Drivetrain Vibration Questions

Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
I don’t believe the factory created this problem and couldn’t fix it under warranty. I ordered new 4 speed Z28’s in 77, 78 and 80 and never had a vibration. Maybe I was lucky but I dought it.
Not so sure about that -it has done it since 79, but I never brought it to the dealer to correct. I love this Z and that is the reason I've kept it for 42 years, but there were 84k of these built and mine was a June 79 build. If you saw how bad the fender gaps are and how the factory paint fades at the bottom of the rockers and the rear bumper, there are definitely things that snuck through QC in those days.
 
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Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
https://www.ccsdesigns.com/_builder/2/live/ie_driveline_service/uploads/files/Power Train Setup Guide.pdf
Hopefully I have posted this link properly as it explains things quite well.
It may have been out since you bought the car new.
Thank you!
This reinforces what my head had gotten to at this point.
The trans output seems to be a couple of degrees too low -at least IMO. So, I found a nice set of GM shims that are sized for the GM crossmember. There are 4 that are 1/8" thick, so I'm going to try these and see what happens.
 

COPO

Veteran Member
Lifetime Gold Member
Sep 15, 1999
21,711
Ontario, Canada
I would have kept bringing the car back under warranty until it was fixed.
I had a water leak in the trunk in my 78 Z28. It took 3 different trips to the dealer before they found sheet metal that was not seam sealed. Many of the stripes on the 78 were peeling around the wheel wells so GM nearly replaced all the stripes.
Bad adhesive.
A2AEBDE5-EA4D-4CBB-A9C3-013F847B651C.jpeg
 

G72Zed

Veteran Member
Sep 8, 2015
3,926
Canada
Oops its 5 degrees not 15 degrees -sorry. I put a straight edge across the tranny output at the seal.
So what would you recommend that I try at this point?

That makes more sense. With the car on level ground, the engine tilt should be around 2-3*, using the damper or even the intake carb pad works well as the intake carb pad has this designed into it in most intake castings, since the carb was designed to work level. Shims at the trans mount should work to get you into the right zone, or a new rubber mount.

Here's my "rules" to setup driveline operating angles.

# 1- 1 to 3* angle, Min. 0.5* Max. 3.0*
# 2 - Must be within 1.0* operating angles of each other
# 3 - Front to rear must be opposite
# 4 - Check rear end location for excessive offset "compound angle"
# 5 - Adjust rear axle pinion angle based on spring pack & bushings, TQ/weight of vehicle.

You want the least amount of total working angles for smooth operation, many forget these cars had engine offsets to the passenger side, and even more offset for the rear ends. Sometimes stacking tolerances got this to the point of a car was just "busy" no matter what was done. Most measure, and focus on total working pinion angles on the horizontal plane only, and forget about the "top view" plane, and this adds to the total compound working angle.
 

checkmate201

1970 SS 350 4sp 06 C
Dec 30, 2005
43
Nanaimo B.C
After you get the angles correct go road test it. If the vibration is still there then mark the driveshaft position on the yoke and remove the driveshaft and have it rebalanced. Once you have confirmed driveshaft angle and balancing is correct you may have an out of balance clutch pressure plate if both of those items do nothing help your vibration.
 

biker

Veteran Member
Gold Member
Dec 7, 2014
4,861
Canada
Thank you!
This reinforces what my head had gotten to at this point.
The trans output seems to be a couple of degrees too low -at least IMO. So, I found a nice set of GM shims that are sized for the GM crossmember. There are 4 that are 1/8" thick, so I'm going to try these and see what happens.
Honestly, I bet that does it. Doesn't take much.
 

Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
It's starting to sink in more, so I think that I'll focus on these three. got back under the Z to be sure I really get clean solid angle measurements -I am pretty confident I have them now;
output shaft 5* down, drive shaft 2* up, pinion 2* up
# 1- 1 to 3* angle, Min. 0.5* Max. 3.0*
I'd like to bring the output shaft up, so that it is only 2* down to match the 2*pinion angle and make their centerlines parallel -is that correct?
# 2 - Must be within 1.0* operating angles of each other
After doing #1, I'll measure the drive shaft/operating angles to see if they are within 1* of each other and fine tune if not?
# 3 - Front to rear must be opposite
They have that orientation now and so should have it after I shim.

Let me know if I have this right and after this, I'll go on if needed.

Thanks all for the guidance.
 

rocket dawg

Veteran Member
May 5, 2015
571
Grand Rapids Mi
The car has to be level to check the angles, or I should say, the floor has to be level. You might have to "shim" your jack stands with thin plywood to get them all at the same height. Support the rear axle, then support the front lower A-arms as close to the center of the front tire where it would hit the ground. If you support the front of the car in any other area,( farther back) it will unload the rear axle. These angles being "off" should be felt in the gear shifter at high speeds. Same with an out of whack drive shaft. A new trans mount is cheap, so do that if you need to adjust the trans up or down.
 

Glava

Veteran Member
Lifetime Gold Member
Mar 23, 1999
458
Central NY
After you get the angles correct go road test it. If the vibration is still there then mark the driveshaft position on the yoke and remove the driveshaft and have it rebalanced. Once you have confirmed driveshaft angle and balancing is correct you may have an out of balance clutch pressure plate if both of those items do nothing help your vibration.
Thanks again G72ZED, Checkmate and others!
So I got a new transmission mount as long as I was going to try and correct the pinion angle with shims. When I took the original one out, I realized it was collapsed. It was approximately 1/4" shorter than the new Anchor industries mount.
I installed it without any shims and the angles were 4* at tranny and 2* at the pinion. The driveshaft angle is 3*.
It seems that this is good -right?
at pinion. It seems that this is good -right?
TOOK IT FOR A LONG TEST DRIVE AND THE VIBRATION IS STILL THERE AT 70MPH -NONE IN THE STEERING WHEEL, BUT IN THE SEAT OF MY PANTS.
If so, I'm on to getting the driveshaft balance checked -right?
If so, I'm on to checking the tranny tail shaft bushing and then getting the driveshaft balance checked -right?
My bad,

ZTrannymount.jpg
 
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