I am not sure when I noticed a low frequency buzz or hum while driving but I seem to recall that shortly after I got the Breakaway I made comment to my brother about this issue.

After I repaired the cracked frame, and stiffened the attachment point,the buzz was much more apparent. At 55MPH not bad, If I leaned forward, I could hear it, at 65 MPH I could hear it sitting in the normal driving position. At 70-75 MPH it was VERY prominent thru out the frontal area. It also seemed to change a bit, wasn't sure if due to the loading effects or of the road conditions or tires.

When 2 of the Michelins started to come apart, I had hopes that it could be the tires. After new tires on the rear, I raised up the rear on the jacks and ran up the drive train, at 50 MPH it seemed like the rear end would shake the entire coach. VERY BAD VIBRATIONS!

I had changed the "U" joints when I did the engine rear main seal and I always grease them before the start of any trip. I was confident it wasn't the "U" joints or that the driveshaft was coming apart.

During the drive to the GTG I made special note to go thru various trouble shooting routines to track down the source of the buzz and vibration. When I got home I double checked to see if there was any play in the "U" joints but all was tight. I also confirmed that the vibration and the buzz was totally dependent on vehicle speed, at 70 MPH no change if transmission was in 5th or 6th. This test ruled out engine or transmission issues

Monday I took the driveshaft out. "U" joints all looked good with no sign of unusual wear. Took the driveshaft to drive line shop for check of straightness and balance.

I got the BAD news (maybe good news) that the driveshaft was severely out of balance and could not be balanced correctly. Over 8 ounces would be required with 5 ounces of that to be on the short or slider end. Driveshaft was straight so something internally was wrong. I never saw any weights on the driveshaft since ownership. Looking we could not find any evidence that there ever was any balance weights on it!

This confirmed my findings and probably why I noticed that the buzz increased after the track bar and frame stiffening was done as it coupled more of the vibration into the frame.

I am hoping to get the new driveshaft today or Monday and test drive. I also will get the old driveshaft back and do a postmortem to try to locate the source of the severe imbalance. The drive shaft shop said that they had never seen a drive shaft that was straight out of balance this much.

Hope another chapter is closed

quote:

Originally posted by MWrench:
I got the BAD news (maybe good news) that the driveshaft was severely out of balance and could not be balanced correctly. Over 8 ounces would be required with 5 ounces of that to be on the short or slider end. Driveshaft was straight so something internally was wrong.

Holy driveshaft, Batman! I've never heard of a shaft that far out. 8 OUNCES! Surprised you didn't tear up u-joints more often. One of those "well, there's your problem" examples. I'm interested in that post mortem inspection. I can't come up with any usual reasons for a simple shaft to be so irregular...

I have to believe your vibrations will be drastically reduced if not gone.

Lot of weight for a 3 inch driveshaft. Must be something inside it. A small bar of gold would do it.

So that's where all that depleted uranium from the N plants went!

Mine is a 4 inch driveshaft although the 4 inch section is very short. The 6 speeds had a much larger/longer driveshaft than the 4 speed driveshaft. The driveshaft is 21 inches long

Drill a hole in the driveshaft and pour some of those balance beads in there, I wonder if that would work?

We recently had to replace a 6' driveshaft on one of our lift station pumps, developed a bad vibration started eating up bearings. The driveshaft was found to be bent don't know how that happened. A shop in Grand Rapids made up a new shaft after that is was perfect.

It will be interesting to see what you find.

Balance beads could not be used as they can not be contained in the area of unbalance, interesting idea though. The slider end is a solid piece and the tube length is only about 3-4 inches. I think he said the major unbalance was on the slider piece. He is marking everything so I can do some research. I will pay him enough for the new driveshaft, I don't have to pay him for research HaHa

It has to be something in the construction or casting, as I mentioned the driveline is straight. I should get the new driveline on Monday or Tuesday.

As a side note, I did have to replace the output shaft seal on the transmission a while ago, the balance problem may have had a contribution to this problem.

If you have a two piece driveshaft you must be sure the universal in the carrier and the yoke are 180 degrees aligned. The zerk fitting on the yoke has to be 180 away from that on the carrier. Easy enough to see if they are on opposite sides. You must also have 1-3 degrees offset for each shaft end so that the universal bearings are preloaded.If they are perfectly aligned , ie straight and true, you will have harmonic rotational vibrations and the bearings will wear very fast. Hope this helps.

Ummmm,

Not sure if your definition of "two piece drive" shaft is the same as mine.

My definition of a two piece drive shaft is two complete drive shafts separated somewhere in the middle by a fixed frame mounted bearing

The ends "180" or "0" degrees alignment will make no difference what so ever in vibration or operation as "180" or "0" degrees is the same rotational plane for drive shaft acceleration and deceleration that happens twice per revolution.

The only alignment that would make a difference would be if the ends were "90" or "270" or some other displacement than "0" or "180" degrees displaced.

I agree that the drive line must have an angular displacement of 1-3 degrees but that is to make sure the bearings are working and there is rotational forces that move the rollers continually, If dead straight the roller bearings on the journal crosses are not revolving and will fresnel the bearing surface resulting in early bearing failure.

Zerk fittings, I don't see how can be used as a indication of proper alignment. On my "U" joint center sections, there are two zerks in two quadrants 180 degrees apart. If I were to assemble the "U" joint I could have the zerks in any of 4 quadrants. Some "U" joints have zerks in the bearing cap that could be installed in any one of four locations.

Mine is a single piece drive shaft, Yes there are two pieces that are connected with a slider but it is considered a single piece drive shaft. It is 21 inches long and weigh 65 lbs. It uses a Spicer 1610 series journal crosses and bearings

You mentioned
"It has to be something in the construction or casting".
One of the few things I know something about is metal, being in the steel business for a long time. Castings are notorious for being far from homogeneous. Perhaps you could have the part that is make from a casting, machined from rolled steel stock of sufficient diameter.

These parts are common and readily available and should be usable. When things are as bad as claimed by the drive shaft guy, then something in either the casting or construction (or both) went wrong.

Until I get the old part back I will not know what is going on. Drive line construction and application is not rocket science but certain constraints and logic must be followed.

One thing to remember is that these Barths' were built during the 55 MPH speed limit, during that time manufacturers could cut corners because speed related issues were reduced. Changing from 8R19.5 tires to 225/70R19.5 the drive line will be turning about 2.5% faster. At 60 MPH my drive line would be turning about 2574 RPM with 8R19.5 tires, and 2640 RPM with 225/70R19.5 tires That doesn't sound like much but it all compounds the situation.

It would get much worse if a critical frequency or chassis resonance would be reached at certain speeds.

I had to move quite far forward to hear the buzz at 55 MPH but after 60 MPH the buzz was very noticeable.

I should get the new drive shaft today or tomorrow. Certainly is interesting!

I added a picture in a previous post

Finally got time to do a test drive with the new drive shaft installed. NO BUZZ now at speeds 75 MPH and below. I think there is an onset of BUZZ above 75 MPH but it is slight. I usually drive at or around 70 MPH and it is very smooth and quiet at that speed.

The yokes are HUGE casting, I did not remove the yokes from either the diff or the transmission for balancing the new shaft. For absolute correct balancing that should have been done but that would have been a lot more work than I wanted to do at this time.

The drive shaft guy had to go thru 3 female slider casting to find one that required less than 2 ounces to bring into balance!

I have not had a chance to do a postmortem on the old drive shaft will do later this winter when things slow down.

Glad you got things sorted out! I chased a vibration at 55-58 mph for years - I found a warped wheel, but replacing it didn't help. Replacing the 2nd one did. And the Alcoa wheels are even smoother.

quote:

The drive shaft guy had to go thru 3 female slider casting

In my days in the steel business, I worked with several casting companies. It's an art form to get a casting truly homogeneous. In rotating parts, they ought to be made out of billet steel.