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how to check rear end axles, if bent?

6K views 19 replies 11 participants last post by  Mitchman 
#1 ·
I have a vibration I believe is coming from the rear end. It comes on at about 50mph and goes away with higher speed. Around 50mph there is a very noticeable shake in the vehicle that clears up with speed. I have changed rims, bought new tires, balanced and rotated and it is still there( which all needed to be done anyway). The only thing I can think of is a axle is bent or maybe a bad bushing in the suspension. When I slowly start to brake it will slow , then loosen , then slow , then loosen with the same pressure on the pedal. So that makes me think its not a bushing, (probably wouldnt hurt to change also)


Looking at the axle and spinning it by hand I can not see any visible movement. I am going to put a measuring gauge on it but how much movement is normal?

84 c-10 truck
 
#2 ·
well I dont think its the axles now . I put a dial gauge on it and it has 4 thousandths run out on the driver side and 3 thousands run out on the passengers side. I guess I am am going to slap the tires back on it and check the run out on the tires again.
 
#4 ·
Check the TIR on the new rims too. Perhaps they are not sitting flat on the registers or they are machined crooked.

Ujoints would be my first guess even though if they don't feel loose if you check them the usual way. It's pretty easy to get a needle bearing jammed against the cap and cross. It's also real easy to get the rear joint misaligned in the rear axle yoke. While your there...check the TIR of the DS.
 
#5 ·
thanks
I dont think its the U joints since it was doing it before and I just replaced those with in the last 6 months and it still doing it.
I am thinking now its the bushing and bad brakes. I think the bushing are just old and weak any slight unbalance is exaggerating the issue. Even though the wheels were balance on a digital balancer at Sams warehouse, by a couple of yahoos for lack of a better term. Going to check the rims now.
 
#9 ·
no its a pretty heavy shake vibration. Enough to see the bed of the truck moving in the mirror. Pretty bad. Like a out of balanced tire but tires have been balanced and rotated numerous times but it still exist. I am going to check the front end (all new bushings and parts)tires and rotors for run out tomorrow. I will be glad once its fixed because the crap is annoying.
I am think its rear leaf bushings. I also have a taller than stock tire on there if it makes a difference. 31x10.5x15 BFG All terrains.
 
#11 ·
Best to have an observer follow you and watch from the rear, could be tread separation on one or more tires. Brother-in-law's (early 80's) Ford van with Firestone "721" tires had all four separate at the same time. Sometimes it's obvious, sometimes not...

Russ
 
#14 ·
A simple "Run out" check using a few simple tools like this is all you need.





Just lift the wheel up off the ground, set up something like this and spin the wheel. About a 1/16" is pretty normal.

Brian
 
#15 ·
Thanks for the great tip on checking run out. I have not had a chance to do anything today but I did run through all the run out test of the axle and rim. I am feeling that my issues are coming from the tires. BFG' All Terrain, 31x10.5x15

While up on the stands and letting the wheels turn I noticed one tire moved laterally more than the others. The rim did not move but the rubber tread moved up and down. Out of round. Its balanced but looks to be out of round.
 
#18 ·
I forgot to tell you that to determine if it's the wheel, or it's the hub or axle is you need to mark the spot where it gets closest to the tool within the wobble. Then mark the axle/hub as well. Remove the wheel from the axle/hub and rotate it 180 degrees so the mark on the wheel is opposite the mark on the axle/hub.
Do the spin again and see where it goes out the furthest in the wobble now. If it is on the same spot on the wheel, then it's the wheel. If it's at the opposite side of the mark on the wheel, matching the mark on the axle/hub, then it's the axle/hub that is bent.

Brian
 
#16 ·
Checking runnout side to side is great, but also as Eric mentioned, check the tread runnout to see if the tires have high spots, or out of round. A lot of tire stores used to true tires, but many states banned the practice, because some were using the machines to cut new grooves to extend tread life.
 
#17 ·
Never thought of that, YEOW!

I need to do all this too, Marge has a vibration at about 45 mph that I need to solve, this will be one of my projects in the coming weeks. I thought it was the 20 year old bias tires that I replaced but nope. The rims were trued when they were powder coated, (though I didn't do it so who knows) and they were of course balanced. But I need to look into the drive train and see about that. The drive shaft on these cars is very odd without any unboltable U joints. I will see what I can do.

Brian
 
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