"live" axle - not so good vibrations

Took the car for a drive today after a few weeks of quality time underneath the rear.

I have a vibration now that starts at about 45mph, and by the time you hit 60 you're going to want to stop. No, this wasn't there before.

Here's what I did back there:

Springs
Shocks (and fixed the ALC compressor too)
Brakes (wheel cylinders, shoes, drums, hardware)
Axles
Wheel bearings and axle seals
Yoke seal
U Joints
Cleaned up and painted the axle (*)

* = I think this may be the culprit. The axle was very rusty and had a bunch of goopy greasy stuff stuck to it. I cleaned it off and painted it. Maybe it threw it off balance?

Or maybe I goofed when I marked the axle, I can try flipping it around 180 degrees and see if that does anything.

Does the alignment of the driveshaft to the transmission output have to be maintained? I didn't put that back in the the same way it came out. I don't see why that would matter.

The problem is road-speed dependent, it does not follow engine RPM (put it in neutral, still does it) and it feels like the entire rear of the car is hopping up and down, that's the best I can describe it.

Is there a possibility that you may have dinged the driveshaft or threw a balancing weight off it? Mine hasa small weight on it.

 Years ago, I remember having a Dodge maxivan in the shop for service. The tech pinched the shaft with the lift.  Instant laundromat  like spin cycle. Thumpitathumpitathumpita....

I doubt the tube got dented in any way, but I will definitely re-check that. I don't believe any weights fell off, I would have seen them on the garage floor if they did. I'm wondering if my painting added weight to the weights, since they sit slightly above the tube, the gap may have filled up with paint.

lamune wrote:

I'm wondering if my painting added weight to the weights, since they sit slightly above the tube, the gap may have filled up with paint.

I did laugh out loud when i read this,...

Unless you have a 3 oz drip of paint on one side of the tube,. i think you'll be fine,..
driveshaft speed is relatively slow with 2:56 or 2:93's (i can't remember what you have)

i would try rotating the shaft 180deg and re-installing,.( assuming you don't have a tight universal)

I would also jack the car up and make sure the axle shaft is turning with no run out,.(i.e no orbital rotation)
mebbe the vision problems associated with the shape of the chinese fella's eyes that drilled the stud holes etc,..? (off center?)

i might paint a witness mark on the drums and 1 stud,. then pull the drum(s) off and rotate it(them) 1 or two studs and put them back on,.

I would also hazhard a guess the vibration/wheel hopping might have been there before but not so noticeable with old springs and shocks,. a good tire balance might do the trick,.

Do you have a FSM? There is talk about checking the pre-load tension before removing the diff yoke and this would give you the tension also needed for the pinion bearing, carrier bearing, axle bearing and seal preload.....Since you had yours apart, did you do this step?

Nick, glad to give you a laugh there. I have no idea how sensitive these things are for balance, so I figured I'd mention what I did.

I don't think there's a centering problem on the centering of the U joints or holes but that can be checked. You know, I did press out and then press back in a new U joint because I did it wrong the first time. I wonder if that may have done something or not, but they seem pretty robust and that doesn't seem to be a likely cause of this problem. But I could be wrong, and I'm sure you'll let me know

First step I think would be to turn the driveshaft around 180 degrees since that's really easy to do. Wheel balance or an unbalanced drum is certainly something to look at as well.

Lance, I do have the FSM and I did follow the procedure there. Well sorta. I measured the torque when I started. It was about 8 in-lb. I put the nut back on when I changed the seal and tightened it just short of where it was originally. Then I measured again and it was about 18 in-lb, which I didn't expect since in theory it should have been looser than it was when I started. Since you can't back that off without a new crush sleeve I left it alone. After putting everything back together and rotating the whole assembly with oil in the case, the torque was 10 in-lb.

I have no idea if that's significant or not, if the thing is really overtorqued, and if it is if that can cause this sort of vibration.

(Yeah I sound like the people I work for. You know, "it stopped working and I didn't do anything!" "Really?" "Well except I did this. Oh yeah and then I did that... on second thought maybe that did break it..." ugh )

I flipped the prop shaft 180 dregrees, we'll see what happens. Oh and to make matters more fun, the yoke seal is leaking way more now than when it did before I changed it.

Did you remove the factory u-joints (nylon injected rings) or did they all have internal snap rings? I ask because forcing out the nylon ring style can really mess up a yoke if not familiar with their removal. I had a driveline shop remove mine as I gave up trying to heat out all the nylon. The propeller shaft/front yoke does indeed need to be marked when removing to be reinstalled correctly. Hopefully by rotating the shaft you nailed the problem.

They were the original factory joints with the injected nylon. I pushed them out with a shop press.

With the prop shaft rotated 180 degrees, the vibration seems reduced, maybe about half as bad. I'll take it in for a wheel balance and see where that leads.

Another thing to think about is a drive shaft balance. It has to have both ujoints to balance it on the machine. It's about $65 to have that done.

I've melted the plastic of the OEM U-joints once, since it seemed to take too much power to get them out otherwise.. But then again I don't have a press, so I must press them in a vise while giving some blows with a hammer, which must be worse than just pressing. So maybe it's OK to press them without melting the plastic. There shouldn't be a problem, if the new U-joint turned normally.

The FSM procedure is to press the originals out and makes no mention of melting the plastic. I don't think anything got bent during removal. The procedure does say to remove all the leftover plastic, which I neglected to do. It also doesn't offer any hint there on how to do that. But I don't see how that plastic being in the groove could cause any problem.

I don't like the feel of the U joint at the diff end, it feels stiff to me. I'm going to try re-doing that, I might have done something wrong there and damaged a roller or.

I always heat the factory joints up get the plastic out,.it puts a lot of stress on the ears with a press to break that plastic,.

I would now hazard a guess that the springs have the car lifted? slightly,. and as u mentioned the rear joint is tight,..

Nick, yes, the car's ride height is back to normal now that the springs and shocks and ALC are replaced.

It did take a pretty massive amount of force to break them free. Maybe it got bent.

The joint feels stiff, like it's binding. I ordered another and I'll swap it out.

Ok, I think I found the source. While the car is up on stands I ran it up to 60MPH and took various videos of the moving parts. Nothing obvious until I viewed the video I shot of the output yoke of the trans. I think my driveshaft is not centered on the u joints. It's very obvious when it starts moving and just before it stops. Here's a video for your consideration.

Now I have to figure out what I did wrong. I hope I didn't bend the ears or something like that. I may be in the market now for a shaft.

i need your password to view the video,...

ah, oops. That should be working now.

HI guys, First post so bear with me.Many moons ago I worked at a parts store that did shop work also.We had large press and all the proper tools I had done 100s of u-joints and thought I "knew the ropes". Had a customer come back and describe the same thing you did.Fortunately,I remembered that one of the u-joints seemed more stiff than the other after they were installed and greased.I worked it back and forth a little and decided that it was just a fluke.When he came back in with a story like yours,I knew where to look for a problem.Pressed it back apart and found a single needle bearing laying on it's side, imbeded in the cap. It was enough to space the yoke sideways as to off-center it.My bad! Pressing in a new one paid for outa my pocket solved all issues.Knew better than to try to salvage and reinstall.Some times the factory pre-lube isn't enough to keep the needles stuck to the sides of the cap.Also, the needles need to be perpendicular to the bottom of the inside of the cap.If they are not,one or more needles has gone missing.I have found one inside the grease galley/port in the cross part of the U-joint.Hope this helps

in all my years i,ve never been able to get the clip on if there is a needle bearing sideways,..

but then again i don't use a hydraulic press,. i like my bfh,..

The press was a biggie,probably an old Dake.I remember that the press stopped about a sixteenth before the little rubber dust seal seated home,but a couple more pumps put it where it should have been. Turns out ,both the cap and the cross are cast and slightly softer than the needle which imbedded itself equally in each.Also.we had a torch set up and always melted out the plastic when present,as it didn't take any time at all.A quick quench at the sink and the residual plastic cooled first and fell down the drain and the yoke was cooled and free of all rust scale,ready to go back together

Thanks guys. Those are some good suggestions regarding the installation of the U joints and the potential pitfalls of using massive amount of hydraulic pressure. I did some troubleshooting today to see if I could eliminate that possibility. I removed the joints and more carefully installed new ones using the press only when hand tools wouldn't cut it. In the process of doing this, I'm pretty sure I do have a slightly bent ear on the transmission side of the driveshaft. However I don't think that's the source of the nasty vibration. But I think this might be:



"Centric" products indeed.

Oh, I'll remove the other wheel and drum tomorrow and re-test (and I sure hope I remember NOT TO HIT THE BRAKES!!!!!) and see what happens, that'll at least eliminate drum and wheel balance as the source. We'll see what that reveals.

Yep, that certainly looks like a hitch in your gitty up.

"somebody" dropped that drum by the look of things,...

take it back,....OR if you are real good with a bfh,.....

Lance!

Nick, that could certainly be. There's a metric ****-ton of balance weights welded onto that one. Maybe one fell off!

With no brake drums on the car, the vibration is gone. Well, I do get a little bit at 70+ which could be prop shaft related, but that certainly points to out-of-balance drums to me.

So in looking at the brake drum landscape, it seems that all the drum choices I have are Chinese made. All have the number 8873 cast in the front of them. (Including these Centrics that I currently own) so I'm going to assume that they're all the same part just rebranded for ACDelco, Raybestos, Centric, etc.

The bulk of the vibration seems to have been the brake drums. I swapped them out for another set, and if the vibration level was at 10 before, it's probably about 3 now.

Are there other car/truck driveshafts that fit the RMW? I pulled a shaft from a 93 Caprice and it's too long. That Caprice was the only B-body at the yard, but there's tons of GM vans and trucks.

I wanted to follow up with this - I took the shaft to Drivelines NW for evaluation. In a nutshell, they had to cut off one of the ears and reweld it back on at the center of the shaft, because it had .040 of runout. Runout now is .007 at one end, and .009 at the other.

I wanted to share what the guy at the shop told me. Boiling it down, he says that the "glued" in stock U joints have a rather wide centering tolerance in mass production. They compensate for this by balancing the shaft with the joints installed. When you put in internal clip-retained joints, they may be better centered, but since the shaft was balanced however it ended up on the production line, even if it's properly centered it may not be balanced anymore and vibration can result.

This seems to make sense to me, and seeing how I did this twice and got two different poor results- combined with the fact I'm talking to a guy who does this every day for a living, I guess I agree with it in concept. But it's news to me and I'm sure plenty of you out there have changed U joints without having to have the shaft cut, welded, and dynamically balanced.

NW Drivelines has been around a long time and know their stuff.  They pressed out my nylon injected joints.  I already bought high end u joints for replacement but they in essence told me that to balance my driveline, I had to go with their joints which were  3 times the cost of the ones I had already purchased.  

After I listened to their spiel, it dawned on me that they in a nutshell are saying that every driveshaft out there that has had u-joints replaced should have been balanced after.  

Probably true, but just have never done it.

I have never heard of cutting an ear off and rewelded for balance; guess that press of yours did a number on it!

what a story,...

I'm not sure I believe the spiel either, but I took it out today and the hum is gone.

cutting off an ear,.rewelding it,. never heard of it,.i call bullshit,.it can't be done,.

more likely cut the yoke off the tube and welded on another,
.

.040 runout,. not unusual,..

Too many wild and wacky stories coming from the west coast,.

they might hold water for some wagon owners,. but not those of us that actually build cars,...

phantom 309 wrote:

cutting off an ear,.rewelding it,.  never heard of it,.i call bullshit,.it can't be done,.

more likely cut the yoke off the tube and welded on another,
.

.040 runout,. not unusual,..

Too many wild and wacky stories coming from the west coast,.

they might hold water for some wagon owners,. but not those of us that actually build cars,...

Yeah, yoke. Not one ear. I can see where it was cut off and reattached.

Well, lesson learned on that. Won't be making that mistake again.

(edit)

Forgot to add, Lance, about what you said about every shaft having joint replacement needing rebalancing according to those guys... he told me that now that the shaft is centered and balanced I could replace the joints with internal clips as many times as I want without affecting balance.

So in conclusion now that I've gotten this figured out, I tackled three sources of vibration and here's how I would rank their impact:

#1 - (presumably) bending the ears on a driveshaft yoke .040: minor impact
#2 - cheap Chinese brake drum out of balance: moderate impact
#3 - dry rotted, cracked and bald tires with flat spots: major impact

And of course, changing a lot of stuff at one time leads you down a lot of ratholes.