Roaring/humming sound when at highway speeds

[slemnah]

Scott, the noise you are hearing sounds like the noise you would get from bad pinion bearings in the rear axle or as another person stated excessive backlash in the ring and pinion. The fluid testing should tell if there is bearing material in the fluid. I would make sure that the slip joint on the driveshaft is free and greased well. You may have more than one problem. :(
Steve

[ScottRussell]

First off, I just want to say thank you to all who are trying to help diagnose this issue.

Second, I want to say it's been almost overwhelming to find a site with so many people who are so friendly and eager to help. I'm new to the RV world, but I've had friends who dabbled in it for years and they always told me what a great feeling of family they had with the RV community. I complete "get it" now. I'm more excited than ever to get out and enjoy more of the RV lifestyle.

Third, since no one really knows me here, I have been an auto technician in my past, and I still work in the automotive industry (as a process improvement project manager). Also, my HOBBY is cars (I'm a lifetime drag racer, and Dean and I both have turbocharged drag radial Mustangs). We do our own fabrication, welding, and though now days we race at a level where we have our initial engine builds done professionally, I freshen the engines ourselves. I've also built/narrowed, and set up rear ends (ring and pinions) for over 25 years (I'm 50 now).

Long story short, I'm not a mechanical novice by any means, but I'm at absolute GROUND ZERO when it comes to an RV, and especially when it comes to heavy truck equipment like the diesel power train in a DP. Also, I have ZERO diesel experience. I just wanted those posting to know that I'm not completely in the dark as far as mechanical knowledge in general, but there's ALWAYS more to learn, and I thank all who post and make suggestions.

I'm headed out to Dean's to help him put a clutch in an elderly church member of his Ranger pick up truck, so I'll be out of pocket till later in the afternoon, but please keep the posts and suggestions coming. I'll gladly take all the information I can get.

Thanks again to all! I'm looking forward to more interaction with you all.

[Crop Duster]

From what you have described that much vibration would cause a fair amount of heat. At each stop I always walk around and feel of each tire and axle. I'm looking for a difference of temperature which is a good indicator of a problem. If your problem is in the rear end, the oil that lubricates the wheel bearings also lubricate the ring and pinion. In that case the temperature out at the wheel hub should be higher than the front wheel hubs, for example. Granted you can't do anything about it while on the road but it helps the mechanic isolate the problem when it gets to the shop. This also works on your car or pickup. Temps are relative to the given day. If it's cool outside, like now, the tire and hub temps will remain cool to slightly warm. On a 100 degree day the tires will be much warmer. What you are looking for is one that is different from the others. Higher temps on one tire can indicate low tire pressure or sometimes a problem prior to a blowout. What you're looking for is a trend.

In this case the first place I would look is the u-joints. As an airplane mechanic I always look for the simple things first. Rule out the low buck items before going on to the Oh S$$t ones. I sure hope it's a relatively inexpensive fix. That is the high dollar end of these things back there.
barryb

[Crop Duster]

Originally Posted by ScottRussell

First off, I just want to say thank you to all who are trying to help diagnose this issue. Second, I want to say it's been almost overwhelming to find a site with so many people who are so friendly and eager to help. I'm new to the RV world, but I've had friends who dabbled in it for years and they always told me what a great feeling of family they had with the RV community. I complete "get it" now. I'm more excited than ever to get out and enjoy more of the RV lifestyle. Third, since no one really knows me here, I have been an auto technician in my past, and I still work in the automotive industry (as a process improvement project manager). Also, my HOBBY is cars (I'm a lifetime drag racer, and Dean and I both have turbocharged drag radial Mustangs). We do our own fabrication, welding, and though now days we race at a level where we have our initial engine builds done professionally, I freshen the engines ourselves. I've also built/narrowed, and set up rear ends (ring and pinions) for over 25 years (I'm 50 now). Long story short, I'm not a mechanical novice by any means, but I'm at absolute GROUND ZERO when it comes to an RV, and especially when it comes to heavy truck equipment like the diesel power train in a DP. Also, I have ZERO diesel experience. I just wanted those posting to know that I'm not completely in the dark as far as mechanical knowledge in general, but there's ALWAYS more to learn, and I thank all who post and make suggestions. I'm headed out to Dean's to help him put a clutch in an elderly church member of his Ranger pick up truck, so I'll be out of pocket till later in the afternoon, but please keep the posts and suggestions coming. I'll gladly take all the information I can get. Thanks again to all! I'm looking forward to more interaction with you all.

Scott, from your last post sounds like you are highly experienced in this already. I bet you already have figured out what's wrong with it. Have fun with the clutch and don't let the transmission fall on you
barryb

[trampsrv]

Originally Posted by t55watson

I would agree with the U-Joint poster. They are the weakest link in the driveline and almost always fail first. The Kenworth guys can check that very easy and an easy repair.

easy fix before it falls off.expensive fix if the drive shaft falls off while driving.good luck.

[ScottRussell]

Stopped by Kenworth on the way home from putting the clutch in the little Ranger pick up.

Gear lube looks good, and scope inspection looked good inside the rear end. There is an obvious driveshaft angle issue. Kenworth is contacting Spartan on Monday to find out the correct ride height.

At this point, the likely suspects are either issues with the bags, or with the level control. I know little about it, but I would assume there is a device somewhere on the coach that senses when it's level and open and closes valves to the front and rear (or maybe individual corners?) to correct? I would think if isn't simply old leaking air bags, it's a leak or leaks elsewhere in the leveling system.

Again, any insight is greatly appreciated. At this point I'm just glad to know the rear end is fine and has no issues. That could have really been an expensive repair. Now if we can just figure out what is causing the low ride height in the rear we'll be golden

[Ted Lambert]

Originally Posted by ScottRussell

Only my 3rd post, but looking to get some insight into this.

97 Holiday Rambler Imperial 40 WDS. Spartan chassis, 8.3 Cummins 325hp, Allison 6 speed.

As speed increases, somewhere around 45mph you can faintly begin to hear an oscillating humming sound. As speed continues to increase, it becomes more of a roaring sound. When I first heard it, it reminded me of a 4wd truck with off road mud tires. It was like I was on the rumble strips on the side of the highway with the tires.

From the driver's seat, it sounded like maybe a wheel bearing noise, but eventually I figured out that I could manipulate the throttle and make it change. It seems much louder coasting than accelerating, and it's pretty loud coasting as well. When going up a fairly step grade, it seems to quiet somewhat.

I just picked this rig up in Florida for a close friend and as I drove back to TN, I stopped and stayed the night with my sister and brother in law in the Birmingham Alabama area. I got my brother in law to ride along and he quickly walked to the back of the coach and said he could distinctly FEEL the vibration under the bathroom floor (above the rearend).

Being a long time drag racer who builds his own cars, my first thought was ring and pinion noise in the rear end, but driveshaft issues also crossed my mind. After talking with someone at the local Kenworth dealership after getting it home, he mentioned that air bag issues that cause the rear of the coach to sit too low, can cause excessive driveshaft angle and cause this kind of noise.

The coach is there (at Kenworth) now and they are draining the gear lube and having it analysed. They are also going to put their scope in and inspect the ring and pinion and bearings for any obvious signs of excessive wear or failure.

In the small tire drag cars we race, the rearend separates from the chassis under acceleration, and squats under deceleration. It would seem to make sense that the RV (too) when accelerating, the rearend separates (pushing the body upward), and when decelerating the body is at it's lowest point in relation to the rearend. If that's true, then I think the guy at Kenworth might have been correct. At least that's what I'm hoping.

I wondered if anyone here has ever dealt with a similar problem? and what did it turn out to be?

Thanks for any feedback.

I just reread your post again and guess what! My unit does the same thing. And you know what. I don't have a problem with it because when it was new to me I thought there would be bugs to work out. If the noise bothers you than it may drive you nuts. The way I am looking at my unit is this. If the noise doesn't change and get worse. I guess it is the norm for it.
If I buy new tires I'm sure there will be a different noise.
These units are light duty trucks. Trucks are noisy.
Some replies say the diff may be the problem or lets say the source.True it could be. But think about this if there is no metal filings on the fill plug. Why worry as the diff is not failing. Differential setup can cause different sounds. IE a little loose a little tight.
My Lexus doesn't make any noise what so ever and it cost as much as my Motor home. But I would still rather drive the Coach.
And by the way that oscillating hum... I just stay out of the speed range that makes it. I believe on mine it is all caused by tires.
Check out the things people are telling you as it cannot hurt. If you check out all the ideas you will get to know your unit and have more confidence in it.
If you find nothing than I would say GOOD TO GO>
By the way if I alter the tire pressure the oscillation speed changes.

[OutAround]

Been here and dealt with this many times.

If your coach has an Alliance rear end then I suspect you will be replacing the rear-end shortly. Alliance rear-ends have no replacement parts available and cannot be rebuilt.

In my experience with two Freightliner chassises with Alliance rear-ends and a total of over 200,000 miles I never had an Alliance rear end last more than 50,000 miles!!

I had many conversations with Freightliner engineers and I got in writing from them I needed to change the rear end fluid at 6,000 mile intervals and use full synthetic fluid. This is ridiculous and obviously shows a design issue.

I did this and it did not increase the life of the rear ends. I had the fluid sampled and sent to Blackstone as well. The fluid, even when the rear end was totally shot always tested good. My own in-house service department did the fluid changes and never once did we notice any metal in the fluid prior to a failure.

I simply stopped bothering to change the rear end fluid and got no less service out of the rear ends as more frequent changes got me no more lifespan.

Frieghtliner knows about this short lifespan but their comment to me was they only design their chassis for an average of 3-5,000 miles a year as that's what most RVers use their coaches for. They stated 50,000 miles of service was an average of 8-14 years lifespan for the average owner and they were fine with that.

I went through a total of 5 Alliance rear-ends in 200,000 miles. This led me to buy a Roadmaster chassis with a different rear-end. I put 60,000 plus miles on an RV.

The noise will get louder and you will start to feel slop in the drivetrain. I could always predict when the rear end started to have issues and how close to failure it was by feeling the vibration in the drivers seat and the floor under my feat while driving. As it gets worse when you press the brakes with cruise control engaged and exhaust brake on you will get a a hella thump and feel the slop. Also, with the cruise on and you try to accelerate using the cruise accel button you will feel the slop when you release the cruise accel button. Finally, you will occasionally notice a brutal downshift from high speeds.

The faster you go the more it vibrates and as it gets worse the speed you notice it gets lower and lower. Eventually the coach won't move and you need a tow.

Have a shop check the slop in the bearing where the yoke and rear end housing meet. It will be out if spec and since there are no parts available and the rear is not rebuild able you have to install a whole new assembly.

Goodluck,

Jim

[slemnah]

Jim, he is on a Spartan Mountain Master chassis and if memory serves me right it is an eaton rear axle. Don't quote me on that though.
Steve

[OutAround]

Originally Posted by slemnah

Jim, he is on a Spartan Mountain Master chassis and if memory serves me right it is an eaton rear axle. Don't quote me on that though. Steve

Ahhh. Thanks. Ignore my post!!! Eaton rear end head and shoulders above Alliance. I just made the assumption was a Freightliner. I guess that's why they say *ss is the first part of assume. Lol

[OutAround]

Even better. He stated he had a Spartan in the OP. Opps.

[tnrvers]

narampa
Not trying cause an argument, but ScottRussell is doing the correct thing by finding out what is causing the noise and more importantly the vibration that is felt over the rear end (see OP). As myself, other forum posters and the KW mechanic believe it is being cause by a height/alignment problem. If you notice in his last post everything except the height checks out NOW. It will not be that way if he lets the problem persist.

You state you have had the same noise since your MH was new to you, in MHO you have been luckly. If your noise is indeed an alignment/height issue at some point you will have a problem and if you are lucky it will only be the drive shaft needing to be rebuilt, not to expensive. If you are not lucky and it is the rear end you are looking at several thousand dollars and up for a rebuild.

I don't know how long you have had your MH and for your sake I hope the noise is related to something else, but if it makes the noise ScottRussell has in his you are living on borrowed time in MHO. While your problem may be different, there are other thing such as bearing that are inexpensive to replace before they fail and cost BIG $$$ if the failure happens while you are rolling down the road.

As I said, not trying to start an argument, just trying to give you some food for thought. Good Luck and Merry Christmas.

Tom and Barb
2000 Bounder 39Z

[KIX]

Scot, We have a Spartan MM chassis. When it was new I had similar symptoms. I didn't know squat about air suspension. The fix for ours was easy. The rod connecting the ride height valve with the rear axle had "popped" out of the rubber grommet that secures the rod to the axle bracket. A really easy fix by a Kenworth shop in Amarillo. They showed me the problem and I carry an extra rubber grommet. The problem has recurred a couple of times and it's an easy fix if there's enough room to slide under the coach while the bags are deflated.

[TeJay]

During any of your travels while it was making the greatest amount of noise did you take it out of gear and allow the engine to wind down? By taking it out of gear you are reducing the torque on the drive line, bearings etc. If it is a bearing or ring/opinion gear the noise will change because of the lower pressure.

We had a 1999 DS (Gas on a F-53 chassis) and the rear end started howling while on a trip to Maine. It was under warranty but nobody would do anything about it. They just said drive it back to AR and we'll look at it. They assured us that even if it is bad it will still get us home. We drove it home and they replaced the rear end.

Another way of finding some noises is to raise the drive wheels and put it in gear. I've done that many time on cars/trucks. The problem with that method is without the weight of the vehicle on the bearings the noise is much harder to find.

You also might have some wind causing the vibration. A piece of sheet metal flapping in the breeze can make some weird noises and vibrations. There are heat shields around the exhaust and cats and to keep heat from entering the floor of the coach.

Just some ideas!!

TeJay