| Author | Message | ||
| Mark R. Obtinario (Cowlitzcoach) (206.163.13.24)
Rating: |
I have a 40' 10-wheel 1969 Crown with a 262 HP NHH220 engine and an Allison HT70 6-speed automatic transmission. I have a very annoying vibration that becomes noticeable at speeds over 50 MPH. I have elinated the drive shaft/u-joints, rear ends, and the tires and wheels as the source of the vibration. The vibration is speed related and not engine speed related. At low speeds and high RPM there isn't any appreciable vibration. The vibration is felt whether you are powering up hill or coasting downhill or just cruising along. Not only is the vibration bugging me but not knowing what the vibration is really bugs me. Any ideas? Mark O. | ||
| Dwight (63.16.168.84) Rating: N/A |
I would consider the drive shaft very closely, it may have lost the balance weight, is it out of time, the two u-joints must be in line (even) to be in time, they cannot be off or it will cause a vibration...this is if the tires have been balanced.... | ||
| Dwight (63.16.168.84) Rating: N/A |
I would consider the drive shaft very closely, it may have lost the balance weight or is it out of time, the two u-joints must be in line (even) to be in time, (the 2 inside u-joint halves must be even (in-line) with each other) they cannot be off or it will cause a vibration...this is if the tires have been balanced.... | ||
| Mark R. Obtinario (Cowlitzcoach) (204.245.250.47)
Rating: N/A |
Perhaps I wasn't clear. I have already eliminated the tires/wheels, rear ends, and the drivelines as the source of the vibrations. As to what is causing the vibrations...well it is starting to really bug me! | ||
| 4104 Bob (162.40.199.176) Rating: N/A |
If you are certain that it is not engine related, ie: doesn't change with engine speed, then it must be another rotating mass. At 50 mph, tires, wheels, bearings, and driveline are the items that are rotating. I don't mean to sound condesending, but I would have a really good driveline shop look at the drive shaft. Unless it has been put into a balancing machine and checked for trueness, you can't be sure it is not the culprit. If you can think of anything else that is rotating and is not changing speed w/ the engine, check it out also. | ||
| tfones (Chapter7) (4.54.84.160)
Rating: N/A |
If not in the rotating group. What remains? Do you have oil-caning of the roof, sides or floor? tony | ||
| Greg Roberts (172.139.55.109)
Rating: N/A |
If the problem appears only at 50MPH you are probably exciting a mass at it's natural frequency. This means that there is a mass that has a natural frequency very near or at the frequency of one of your spinning masses in the bus. to solvw this issue you will need to determine which spinning component of the bus drive train is the exciting component. Learning this will lend clues. Most likely culprit is the drive shaft. What you have to do is mount and accelerometer on the various stationary components near to the rotating components and see if the high amplitude frequency matches the calculated frequency of one of your drive train components. Another thing to do is measure your natural "ring" frequency of the various components of the bus. The offending vibration can be of various multiples or "orders" of a rotating component rpm. I realize this is pretty complicated but if you want to cut to the chase find a vibration analysis company and pay them a couple of hours to analyze your rig. WIth a little instrumentation you will have your answer. Ok, the cheap method of learning the problem: Add balanced mass to your drive shaft and see if the vibration moves to a different speed. This has the effect of changing the mass and therefore changing the natural frequency of the rotating component. Simply add enough secure mass to the offending rotating component until the natural ring is out of your normal operating range. Imbalance can be a huge factor in exciting various masses. Be sure this is out of the way first. Hope this helps and doesn't confuse too much. - Greg | ||
| Frank Rowe (198.60.102.43)
Rating: N/A |
In my past, I have located out of balance shafts etc, by using a large hose clamp and a few flat washers. After locating the driveline weights, the hose clamp and washers are attached. The location is marked with a marker pen. Each test ride will show different results as the clamp and weights are moved. Nah, it's not hi tech, but the method is cheap and effective. The amount of weights [washers] may also be changed. A few times, missing weight locations were found. Long term repairs have been made by wrapping clamp with racer's tape [duct tape]. To avoid all the trial and errors, a $200 trip to the drive line shop, will work too... Frank Rowe | ||
| Tom Hamrick (Tomhamrick) (65.204.251.231)
Rating: N/A |
www.balancemasters.com has active driveshaft balancers for $55.00 to $65.00 depending on drive shaft size. Looks like a good idea. Tom Hamrick Eagle 10S | ||
| dougthebonifiedbusnut (24.147.153.205)
Rating: N/A |
hey mark i have a 65 crown 40' that i will be putting on the road very shortly tel yoiu if i have the same problem in the mean time how did you eliminate the drive shaft as the source of your vibration | ||
| Kirby (12.94.0.38) Rating: N/A |
Mark, reference your third paragraph about having eliminated certain items as the cause of the vibration, take the bus for a ride and warm up the tires. Then jack up the bus and check the tires again for out-of-round. Check all the tires. Take two aspirins and let us know in the morning how much out of roundness you found.... I chased a vibration on my bus a while back and found that I had a tire out of round. |
