'81 Z28 Driveline angles / Vibration

[77 cruiser]

Check the DS runout. I had a similar deal with a new shaft, I had to just move the u joints a bit as they were slightly off center.

 

[jthomas]

I chased similar vibrations for years. Bit the bullet and bought a Denny’s Driveshaft. Solved part of the problem. Finally found the last issue: Rotors and drums. See this thread: https://nastyz28.com/threads/new-rotors.327836/

Had a machine shop machine and balance brand new rotors and drums that came right out of the box and smooth as silk now.

 

[PBZ28]

Ditto here. Deceleration was worst vibration. Replaced driveshaft & vibration gone!

 

[CamaroYYZ28]

I agree 100%. Take the shaft out and get it balanced with new U joints. I had violent vibrations at high speed that I could not “drive through”. Did the above and it removed 95% of the vibration. The other 5% I have narrowed down to lack of hub centric rings on my aftermarket 18” aluminum rims. I have a set on order now and hope to solve the vibration once and for all

 

[junkyarddawg]

Before you start throwing $ at it perhaps you can try some methodical type diagnosis? (Carefully) Try to put the car up on jack stands, with the weight of the car on the springs, and run it up through the problem area and note where it starts and where it diminishes, if it does. This is assuming that you have already determined that the vibration is not engine related by slowly free revving the engine through the speed range where you feel the "driving" vibration. If it is not engine balance related then at this point you should know how much of the vibration is from the rear of the car and compare it to the total amount you feel when driving. You could further isolate this by removing the rear wheels and bolting the drums or rotors to the axles with open lug nuts and note any changes, then remove the drums or rotors and continue to quantify the differences. You can further expand the diagnosis this way and could even bolt the front wheels on the rear as a test if they will fit. Try to keep it simple and methodical while attempting to resist the temptation to stereotype the problem or throw $ at it. There are some free vibration analysis apps for cell phones which you can try to use to objectively quantify the changes. Best Regards....

 

[ruthlessz28]

not to dismiss anyone's suggestion, but only one person addressed your driveline angle question.if I remember correctly your trans tail shaft and diff should run in the same plane. and yours is running in opposite. shim your trans up but keep in mind the front of the motor will come down. try to get the trans running parallel with the the rear diff.at ride height.

 

[jthomas]

While the above is true on certain setups, it is not true on a leaf spring setup.
If you are running leaf spring suspension without caltracs or other devices to prevent axle wrap, you need the pinion angle DOWN and the transmission angle down. A lot of guys make the mistake of shimming the axle so the pinion is pointing UP to try to get that equal and opposite 2-3 degrees down in the front and 2-3 degrees up in the back. The equal and opposite is needed UNDER LOAD (car in motion) which you can’t measure without special tools. Leaf spring suspensions are always a trade off to find the sweet spot at the right speed and torque conditions.

Here is a great thread by another NastyZ member, Daniel, who videotaped his driveline under load to show GM purposely engineered both trans down and pinion down. Tremec app will show red angles. http://www.nastyz28.com/forum/showthread.php?t=246042.

 

[ruthlessz28]

While the above is true on certain setups, it is not true on a leaf spring setup.
If you are running leaf spring suspension without caltracs or other devices to prevent axle wrap, you need the pinion angle DOWN and the transmission angle down. A lot of guys make the mistake of shimming the axle so the pinion is pointing UP to try to get that equal and opposite 2-3 degrees down in the front and 2-3 degrees up in the back. The equal and opposite is needed UNDER LOAD (car in motion) which you can’t measure without special tools. Leaf spring suspensions are always a trade off to find the sweet spot at the right speed and torque conditions.

Here is a great thread by another NastyZ member, Daniel, who videotaped his driveline under load to show GM purposely engineered both trans down and pinion down. Tremec app will show red angles. http://www.nastyz28.com/forum/showthread.php?t=246042.

i run caltracs, but i also haven't set up my angles . that thread you posted is very informative. once i put my new set up in ill have to check it all out .
funny thing is i have had a picture of "correct" driveline angle in my tool box for soosooo long that you don't relise they maybe wrong for your application until someone posts more accurate info. and for this i thank you.

 

[G72Zed]

While the above is true on certain setups, it is not true on a leaf spring setup.
If you are running leaf spring suspension without caltracs or other devices to prevent axle wrap, you need the pinion angle DOWN and the transmission angle down. A lot of guys make the mistake of shimming the axle so the pinion is pointing UP to try to get that equal and opposite 2-3 degrees down in the front and 2-3 degrees up in the back. The equal and opposite is needed UNDER LOAD (car in motion) which you can’t measure without special tools. Leaf spring suspensions are always a trade off to find the sweet spot at the right speed and torque conditions.

Here is a great thread by another NastyZ member, Daniel, who videotaped his driveline under load to show GM purposely engineered both trans down and pinion down. Tremec app will show red angles. http://www.nastyz28.com/forum/showthread.php?t=246042.

jthomas makes some KEY points, and thanks for that nastyz28 link. There is a lot to leaf springs based on what the car is being used for and the basic geometry you have to work with (or around) or build to.

Yes, it's a 100+ year old design, long in the tooth, and time and technology has moved on light years ahead. BUT, if you do your work, you can get these to work amazingly well, to the point of some companies not liking some cars performing on par, or better than the more advanced and much more expensive setups for our cars.

Reading the link, and looking at my notes (if I can't remember) I have these key points that have served me well:

1- Equal and opposite work, but in a Dynamic & loaded state, how dynamic and loaded is the issue to figure out
2- The garage floor has nothing to do with drive line angles
3- There are 3 angles to consider- Trans/slip yoke, Rear pinion yoke, and total compound angle as viewed from the top (AKA rear end offset)
4- Spring design, pads and bushing design and materials dictate how much pinion angle is needed to start with
5- Weight/converter/gearing and stating line ratio with TQ factor in the pinion setting equation must be used
6- The less working angle the better for power transfer, U joints are cheap and is a consumable part like tires
7- Engine is set at 2-3* angle down to the rear, intake carb pad set at "0"
8- Key issue is if the rear pinion is higher or lower than the trans output shaft.
9- You do not need a drive shaft to measure angles
10- The sub frame is not used as a datum line.

Again, i could be wrong, and may be missing notes, but that's what I have down. I'm sure some will agree, and some will not, please share your experiences as we all learn quicker that way.