72 Small block charger Ring and Pinion Trouble

[72RobCharger]

Hello everyone,
I recently had my 8.25 rear end went thru again in 2024. It was first originally redone in 2018. I had a limited slip installed with a 3.90 gear installed from a 2.76. Being my luck it wasn't right and vibrating on deceleration in 4th at highway speeds. The mechanic didn't tell me till after that he installed them by "feel" which im not trying to downplay because he builds dirt track cars. However, Had i known he didn't own a dial gauge i wouldn't have let him touch it. Fast forward to this year , i recently rebuilt my 318 which was talked about in another thread. After the 2018 ring and pinion install i chased around this vibration on deceleration in 4th gear... New trans mount, New balanced drive shaft. Hell, even thought my Od trans was taking a dump on me so i replaced it too with a rebuilt iron case one from a dude in florida. Today i have been doing some research and i came across a discussion on how the pinion angle could cause vibration on decel. Then i dug deeper, I looked thru old photos and found right before i had the ring and pinion redone i had rebuilt the front and rear suspension. The rear leaf shackles being suspect. I ordered leaf springs P4452983, and a shackle kit from ebay. The ebay shackle kit is what i am suspect of. The shackles have 2 sets of holes. In the description it even says it offers 1.5" lower than stock ride height. I am wondering if by using the upper holes that actually lowered the rear by 1.5" if that has affected my pinion angle enough to cause this deceleration vibration .

 

[493 Mike]

The only way to know is to check the angles.
Mike

 

[pnora]

Ring and pinion rarely cause a vibration. Vibration can be tough to pin down. Wrong angles are the most common problems. For what its worth I would trust the seasoned mechanic without the dial indicator more than a mechanic that always needs tools or cant do a job because he does not have the tools. Myself I rarely use a dial indicator on back lash or a torque wrench for pinion preload. I do occasionally check my work especially if I have a helper. I explain and let him see and feel what I am doing along with him seeing how close the set up is without using tools to measure.

 

[72RobCharger]

Ring and pinion rarely cause a vibration. Vibration can be tough to pin down. Wrong angles are the most common problems. For what its worth I would trust the seasoned mechanic without the dial indicator more than a mechanic that always needs tools or cant do a job because he does not have the tools. Myself I rarely use a dial indicator on back lash or a torque wrench for pinion preload. I do occasionally check my work especially if I have a helper. I explain and let him see and feel what I am doing along with him seeing how close the set up is without using tools to measure.

My buddy thinks the pinion is way to deep in the ring gear. The Yukon manual said start with a 30 thou shim. The shim that was in it from the first ring and pinion build was like a 70 thou. from what i am reading to , i also am lead to believe that a ring and pinion setup would not cause any vibration, more like it would just be noisy. I don't know **** about ring and pinion set up other that what i read and try to understand. I really think this problem occurred after i changed leaf springs and the shackles. We moved the leaf springs to the original ride height today and that... kind of seemed to help but the vibration was still there in 4th gear. I am gonna get an angle finder and see what my angles are. Does anyone know where to find what the factory driveline angles are supposed to be? It looks like my pinion is still slightly pointed upward. I'll report back once i get the numbers. You wouldn't think new leaf springs would change that much but i guess its possible.

 

[72RobCharger]

I know the short answer to all of this is check the angles. Which i plan to do. I realized that the rear replacement shackles i bought are the hotckis HSS-17367. Which are 4" long. I read in this group from a google search that stock b body rear shackles are 3.5" long not 4. I just am wondering if between the new leafs, front and rear shackles if that was enough to piss off the pinion angle? Pnora I like your take on the ring and pinion rarely cause a vibration too. My friend calls the vibration a noise but to me a noise would be a noise... not a vibration. Yes a vibration will make a noise but this is definitely a vibration when u let of the throttle at highway speeds. Also one other thing , does the front end ride height affect pinion angle?