Wheel hop problem

[770G]

It's seems all of a sudden that my grader has decided to start wheel hopping. It's 2 years old and has never done this before. It starts to bounce about 6 hours into grading. Any ideas??? I've try'd a few things and nothing seems to work.

 

[ovrszd]

This is a much discussed problem. I'm assuming you mean "bounce", as in the whole grader starts bouncing along causing ripples in the roadbed?? Almost everyone will tell you that you are going too fast. I'll just say you are going the wrong speed because sometimes a little more speed will fix the problem. Good thing about a Deere's cruise control system is you can regulate your speed very precisely, down to .10 mph changes if needed.

You didn't give much information so I'll just stumble along with suggestions or ideas.

Changing tire air pressure can alter or change the frequency of bounce. What tires are you running and how much air? I run Micheln 17.5 tires with 40 psi in the rears, 45 psi in the front. If I'm carrying a snow plow I'll boost the front pressure to 50 psi.

Changing speed, even as little as .10 of a mph can change bounce. I've learned with a Deere machine and radials you can't run in the 4.5-6.0 mph range without bounce. With my D model it would run 7.0 mph and not bounce. With the current G model it has to run slightly slower, 6.8-6.9 mph range. At 7 mph it bounces, especially going downhill.

I've also noticed I sometimes have to adjust my speed depending on which road I'm blading. Differences in dirt composition, traffic load, etc., will make the machine react differently to a certain speed.

An operator in the next township always used to run 4.0 mph or less. He's decided to try faster speeds because he sees me running faster. He told me the other day that it's not working because he has bounce. I asked how fast he is running and he said he never noticed...... I said what gear and what engine speed? He said fourth about 1800 rpm. I said you are going too slow. He looked at me like I was a total idiot. Nothing I said after that mattered. He was trying to run in that 4.5-6.0 range with a JD672D on bias ply 14.00 tires. Won't work.

So, I've probably not told you anything you didn't already know. But let's get more information then maybe we can find a solution. Tell us details about the machine, tires, air pressure, mph you are running, uphill/downhill, etc., etc.

 

[smoothoperator]

I agree with everything ovrszd said. Are you doing road construction or maintenance? You may have had a tire (or two) that has gone bad on you. We've seen that before.

smoothoperator

 

[bigshow]

It has happened to me before, I noticed which speed it happens at and in what grader and I stay away from that speed that causes it. Sometimes it happens carrying different blade loads too, at least to me anyways. I'm just curious as to why it does hop at certain speeds, I'm sure it's something scientific regarding the ratio of earth to the sun, the angle of the dangle but I would still like to know why, thank you.

 

[770G]

Yes I ment bounce, but I've always called it bounce I'd it's fronts and hop for the rears(it's the rears only)... I'm running michelin snows, and 45psi all around. I for the most part do maintaince, but do also get into some fresh belly dump gravel.

The problem only starts after around 6hrs of grading, and never under load(1st or 2nd cut) always when making finishing pass.

The part that is driving me crazy is its after 6hrs or so, before that all works perfect...... I so gotta get this sorted out before spring grading begins! Lol

 

[smoothoperator]

Something I have always wanted to try- top off the fuel tank in the middle of the day to see if fuel slosh in the tank has ANYTHING to do with this. Tanks are baffled, but what else changes during the day? Temperature of tires? Viscosity of fluids? Location of lunchbox? When somebody finds the answer, let us know.

smoothoperator...I had the answer written down, but my dog ate it.

 

[770G]

The other thing I should add is that I've been ruining this 2year old John Deere 770G since new, and this only started recently. I am carrying the Craig wing around but I have been every winter since new. I'm not doing anything different. My first guess was mechanical. And its almost due gor service do I'm gonna hit the Nortrac guy with questions

I too wondered about tire temp and pressure change..... Maybe I should hit up the boss for nitrogen filled tires

 

[Radrock]

Richard, you air your tires up just the opposite as I do. I run 45 in the rear and 40 in the front. I always felt like the front tires are running over the rough material so i want more give to my tires. I can really tell the difference when plowing snow. Runnig the front tires a little soft helps alot, expecially when plowing in 7th or even 8th gear. One problem we have is that the service people will see the tires squat (radials) and they think the tire is low and pump them up until the don't squat anymore (usually about 65 psi) and then they really bounce like heck. I've said a few choice words a few times. I did contact Michelin once and they said that sometimes offsetting the rear tires will help. Never heard of that before but what he meant was to put 40 psi in the front tandem and 45 in the back tandem. Never tried it though. A lot of time when your grader starts to bounce like that you can turn your moldboard a little more square.

770 I would sure check the tire pressure all around. Even dropping the left side of your tandem to 40 and keep the wing side at 45 won't hurt anything.

 

[brieneqservices]

I could be your the air pressure in the tires thats causing it. we run 35psi on the rears and we criss cross the pressure we put on one side 35psi and 40 psi. then on the other side we do the same except opposite of the other side. we had the same problem on a county grader and did this and it solved the problem.

 

[watglen]

On ag tractors the bouncing is called power hop. However, it only happens under heavy load. The bounce becomes resonant between axles, and can get pretty crazy. The solution is always to drop the tire pressure on one axle, raise it in the other. By doing so you change the traction characteristics of the axles, and prevent the resonation.

This grader hopping doesn't sound like that though. Can't imagine what would do it on a finish pass.

Not that i know anything about graders.

 

[770G]

Brieneqservices

That's sounds like a super cool idea and I'm gonna give that a shot. So this was to fix wheel hop when the grader was barely workin... Finishing pass?

 

[Showpony]

770 check the wear on your lower blade rail bushes, if they are shot take a couple of shims out of the top rail guides this will keep you going until the shop can fix your lower bushes, the JD replacements are expensive, we use a rolled piece of ultra high density plastic instead, settles a jumpin johhny down quick time.

 

[770G]

Thx showpony!! Nortrac is coming for a service Wednesday morning and I'm gonna hit him with that and a couple other ideas from this post.

THX TO EVERYONE FOR YOUR INPUT!!!!!!!

 

[ovrszd]

It has happened to me before, I noticed which speed it happens at and in what grader and I stay away from that speed that causes it. Sometimes it happens carrying different blade loads too, at least to me anyways. I'm just curious as to why it does hop at certain speeds, I'm sure it's something scientific regarding the ratio of earth to the sun, the angle of the dangle but I would still like to know why, thank you.

Yeah, it's definitely a frequency thing that as you said, would be too scientific for me to understand. So I just stumble along until I find a solutioin

 

[ovrszd]

The problem only starts after around 6hrs of grading, and never under load(1st or 2nd cut) always when making finishing pass.

I don't have an answer for the timing part, other than what someone suggested about less weight due to fuel burning.

As for the finish pass, I leave loose material in the middle of the roadbed, not a big windrow, I mean I carry the blade a couple inches off the roadbed. If I run the blade down against the hard roadbed I get bounce real bad. But I finish at 14 mph, not sure if contacting the roadbed on finish pass would have the same result at 6 or 7. You never said how fast you blade though.

 

[ovrszd]

Richard, you air your tires up just the opposite as I do. I run 45 in the rear and 40 in the front. I always felt like the front tires are running over the rough material so i want more give to my tires. I can really tell the difference when plowing snow. Runnig the front tires a little soft helps alot, expecially when plowing in 7th or even 8th gear.

That's interesting how different machines react differently. I can't run 40 in the front, get bounce real bad. As I mentioned before I have to increase pressure to 50 when carrying the plow. I plow snow at or around 14 mph depending on the type and amount of snow.

 

[ovrszd]

On ag tractors the bouncing is called power hop. However, it only happens under heavy load. Not that i know anything about graders.

I get that if I'm carrying a very heavy load, uphill, and begin to get wheel slippage. Locking the diff lock will usually stop or control it. If it's bad enough it requires separating the load and making another pass

 

[ovrszd]

770 check the wear on your lower blade rail bushes, if they are shot take a couple of shims out of the top rail guides this will keep you going until the shop can fix your lower bushes, the JD replacements are expensive, we use a rolled piece of ultra high density plastic instead, settles a jumpin johhny down quick time.

Yep, I've improved bounce by tightening the blade slide too. And you are right about the JD replacements being expensive. They don't last as long as they should either!!!

 

[Radrock]

That's interesting how different machines react differently. I can't run 40 in the front, get bounce real bad. As I mentioned before I have to increase pressure to 50 when carrying the plow. I plow snow at or around 14 mph depending on the type and amount of snow.

I think you said you are carrying a front plow didn't you? I know with a plow it will bounce because of the weight shift from those heavy critters. Of course that hop has a lot to do with speed too. I'm always trying to go to fast when running a haul road and plowing snow.

 

[Radrock]

I have another question for everyone. Do you ever run recaps? Our company has the habit of using them all of the time because of the flint rock here. They use 20 - 24 ply rock tires. I hate them with a passion but they are a lot better than 12 ply standard tires. I think a good radial does just as good though. But anyway did you know that some different tires are larger than others? When I first started for this company some 22 years ago they gave me some new recaps on my grader. Heck they never matched up anything. I told the boss that they would not work because one of the tires was a general tire. I said they were a lot bigger than most tires. He laughed at me and said he'd been doing that for 20 years and that I didn't know what I was talking about. I just went on to work and going down the paved road it was leaving black marks all the way down the road. I could feel the drag it was so bad. Within 100 yards of getting onto the fill (lots of flint rock on this one) I blew one of those new recaps all to pieces. It was funny as hell. I told the boss, "I guess I just don't know what I am talking about" and laughed.. I think he wanted to fire me but knew better. I knew from previouse experience that a General tire was up to 7" larger in circumferance than most other tires. I don't know if they still are.