I have a problem with my 790 that I am hoping maybe someone could help at least point me in the right direction. I have been doing a lot of digging with the bucket in loose sand so I have kept it in 4wd. Yesterday I took it out of 4wd and there was a clunking noise every few feet from the front axle. When I put it back in 4wd the clunking goes away and the 4wd works. Anyone have any ideas what it could be? Or does anyone have a drawing of the front axle I could use if I decided to take it a part. Thanks
JD 790 Front Axel
- Thread starter berkompt
- Start date
- Views: 29809
kennyd
Advertiser
Welcome to TBN
The diagram for the axle is available for free if you register at www.jdparts.com
Not sure what the clunking is-but I would not not it go to long before you figure it out!
Attachments
manganos
Platinum Member
Don't shoot the messenger but my co-worker has has his front end re-built 3 times for the same issue. I have also heard of other people having front end issues but that is the only complaint I hear about the 790.
Good luck and keep us informed on what it turns out to be and how it was fixed.
Good luck and keep us informed on what it turns out to be and how it was fixed.
JD755
Platinum Member
On the left side of the page click on John Deere Parts Catalog, just below Start Searching Here!.
RoyJackson
Rest in Peace
- Joined
- Nov 17, 2001
- Messages
- 24,646
- Location
- Bethel, Vermont
- Tractor
- John Deere 4052R Cab,, Deere 855D UTV, Z920A Zero Turn Mower and assorted implements
The 790's front axle is pretty strong but it is designed to be strongest when pulling in a forward direction. Pulling in reverse reveals it's limitations.
There were a few posts concerning front axle gears failure on TBN about 3-5 years ago. Seemed like a real rash of them for a while.
If berkompt has been doing heavy pulling in reverse gear, he may have broken a tooth off the spur gears in the front axle.
However, before pulling the axle, have someone observe the tractor (as close as possible) while operating in 1st gear low and reverse low. This is to try to determine exactly where the clunking noise is coming from. The tractor will be moving about 1 MPH.
There were a few posts concerning front axle gears failure on TBN about 3-5 years ago. Seemed like a real rash of them for a while.
If berkompt has been doing heavy pulling in reverse gear, he may have broken a tooth off the spur gears in the front axle.
However, before pulling the axle, have someone observe the tractor (as close as possible) while operating in 1st gear low and reverse low. This is to try to determine exactly where the clunking noise is coming from. The tractor will be moving about 1 MPH.
I was actually going in reverse up a very steep grade with full bucket before the noise started happening. The thing I can't figure out is it only makes the clunk going forward and in 2wd. If it did break a spur gear is it hard to fix? I have worked on many cars before. Is it fairly straight forward? Will I need any special tools or press or anything? Thanks again for all the help! Travis
RoyJackson
Rest in Peace
- Joined
- Nov 17, 2001
- Messages
- 24,646
- Location
- Bethel, Vermont
- Tractor
- John Deere 4052R Cab,, Deere 855D UTV, Z920A Zero Turn Mower and assorted implements
The first thing you'll want to do is buy the service manual for your 790. Make sure you get the correct one...there's been two or three (mine is actually for a 670, but there is addendums for the 790...I really need a newer manual). Your dealer can get you the correct manual if you provide the tractor's serial number (it's on a plate above your PTO guard).
Once you review the work involved, you can decide if you want to get into pulling the axle. I understand it's about $1500 or so if you take it to a dealer. I have no idea how much is for parts and how much for labor.
Once you review the work involved, you can decide if you want to get into pulling the axle. I understand it's about $1500 or so if you take it to a dealer. I have no idea how much is for parts and how much for labor.
arrabil
Veteran Member
Its possible the noise only happens in 2wd because the gear teeth aren't under load so they have lots of play and can bang around. While in 4wd they are loaded and have less give to them to make noise.
I imagine there is a king pin in the wheel assemblies. They are generally difficult to get out. If its a spider gear, the real difficulty is getting to the axle to replace them. The spider gears themselves are pretty easy to change out. The ring and pinion requires some know-how and specialty tools to setup properly for maximum strength and life.
I can't imagine if you lost a tooth on any of those gears that your axle won't lock up at some point from the tooth getting wedged somewhere but anything is possible.
Roy, when you say the reverse is weaker than the forward, do you mean because running the ring gear on the coast side of the teeth is inherently 20% or so weaker than running the drive side or is there some other design feature that makes it weaker?
I imagine there is a king pin in the wheel assemblies. They are generally difficult to get out. If its a spider gear, the real difficulty is getting to the axle to replace them. The spider gears themselves are pretty easy to change out. The ring and pinion requires some know-how and specialty tools to setup properly for maximum strength and life.
I can't imagine if you lost a tooth on any of those gears that your axle won't lock up at some point from the tooth getting wedged somewhere but anything is possible.
Roy, when you say the reverse is weaker than the forward, do you mean because running the ring gear on the coast side of the teeth is inherently 20% or so weaker than running the drive side or is there some other design feature that makes it weaker?
Well I jacked it up last night and I noticed that turning the front wheels by hand the left side one would stop at a certain point. So took it all apart and the lower pinion gear and the large gear the connects directly to the wheel were missing teeth. Since they are really pressed on I had to take it to the dealer to have them change the gears out for me. Thanks for all the help!
RoyJackson
Rest in Peace
- Joined
- Nov 17, 2001
- Messages
- 24,646
- Location
- Bethel, Vermont
- Tractor
- John Deere 4052R Cab,, Deere 855D UTV, Z920A Zero Turn Mower and assorted implements
I am no gear design expert by far...let's get that out of the way.
Gears can be designed to bear more load in the driven direction (in the case of the tractor, the "driven direction" is normally forward...but when I write "driven direction", this would be the side of the teeth that mesh first. The design considerations may be the root radius (radius at the bottom of the teeth) or how the teeth are heat treated or the actual angle of the "front" face (side that meshes first) of the tooth vs. the "rear" of the tooth.
Also, the backlash is set to the "front" face. An improperly set back lash can be make the "clunk" noise or a whine. Improperly set backlash can also result in premature wear.
I've not had to do any major maintenance on my 790 (thank goodness) and I'm not really set up to do this kind of work any more. But over the last 30 years, I've done enough (as an amatuer...I'm way too slow to make any money at this kind of work) to be reasonably capable.
arrabil
Veteran Member
I gotchya. the front of the tooth is called the "drive" and the rear is called the "coast." Backlash is inherently the same on both sides of the tooth. I've done my share of gear setups.....
I find it interesting that the ring gear would break before the transmission while doing hard work in reverse. Speaks well of the quality of JD's transmissions. I wonder if its designed that way on purpose? Break the easier to get to parts before the hard to get to ones?
I find it interesting that the ring gear would break before the transmission while doing hard work in reverse. Speaks well of the quality of JD's transmissions. I wonder if its designed that way on purpose? Break the easier to get to parts before the hard to get to ones?
RoyJackson
Rest in Peace
- Joined
- Nov 17, 2001
- Messages
- 24,646
- Location
- Bethel, Vermont
- Tractor
- John Deere 4052R Cab,, Deere 855D UTV, Z920A Zero Turn Mower and assorted implements
I think Deere expects the tractor to do the majority of it's hard work going forward.
As far as being designed that way on purpose...good question. I have no idea. I think the first consideration is cost of manufacture.
arrabil
Veteran Member
Yeah probably. I'm as cynical about it as anyone but you gotta figure there are some engineers in the design office thinking about doing it "right" too. At least I hope so. Certainly I buy JD because I believe they are built and designed better.
On second thought though... backwards, uphill, with a heavy load, turns the front axle into the drive axle on its weakest side. Probably does stress it past any design considerations. They do make the rear axle the strongest on pretty much all vehicles for a reason and this would be it.
berkompt, if it makes you feel any better, before hour ten of owning my tractor I put a stick through the radiator because I didn't know you shouldn't keep going back and forth over them... sooner or later one will pop up and nail something important. The hard way always teaches best.
On second thought though... backwards, uphill, with a heavy load, turns the front axle into the drive axle on its weakest side. Probably does stress it past any design considerations. They do make the rear axle the strongest on pretty much all vehicles for a reason and this would be it.
berkompt, if it makes you feel any better, before hour ten of owning my tractor I put a stick through the radiator because I didn't know you shouldn't keep going back and forth over them... sooner or later one will pop up and nail something important. The hard way always teaches best.
We have had a 790 for 3 years, the front axle issues you are experiencing has occured 3 times to us. It has to do with the berings and gears. Each time John Deere has replaced the parts under warrenty and each time it was on the right side. Three weeks ago my tractor broke in half from simply picking up a load of dirt. John Deere does not stand by their product. We struggled to keep the tractor and our small family business has now failed because we owe on a tractor that is useless. John Deere out right said we pulled the tractor apart... My advice.. buy a FORD!
Tractor King
New member
- Joined
- Nov 9, 2010
- Messages
- 14
Have been working with the compacts and I see that a lot of the 790 users aren't using enough ballast...say loaded rear tires and weight box like JD says...so they are taking out their front ends. Without a lot of ballast you are overloading the front end and they cannot withstand this. Also constant use in 4WD heavy turning etc will all waiste them. The 4x4 is an assists arrangment. I don't think the 790 is a very good loader tractor as the front is a little light from the factory. Nice small tractor but it needs a smaller loader and sensitive care. Go on up the higher series for your loader tractors.
OneMarineE5
Silver Member
By higher series....do you simply mean larger tractor? Are you aware of this issue with say the 2305 or the 2X20 series?
Tractor King
New member
- Joined
- Nov 9, 2010
- Messages
- 14
John Deere beefed up the pump on the 790 and used the 5' bucket and a heavy loader. End result self destruction. I have a JD4400 and it has twice the front end of the 790. The 790 was built on the 670 frame. Just not a loader tractor. Look at the front axle housing...they look at their small size.
Here are some similar links:
