| Author | Message | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 121 Registered: 4-2009 Posted From: 208.54.14.50  Rating: N/A |
going down the freeway, it feels like the the front of the bus is bouncing up and down, like flipper on steroids. EDIT: it happens on uneven roads, on smooth roads it doesn't happen. just to make it clear. what are some of the causes for this condition? background : the bus had front axle bearing that weren't properly lubricated. (low oil) the tires are wearing with some flat areas and outer areas wearing more, though after proper lubrication, the uneven wear is reduced. it's noticeable on uneven roads travelling at 55 - 65 mph, more than other vehicles. (Message edited by WhiteBus on July 09, 2009) | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 875 Registered: 10-2006 Posted From: 76.216.70.120  Rating: |
The road was built by the 3rd cousin of the State Roads Commisar. I-10 in FL is one of the most noted CRAPPY bouncy roads in the USA. But I would try the CORRECT shock absorbers in the front as a start. NOT "universal" but the Shocks for YOUR bus. FF | ||
| Wec4104 (Wec4104)
Registered Member Username: Wec4104 Post Number: 56 Registered: 7-2008 Posted From: 68.80.242.72 Rating: N/A |
When I first purchased my 4104, it had some pretty noticeable porpoising. There were certain roads that would set up a harmonic bounce that would toss stuff around in the cabin. As FF mentioned, shocks are where I would start. After all, their function is to damp out these oscillations. I installed a pair of adjustable Konis on the front axle. I set them for them for the middle range and tried them for a bit. Later, I went back and reset them for close to the firmest range. The ride now is near perfect. No porpoising, and the ride still feels soft with no harshness. It made such an improvement that installing new shocks on the rear axle has dropped to about 287th on my to-do list. | ||
| Mel La Plante (Mel_4104)
Registered Member Username: Mel_4104 Post Number: 129 Registered: 7-2006 Posted From: 99.199.168.111 Rating: N/A |
the 3 main reason-poor road design and upkeep - too much load behind the rear axel, poorshocks. #1 vote in the people that will fix the road,if you can find one. #2 go to the weigh scales and have them weigh the front axel and then the rear axel then do a look see what you have behind the rear axel and see if you can shift part of it into the center of the bus to put more weight on the front end. #3 as stated check the front shocks and if in dout throw them out and replace them as they are not that expensive fron a truck parts co. the farmers put cal.-clo. in their tractor front tires to stop some of the bounce and fluid in the rear ones for traction. this is called loading the tires and not to be done on your bus. while you are at it be sure to check the rear shocks as they will also add the the bounce of the ride. | ||
| Paul Lawry (Dreamscape)
Registered Member Username: Dreamscape Post Number: 527 Registered: 5-2007 Posted From: 64.40.216.34  Rating: N/A |
You also might try a dual action shock on the front. That has helped stop Eagles from doing the roller coaster. | ||
| Kyle Brandt (Kyle4501)
Registered Member Username: Kyle4501 Post Number: 496 Registered: 9-2004 Posted From: 65.23.106.193  Rating: N/A |
Do you have a tag axle? if so, does it have the correct amount of air in the suspension? | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 246 Registered: 2-2007 Posted From: 205.188.116.203 Rating: N/A |
I'd take a real good look at those flat spotted tires. Jack it up, put a straight edge across the tread and spin the tire. If they are deformed from ply liner damage, be careful, they can even blow out while you are looking them over. Check the toe for straight up or a very slight toe in. 1/16 or 1/8 max. Check it as high as you can without touching the undercarriage. If it didn't smoke those bearings, thats likely a non issue. Look for a broken shock or shock mount. Look for oil leaking from a shock or signs that one has lost its fluid. Eagles porpoise, I've never experienced anything like an Eagle porpoise in other equiptment. Porpoising to me reguires a rear axle follow through, do you have that or just front end bounce? | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 122 Registered: 4-2009 Posted From: 204.62.111.51 Rating: N/A |
the shocks on this coach with 60k miles on it look pristine, no leaks, no damage. no noticible rear axle "followthrough" as far as I can see, and I do not have a tag axle. it's definitely related to the speed at which I travel, when traveling under 40mph, I never notice any despite some real rough roads. it has at least something to do with the road condition. Traveling on a country road (california, from coast to I5) at night I hit a spot which I believe actually launched the front end off the tarmac, going at around 55mph. Can overfilled air ride system contribute to this? I noticed that my bus rides kind of high, compared to other buses of same manufacturer, at least seeing the pictures from the web. | ||
| David Guglielmetti (Daveg)
Registered Member Username: Daveg Post Number: 77 Registered: 2-2009 Posted From: 71.139.244.152  Rating: |
How do you check shock absorbers? Run it down the road for a while and then feel the lower body of the shock, if it is working it should be warm from the fluid inside. Otherwise, look for signs of leakage (not to be confused with "misting"). | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 123 Registered: 4-2009 Posted From: 204.62.111.51 Rating: N/A |
I don't know what ply liner damage is. I had two front tire that is worn on the outside, taller inside. classic underinflation wear. I did have flat spots on the inside, but recently those started getting less noticible, ever since I filled the oil to capacity. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 205 Registered: 1-2009 Posted From: 24.129.232.219  Rating: N/A |
flat spots like those cause from skidding make for wheel hop from the severe imbalance; uneven wear also cause dynamic imbalance & may also cause the problem, along with bent rims or a failing tire casing. The speed related issue is the tip off. A process of tire rotatingto different locations may change the problem and narrow down the guess work. | ||
| Peter E (Sdibaja)
Registered Member Username: Sdibaja Post Number: 300 Registered: 5-2002 Posted From: 201.143.185.51  Rating: |
1. check the air pressure... set them at what the manufacturer says it should be with the actual load you have on them. get it weighed if you need to, it does make a difference. 2. replace the shocks, they are not expensive. | ||
| Tony LEE (T_lee)
Registered Member Username: T_lee Post Number: 65 Registered: 11-2007 Posted From: 59.154.2.62 Rating: N/A |
"Can overfilled air ride system contribute to this? I noticed that my bus rides kind of high, compared to other buses of same manufacturer, at least seeing the pictures from the web." Sounds like it is worth checking this out first. Just needs a bit of flat concrete and a tape measure. | ||
| Wec4104 (Wec4104)
Registered Member Username: Wec4104 Post Number: 58 Registered: 7-2008 Posted From: 68.80.242.72 Rating: N/A |
If the bus has lees than 60K on it, and they are the original shocks, and for the exterior they look "pristine", I'm going to back off on my earlier comment, putting the shocks in the cross hairs. If even flat, even, road surfaces give you a porpoising at specific speeds, I'd go after tire/wheel related factors. If it seems like certain stretches of highway cause it, and the coach just can't compensate and damp it out, I'd test it with different air ride settings. | ||
| Peter River (Whitebus)
Registered Member Username: Whitebus Post Number: 125 Registered: 4-2009 Posted From: 204.62.111.51 Rating: N/A |
ah, I should have made it clear. on flat well maintained highway, no, it doesn't porpoise at all. I have actually taken it to 85mph going down a mountain pass, without a wobble. it does happen when there is some harmonic undulation or a dip in the road. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 206 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
oh then perhaps you need one of those "hover buses" to fix this bumpy road problem. | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 944 Registered: 7-2006 Posted From: 74.162.79.208  Rating: N/A |
Pete - Check the leveling valves, and make sure they're adjusted to your bus specifications. If they're too sensitive (improperly adj), the stupid bus will try to be level with each dip in the roadway. | ||
| Douglas Wotring (Tekebird)
Registered Member Username: Tekebird Post Number: 401 Registered: 10-2004 Posted From: 71.59.75.212 Rating: |
not sure what you have for a bus....but from the looks of that photo it might be a very short wheelbase issue | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 901 Registered: 8-2006 Posted From: 76.171.79.185 Rating: |
Pete, Porpoising and shimmy are two different things. Porpoising is up and down with the front and back ends, while shimmying is a shaking of the front tires, and then the steering wheel, caused by a worn front end. Shimmying can quite often be stopped by applying the brakes,(until the next bump.) Porpoising is worn shocks, and shows up on concrete roads with expansion joints. Shimmy shows up after bumps, at the speeds you described. The wear you are describing on your tires is caused by excessive toe-in. Larry has described the cure above. Low air pressure will cause the outside AND the inside of a tire to wear more than the middle. Greatly over-pressured tires will wear out the middle before the edges. Too much toe-in will cause the outsides of both tires to wear, and the little flat spots, which are known as "cupping." If you are ambitious, you can measure your own toe-in with a nail driven thru a piece of 2X4, with the point sticking out about half an inch. Jack the front axle just so the tires can turn, and hold the board against the ground so the nail point drags on the middle smooth part of the tread, and turn the wheel a complete revolution, to make a thin line on the tire. If you really want contrast, spray white paint on the middle of the tread while turning the wheel, then drag the nail in the middle of the paint, so you get a thin line. Then measure the EXACT distance between the lines, as close as possible to halfway up the tire on the front and the back. If the front measurement is 1/4 less than the rear measurement, the wheels are toed in 1/8 of an inch, etc. Larry is right on again, I wouldn't have more than 1/8" either, and I will bet you find you have nearly 1/2 inch difference between the numbers. Camber, measured in degrees, is the difference in distance between the tops and the bottoms of the front tires, and the tops want to be slightly farther apart than the bottoms. Caster, also called king pin inclination, is the relationship of the top ball joint to the bottom one. Positive camber means the front axle is leaning slightly forward. Correct caster makes the bus much easier to keep going straight, and makes the steering wheel want to return to center after you turn a corner. Toe-in is the only one you can do yourself, and the only one that really matters, because a front end that is either too much in, or out at all, wanders, and really wears tires. HTH, George | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 247 Registered: 2-2007 Posted From: 205.188.116.203 Rating: |
Peter, The tire gets its strength from the ply liner. It's the cord windings inside the casing. If there is damage to the ply liner, it first becomes visable in the form of a small bubble or distortion to the shape of the tire. They can grow until the tire has a huge fat spot that can circle the entire tire, but they generally blow out before they grow that much. Thats why when a casing first starts to distort, you may need something like a straight edge and rolling the tire through to visualize the damage unless you are experienced at spotting this kind of damage. If an experienced tire man ever sees a tire begin to distort when airing one, they will run like hell, because this is the one that will explode and kill them. The more wear patterns like you have described that are present, the more likely that the ply liner is giving up. The vibration from a tire comming apart should be present under all driving conditions though and not just when you upset things with rough pavement. The suspension can mask some of a distorted casing and its possible that bumps put the suspension over the line and then it fails to mask the problem. In the days of the old fabric casing they would stretch and lose their shape very slowly. You could true those casings and get more miles out of them some times. When a steel casing tire loses its shape though its all over. They will fail in a short period of time and there is no trueing procedure that will make any difference, because steel does not stretch, it comes untied and self destructs. In the transportation industry good operators will remove a tire that has any kind of puncture damage from steer tire duty because even a small nail can damage the casing and reduce its life span. It may or may not blow thousands of miles later. Even a small nail will allow water to penetrate the steel cords and start a rust situation that will slowly destroy the casing even after repair. (The patch goes on the inside and when the tire rotates in water it pumps water into the steel cords, rust eats the steel). This is extra important to most coach tire maintence because they stay on a lot longer than transportation industry tires that many times are worn out and gone in less than 2 years. From the amount of wear you have described on your steer tires, if it were mine I would replace them with the best I could find, set the toe and see if the issues are not resolved. For many years trucks were manufactured without shocks on the steer axle and you could not tell if the truck you were driving had shocks or not. Your coach is somewhat different from that though. If your shocks are the problem the front should have a bounce that decreases in severity with the first bounce being the biggest and it finally leveling out and then starting again when you hit another bump. That is the problem you described though so it's probably shocks, but you asked about ply liner damage and now you know what I know!!! | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 877 Registered: 10-2006 Posted From: 76.216.70.120 Rating: |
One other item that will assist bouncing is tires filled for the wrong weight. Folks that "fill to the sidewall pressure" are loosing a good deal of the tires ability to absorb road shocks. WEIGH the coach F&R at a truck stop, maybe $6.00 and go to the website for your brand and model tire and there will be a graph for the proper air pressure at different weights. They went to a load of trouble to work it all out, so it might pay to follow their lead. Newer sites will also list a rolling resistance rating for many tires, worthwhile if you are buying and looking for better fuel mileage. FF | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1294 Registered: 5-2001 Posted From: 74.47.99.20 Rating: N/A |
I took a look at Peter's coach by way of a Google search and concluded that Doug is right; short wheelbase is making his coach susceptible to porpoising. Strong shocks are the best preventative. Currently in the Kingman area, where there are some friendly busnuts. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, alaska | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 208 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
isn't that why some install two shocks per wheel, for and aft of wheel inclination axis, like the racing off roaders (with air adjustable) & the monaco motorcoach & newell coach ??? good related notes fellow bus nuts ! however I think your first attention is to good steer tires , with even tread wear & balanced , properly inflated to weight , no original components with excessive wear or leaks; then perhaps move on to modification concerns if there is money & concern remaining. I wasn't clear on your description of "flat spots", different than "cupping" in major causes of miss alignment but both defects will cause unstable ride characteristics at different conditions . They Might be acceptable to save for use on the drive axle. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 209 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
ahhem ...almost forge - & dual shocks for & aft , installed on MCI's, just like the dual bags. |
