Well I'm at a loss now, I have a 1978 Z28 (4-spd, 3.73 posi, all original except engine)which I just built and installed a ZZ430 clone for this summer. When I am driving I get a very strong vibration in the floor and thru the shifter **** at around 4000 rpm and above. Now I have taken to around 85mph (4250rpm) and shut the engine completely off and put the clutch in, to eliminate the engine as the source, and it still vibrates just as bad. Also this vibration has been in this car for 7-8 years now, but more pronounced after the engine change. Also I took the drive shaft to Universal Joint and they said it was bent, so got a new tube, installed it and no change in vibration. When the tranny was out for rebuild checked end play on input shaft and looked real solid. So any suggestions as to where or what to look would be greatly appreciated as I am at a loss right now. Thanks

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1978 Black Z28
ZZ430 Clone (coming this winter)
4-spd

 

My 69 always had a slight vibration turned out the right side axle was bent. pull them this winter and send them to moser eng.

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Cranberry Red 69
SS Convertible
95 LT-1 / 4L60E

 

drive shaft out of balance?

 

Are you sure that your tires are still balanced? Some shops don't take the added time to make sure they are balanced properly. Also you said that you checked the tailshaft end play and you feel the vibration mostly in the shifter, it seems that the vibration is comming from the trans or from other rotating parts attached to it like the drive shaft but you said it was ok. Did you check the input shaft and all of the interior rotating assy? Your trans might have worn bearings inside and causing the vibration. Also did you change the flywheel, clutch and pressure plate when you swapped the motor? This is another area to look for vibration. I know you said you shut the motor off but the clutch pad is still spinning unless you put the trans in nuetral and let out the clutch to stop the front half of the trans from spinning. Check these few things out and if you find it repost and let us know.

Take care,

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Wayne Best
Best Racing
67 rs Camaro

• 355 cu in Chevy
• 12.5:1 compression
• 10.90s @ 120 mph

87 Formula 350 w/388cu.in. motor

www.geocities.com/best_racing

 

It sounds like it's actually speed related, rather than RPM related, gien that if you declutch at 85 MPH, the revs drop but the vibration remains. If that's the case, the problem is almost certainly somewhere backwards of the tranny tailshaft. A bent or out-of-balance driveshaft is most common, but a shot tranny tailshaft bearing or pinion bearing can cause the same problem.

If the vibration is rather high frequency. Kinda like somebody just "paged your car." You know, vibrating the whole car like you're inside a beeper when it goes off- then it's usually between the tranny and pinion gear. If it's a lower frequency then it's more likely related to the wheels, tires, bearings, etc.

Not that I'm a big fan of diagnosing stuff like this BUT..... I have fixed mysterious vibrations by jacking up the rear of the car and running the revs up in a high gear. Just make sure it's WELL supported- no floor jacks.

 

Thanks for all the great info guys, the first thing I am going to do this weekend is take the car to my buddy at goodyear and have him check the balance.

bestracing: I will have to check the car out again as when i did I only put the clutch in and shut the engine off. I will go back and check it by putting it in neutral and then letting the clutch back out.

Damon: It is exactly like you said, it feels like I am being paged in the whole car.

More to follow, thanks

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1978 Black Z28
ZZ430 Clone
4-spd, 3.73 Posi

 

A stock balanced driveshaft can be 180 degrees off.Remove the u-joint bolts and turn it halfway and bolt it back up.Just a thought.Good luck.

[This message has been edited by clydes ryds (edited August 29, 2002).]

 

If it has drums instead of disc's see if one of the wieghts came off (factory balanced). you can jack up back and run up to speed with and without drums to see if vibration is gone but remember not to use brakes to stop the rear wheels as you can blow the wheel cylinders apart. also check the pinion for slop sometimes the pinion nut comes loose.

[This message has been edited by TAYLORMADE (edited August 29, 2002).]

 

Update....

Had the tires balanced and rotated this past weekend and didn't help the vibration. So we jacked the rear end of the car up and took the driveshaft out. Then started it up and ran it through the gears and the vibration was gone. Then put the shaft back in and ran it up in the air and the vibration was back. Also tried rotating the shaft 180 degrees but that didn't help either. So if my logic is correct, I am now looking at the rear end, since the driveshaft is newly retubed and balanced. Any suggestions? Thanks.

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1978 Black Z28
ZZ430 Clone
4-spd, 3.73 Posi

 

jack it up and start taking off parts 1 at a time...

wheels, then give it a try
then brakes..

also take off the tires and look at the hubs with them spinning, I had a vibration in a 95 formula because the very end of the axel was slightly bent which made it look like it was wobbling (but it was tight on the bearings) New axels fixed it.


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69 Camaro among other toys.