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ebnel
ebnel, Technician
Category: Heavy Equipment
Satisfied Customers: 282
Experience:  master certification diagnostics and repair
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I have a John Deere 7410 FWA tractor. It now has 4170hrs on

Resolved Question:

I have a John Deere 7410 FWA tractor. It now has 4170hrs on it and is back in the shop for the third time in 600hrs with front end problems. At 3600hrs bevel gears and crown and pinion bearings were replaced. After that repair the tractor shook so badly that it was breaking off fender mounts. We took it back and they replaced a u-joint between the engine and transmission. After a week it shook both front fenders off again. Now it has been back at the dealer for over a month, and all they can tell us is that they think it needs different tires on the front. The tires that are on it are the originals, and have normal tread wear. Any other ideas?
Submitted: 3 years ago.
Category: Heavy Equipment
Expert:  ebnel replied 3 years ago.

ebnel :

Hello, If this problem started only after front axle repair, I would have them check part numbers of gear set installed. Sounds like ratio is incorrect, and will cause excessive vibration and damage. Your shop would need to disassemble mfwd axle again and verify part numbers along with axle model.

Customer:

That is exactly what I have been thinking. They have measured, and the front end is under driving by 6 or 7% when in FWA. I asked if they could have installed the wrong gears and they say that changing only the bevel gears and not the crown and pinion could not change the gear ratio. Is that right? I also think that we would not have seen such a drastic change in operation from simple tire wear as we would have with a gearing problem.

Customer:

They also seem very hesitant to tear apart the axle as they would be responsible for any improper installations that may have occured.

ebnel :

Thanks for that info. Axle is under driving? Front axle is designed to over drive 1 - 5 %. Yes I believe they have incorrect gears installed. If this all started after repairs, I would hold them responsible to get issue corrected. New tire's will not correct this problem, they might only speed up 2-3%, which is not enough.

Customer:

Since I am not a mechanic, I don't know, is taking apart the axle to check on these gears a large project? As I have said they have had our tractor since before christmas and have not looked at these gears. Now I have found out that the manager is gone for this whole week so we will likely not see any progress before we talk to him.

Customer:

I am new to this website, if I click this accept button, I'm guessing that you then get paid but I couldn't ask any more followup questions. Is it alright if I wait to see some results from these guys before I do that? Thanks for your help so far, you have given me more confidence in my opinions of what has been going on.

ebnel :

Just get back to me when you get issue resolved. Not good tractor has been held all this time, hopefully they will stand good for repairs.

Customer:

Hello again. I just got off the phone with the manager we are dealing with. He told me that the have decided that tires are the answer and that they would pay half to replace them. I told him that other experts (you) think that it is a gearing issue. He asked me what could be wrong with the gears when they did not change the crown and pinion and once again suggested that there is no need to open up the front end. I told him that I would not be satisfied until they had at least checked things out in there and that they had to take it apart. They will do this (at my expense if there is no problem in there) and then call me to look it over when they have it apart. My question then is what am I looking for when I see the guts of this thing? Cracks, wear, counting cogs, what about the plates that control the differential? I have only seen pictures of this on their parts screen and have no idea how it works?
Any tips would be greatly appreciated. Thanks again.

ebnel :

Hello Do you know if any addiative was added to oil when axle was apart first time?

ebnel :

Also do still have slip or bill with part numbers that were installed?

ebnel :

I don't think tire's are the problem. This vibration is only present when mfwd is engaged, right?

ebnel :

A while back I had front axle with chatter issue that ended up being resolved by adding GM gear oil additive. Was nothing wrong with gearing, however this certainly wasn't shaking/breaking fenders like your's.

Customer:

No additives added, using John Deere Hy-guard oil.

Customer:

Yes, only vibrates in MFWD, smooth in 2wd. They talked about the additives, but said it was only used in older models than ours.

Customer:

I have the bill with all part #s and description of work performed. It's a long description, but here it is.

Customer:

Installed the differential and right hand front axle housing with four bolts. Checked the rolling drag and disassembled for further assembly. Assembled the input pinion with new bearings. Measured the dimensions as per tech manual to obtain the proper shims for pinion bearings. Installed the pinion and tightened the flange to check rolling drag. Removed the pinion and changed the shim thickness. Rechecked to obtain the rolling drag of seventeen inches/lbs. Installed the differential and right hand housing. Checked back lash, too high. Disassembled to change the shims. Reassembled and rechecked but it was too tight. Disassembled to change shim and reassemble to .009" backlash. Checked the wear pattern on the teeth, all ok. Reassembled the final time and torque right hand front axle to specifications. Removed the input flange, installed a new seal and tightened to specifications. Installed the drive shaft, guards and front drive wheels and torque to specifications.

Customer:

Expensive parts were 2 N L101697 bevel gear, 4 N L101698 bevel gear and 1 N L101699 housing.

ebnel :

Thank you for that info, I don't see anything wrong with these part numbers. To help you avoid unnecessary expenses I would have them install additive and check operation before disassembling again. The tractor I had chatter trouble with was 7420.

Customer:

Thanks for all of your help. Friday they disassembled the front end and we had a look, everything looks fine. So once again we were lost without an answer. Yesterday though I got thinking about everything they had told me about their measurements as to front end travel. They had driven the tractor for 10 revolutions of the front tire in 2wd then 10 revolutions in MFWD. The tractor travelled 90 inches less distance on the ground in 4wd, and they told us that it was underdriving by 6-7%. It finally occurred to me yesterday that this is in fact overdriving, not underdriving. The front axle would make its 10 revolutions at the same point on the ground no matter what tires were on the front because the gears can not do anything else. So if it travelled less ground distance in 4wd than 2wd, it had to spin the front tires that 90 inches extra on the ground in the distance the tractor had covered. I now believe that if they install new front tires that are 3 to 5 inches shorter than the tires that are on it now that we will see 2wd and 4wd distances match much more closely. What do you think?

ebnel :

The front axle is designed to "overdrive" couple percent. When MFWD is engaged front axle is pulling tractor and should cover more ground in MFWD, not less. What it sound like right now is with front end engaged,tractor is pushing front wheels.

ebnel :

There are other part number bevel gears for this front axle, are they sure they used correct serial # XXXXX part numbers?

ebnel :

Are old parts still available to measure? I still don't think tire's are the problem, your problem didn't show up till front end was worked on, have they consulted with Deere technical dealer support? DTAC, dealer has technical support available and should be able to solve this problem for you.

ebnel, Technician
Category: Heavy Equipment
Satisfied Customers: 282
Experience: master certification diagnostics and repair
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