Outback Man's Flyer still vibratin'

[Outback Man]

Well, I have traveled from Tennessee to South Dakota since I last posted about the vibration in my 1980 Flyer w/903 Cummins, V730 tranny. I thought I possibly had a tire vibration, so I bought 4 new tires for the rear and had them balanced to make sure they were not the source of the vibration. The tires were definitley in need of replacement so that was money well spent. I had bought two new tires for the front a year ago and have probably 6000 miles on them so they should not the cause of the vibration. I also had them balanced when they were put on.

    The tires were not the cause of the vibration unfortunately. The vibration is slowly getting worse. Around 40 to 50 it is the worst and it slacks off when I let off on the throttle and gets worse again under power. It vibrates less after 50 but starts again around 60, which unfortunatly is about top speed so it makes it difficult to get a downhill run at hills. I checked the U joints before I left and again when I got up here and can't find any slack in them but the rear one seems to have a little glitchy feeling when I twist against it by hand. That seemed to be more pronounced when I got here and it was still warmed up. Now after it has set for a few days, I can't feel it as bad. So I'm thinking that is my problem as the tranny shifts OK and the oil is not burnt smelling or brown, looks real clean and fresh. What I'm wondering about is this: are these U joints [spicer], standard big truck parts or are they a special bus thing? Anyone out there have any know how about that?  Also, does the drive shaft have a spline on the tranny side? It appears to have a knurled nut and some fine threads on the tranny side that would release pressure on the grease seal so it would slide. Any ideas on this would for sure be appreciated. Thanks..............Outback Man

[Sojourner]

Telltale of bad "U" joint is not only rotating drive shaft for  slops but look for "rust" between "center joint" & seal or try moving shaft up & down to look for very small "center joint" to bearing end cap play...if non...it usually bad sign of dried binding bearing.

Caution...Most person will think No Movement is OK...BUT it may be a joke...it may have binding tight needles in rusted condition. I have replace many of customer car & truck joints from dry rust to point of worn out condition to point of dropping. A binding dry rusted needle bearing will cause vibration every time.

So for yours safety....recheck both ways. Rotation and "center joint" to bearing end cap play. If no rotating play between yokes and very small end play before re-grease is good "U" joint.

Keep them grease often and see if grease seep out of all four bearing caps....otherwise replace them.

FWIW

Sojourn for Christ, Jerry

[Stan]

My suggestion to confirm or eliminate a driveline as a source of vibration is to remove the entire driveline including the mating connection to the transmission and differential. Take it to a driveline shop that can check it for balance and vibration as a complete unit. Make sure that the U joints are in the correct relationship as per the bus manufactuer's specs. Take a copy of those specs with you to the balancing shop as sometimes they are not the conventional system.

While you have the driveline out, check the shaft splines in the transmission tailpiece and and the differential pinion shaft. You will likely need a new nut ($$) for the transmission end and a new crush spacer for the pinion shaft when you put it back together.

[TomC]

Most bus drivelines are the same as a truck.  I would just take out the driveshaft, have it balanced and install new U joints whether you think it needs it or not-not very expensive.  At the same time that the driveline shop has it have them check on the sliding spline to make sure that is tight also.  Good Luck, TomC

[Sam 4106]

Hi Outback Man,
If the splined joint in the drive shaft is between the u-joints (as opposed to to into the transmission, as it is on a lot of cars) check that the u-joints are aligned. If someone put the splined joint together one spline off, thus misaligning the u-joints' it will cause a vibration and premature joint failure. The yokes on the driveshaft must be in the same plane. If the driveshaft were laying on a flat surface, both yokes would be flat on that surface. I hope I have explained this adaquately, if not, ask any questions you have so that I can try to make it clear.
I drove one summer for the local Drum and Bugle Corps. as a volunteer. On the first leg of the trip the truck had a bad vibration. I asked the owner of the truck if he was aware of the problem. He said he was and thought the vibration was caused by the output shaft bearing in the transmission. Since it was his truck and he was aware of the problem I didn't pursue the issue any farther. Two nights later, (we traveled at night since the kids practiced during the day and performed in the evening), the front u-joint failed. The next day a mobile mechanic from a T/A truck stop came to fix it. When I noticed that he was putting the shaft back in with the u-joints misaligned I commented about it and he said he was putting it back the same as he took it out. He showed me the mark he had put on it before he had removed the shaft. Sure enough the u-joints were out of alignment. After he took it back apart and corrected the alignment,there was no more vibration. It made me wonder where he got his mechanic training, that he didn't know that a driveshaft needed to be aligned. He had  worked as a mechanic for at least ten years, judging by his age.
Good luck with finding and correcting your problem, Sam 4106

[Stan]

Sam 4106: You are quite correct about aligning the U joints on some vehicles, but read my comments above about using the manufacturer's specs. Some call for the U joints to be in line, some at 90* and at least some models of MCI called for 45*.

[Sam 4106]

Hi Stan,
Thanks for your comments. I sure was not aware that any vehicles specs. called for 90 or 45 degree u-joint alignment. That is why I enjoy reading the bus boards. I learn a lot and learning is a lifelong endeavor.
Thanks, Sam 4106

[kyle4501]

Sam 4106: You are quite correct about aligning the U joints on some vehicles, but read my comments above about using the manufacturer's specs. Some call for the U joints to be in line, some at 90* and at least some models of MCI called for 45*.

I'd sure like to see the drive line that calls for the U-joints to be phased like that. I'm having a hard time visualizing what would necesitate that. (I'm not saying I don't believe it - I am saying I don't understand why it would be needed & would like to learn.)

[Stan]

kyle4501: I was never concerned enough to ask, but my MC5A definitely called for 45* U joint alignment. Previously I had seen trucks that called for 90* alignment so I just took them at their word. Maybe a call to MCI Tech Support might get an answer. One possibility is that in that bus the engine sits at more than 90* to the differential requiring the driveshaft to flex in two directions simultaneously. Other than that wag, I have no idea.

Driveline vibration is probably the hardest problem to solve on a bus. It can occur at resonance points in many places and at many different frequencies. One frequently overlooked cause is a tapered wear in the U joint yoke cup seat allowing some wiggle in the cup although the cup appears to have a snug fit. Since the driveshaft assembly is  the most frequent cause, the first step is to be sure that it meets spec in all aspects. Once you are sure it is good, you can start looking at what is connected to each end.

[skihor]

Our 5A developed a vibration and it turned out to be incorrect ride height. I replaced the U joints, balanced the assy, etc... the vibration was still there. PO had installed individual leveling valves and defeated the factory automatic ride height adjusters. I keep them at 60# and it seems to work fine.

Don & Sheila