Smitty454

Ive been chasing a shaking type of vibration for a good year now. I finally had the time to do this little experiment where I flip the drums to seem how true the axle is and as you can see, it doesnt look good.

The shaking really starts to come on at around 65mph give or take and tends to smooth out the faster I go, but doesnt totally go away. Ive adjusted the pinion angle a million different ways with no relief. I bought new wheels and tires and had them balanced twice with no change. Also bought new balanced quality drums as well. No change.


Take a look and let me know what you think. Both sides have the wobble.

1970 Chevelle 12 bolt eaton posi 4.11s

jmd

iTrader: (4)

I'd say it's definitely a problem. It appears to possibly be a bend of the axle; if so, it could be worse at the outer edges of the tire circumference.

Hand-rotating an axle, is there runout at the face of the axle, or the edge of the axle flange?

Wheel bearings are another question, but it appears to be a consistent lateral wobble, not a random axle flopping around type.

What was the history of the axle's usability before 1-yr ago? Was it a project with no known history? Or was it used in a way that could have indicated this before?

Bad Apache

Dial indicator on the axle wheel flange face and slowly turn the axle. That'll tell you 100% if there is a problem or not. It would appear there is, lol. But to be sure, do that. Seen bent axles a few times in the last 30 years. Good luck!

LetsTurboSomething

Do the dial indicator like they suggested above. The only other thing I can think of is if it showed up right after getting new brake drums installed and got a crappy batch of Chinese drums or something that were that far off.

Smitty454

Setup the dial indicator and here is what I found. Looks like runout is around .001 if im reading this correctly.

Drivers side

Passenger side

LetsTurboSomething

I slowed the video down, I thought the needle was bouncing more. .001 is straight according to GM. Anything up to .003.

Warped drums?

Smitty454

I read it wrong. Looks like it's .01 not .001

LetsTurboSomething

Then that's toast lol.

gofastwclass

iTrader: (2)

Hard to see but judging by the swing of the needle it does look like .010" or really close to it.
More accurate (and safer) method to test with the indicator is turn the axle slowly by hand so you can see the minimum and maximum swing. The surface finish on an axle hub is pretty coarse and can really mess with an indicator at the speed you showed.

If the reading is similar using the method I described I would stop driving the car and start looking for aftermarket axles.

Smitty454

I tried that at first and the axles was too hard to turn by hand. I tried turning it with a lug wrench and I couldn't get a full turn in because it would run into the dial indicator so I said eff it and put it in drive.

Is there an easier method to turn it by hand?

Mikes64

Remove driveshaft

gofastwclass

iTrader: (2)

Just place the transmission in neutral, no need to remove the driveshaft.


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Leave a wheel on the opposite side and have a friend turn the wheel.

Smitty454

Ok I pulled the driveshaft and redid everything.

The driver side still has a significant sweep up to ~.009 in one spot while the passenger side is definitely less pronounced with a sweep of at most .003.

Is there something could that drivers side be bent enough to be causing my problem?

I bought the 12 bolt from an old Chevelle guy who had it laying in his backyard.

I took the 12 bolt to a shop I thought was reputable to have it rebuilt with a new eaton posi unit. The shop I later found out wasn't reputable. They had a name very similar to to the shop I meant to take it to.

I can't recall if they replaced the axles since it was 12 years ago. I do remember that it had saver bearings in it.

LetsTurboSomething

So if the face of the hub you dialed off of is clean and not rusted to hell and you're getting a true measurement of the face, then the factory acceptable measurement is .001" to .003". Anything more than .003 is considered a bad axle.

That .009 is your problem. How it went bad I don't know. Who ever pulls it apart will be the one to figure that out.

Smitty454

Yeah its pretty clean. There are a couple little pock marks that made the dial skip but the did a few revolutions back and forth and there is definitely more runout than .003. The difference between driver and passenger side was pretty normal. I may just take it to a shop and have everything checked and see if they come to the same determination that I do.

LetsTurboSomething

I build a lot of stuff myself, even my own transmission rebuilds sometimes. But I still take like taking my axles to a gear and drive line shop because it's like the one part on the car where if it lets go at full boogie the wreck can be catastrophic. Give me a scattered engine at 100mph over an ejected axle anyday of the week, ya know?

Smitty454

Yeah that's what I'm thinking.

When they "rebuilt" it they didn't even bother checking the pinion. The little tabs that keep the ujoint centered were broken off. I fixed that a few years ago but that goes to show how much attention was paid to the rebuild

gofastwclass

iTrader: (2)

Someone probably unloaded it from a truck solo and it landed on the now bent side.

No need to take it to a shop, only takes one bent axle to make you car feel odd, been there. Your bent axle is a failure waiting to happen. Difference is you caught it before something happened and I found mine while driving and I have a souvenir from that situation. Short version: in my early 20's I bought a car that later developed a vibration I couldn't trace for months no matter what I tried or who I asked. While evading a drunk driver the flange broke off the axle, got lucky with no real damage to anything as I was going slow. Inspection after getting home is the axle was cracked more than 50% through from before I bought the car and got worse the more I drove. I saved the flange as a reminder on how thorough I need to check things - even the illogical 'it can't be that' items.

I would throw down on some quality aftermarket axles (Moser, Strange, etc.) with Timken bearings and not look back. If you're concerned about the build quality of differential, check it out while you've got the back off and the oil out.

Smitty454

Ok will do. Im torn between taking it to a shop and doing it myself. I dont have much experience with rear ends and Im not sure what to look for. I suppose I have some research to do.

CattleAc

iTrader: (7)

This. Take it apart and check the splines also. I'm willing to bet they will have significant wear. New axles will be a win, win.