukee Wisconssin
I'm looking for suggestions on what to look for to help diagnose a vibration issue I've always had with my '95. Vibration starts getting pretty bad after about 55 mph. The vibration is only there when I'm on the accelerator. If I get off the gas, it goes away. Vibration is the same in 5th and 6th gear and it seems to be in rhythm with the exhaust drone. It seems to be coming from the back half of the car. Occassionally, I can feel it through the steering wheel, but I think that has more to do with the road I drive on.
Thus far I have replaced all 6 U-joints. I've replaced the rear hubs. I've had the tires balanced and had the front tie-rod ends replaced along with a 4-wheel alignment. None of these efforts have made a difference.
The car did sit in a barn for a couple of years before I bought it. The tires are about 8 yrs old (from the date codes). Any ideas/areas I need to look at next?
Thus far I have replaced all 6 U-joints. I've replaced the rear hubs. I've had the tires balanced and had the front tie-rod ends replaced along with a 4-wheel alignment. None of these efforts have made a difference.
The car did sit in a barn for a couple of years before I bought it. The tires are about 8 yrs old (from the date codes). Any ideas/areas I need to look at next?