rear end problem

hunterjo · September 20, 2013

i have 2001 sudurban 1500 4x4. carrier bearings went bad 3 months ago and it wrecked the rear end. itook it on my self to rebuild it. replaced ring&pinion and all bearings. set it up like i read in manuals. i ended up with a winn on coast and a vibration at 64pmh and up. took it apart again and could not see problem but did nitice the axle where up to .030 out of round. drove it that way until 2 days ago and i took apart again and put in different ring & pinion and pinion bearings. still have same problems. could it be the out of round axles or something i am missing. could use all the help i could get.

thanks hunterjo

Doug_Scott · September 21, 2013

Being a fellow machinist myself, I gotta ask the dumb questions. Did you turn the centre down on the headstock first? And did you try mounting something else of equal length and thickness for comparison? Both ends ran 0.000" I'm assuming, and I'm also assuming it ran 0.000" along its length... .030" sounds like a lot to me man, I've never chucked up an axle that size before but I've done a fair amount of driveshafts. Just think, .030" on a driveshaft would vibrate like crazy....

This topic is quite interesting to me. After all these years, I have never heard of anyone measuring sxle runout this way.

There is a fairly large difference in rotating speed between drive shaft and axle. Anywhere from 3.08 - 4.10 times faster for the driveshaft.

I have no idea what the spec is for runout on an axle when measured that way. I have only ever measured the axle flange for runout,

You need to keep in mind that the way he is measuring the runout, the axle will actually be 0.015" out from centreline. Any axle that I found to be bent was found to be bent by measuriung the flange runout. Never measured the actual shaft for runout. That being said, if the axle shaft has 0.030" runout, then that should be passed on to the flange as well shouldn't it? For example... if you take the axle, and support it at the axle bearing and at the splines. Now, push down on the centreline of the axle, making the axle slightly bent. If you follow that back to the flange it should now also be off centre, with the flange in at the top, and out at the bottom. There is likely enough clearance in the axle bearing to allow some of the runout to be passed through to the flange.

Something that I do wonder about though is does the axle pick up a slight "wow" in it from the weight of the vehicle being applied to the flange, with the axle being supported by the axle bearing about 4 inches away from the load, and then not supported again until 48" later. Will the axle do any flex between the axle bearing and diff side gear from the large weight load 4 inches before bearing? If it does, the flex will not cause a vibration because the load stays stationary when shaft rotates. I would expect the shaft to get warm/hot if this does cause a flex in the axle. I do see it not being a lever with any mechanical advantage when you look at fulcrum, load and distance.

Prokopchuk_9 · September 21, 2013

Being a fellow machinist myself, I gotta ask the dumb questions. Did you turn the centre down on the headstock first? And did you try mounting something else of equal length and thickness for comparison? Both ends ran 0.000" I'm assuming, and I'm also assuming it ran 0.000" along its length... .030" sounds like a lot to me man, I've never chucked up an axle that size before but I've done a fair amount of driveshafts. Just think, .030" on a driveshaft would vibrate like crazy....

This topic is quite interesting to me. After all these years, I have never heard of anyone measuring sxle runout this way.

There is a fairly large difference in rotating speed between drive shaft and axle. Anywhere from 3.08 - 4.10 times faster for the driveshaft.

I have no idea what the spec is for runout on an axle when measured that way. I have only ever measured the axle flange for runout,

You need to keep in mind that the way he is measuring the runout, the axle will actually be 0.015" out from centreline. Any axle that I found to be bent was found to be bent by measuriung the flange runout. Never measured the actual shaft for runout. That being said, if the axle shaft has 0.030" runout, then that should be passed on to the flange as well shouldn't it? For example... if you take the axle, and support it at the axle bearing and at the splines. Now, push down on the centreline of the axle, making the axle slightly bent. If you follow that back to the flange it should now also be off centre, with the flange in at the top, and out at the bottom. There is likely enough clearance in the axle bearing to allow some of the runout to be passed through to the flange.

Something that I do wonder about though is does the axle pick up a slight "wow" in it from the weight of the vehicle being applied to the flange, with the axle being supported by the axle bearing about 4 inches away from the load, and then not supported again until 48" later. Will the axle do any flex between the axle bearing and diff side gear from the large weight load 4 inches before bearing? If it does, the flex will not cause a vibration because the load stays stationary when shaft rotates. I would expect the shaft to get warm/hot if this does cause a flex in the axle. I do see it not being a lever with any mechanical advantage when you look at fulcrum, load and distance.

I get what you are saying, but if it's 0.000 at either end and it's .030 in the middle that indicates something is wrong in my head....especially mounted between centres with no keyway or anything to make it sag...

Doug_Scott · September 20, 2013

When you say axle is 0.030 out of round, where are you measuring this? Does the axle flange move up and down or does it wobble in and out? Tough to describe this.

You do not say if the ring and pinions you have been trying are new or used. What gear ratio is it?

Is the vibration a hunting type (vibration seems to be looking for a specific speed) or just a constant "jiggle".

When you took it apart the first time, did you mark the position of the driveshaft? By this I mean you marked which cup went into which spot on the pinion flange. Did you take the driveshaft out completely? Does it have a hanger bearing mid shaft? It is possible that the shaft is now "out of phase". Out of phase vibration is described as being "hunting". Vibration fades in, stays briefly, then fades out. If you do not recall marking the shaft or paying any attention to the installation location, I would disconnect shaft from rear end, give the shaft half a turn and put it back together. Road test and see if any change.

When the driveshaft was not connected, did you check the u-joints? U-joints must be freely moving, with no rough spots when turning the cup. Do not just grab the shaft and push it up and down to check u-joints. At the very least, the shaft should be removed from truck, and each joint checked and verified no rough spots or missing needle bearing. A seized u-joint is hard to find if the shaft is still in the truck. A fair number of people I have seen working on cars would only look for worn u-joints that had play in them. They did not get that a seized u-joint does not move, and that is a bad thing.

hunterjo · September 23, 2013

i have thought of that but have not done it yet.

hunterjo · September 20, 2013

i took run out with axle chucked betweet ceners on lath. run out worst in center of axle

ffirst ring &pinion was new and second was used. i was tring to isolate problem. it has 3.73 ratio.

vibration starts at 64mph (always same speed) and alittle better at higher speeds. no vibration until 64mph.

i had drive shaft trued up and balanced with new u-joints after i had vibration problem

Doug_Scott · September 21, 2013

I get what you are saying, but if it's 0.000 at either end and it's .030 in the middle that indicates something is wrong in my head....especially mounted between centres with no keyway or anything to make it sag...

Sorry, should have been clearer. The sag I was referring to was not just the axle sitting there, it was with somewhere near 1500 pounds of force pushing the wheel flange up(or the bearing down, depending on optimist/pessimist), using the bearing as a fulcrum, and the diff side gears holding far end of axle stationary.

I get what you are saying, and I think we are both in the same boat, neither have ever heard of measuring axle run out that way. I would say that the reason we have not heard of it, is simply because any kind of auto repair shop other than a machine shop, will not have a device capable of mounting the axle that way to measure. I know I always did the measuring on the face and edge of the wheel flange on the end of the axle, with the addition of measuring a mounted rim to negate any issues with the outside edge of the flange not being round.

To get back to the OP, has he considered the front axle for the source of vibration? When truck is vibrating, slip it into neutral, see if the vibration changes immediately, change in frequency is what I mean. Same for acceleration, I see that you said it is less after 64mph, does it ever stop at speeds over 64mph. I find the speed number to be an odd number as well. Why 64? Or better yet, how are getting the speed? GPS? Have you tried moving tires around? A simple front/back rotation to begin with, and see if there are any changes. I know you said it only started after you changed the bearings and ring and pinion, but, you may find the vibration was there with the damaged diff, but, due to the effect of that, you may not have noticed the vibration. Now that it is quiet and smooth(under 64), are you noticing stuff that was hidden before?

hunterjo · September 24, 2013

one last up date. took rear drive shaft out and test drive it. had no vibration like before. sure points to drive shaft proble to me. any one else feel that way?

hunterjo · September 24, 2013

i

hunterjo · September 24, 2013

thought about leaving just carrier in but have not tried that yet. i did take rear drive shaft out and test drove car.no vibration. acks like balance problem to me. any one feel thing way?

hunterjo · September 23, 2013

yes it has a balance weight on it. transcase full of oil. i have a one piece drive shaft. it vibrates in 4wd&2wd. under load and coasting. i took some run out readings on axle flange with axle installed in diff. and found .000 to.001 on flange face on both axles. also took run out on flange machined hub of flange got .000 to.001. i just rotated axle by hand to get readings. i am going to take out rear drive shaft and drive it again to check for vibration. last time i did this the problem went away. will let everyone tomorrow the results.

one last thing i checked was axle bearing clearence and that was.007 to.008 on both axles. i just moved the axle up & down to measure clearence.

Prokopchuk_9 · September 23, 2013

How is the pinion bearing? I had an issue like this once and it was a missing weight on the driveshaft

I'm gonna bet a green one it's an unbalanced shaft! It's easy find out if something Is wrong if you have a lathe. Found a decent write up on another forum I'm on.

http://www.practicalmachinist.com/vb/general/balancing-driveline-shop-202792/

It have seen driveshafts that were almost new that were out of phase...somethibg to check!!

hunterjo · September 23, 2013

the pinion are new. when i put back in the old ring & pinion.( that was test to see if prblem went away but it did not

chas0218 · September 23, 2013

Can you put only the carrier back in and test to see if the driveshaft that is giving you the vibration? Make sure and fill it with some fluid.

hunterjo · September 22, 2013

i have a little more info. i used the lath to just hold the axle so i could get some kind off reading. no i did not cut the center at the chuck because i was not planning to make a cut on axle. i realize my .030 is .015 off center.( i will take wheels & brakes off and take run out on axle flange. )

i did take front drive shaft out and problem still there. took rear drive shaft out problem went away. i am wondering if the drive was not done right or the tranfer case has problems. i put different tires & wheels problem stiil there. the vibration done not go away when put car in neutral only changes with mph.