Rocking suppression? January 22, 2008, 11:47:53 am Yahoo Message Number: 88696I've got a 1993 23.5" Rear Twin King built on a Ford E350 chassis. Sometimes when travelling at highway speeds a bump or a blast from a passing truck will hit the resonant frequency of my rig. As a result it will rock side to side with increasing amplitude in a way that I find kinda' scary.I run the tires 10 pounds over recommended pressure.The rear shocks are Bilsteins bought from LD with 15K miles on them. I haven't replaced the fronts since it bought the rig 25,000 miles ago but they look OK and a jump on the front bumper returns to level without rebound.What else can I do to get rid of side-to-side rocking resonance?ThanksChris
Re: Rocking suppression? Reply #1 – January 22, 2008, 12:03:46 pm Yahoo Message Number: 88698Chris, That's really strange! My '05 LD is pretty much impervious to passing trucks and reasonably strong crosswinds. Check the rubber mounting bolts that connect the chassis frame to the motorhome "box".bumper
Re: Rocking suppression? Reply #2 – January 22, 2008, 12:06:02 pm Yahoo Message Number: 88699"What else can I do to get rid of side-to-side rocking resonance?"ChrisIt's difficult to manually bounce an 11,000 lb. vehicle. The shocks should to be pulled and checked. Odds are the front shocks are gone. The backs also could be bad. Looking at them, while they are in the vehicle, will only show if the rubber bushings are still there and if there is an oil leak. Another thing you can do is adding a sway bar to the rear and possibly upgrading the front sway bar to a larger size. Replacing the front sway bar bushings with polyurethane ones can help too, especially if the bushings are old and/or worn.Our old 1983 LD had a lot rocking in the rear that was not totally solved with shocks and sway bar. It needed more rear spring. A set of rear axle air bags eliminated the problem and lifted the rear several inches.Hope this helpsLarry
Re: Rocking suppression? Reply #3 – January 22, 2008, 12:14:40 pm Yahoo Message Number: 88700"Check the rubber mounting bolts that connect the chassis frame to the motorhome "box"While I have never seen loose 'rubber mounting bolts', I have tightened many sets of the bolts that attach the coach to the frame. Every LD that I have checked (about 15 now) has has several very loose nuts, many that are not even finger tight. The symptoms are are usually a booming sound on rough roads, coming from the rear of the coach.Larry
Rocking suppression? Reply #4 – January 22, 2008, 12:18:38 pm Yahoo Message Number: 88701Hi Chris I have exactly the same rig as you. I also run my tire pressure, if not 10 above, at least 6 or 8 psi above tire chart pressure for my weight. I have never experienced the problem you are having. What troubles me about your situation is that your rear shocks had 15K on them when installed. That means you had used shocks installed? Someone got rid of them for a reason. I would look there first. Of course one of your front shocks could have failed but unlikely. If not the shocks, it may be time to have a suspension specialist look at your rig. It is possible they could recommend a front or rear sway bay. I recommend you not throw money at the problem unless you are very sure. Don't install sway bars just because you think it *could* improve things.Tom Johnston, Red '99TK, Whidbey Island WA, clear, sunny, and cold (for us) about 30 degrees
Re: Rocking suppression? Reply #5 – January 22, 2008, 12:32:01 pm Yahoo Message Number: 88702"Tom Johnston" wrote: I recommend you not throw money at the problem unless you are very sure. I agree completely! You need an accurate diagnosis of why your rig is having these problems before shooting from the hip! I suspect that the problem(s) may have "multiple" causes, but a competent frame/suspension shop experienced with working on "truck" suspensions should be able to provide an accurate disagnosis and recommendations for "fixes".Joan
Re: Rocking suppression? Reply #6 – January 22, 2008, 12:41:27 pm Yahoo Message Number: 88703TomI was less clear than I hoped: I had new rear shocks installed and have since driven the rig 15K miles. I have never replaced the front shocks and I'm at 48K miles total on the rig.Chris
Rocking suppression? Reply #7 – January 22, 2008, 01:15:18 pm Yahoo Message Number: 88704Oh. Sorry about the misunderstanding. Have you checked your frame to coach bolts for tightness? Some of us did this a few months back when it was an item on this list, discovered by, I believe, Larry Wade. Not just a few folks found loose ones. These are the bolts which extend through the floor of your coach, through the transverse frame members, with nuts and lock washers on the bottom. If loose, I think about twenty foot- pounds of torque should be just right. You don't want to just muscle them up tight, as that will just compress the wood floor. You don't need a torque wrench. Just be easy with the wrench. You need a 9/16 deep socket, a ratchet wrench, and a 10 inch extension. I also added nylock nuts under the regular ones to lock them in place. Good luck. Let us know. Tom
Rocking suppression? Reply #8 – January 22, 2008, 01:17:51 pm Yahoo Message Number: 88705Oops! I just saw Larry's response as I hit the send button :>( Tom
Re: Rocking suppression? Reply #9 – January 22, 2008, 02:54:38 pm Yahoo Message Number: 88709QuoteWhat else can I do to get rid of side-to-side rocking resonance? I don't know how the waste tanks are in that model, since we have a FL. However, our tanks are in the rear, and are arranged perpendicular to the centerline. When our tanks are partially full, I notice a reduction in straight-line stability, due to the tank contents sloshing from side-to-side. However, it does not 'oscillate' - the shocks damp it out. Another possibility is a problem with the rear anti-sway bar hardware or attachments. Have that inspected. Severe overloading could of course do it too.Steve
Re: Rocking suppression? Reply #10 – January 22, 2008, 05:25:30 pm Yahoo Message Number: 88714The problem might be balance in dampening effect between the Billstein that are stiffer than new OEM shocks and definitely a lot different than well worn OEM shocks. If everything is attached ok underneath. I would change out the OEM front shocks with a pair of Billsteins.Lloyd, in cold Vermont, a LD owner wannabe.[Non-text portions of this message have been removed]
Re: Rocking suppression? Reply #11 – January 22, 2008, 10:43:39 pm Yahoo Message Number: 88732Chris: I have a 95 23.5 rear bath on the Ford 350. When I first purchased it I didn't like the swaying motion in and out of service stations, etc. I thought that emergency moves on the freeway would be difficult. I put an IPD heavy duty sway bar on the rear and it made a big difference without changing the ride. I think my 95 chassis had a rather light sway bar on the front and none on the rear. I now have over 30K miles with the original shocks, and run the factory manual suggested 55# in the duals. I haven't seen many ads lately for the IPD sway bars out of Portland, Ore., But they were highly recommended at the time. Its a very heavy bar - about 1.5 inches. Your "rocking" may be different than mine. Good luck - Les Bowers
Re: Rocking suppression? Reply #12 – January 23, 2008, 02:33:57 pm Yahoo Message Number: 88743FolksThanks for all the suggestions...I'll dig into them. Also, I found a Ford Technical Service Bulletin for the 93 E350 which says that many of the cutway model have extra sway because they use a 3 leaf or 5 leaf spring instead of the 8 leaf spring on the 92's and earlier. They recommend replacing with the 94 style 9-leaf spring which give higher total interleaf friction.Now, I've got enough clues to try to figure out what is going on.Thanks againChris
Re: Rocking suppression? Reply #13 – January 25, 2008, 10:30:28 am Yahoo Message Number: 88814Let some air out of your tires... Garry
Re: Rocking suppression? Reply #14 – January 25, 2008, 11:40:23 am Yahoo Message Number: 88823"I run the tires 10 pounds over recommended pressure."May I ask why? Overinflation isn't as dangerous as underinflation, but it's certainly not recommended by tire manufacturers. It causes tires to wear unevenly (center tread goes first), and results in a harsh ride that's not only uncomfortable, but is more likely to loosen up fittings like your chassis bolts.Having your rig weighed (front and rear axles separately) and then following the tire manufacturer's recommended pressures for those axle weights is the safest and most comfortable way to go.I'm not saying this will cure your rocking problem--as others here have said, that's most likely related to your shocks--but it's the smart thing to do. :-)Andy Baird http://www.andybaird.com/travels/
Topic: Rocking suppression? (Read 9 times)
previous topic - next topic
Topic: Rocking suppression? (Read 9 times)
previous topic - next topic