Powertrain/ ??? vibration

Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
I have been trying to get find the source of a drive train, seat of the pants, vibration that my 79 z/28 with a four-speed transmission has for as long as I can remember.
It probably is going to end up being one or more of the retro Goodyears, which have about 600 miles on them, not being able to be balanced.
The best test is next week when a garage friend of mine is going to swap the rims/ tires off of his sons 79 Trams Am onto the Z/28 and see if the vibration goes away.
Quick recap; it is a 31k original mile Z/28 that I've had since September 79 -it was a June 79 build.
I checked the pinion/ shaft angles and they appear to be OK. I did change out a bad rear transmission mount.
The vibration is at just over 60MPH, and most often I just run around town, so it hasn't been a major issue, but I want to get it fixed.
The vibration was there with the original Uniroyals and seemed to be the same or maybe a little better when I got the new Goodyears -so last year I actually had the Goodyears road force balanced to see if it could be fixed and they actually seemed a little worse..
One thing that I had thought was that one of the original rims may have been the problem - I did change one that they said was out of round years ago and it made no real difference.
I also wondered if the drive shafts for the auto and standard were the same length, and did find that the M21 Borg Warner T-10 had its own driveshaft part number -PN 7819345. So another longshot question is if they put in the other drive shaft PN 7819344, if it even fit, could that cause a vibration in the driveline?
I'm not sure where i can find the lengths etc., to compare.
My drive shaft has two 1" wide yellow stripes about 5" apart.
Anyone know if that could be an issue?
Now it is possible that everything will hopefully be sorted out when we do the rim/ tire swap testing.
If no vibration, we can swap in mine one at a time and find the bad one for sure -fingers crossed.
 

kenny77

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Lifetime Gold Member
Jul 31, 2001
3,275
Ft. Lauderdale, FL
See a post I just made in the wheel/tire/brake section about Flat Spotting tires. Not saying this is for sure your problem, but if the car just sits like mine does sometimes........maybe.....

Anyway, run it up to that speed that you usually feel it at. Then try doing it in a lower gear. If the vibration happens at the same road speed you know it's the wheels/tires
IF while in the lower gear, say third gear...you feel it at a lower road speed...then its in the driveline
 
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COPO

Veteran Member
Lifetime Gold Member
Sep 15, 1999
21,709
Ontario, Canada
When I owned my 80 Z28 from new for 10 yrs, I never had a vibration at any speeds. Pic taken in 1990.

E5333A22-944E-42D2-987A-8EBEF4475279.jpeg
 

xten

Veteran Member
Sep 24, 2014
4,760
Pittsburgh, Pa.
Glava, please let us know if this works, or you do find the problem. I'm sure I'm not the only other one that has been trying to find the same problem. I think I have narrowed it down to the tailshaft bushing in the M21, but haven't done anything about it yet. I was going to switch the tires and wheels from the 77 to the 73, but I think the 77 tires will rub on the 73.
 

Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
See a post I just made in the wheel/tire/brake section about Flat Spotting tires. Not saying this is for sure your problem, but if the car just sits like mine does sometimes........maybe.....

Anyway, run it up to that speed that you usually feel it at. Then try doing it in a lower gear. If the vibration happens at the same road speed you know it's the wheels/tires
IF while in the lower gear, say third gear...you feel it at a lower road speed...then its in the driveline
Good idea on the 3rd gear run over 65 -hopefully with the 3.73 rear I can go that fast LOL.
 

Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
Glava, please let us know if this works, or you do find the problem. I'm sure I'm not the only other one that has been trying to find the same problem. I think I have narrowed it down to the tailshaft bushing in the M21, but haven't done anything about it yet. I was going to switch the tires and wheels from the 77 to the 73, but I think the 77 tires will rub on the 73.
Yes, I'm glad we can do the switch and get a good comparison -i'll definitely post the results!
 

COPO

Veteran Member
Lifetime Gold Member
Sep 15, 1999
21,709
Ontario, Canada
not sure how this helps me ... but wondered why the rims are not painted the same as the Z? Did you paint them or did you change them.
It won’t help You. Just stating that when you said it’s been like this since day 1. Well I would have kept taking it back to the dealers until they fixed it or asked for another Z. This is not acceptable for a new car.

The rims. I dislike body color rims especially on the red/orange so I painted them the color my 77 Z28 was. Just too much of the same color. GM didn’t do it in 70-74 so why in 77-81? It would have been so simple to have 1 paint formula in the gun as before instead of 1 for each color car.
 
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