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car vibrates in 3rd gear

1097 Views 10 Replies 5 Participants Last post by  Mike A
I have a '76 280Z that vibrates in 3rd gear. The vibration occurs as I am accelerating to shift into 4th and seems to always begin at 2600rpm. It doesn't happen every time but it is a regular occurance. Usually the vibration is subtle but sometimes it is violent. Accelerating to 3000rpm usually will bring the vibration to a stop as will decelerating to below 2500. Can anyone tell me what the probable cause of this is and what I will need to do to fix it? Thank you, Mike
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accelerate from 2000 to 3500 in each gear. See if it is gear related

Also note speed at which vibration occurs. It could be speed related.

Does vibration seem like front wheels? Can you feel it in steering wheel?

Can you feel it through shift lever?

What happens if you pedal brake gently while accelerating through the vibration

What happens if you hand brake .....

Does it sound like heat shield?
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Thanks for your quick response Blue.

It only occurs in 3rd gear.

It only occurs at 2600rpm in 3rd gear although it will continue to about 3000rpm.

The entire automobile shudders, but yes, I do feel it in the steering wheel.

Pedal brake does cause the shake to stop. It seems the vibration discontinues when I decelerate below 2500rpm.

Haven't tried the hand brake.

There is no sound involved.
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Might wanna think about the drive shaft, if you have had it out, may need to be turned, It will cause alot of strange problems. Just a thought, if you havent had it out then forget it.

Thats a weird one but it must be transmission related because the drive shaft turn rate is governed by speed not by gear.

There is a fuel threshold at this same rev range but it would not cause a shudder.

Also the exhaust resonates at this rpm range but it is not gear related.

The only item would be the transmission, but they usually whine or grind?

I am at a loss :(
My car had a similar problem. Check the driveshaft u-joint that goes into the differential. Mine only had 2 bolts instead of the necessary 4 and they were loose.
if all your bolts are tight and u joints are good....
does your car have lowering springs?
i have a 77 that had the same 3rd gear vibration. everything checked out fine as far as joints and bolts. i noticed that my car sat a liitle lower than it used to. it had lowering springs(old ones)
the rear half shafts were at too steep of an angle with the car sitting this low. after i replaced the springs...no more vibration. just a thought... hope this helps
Thanks Charles, I appreciate your help. I actually just put in a rebuilt driveshaft the day before I posted this and that did not solve the problem...but it did solve the clunk in the transmission :)
Thanks Blue, this is a weird one and I am at a loss too.
Thanks for your help, but I replaced them the day before I posted this.
This may do it. Thanks for the advise!
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