Oil & Fuel John Deere 3120 front differential seal leak

chadlough · Aug 18, 2018

My John Deere 3120 front differential is leaking oil out of the driveshaft (rear)seal. Any information or tips on changing this seal? is this a job for a fairly knowledgeable do it yourselfer , or is this a job for the shop?

beenthere · Aug 19, 2018

:welcome: to TBN

Have not done it, but imagine it is similar to replacing other seals.. care and cleanliness #1.

If you don't have the service tech manual, I'd suggest getting it. Also go look at the parts you will need to deal with on jdparts.

Wish you well, and hope you include us in the fix.

oosik · Aug 19, 2018

I helped the neighbor replace this exact same seal on his BIG IH Case. He knew exactly what he was doing - I was the grunt.

I would strongly suggest having a helper - grunt. The drive shaft, in this case, was very heavy and rather tricky to get the floor jack in exactly the right place to engage and lower the drive shaft. He could stay situated under the tractor and not have to crawl out every five minutes to get something else - I was there. Hand him tools, parts, rags, hold new seal in place while he seated it etc, etc.

Since you will have pulled the drain plug and drained any remaining oil on the front differential - install drain plug and refill differential.

Before you start this job - look at shop manual and see what "weird or unusual" tools you might need. He needed a slide hammer seal puller for the old oil seal and for the U-joint. He needed a large snap ring pliers - the oil seal was retained with a large snap ring. Need a method of removing the large nut that holds the U-joint on the drive shaft stub. He had an air impact wrench.

This is definitely a doable job if you have the necessary tools, a helper and a relatively clean environment to work in.

oldtimer 66 · Aug 19, 2018

Chadlough here is the info I can supply and you may want to grab a bite to eat before you get into this. LOL. When my tractor, a JD 4230 compact, was less than 2 yrs. old the front seal on the differential started to leak. This was covered under warranty. The dealer said that the front differential was bullet proof and had never seen this problem before. The dealer had the tractor for approx. 1.5 weeks and his biggest problem he had was getting a thin wall 1.625 deep socket to remove the pinion nut. I am not sure if yours is the same. He removed the front axle to replace the pinion seal. My tractor and yours are similar in design. There should be a plastic front drive shaft guard with a band clamp and (2) bolts on the forward end. Remove that hardware and collapse the plastic guard to expose the splined couplings on each end of the drive shaft. There are no u-joints on this design. The couplings are located with 4 X 30 MM rolls pins (2) , one on each end. You will need a .125 pin punch to remove them. If possible only clear the roll pins of the drive shaft but still engaged in the coupling. They are really small and can get lost easily or just get extras when you order your parts. Slide the couplings towards the center of the drive shaft to expose the ends of the drive shaft and aside the drive shaft and cover. You can now disconnect the (2) hydraulic lines to the steering cylinder. Zip tie the hydraulic lines out of the way. Next you will probably need to remove the grill guard and the mower front supports if your tractor has those options. Mine come off as a assembly. Next jack up the tractor so that the front wheels are off the floor. I supported my tractor by the 2 lower FEL mounts. Next remove only the front trunnion, (4) bolts holding the front trunnion in place while supporting the axle asmy with a floor jack. Once the front trunnion is removed you can wiggle and pull the front axle asmy out from the rear trunnion and from under the tractor. Have a helper support the axle asmy because it wants to rotate to the pinion down position. Next block up the axle asmy with the pinion in the vertical position and on top. Now you have easy access to replace the seal. Use your air nozzle and keep everything clean. Like I said I am not sure what the hex size is of your pinion nut is. Just to back up for a minute you do not need to drain the differential oil and you do not need to remove the front wheels. I have removed numerous axle, wheel and pinion seals over the years. Each one seems a little different. You just need to pry it from thr back side with something. They make universal seal puller that would probably do the job and they are not very expensive. They look like a double ended rolling pry bar but only .19 thick approx. You can buy the seal kit as show on line, but I would reuse your existing spacer. The seal kit is a nut, seal, spacer and O-ring. You can just do the seal and O-ring but I would suggest a new nut also as a minimum. You need to get the torque value of the pinion nut. Mine is 190 to 210 Lf/Lbs. and yours maybe different. To drive in the new seal I some times use a large socket and or a piece of pipe. Get it square and seated. Now if the pinion shaft is grooved or scored where the seal rides on the pinion shaft you may want to adjust the depth that you drive to seal to so that it can ride on a cleaner portion of the shaft. This all depends on clearances. I have done that on a couple of timing chain covers that had a grooved crankshaft. Last item. Inspect the bushings, thrust washer and seals for the trunnions. You may want to replace those items at this time. Inspect the front axle trunnion pins for scoring. You may want to dress them with some emery paper before installing new bushing. These part details are shown on the JD web site. One more item you should really get the maintenance CD. I have one for my tractor and at the time it was $80. It is a searchable PDF and it has paid itself back numerous times. I will add some pics for reference. All of the above assumes that the seal is worn and there is not a secondary problem like the pinion bearing is loose or starting to fail. Later.

joecdeere · Aug 21, 2018

I have a PDF of the technical manual that you're welcome to, shoot me your email if wanted

Joe

chadlough · Feb 18, 2025

oldtimer 66 said:
Chadlough here is the info I can supply and you may want to grab a bite to eat before you get into this. LOL. When my tractor, a JD 4230 compact, was less than 2 yrs. old the front seal on the differential started to leak. This was covered under warranty. The dealer said that the front differential was bullet proof and had never seen this problem before. The dealer had the tractor for approx. 1.5 weeks and his biggest problem he had was getting a thin wall 1.625 deep socket to remove the pinion nut. I am not sure if yours is the same. He removed the front axle to replace the pinion seal. My tractor and yours are similar in design. There should be a plastic front drive shaft guard with a band clamp and (2) bolts on the forward end. Remove that hardware and collapse the plastic guard to expose the splined couplings on each end of the drive shaft. There are no u-joints on this design. The couplings are located with 4 X 30 MM rolls pins (2) , one on each end. You will need a .125 pin punch to remove them. If possible only clear the roll pins of the drive shaft but still engaged in the coupling. They are really small and can get lost easily or just get extras when you order your parts. Slide the couplings towards the center of the drive shaft to expose the ends of the drive shaft and aside the drive shaft and cover. You can now disconnect the (2) hydraulic lines to the steering cylinder. Zip tie the hydraulic lines out of the way. Next you will probably need to remove the grill guard and the mower front supports if your tractor has those options. Mine come off as a assembly. Next jack up the tractor so that the front wheels are off the floor. I supported my tractor by the 2 lower FEL mounts. Next remove only the front trunnion, (4) bolts holding the front trunnion in place while supporting the axle asmy with a floor jack. Once the front trunnion is removed you can wiggle and pull the front axle asmy out from the rear trunnion and from under the tractor. Have a helper support the axle asmy because it wants to rotate to the pinion down position. Next block up the axle asmy with the pinion in the vertical position and on top. Now you have easy access to replace the seal. Use your air nozzle and keep everything clean. Like I said I am not sure what the hex size is of your pinion nut is. Just to back up for a minute you do not need to drain the differential oil and you do not need to remove the front wheels. I have removed numerous axle, wheel and pinion seals over the years. Each one seems a little different. You just need to pry it from thr back side with something. They make universal seal puller that would probably do the job and they are not very expensive. They look like a double ended rolling pry bar but only .19 thick approx. You can buy the seal kit as show on line, but I would reuse your existing spacer. The seal kit is a nut, seal, spacer and O-ring. You can just do the seal and O-ring but I would suggest a new nut also as a minimum. You need to get the torque value of the pinion nut. Mine is 190 to 210 Lf/Lbs. and yours maybe different. To drive in the new seal I some times use a large socket and or a piece of pipe. Get it square and seated. Now if the pinion shaft is grooved or scored where the seal rides on the pinion shaft you may want to adjust the depth that you drive to seal to so that it can ride on a cleaner portion of the shaft. This all depends on clearances. I have done that on a couple of timing chain covers that had a grooved crankshaft. Last item. Inspect the bushings, thrust washer and seals for the trunnions. You may want to replace those items at this time. Inspect the front axle trunnion pins for scoring. You may want to dress them with some emery paper before installing new bushing. These part details are shown on the JD web site. One more item you should really get the maintenance CD. I have one for my tractor and at the time it was $80. It is a searchable PDF and it has paid itself back numerous times. I will add some pics for reference. All of the above assumes that the seal is worn and there is not a secondary problem like the pinion bearing is loose or starting to fail. Later.View attachment 567596 View attachment 567597 View attachment 567598 View attachment 567599 View attachment 567600 View attachment 567601

Thanks so much for the detailed information.