How to eliminate rear bounce

[KMS]

When driving my 2018 Jayco Seneca in freeways the rear of the coach bounces severely. So much so that occupants in the rear of the coach get ill. Is there something I can do to eliminate the bounce?

[oldmanAZ]

Welcome to the forum.

I'm sure you'll hear from Seneca owners before too long.

Is the bouncing your passengers feel vertical motion (ie 'up and down')? Most handling issues are complaints of 'side to side' from wind, passing trucks, etc. Have you let someone else drive so you could feel it for yourself?

[KMS]

It's up and down, when lying on the rear bed it literally throws you up in the air. My son was on the bed and he flew up over a foot off the bed onto the floor. He ended up throwing up due to motion sickness. It's a constant bounce when on freeways, smooth roads there's no problems. Between 45-65mph. Haven't tested while towing to see if that settles it down. My F350 bounced like it due to the heavy duty springs but when I towed it settled down completely. Thanks for any advice...

[KMS]

I had my wife drive and yes, I sat on the rear bed and it was bouncing a lot. Can only sit near front cab to not feel it anymore.

[WinnieView]

What is your rear tire pressure?

[wags999]

Sounds like road harmonics.. Sections of some roads are not flat, if your wheel base is the right dimension, you will get front going up while rear is going down. Slowing down will help, but, other than moving to a different roadway, not much you can do about it. I typically have run into this on concrete rather than blacktop, and only in certain areas. If the slab is longer or shorter you don't run into this. Good Luck.

[Robbbyr]

Originally Posted by KMS

When driving my 2018 Jayco Seneca in freeways the rear of the coach bounces severely. So much so that occupants in the rear of the coach get ill. Is there something I can do to eliminate the bounce?

What others have said is applicable, certain road and speed combinations can set up a repetitive bounce that can be quite pronounced. My year Seneca did not have the Bilstein front shocks the later models came from Jayco with, putting them on mine helped considerably by keeping the front end under better control. But I thought the newer ones had the Bilsteins standard with the J-Ride package. They are blue and silver and easily seen, especially if the front end is tipped up.

I am also wondering if there could be an issue with your Airliner rear suspension. If somehow the ride height was set too high the leveling valves could be keeping the air bags too full which would result in a jarring ride. Does the coach sit level side to side? Does it look level front to rear sitting on a level surface or does it ride tail high? Do you run with your freshwater tank empty? If you do, try doing a test drive with it full and see if the ride improves. If it does it might also confirm that the rear airbags are too full thereby not allowing the rear suspension to have any compliance.

If you still in your Freightliner warranty (you likely are) you might try having them check the rear ride height. They measure the height from the framerail to the ground and can determine if it is within specifications. Too high (too much air in air springs) could make it stiff, too low might be not enough air and it is bottoming out which also will lead to a punishing ride.

I can tell you my Seneca rides better in the rear than my previous two Ford-based Class C units. They would bounce you right off the bed on rough roads. But while not as good as in the front, it is tolerable in the rear of mine now after my front shock upgrade. But you also have to remember there is a lot of rear overhang in a Seneca which leads to increased motion regardless. That is just physics and long levers at work!

[Brianxs650]

I also have a 2018 Seneca. After I purchased it I noticed a vibration in the rear. Not a bounce like yours but a very predominant vibration. After a month of tracking down the problem I finally solved the mystery. My first stop was a Loves truck stop to balance my brand new Michelin tires. Which is seams crazy, but so was the vibration. The part time guy put some new weights on the rears but that did not work. He was more interested in what time he got off than my problems.

Next I went to Freightliner and had them do a vibration analysis on the drive line. They road tested and checked all the up down angles on the drive shafts. Everything was in spec. They adjusted the ride height like previously mentioned but that only fixed a slight right lean. Full water tank or empty take the vibration was the same on my unit but a very good point.

So here is How I fixed it. I found Best One Tire Shop, its a national chain service shop. They have a tire balancer that will check "run out" or up and down movement as well as side to side movement of the tires. We found that one of my rears was deemed unbalanceable. That meant that after spinning the tire around on the rim several times. The tire had such a severe up and down movement that no amount of weights would fix. We did check the rim as well and it was not bent. Michelin replaced the tire and my vibration problem was solved.

I hope you figure out your problem, I know exactly how frustrating it is to have new unit you don't enjoy driving.

Brian

[RVermont]

It can be very difficult to try to correct this as we all experience the same thing in different ways. My wife frequently sleeps in the bed room while I drive as I tend to drive very early in the morning. I asked her if she found the ride rough, she did not feel it was overly so. She did mention that the best seat for ride comfort is the dinette which makes sense being mid coach and ahead of the rear tires.

If you are near a dealer it might be worth taking a new unit for a ride to see if you experience the same thing, if they are vastly different then you know you can correct the issue.

As others have mentioned look at the airbags to be sure they are set correctly, check the ride height, also the rear shocks could be a problem if one of them has failed, not likely but not unheard of.

Tire pressure, Based on the weights of my coach I could run 75 psi but i keep them around 82 all the way round. This made a huge difference in steering and tracking as well as softened up the road feel. get your unit weighted and look at the Michelin tire guide to see what pressure you should be running.

[hoppers4]

I would not ride in the rear of any of the MHs I've had. It's the nature of the beast. These rigs are set up rather stiff anyway because, after all, they are tiny houses on truck bodies and have to have a stiff suspension.

[Brianxs650]

Update

After fixing the majority of my vibration with the steps posted above, I still notices a high speed vibration most noticeable at the kitchen table. So here is what I did to fix it.

Removed driveshafts and took them to Chattanooga Driveline Service 423-624-4194
https://www.chattanoogadrivelineservice.com

Tommy at CDS replaced all U-joints and carrier bearings. Then tried to balance each shaft individually. Found the #1, #2, #3 driveshaft yokes were out of phase for the factory.

He removed the welds and re-phased all three yokes. Just installing the yokes at a different spline angle did not fix the problem. It just made it worse. After re-phasing he balanced all 4 drive shafts individually. Then balanced all 4 shafts as on unit just like it is installed on the coach. #4 took the most weights. The set up they have to install all 4 shafts together and balance them is impressive.

This fixed the high speed vibration and made the ride enjoyable again. It is amazing the difference balanced drive shafts make.

[Cturrisi]

Does anyone know what the dimensions for the rear ride height should?