1987 Honda Fourtrax - Rear Diff and No Oil

[Hank_tank 0]

Hi all, recommended to post here by Goober. I picked up a Fourtrax 350 a few years ago and finally getting around to cleaning and maintaining her. She runs like a beast, but when I checked the diff fill plug on the rear differential, the casing is muddy/silty inside, and there is literally no oil to drain. What am I looking at on keeping it going? Thanks!

[jeepwm69 7,750]

Welcome aboard!

 

Since you can no longer get gearsets for those 350 diffs, and they are in high demand for 300 rear end swaps, were it mine I would pull the rear end, take the diff apart, and clean the crap out of the inside of it.  Make sure the bearings are tight with no play (if bearings have play, replace them) and then reassemble with fresh gear oil. 

 

It will be a bit of work, but shouldn't cost you much if anything more than time.

 

 

[Fishfiles 20,147]

Hi Hank , there are so many different scenarios  that could occur when you " Try " and take it apart  , best to have a few speciality tools and some knowledge to take it apart -----------   could be as simple as  just replacing a couple of seals , to needing a whole new diff and / or an axle -----------   that rear diff  is no longer available , like Jeep mentioned there are no replacement gear sets  and that rear end used  is pretty hard to find these days and it is expensive ---- no oil and muddy does not sound good 

 

start by jacking the rer off the ground and checking  for play and smooth rotation 

[shadetree 5,973]

pull the rear diff out the rear end, split it, clean it all out, put fresh new gear oil back in. while you have it apart, now is the time to check the bearings, replace the oil seals if you can still get them ?. 80w-90 gear oil is what i run in all my diff's.

[Hank_tank 0]

3 hours ago, jeepwm69 said:

Welcome aboard!

 

Since you can no longer get gearsets for those 350 diffs, and they are in high demand for 300 rear end swaps, were it mine I would pull the rear end, take the diff apart, and clean the crap out of the inside of it.  Make sure the bearings are tight with no play (if bearings have play, replace them) and then reassemble with fresh gear oil. 

 

It will be a bit of work, but shouldn't cost you much if anything more than time.

 

 

 

3 hours ago, Fishfiles said:

Hi Hank , there are so many different scenarios  that could occur when you " Try " and take it apart  , best to have a few speciality tools and some knowledge to take it apart -----------   could be as simple as  just replacing a couple of seals , to needing a whole new diff and / or an axle -----------   that rear diff  is no longer available , like Jeep mentioned there are no replacement gear sets  and that rear end used  is pretty hard to find these days and it is expensive ---- no oil and muddy does not sound good 

 

start by jacking the rer off the ground and checking  for play and smooth rotation 

 

2 hours ago, shadetree said:

pull the rear diff out the rear end, split it, clean it all out, put fresh new gear oil back in. while you have it apart, now is the time to check the bearings, replace the oil seals if you can still get them ?. 80w-90 gear oil is what i run in all my diff's.

Much obliged, all. I'll start taking the rear axle out and getting going. Where does one pick up new oil seals if needed on something this old?

[Goober 1,555]

Start by using the OEM parts finder at Rocky Mountain atv and Partzilla. Get part numbers and start searching for, pricing parts.

 

download the service manual from the service manual forum and or buy a printed Honda manual.

 

fleabay is a good source to get NLA overstock

Edited June 8, 2022 by Goober

[jeepwm69 7,750]

If you're lucky you'll be able to clean it out, put it back together, and add oil.

 

As long as the pinion gear isn't wobbly (worn pinion bearings) anything you might need to do will be easy (the ring gear bearings and seals are easy).