Driveline vibrations, round II

[goodtimes]

'03 TJ (rubicon). 3.5" lift, fixed lowers, adjustable uppers and adjustable track bars. Axles are centered. Rear CV shaft (tom woods). New tires.

Cyclical vibration starts about 55mph, becomes prominent at ~65mph, and just gets worse up to 75mph *under load* (any load...even flat freeway....as long as I am on the gas). When I coast (in gear or out of gear), the vibration becomes constant, and less severe. This is the case with both driveshafts installed, or just the rear. With the rear shaft out (now in "front wheel drive"), the vibration is non existant, up to 75mph (don't drive much faster than that). This has been the case since the day I installed the lift and CV driveshaft ~10,000 miles and 2 years ago. Vibration has slowly gotton worse.

The rear driveshaft was showing some wear in all the joints, so they have all been replaced w/new components, and the shaft was rebalanced this morning. This helped. It probably reduced the intensity of the vibration by 50%....but it is still there.

After balancing the shaft, I moved the pinion angle up to match the driveshaft angle.

Road test. Same problem.

Lowered pinion angle by one turn on the upper arms.
Road test. Same problem, not as severe.

Lowered pinion angle by one turn on the upper arms.
Road test. Same problem, got a little better.

Lowered pinion angle by one turn on the upper arms.
Road test. Same problem, little change (measured via "seat of my pants").

Lowered pinion angle by one turn on the upper arms.
Road test. Same problem under load, but under coast, the vibration got worse. Pinion was now +/- 3* below driveshaft.

Raised pinion by 2 turns on upper arms.

Called Tom Woods. Based on the info above, they say it is not a angle problem (now that I moved the pinion back up). They suspect either the shaft is bent, out of balance, not running on center, or I have a damaged yolk. Local shop which just balanced the shaft claims it is strait and balanced (obviously....since I just paid them to do it).

Now, the rear pinion yolk has been bounced off of a rock or three in the past few years, but nothing too dramatic. It has a few scars on it, not much else. Has anyone heard of, or had, a damaged yolk that doesn't have any obvious physical damage, cause a vibration? I wouldn't be opposed to replacing it, as I'd like to get rid of the u-joint straps anyway....but I am in a time crunch. I am off to Colorado on Saturday....

Any thoughts or suggestions would be appreciated.....

[aston]

Tucson driveline and balance, on Stone, did a nice job for me with quick turnaround.

[goodtimes]

At this point, I think I will have them check it out tomorrow. I'm quickly running out of options.

(btw, that was me on Golf links this morning).

[goodtimes]

Progress....sort of.

Tucson Driveline noticed that the two ends of the shaft were not lined up properly ("timed"....as they put it) Basically the two ends were not indexed properly before being welded together. They corrected this, and claim to have straitened the shaft, and balanced it. I installed it, and low and behold.....I have the same F'ING problem!

Recheck the pinion angle.... ~1 degree down. Same problem.

I put a dial indicator on the shaft, and here is what I find.

On the adaptor ring (used to mate the driveshaft to the balance ring DC puts on the rubicons), has .008" radial runout. The driveshaft tube (immediately to the rear of the CV joint), has .018" runout, and the far (rear) end has .009" runout. With the middle of the shaft having twice as much runout as either end, I am thinking that it is still bent.

Question is, how strait does it need to be? In a perfect world..... zero runout is "right". In the real world, is .018" "acceptable"?

[blkTJ]

paging tom woods...

it sure would be nice if we had a good driveshaft guy on the board. :thumbs_up

[goodtimes]

paging tom woods...

it sure would be nice if we had a good driveshaft guy on the board. :thumbs_up

I have talked with him at least half a dozen times over the past 2 years trying to straiten this out. I am ready to send the shaft back to him and tell him where to shove it.

[aston]

Holy shite what a PITA.

The only thing I can offer is that I'm glad it's not me.

[blkTJ]

I emailed him your post, this is the responce.

You certainly shouldn't be getting anywhere near .008" rub-out on the
adapter. These are made on a CNC and are usually dead on. Of course both man
and machine are capable of an error. Did you measure on the pilot on the
center or around the perimeter of the shaft. You may also want measure for
any rub-out on the pilot of the mass vibration dampener hub. If this is off,
everything else would be too.

.018" on the drive shaft tube is a bit more than we'd like to see too but
again if either of the pilots are off this would account for nearly half of
what you're reading. The tube itself will never be perfect as this is
formed rather than turned and then of course it is welded which will
distort.

Please double check that the flange adapter doesn't have anything which has
prevented it from bolting down squarely and that the pilot on the mass
vibration dampener hub is true.. After that I think the next best thing to
do would be to send another adapter and let you see if this takes care of
things.

Please include this text in any reply.

Tom Wood
Tom Wood's Custom Drive Shafts Inc.
Toll Free US 1-877-497-4238
Worldwide 801-737-0757

[goodtimes]

I have spent the afternoon down at Tucson Driveline, with my jeep on the rack out back. We pulled the shaft again, and measured the stub rather than the tube (because, as mentioned above, the tube isn't the best place to check). There was .007 runout. They torched it and took .004" out of it, so now it is at .003". Of course the vibration persists (12 hours until I am supposed to leave for Colorado for some 'wheeling).

But, the adaptor still has a ton of runout, measured on the OD of the adaptor. Of course, if the OD was machined after the pilot, and the part was removed from the chuck, this could account for some error which would not have a drastic affect on performance (because the pilot is what locates the adaptor). Once my jeep cools off, I will check the runout on the pilot of both the adaptor and the t'case.

I also measured the distance from the ID of the adaptor to each of the 4 bolts (where the flange on the CV joint bolts to the adaptor). 3 of them are within .002, relative to each other....but the 4th is .005" off, compared to the others. This was far from a precise way to measure this...but it was late and I was tired......and I had to get up for work early this morning.....

[goodtimes]

pilot on the adaptor, which locates the driveshaft: runout = .008"

pilot on the t'case flange, which locates the adaptor: runout = .001"

Tom Woods is closed for the weekend. Bastards.

[goodtimes]

OK, I hate my jeep. (not really).

I removed some material from the ID of the bore for the pilot on the adaptor ring, put an indicator on it and moved it around with a hammer until I have less than .001" of runout on the pilot for the driveshaft . Still have the same vibration.

So......I measured the offset of the pinion, relative to the frame rails...it is about 3/4" to the passenger side. Next, I measured the offset of the t'case output, relative to the frame rails....it is offset 2 1/4" to the passenger side. Doesn't seem right...it should be pretty damn close to what the rear pinion is...right?

So, I drop the belly pan (which I built a year or so ago....*after* I started having this vibration problem), move the t'case mounting holes 1.5" to the drivers side in order to line the t'case output shaft up with the rear pinion. Well....the f'ing engine/tranny/t'case doesn't like it that far to the drivers side. In fact, I can't get it to move that far to bolt it all back together. Working alone, I can't push on the t'case and look around for interference at the same time....but it feels like I am pushing against the motor mounts....I push, it pushes back. It is really happy right there at 2 1/4" to the passenger side.

So, does anyone know how far the t'case output shaft should be, relative to the frame rails? Are the frame rails basically mirror images of each other? It is possible that the t'case is centered, and the frame rails are different, thus my measurements being off....anyone ever measured it? Anyone want to? Anyone want to shoot me in the head and end my pain and suffereing?

[goodtimes]

For future reference, I have read that the driveline on TJ's are offest 19mm to the passenger side. True or not....I couldn't tell ya.

The frame rails also appear to be mirror images of each other, based on the FSM drawings.

[aston]

Bloody hell. I'm so glad I'm not you.

[Pfeiffer]

Try contacting Coast Driveline in Ventura, Ca. They have a shaft that doesn't require an adapter and uses a 1350 CV.

[goodtimes]

There is a problem other than the driveshaft at this point. It makes no sense to sink several hundred dollars into a driveshaft when the transfer case output shaft is not where it is supposed to be.


So here is the latest. After spending more time underneath this bastard, it just *looks* wrong. The engine/trans/t'case is crooked, relative to the frame. You can see it, thats how far off it is. You can see it where the t'case sits under the body, how the fan lines up with the radiator and shroud, you can measure it anywhere you want....the damn thing is crooked!

My first thought was the frame not being square. If the drivers side frame rail was pushed back relative to the passenger side, this would kick the t'case output shaft to the passenger side.

Using the low-tech method of hanging a plum line from known points on the frame (approximating these locations), transferring them to the floor of my garage with a black marker, then using the trusty old tape measure.....

The front half of my frame is strait (the half I was concerned with because it locates the drivetrain, via the motor mounts). In the linked image above, the front 2 "boxes" are dead on. The rear "boxes" are off a bit though. That could be my low-precision method of marking locations...not sure. Overall, measuring to the 4 extreme corners, the frame is within 1/4" of square.

That said, the front half being what locates the engine/transmission/t'case assembly, I don't think the frame is the problem.

Next suspect, the motor mounts not aligned correctly. So I loosened them up and tried to move the eng/trans/case over where it belongs. No joy. The though crossed my mind that the frame jig was off (or more likely, the robot that put the motor mount ears on the frame wasn't programmed correctly), and they welded a motor mount on in the wrong spot...but I have nothing to reference off of. The passenger side motor mount is farther back on the block than the drivers side (by about 1 1/2"), so I can't simply pick a spot on the frame and compare the two sides to each other.

I don't see anything else that will cause this problem. What am I overlooking?

I could unbolt one motor mount, line up the t'case and rear pinion like they should be, open up the hole in the mount so the bolt will fit, and put it all back together....but that is an aweful lot like putting a band-aid on the problem. Unless of course the problem *is* the motor mount(s)....