vibration !!!!!

[Dan Cuda]

I have a major rear end vibration problem.
I have a 74 duster that I put an 8 3/4
in with cut down c body axels with 11 inch
brakes. I have a brand new drive shaft that
has been balanced. With 323's the car starts
a violent vibration in the rear-around 60 mph. It's hard to
describe- it goes rrrrrrWWRRrrrrrrWWRRrrrrr
(please dont laugh too much). When I changed to 391's the vibration appeared at 50 mph.
Going with this theary I put in 430's and it moved to 40 mph. So I figuered it has to do
with wheel rpm's. Any ideas???
list of what I have done-
8 3/4 change over with c -body axels cut
down by Moser, green bearings, 11 inch brakes,new drive shaft, new pumkin(all new bearings), wheels and tires spin balanced.
Also new tranny mount, and I checked the
pinion angle


[This message has been edited by Dan Cuda (edited December 29, 1999).]

[johnjdodge]

Have you checked the trans rear yoke bushing?
Not the seal, but the bronze bushing which the front yoke rides on. I have seen too many trannys "rebuilt" without addressing this part, and the shaft will vibrate.
Slide a spare yoke into trans & see what kind of side-side/up-down movement you have with yoke say 75% inserted.

[Dr. Righteous]

I chased that same annoying noise and vibration in my '69 Coronet. I changed all the wheel bearings, both U-joints, had the drive shaft spun, then had the 83/4 chunked rebuilt. I still had the problem. By process of elimination I decided it had to be something to do with the tranny. but it was the rrrraaaaaarrrrrraaaaarrrraaaa noise at highway speeds that is typical of a U-joint or wheel bearing.
I never fixed the noise before I started the big block changeover, after this there will be a totally new drivetrain. If it still makes the noise I am going to jump off a cliff.
Is that bushing wearing out in the tail of the tranny pretty typical in a 904?

------------------
Stress is a relative thing. Now please shift into 4th.

[PRO]

I'm fairly certain you have a pinion bearing problem,you didnt state if all 3 sets of gears are in their own center sections or if you had them installed on the same center section,if you used the same center section I would seriously inspect the pinion bearing.Can you move the yoke of the 3rd member up and down at all? it shouldnt move.When you rotate it w/the 3rd member out of the housing does it have tight spot? You are having these professionally set up right? if not it could be you carrier runout is too excessive or even you side play is too much.get a known good center section and istall,if its gone you at least have narrowed it down.Hope this helps you ...PRO...

[340king]

When I had this problem with my '74 B-body, it was with the wheel bearings, but the symptoms you describe are on the input side of the rear end. I would start at one end or the other of the drivetrain to eliminate and check every possible source of the vibration. Starting with the transmission output and going to the ring gear of the rear end.

[V10nacuda]

I would have to agree with John... I had the same problem in my barracuda.... Swapped the tail shaft & ba da bing problem solved!!!!!
Are you sure the axles are TRUE & Straight??
Good luck, let us know the results

V10

[360duster]

Is it a vibration or a roar?If its more a roar i will go with PRO on this one but if the whole car vibrates i would take a closer look at the driveshaft or the pinion angle.I had the same problem in a 65 cuda that someone had put a 9 inch ford in.It was the pinion angle,it was way off.If it was not doing this before the swap it`s got to be in the shaft or the rearend.Also be sure that shaft is not too short.You should only have about 1 inch free play that you can slide it into the trans with it installed,if you know what i mean.I`m not good at explaining things.good luck with it. KB

[Maxwedge]

a similar problem happened with a friend of mine that ordered a 360 crate motor to replace his stock 318 and automatic.
he had come into some money so he ordered the motor from summit and when he asked them if it was just a bolt in affair they said "yes, no problem"
well there was, the 318 was internally balanced and the 360 ISNT. Torque converter issues insued.
i didnt hear the car run when it was bad, but he said it made an intersting sound and vibration.
just a thought
Maxwedge

[timty2]

Does anyone know the basics on setting up the pinion angle correctly or how to visually check to see if it is incorrect?

[ehostler]

I had a similar problem on my '68 Charger. I was never able to track down the problem.
After a couple years of driving the car, the tranny got wasted (unrelated). After the tranny was rebuilt and I put on a new torque converter, the vibrations completely disappeared.
It was something out of balance in the tranny or the torque converter was out of balance.

the rear wheel rpms are the same at a set speed
regardless the rear end gears used.