67 Rear axle bounce

[oldman3]

OK guys, I'm bringing up this old thread to update on the rear axle bounce.

A short story first, this thread is about 18 months old, Jimbo's wife had their baby, and has since had another, so his time as been limited to doing anything with the truck. We also had to change the engine (posted in his build thread today, last 2 pages). While we did that we also change part of the drive shaft alignment. I talked with several different drive shaft makers and they all said that it was possible that the 2 piece drive shaft could set up a wobble to cause the bounce. What we did was knock out the rivets from the carrier bearing bracket, and turn it upside down. Took a string from trans to rear axle pinion to make a straight line. Moved the bracket up till drive shaft was it line. Marked and drilled 4 holes, installed grade 8 bolts and tightened down. After breaking in the new engine, we when out on the four lane and man what a difference. We pulled a couple hard throttle pulls to 5,000 rpm in drive (3rd gear) and was smooth. Got up to 90 mph and still smooth. We still have a little vibration, so he is going to take the wheels and tires to a new shop in town that has a laser balance machine and works alot with large wheels. Here's a few before and after shots of the change..Jim

[oldman3]

In the old pictures above you can see how the bracket was mounted above the drive shaft. In the after pictures you can see were we moved it down, and is now under the drive shaft, making a more straight line for the drive shaft.
First pic is looking from rear toward engine
2nd pic is looking from front toward rear axle
3rd pic just a little different angle.
You can see were the old holes from the rivets where.

Hope this may help someone else. Thanks everyone for all your ideals and suggestions. Glad we final got this taken care of...Jim

[MySons68C20]

I really appreciate when someone posts the solution to their problem. Thank you!

[oldman3]

Originally Posted by MySons68C20

I really appreciate when someone posts the solution to their problem. Thank you!

So do I, and thank you for checking it out...Jim

[jjzepplin]

So I was right!!! BWAHAHAHA! (In my best vampire like voice)
So you raised the middle bearing?
I hope the tire balancing takes care of the rest of the vibration.
Good luck sir and wow that is a magnificent undercarriage!

[oldman3]

Originally Posted by jjzepplin

So I was right!!! BWAHAHAHA! (In my best vampire like voice)
So you raised the middle bearing?
I hope the tire balancing takes care of the rest of the vibration.
Good luck sir and wow that is a magnificent undercarriage!

Yes you were. Yes raised the bearing and it made all the difference. Thanks for the compliment...Jim

[Hart_Rod]

Originally Posted by oldman3

OK guys, I'm bringing up this old thread to update on the rear axle bounce.

A short story first, this thread is about 18 months old, Jimbo's wife had their baby, and has since had another, so his time as been limited to doing anything with the truck. We also had to change the engine (posted in his build thread today, last 2 pages). While we did that we also change part of the drive shaft alignment. I talked with several different drive shaft makers and they all said that it was possible that the 2 piece drive shaft could set up a wobble to cause the bounce. What we did was knock out the rivets from the carrier bearing bracket, and turn it upside down. Took a string from trans to rear axle pinion to make a straight line. Moved the bracket up till drive shaft was it line. Marked and drilled 4 holes, installed grade 8 bolts and tightened down. After breaking in the new engine, we when out on the four lane and man what a difference. We pulled a couple hard throttle pulls to 5,000 rpm in drive (3rd gear) and was smooth. Got up to 90 mph and still smooth. We still have a little vibration, so he is going to take the wheels and tires to a new shop in town that has a laser balance machine and works alot with large wheels. Here's a few before and after shots of the change..Jim

Glad you figured this out Jim. Come to find out my vibration was caused by a new set of Moser axles that were machined incorrectly...... go figure.... Oh well, at least I have it figured out now. Hopefully they will do the right thing and replace the axles free of cost.

[oldman3]

Originally Posted by Hart_Rod

Glad you figured this out Jim. Come to find out my vibration was caused by a new set of Moser axles that were machined incorrectly...... go figure.... Oh well, at least I have it figured out now. Hopefully they will do the right thing and replace the axles free of cost.

For the longest time I thought that was our problem. We had installed new axles from CPP, but after checking when truck was off the ground and spinning the tires at low rpm, they didn't show out of kilter, or anything. Hope you get yours taken care of. Let us know if Moser replaces for free..Jim

[jjzepplin]

Originally Posted by Hart_Rod

Glad you figured this out Jim. Come to find out my vibration was caused by a new set of Moser axles that were machined incorrectly...... go figure.... Oh well, at least I have it figured out now. Hopefully they will do the right thing and replace the axles free of cost.

WOW! MOSER-would have never guessed that. Seems nobody is perfect after all.

[Hart_Rod]

Originally Posted by jjzepplin

WOW! MOSER-would have never guessed that. Seems nobody is perfect after all.

Quick update on vibration issue. Turns out it wasn't the axles, sorta. I put the new axles in but the vibration didn't go away. So I started looking at the hub where the wheels go on the axle. With the car on jack stands and running you can see wheel hub is off centered which is causing the up and down bounce. It appears that my Billet Specialty wheels aren't centering up when I bolt them on. I think this is happening because the thickness of the CPP rear rotor. They don't let the axle hub stick far enough past the rotor to engage the wheel hole, thus preventing them from centering up. I'm not sure how to fix this....

[michael bustamante]

You said you have 5" drop springs right? But the sway bar you have isint long enough for drops more than 4". Probably not the issue causer but chances are the rear end isint centered.
Since everything on the rearend suspension is new id get a set of original style steelies with probably 225-75-15 tires on them and see if the rearend still hops on those. If so, id say new axles are machined wrong.....
Oops sorry. I just read your last post.

[jjzepplin]

If your wheels have acorn style lugs they should be centering themselves anyway. Just a little harder on the wheel if the hub is not engaging. I suppose a good machine shop could weld up some steel on the hub. Or you could reorder them possibly from Moser with deeper hubs maybe.
Kinda sounds like they are machined wrong anyway. You should not see any out of round movement when on the stands.
Can you see it with the wheels on too?
Maybe try your old axles for reference.