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Bounce slow motion video


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Well it is definitely the front causing the issue! Don't know which side yet, but it looks like I will be buying replacement drums!

Video looking at the rears is smooth with no bounce at all!

Will try to get a cleaner video, but the first bounce starts at about 20 seconds in and ends abruptly at about 2:32...

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With a bounce that bad, I'd think if you jacked the front wheels off the ground and spun them you see which one . Than I'd start at the tire and move in from there. Your suspension has been checked? Paul

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With a bounce that bad, I'd think if you jacked the front wheels off the ground and spun them you see which one . Than I'd start at the tire and move in from there. Your suspension has been checked? Paul

Balanced at the Mack Dealer! It only does it at 22 mph and 44 mph...no trace at other speeds! New king pins...wheel bearings tight...Everything that rotates on the front is new with the exception of wheel hubs and brake drums...

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Removed the drum on the pass side today, as it was the one that has a heavy spot...with the rim/tire off, that one always rolls heavy side down...

Took the drum off, everything "looks" okay...reinstalled the wheel and tire...no change in the bounce! Dammit! Before I pull the other side, I am goin to temporarily put the steers on the back and air them down...if it is a front rim or tire problem, it should be evident,,,

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Removed the drum on the pass side today, as it was the one that has a heavy spot...with the rim/tire off, that one always rolls heavy side down...

Took the drum off, everything "looks" okay...reinstalled the wheel and tire...no change in the bounce! Dammit! Before I pull the other side, I am goin to temporarily put the steers on the back and air them down...if it is a front rim or tire problem, it should be evident,,,

I think that's your best bet,swap the tires and rims and see what happens..

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Dammit!...Dammit!...Dammit! Talk about frustrating! I'm in the mood right now to park it and make it a lawn ornament! Swapped the drivers side steer and front rear tire/rim...NO CHANGE AT ALL! Tomorrow I will do the same thing on the other side, and when that doesnt do anything, I will remove the drum on the drivers side, and when that doesnt make any difference, I might drive it off a cliff with me in it! Maybe the SOB is possessed!

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:SMOKIE-RT:

You said something about a drum with a heavy spot,but without the drum it still does it? I'd think THAT'S your problem.

Maybe if you find the place that hub and drum settles to,re-install the wheel and add a few ounces of wheel weights to that wheel at the top,opposite the "heavy side",and try it-see if anything changes. Might have to adjust the amount of weight to counterbalance the heavy side. Or,If you could borrow a different hub to try for a couple of miles that might tell you if the hub is the problem-maybe it's machined wrong or has a casting flaw that upsets the balance.

Speed

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:SMOKIE-RT:

You said something about a drum with a heavy spot,but without the drum it still does it? I'd think THAT'S your problem.

Maybe if you find the place that hub and drum settles to,re-install the wheel and add a few ounces of wheel weights to that wheel at the top,opposite the "heavy side",and try it-see if anything changes. Might have to adjust the amount of weight to counterbalance the heavy side. Or,If you could borrow a different hub to try for a couple of miles that might tell you if the hub is the problem-maybe it's machined wrong or has a casting flaw that upsets the balance.

Speed

:SMOKIE-LFT:

Look at the back side of the spokes. They rust badly and eventually start to "chip off" internally. You could have lost a few ounces due to this and the unbalance rotating mass could be the problem.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Look at the back side of the spokes. They rust badly and eventually start to "chip off" internally. You could have lost a few ounces due to this and the unbalance rotating mass could be the problem.

Have you had the tire spin balanced while mounted to the hub? This would readily reveal this problem.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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The Mack Dealer spin balanced both steers on the truck...on the pass side, there are two pcs of flat steel welded to the back side of the hub presumably for balance...

The drum wheel combo (pass side) has a heavy spot, when I took the drum off and mounted just the wheel, there was no heavy spot.

When it warms up a little, I will remove the drivers side drum, and swap front rear tire on the passenger side...

post-6773-0-80982700-1323437766_thumb.jp

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The Mack Dealer spin balanced both steers on the truck...on the pass side, there are two pcs of flat steel welded to the back side of the hub presumably for balance...

The drum wheel combo (pass side) has a heavy spot, when I took the drum off and mounted just the wheel, there was no heavy spot.

When it warms up a little, I will remove the drivers side drum, and swap front rear tire on the passenger side...

post-6773-0-80982700-1323437766_thumb.jp

I've seen old drums present the problem also. Some of those can be difficult to acquire new. You might have that hub assembly balanced while it is apart by welding, and grinding for balance. This can't hurt.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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I still think you're barking up the wrong tree. The front end is swaying in the sprung weight, the unsprung weight is reacting to it. I have seen this in brand new Superliners in the 70 and other trucks over the years. the only way to stop it on the Superliners was to put inside channel in the frame. The frame takes on harmonics at certain speeds and will not come out of it untill you get out of that speed. If the balance was that bad as in the Video the tire would actually lose contact with the road. I would like to see a happy outcome from all this.

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I have an idea, Maybe if you would mark the back of the tire in four spots and drove it down the road with your camera. You might see that if say mark number 3 is always on the ground when the hop starts then you might have idea where to start. If the position of the tire has no bearing on the hop then you know to try another area. If its a rotational out of balance problem it should have a cosistant mark hitting the ground.

15 gears...no waiting!
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He's already had them spun balance and the passes, I think you,re looking for something that is not there

I can't watch the video. Are you stating the tire/wheel assembly is not "hopping" at the posted speeds? If the tire is not oscillating or hopping at any given speed an imbalance condition prolly doesn't exist. If the bounce is from an unsprung condition, this could start at many places through the truck and transfer forward.

If you can, restrain one frame rail of the truck and use the engine to inch forward, and rearward noting the movement of the left frame rail with the right rail stationary, (you don't even need to come off of idle) then repeat with the left rail stationary. If you notice more than about a half inch of movement in either rail, start blowing the rivets retaining the xmembers, and replace with grade eight bolts very tight. Also make sure the 5th wheel plate, (if equipt) is very tight to the frame if not welded. Loose xmembers are bad about doing what you are experiencing; once a vibration starts anyplace on the truck, it can transfer anyplace else till it finds a place to freely oscillate.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Finally was able to watch the video. Although unclear, I would not be looking at an unbalance condition. I do not see evidence of wheel tramp, or out of round to the tire/wheel assembly. That is somewhat of a linear oscillation to the frame rapidly unloading the spring and suspension. This is probably set up and amplified distant from the point of notice. What I cannot tell from the video is if the oscillation is linear from side to side, or more pronounced on a single side.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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This is getting complicated,I hope for your sake that the problem lies in the other tire or drum.

The symptoms are indicative of loose crossmembers in a light duty full frame vehicle such as a pickup truck when the frame has been straightened from a "diamond" condition. If the retaining rivets are not replaced with bolts that retain the crossmembers, the vehicle usually suffers from symptoms such as Leslie is experiencing. Given a heavy truck has much stiffer springs and heavier components, this is easy to become violent once conditions are right.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Last several post are very interesting...WIth the front tires on the rear, absolutley no change in the bounce...I am stil going to remove the left hand drum just so I can say I KNOW it is not the drums or the tires on the front...

Anyhow...I took about ten videos today and though the truck is still bouncing, I cannot see it in the video, front or back at all...the rears have never moved...BUT...I took two videos with the camera mounted on the airtank (about mid frame under the battery box) and it looks like the camera was moving up and down, but not the front or rear axles! I was dumbfounded untill I read the last few posts...

In the morning I will touch every bolt on all of the crossmembers, and also look for signs of any movement between the crossmembers and frame (if it is flexing, it should leave a mark)

Still doesnt explain why it happens at one speed, and exactly twice that speed, and only a range of +- 1 or 2 mph....that is, 22 mph and 44 mph...If I air up the tires to 100 psi, all it does is raise the bounce mph to 25 mph and 50 mph...

Thanks for all of the comments!

(It takes a community to raise a truck)

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I'm certain this is not your problem but one time I had a driver who kept complaining that there was something wrong with my truck,said it bounced like a bronco but only in the morning and then it would go away,I checked everything and couldn't find the problem,turned out to be the road he was taking to the job site.lol

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