4104 vibration at speed

[Nova Eona]

Hey all, I just woke the bus up from the winter and am hoping to take it on a few hundred miles' trip in two weeks, but I'm still chasing some vibration that appears at speed.  Engine runs smooth and everything cruises nicely around town, but getting upwards of 40 mph there's a distinct vibration strong enough to rattle some of the windows (and the stove) and make the passenger side mirror visibly vibrate.  Last year I had the driveshaft replaced (separate issue) and did the rear radius arm bushings, but have not yet gotten to the front radius bushings yet.  Tires are two years old and were all checked on the spin-balancer to make sure they weren't the issue.  Wheel bearings have been checked by a good shop as well.  Haven't tried this specific test this year, but last year if I shifted to neutral while going 50-ish the vibration was still constant.

Question is, could bad front radius bushings cause that much vibration, or should I be looking at other potential causes as well?  With just two weeks to work with I want to make sure I maximize my time working on it, it'd be a shame to focus on the front bushings only to find they weren't the cause.

[Jim Blackwood]

Could it be thumpy tires?

Jim

[dtcerrato]

Your mention of driveshaft replacement gets my attention. Have you examined the drive shaft since replacement? I ask from past experience. A bad universal joint can send vibration all through the coach and so can a sloppy slip spline on the drive shaft that is not kept greased well & frequently. There are other things it could be but wanted to make mention of what came to mind. I don't see radius rod bushings creating "vibrations" as much as thumps or clunks when hitting road irregularities. HTH.

[Jim Blackwood]

The speed of the vibrations can tell you a lot.

Jim

[richard5933]

Was the driveshaft tried 180 degrees offset from the current placement? I've heard of it causing vibration problems if it is mounted out of sync.

Do you still have the handbrake by the driveshaft? If so, is it possible that it's loose or missing a chunk?

[Nova Eona]

Your mention of driveshaft replacement gets my attention. Have you examined the drive shaft since replacement? I ask from past experience. A bad universal joint can send vibration all through the coach and so can a sloppy slip spline on the drive shaft that is not kept greased well & frequently. There are other things it could be but wanted to make mention of what came to mind. I don't see radius rod bushings creating "vibrations" as much as thumps or clunks when hitting road irregularities. HTH.

I have not looked at it too closely since it was done, but I'll give it a wiggle next time I'm looking at it.  I had the bus at a heavy truck shop last summer and they found that one of the yoke pieces was out of round, so they had a well-respected driveline shop nearby fab a new shaft to replace it, did the pinion seal and new shocks while they were at it too.

[Nova Eona]

Was the driveshaft tried 180 degrees offset from the current placement? I've heard of it causing vibration problems if it is mounted out of sync.

Do you still have the handbrake by the driveshaft? If so, is it possible that it's loose or missing a chunk?

Have not tried that, how much of a nuisance are these shafts to rotate like that?  I had the shop do the install last year, so it'd be a question of whether it's worth having them do it.

Handbrake has been removed.

[richard5933]

I'm assuming they balanced the driveshaft, right? Did they replace the u-joint bearings and such?

I think there are details about marking the driveshaft position when it's pulled to make sure it goes back the same way. Check the manual for details about total replacement re: position.

[chessie4905]

check for bolts or caps coming loose. Especially be sure both joints are in phase. In other words, all four caps are in same location as other end. If front joints caps are 12, 6, 3 and 9 o'clock, rear joint should be the same. Also if any tires have nylon in casing, expect 20 miles to round them out again. Nylon flat spot when sitting and vibrate till warmed up. I don't  know if they use that any more.

[Jim Blackwood]

It's not just nylon, although they seem to be the worst. Even modern tires can flat spot from sitting. If it's a thump about every time the tires go around that's probably it. If it seems to wobble about 4 or 5 times that fast it's likely the driveshaft. Look closely at what was changed first. U joints out of phase can happen. The front one and the rear one need to line up exactly, in other words if the caps on the input yoke are up and down the ones on the output yoke need to be up and down. Some shops build but do not balance. Look for new welded on balance weights as evidence that they did.

Jim

[Nova Eona]

I think I may have found the source of the vibration!  Now, correct me if I'm wrong, but see attached pic - pretty sure the old parking drum's edges should not look like that!

Now, that brake is obviously not in use, what's the process for deleting that drum?

[chessie4905]

Wow! No wonder it vibrates with half the lip gone. Easy to remove. Just remove all the bolts attaching drum to trans output yoke. About 8 of them. May be wire tied. Once drum is off, you can remove brake shoes and mounting plate. You'll need to disconnect driveshaft to do it. Be careful not to lose any needles in caps. You'll then have a nice increase in room in that area.

[richard5933]

Nice find. That's exactly why I was asking about the hand brake earlier. A missing piece like that seems like a prime suspect in your vibration.

[dtcerrato]

@Nova Eona
Do yourself a favor and just remove the circle of bolts at the very end of the driveshaft - both ends. These are the companion flanges which mate up to the output shaft of the transmission and the differential leaving the two u-joints totally in tact. The companion flange at the transmission end has to come off anyway to remove the parking brake drum. I done it this way several times. Remove the differential end 1st so the shaft can move away from the transmission. Keep in mind the prerequisite to doing it this way AND to remove the parking brake drum w/o removing the tranny is to have an enlarged hole (opening) in the bulkhead the drive shaft passes thru. I mention this because it was a common modification that lent itself to much quicker & efficient unit repairs in this area. I can post photos if it you'd like.

[Nova Eona]

@Nova Eona
Do yourself a favor and just remove the circle of bolts at the very end of the driveshaft - both ends. These are the companion flanges which mate up to the output shaft of the transmission and the differential leaving the two u-joints totally in tact. The companion flange at the transmission end has to come off anyway to remove the parking brake drum. I done it this way several times. Remove the differential end 1st so the shaft can move away from the transmission. Keep in mind the prerequisite to doing it this way AND to remove the parking brake drum w/o removing the tranny is to have an enlarged hole (opening) in the bulkhead the drive shaft passes thru. I mention this because it was a common modification that lent itself to much quicker & efficient unit repairs in this area. I can post photos if it you'd like.

Well the hole seems plenty enlarged already, so I suppose I lucked out there at least.  Those bolts within the drum are not fun!  Got all 8 of the drum bolts out and 6/8 of the flange bolts on the transmission end before I ran out of light today, was hoping I could get away with just doing one end but it sounds like I'll have to do the pumpkin end as well.  Can't wait to see how much nicer it drives after all this.  Anyone know offhand what the torque spec on those bolts should be when going back in?