990 rear diff problem

[kenmore99]

I've been happy with my JD 990 7year old tractor until it started knocking last week--I baby this tractor and it only has 340 hrs and now its getting a new rear differential! wow- going to pay the JD dealership for the repair and may go look at Kubota--Ive always serviced on time etc--I'm bummed--anyone else had this happen???

 

[RoyJackson]

I've been happy with my JD 990 7year old tractor until it started knocking last week--I baby this tractor and it only has 340 hrs and now its getting a new rear differential! wow- going to pay the JD dealership for the repair and may go look at Kubota--Ive always serviced on time etc--I'm bummed--anyone else had this happen???

This is the first time I've read of a 990 breaking.

 

[kennyd]

This is the first time I've read of a 990 breaking.

Me too...

Welcome to TBN kenmore
Can you give us some more details? What exactly broke?

 

[kenmore99]

The JD dealership at first couldnt find the knock--after a week I told them to keep looking bc when it started knocking in the rear it would scare the daylights out of him--a week went by,I called yesterday and the mechanic stated he was "so busy sorry I havent called but your rear dif. is gone and I've ordered gears to replace" I told him I was upset since that sounded expensive and he hadnt cleared it with me and he stated "well,you cant drive it now bc the rear's in pieces and its not my fault it failed and I dont know the cost till I'm done"--so...my overall disposition will be determined when we see what the repair bill is...next week

 

[Nitro-Fish]

Doesn't the 990 have a planetary set up? I would think it would take quite a bit of abuse to damage one!

 

[arrabil]

Wow, never seen an axle quite like that before. Yep... its a planetary axle drive system. And I agree that looks REALLY stout. But, its still driven by one pinion from the transmission. Thats probably where it broke is my guess.

I'd imagine if the diff lock got stuck, or was used incorrectly, that planetary drive would transfer a tremendous amount of strain to the transmission pinion.

kenmore, you should ask what specifically broke... the drive axles themselves look indestructible.

[I'm perusing the 990 tech manual btw.]

 

[kenmore99]

I'll ask specifically what broke--I spoke with the head service person and he said not only was the differential replaced but 2 wheel bearings also were replaced and I'll find out the total cost next week (at least 2k so far)--my only symptoms were an infrequent loud rear knock every so often out of nowhere--it never shook,stuttered,or affected the pull of the tractor--since i am mechanically illiterate, I hope I'm not getting suckered--I'm asking for used parts next week to see what the condition was and let you know.thanx--again, this tractor was babied and pampered--I'm sick

 

[arrabil]

my only symptoms were an infrequent loud rear knock every so often out of nowhere

That could be the differential skipping a tooth like I was guessing. Any particular reason you didn't take it in after hearing the first loud knock?

 

[kenmore99]

I took the tractor in for repair the 3 rd time I heard the knock--the knock only lasted 2 or 3 knocks the first 2 times but I took it in the 3rd instance when it knocked 4 or5 times--it took the dealership 2 weeks to get it to knock again--the dealership reiterated today that the tractor would have to be pushed past its limits to strip the rear gears but I can attest that didnt happen--it will be finished repair tuesday--I looked at the KubotaL4400 yesterday and it just plain looked less sturdy/less solid than a JD410--going to pay for this over 2k repair and look the JD4105 and the MF1643--anyones opinion on those 2 trac would be appreciated...

 

[arrabil]

Why would you spend $2K on repairs and then dump the tractor at what has to be a loss?

You use the diff lock a lot?

 

[kenmore99]

This is a 7yo 350 hr tractor but I only bought it 1.5 yr ago from a friend who i know took care of it and didnt abuse it (of course,thats debatable now)--so I am considering buying a new tractor bc I want one that is going to last 15 years at least and if the rear end drops out at 350 hr, what does that say about the condition of the motor and other components--I cant buy a tractor in 2 years with 2 kids in college so its either suck it up and pay now or pay more later--either way I realize I'm screwed financially but this is my only toy and I work hard for it...thanx

 

[arrabil]

if the rear end drops out at 350 hr, what does that say about the condition of the motor and other components

The rear end says absolutely nothing about the other components.

So did you use the diff lock a lot?

 

[kenmore99]

I've never used the diff lock in the 45 hours I've had the tractor--and the wheel bearings having to be replaced? thats why I'm skittish on this tractor--what do you think other than abuse could cause this at 350hrs?

 

[kenmore99]

Final repair bill today--2450$-included a new "spider gear" for the rear diff and new wheel bearings and regular servicing--spoke with the JD manager and he said the tractor is a tank,looks good and chalk it up to bad luck so I've settled down and going to keep it for now and Craigslist or ebay if it acts up again and go tractor shopping..thanx

 

[arrabil]

A spider gear normally won't break unless you really put a lot of torque to it, like while you're stuck, or its just a freak thing. I'd be keeping it.

 

[RoyJackson]

A spider gear normally won't break unless you really put a lot of torque to it, like while you're stuck, or its just a freak thing. I'd be keeping it.

Yep, I agree...unless there was a defect in the casting or billet that wasn't found.
That dealer is right...the 990 is a tank and you were just the unlucky recipient of wha may have been a manufacturing defect (or the previous owner did abuse it without realizing it).