05 honda forman 500 four wheel drive won't engage

[cdyoder 5]

Hello guys, I could use some help diagnosing my problem on my fourwheeler. 

  I have it completely off the ground and when I hit the four wheel switch the light comes on in the dash but the front wheels don't turn. The axle coming out of the engine does turn. I also don't hear anything engage when I flip the switch.  I'm not sure where I should start to look for the problem.

     I replaced one of the cv axles because the old one was locked up and someone just cut it so they could still ride it. Both cv axles pivot fine now. Maybe when the old cv axle locked up  it damaged the shift motor? What do you guys recommend I check out?  I appreciate any help! Thanks

[jeepwm69 7,674]

Welcome to the forum.  Most likely your splines are stripped on your front driveshaft.   Unbolt the front diff (3 bolts) and pull it forward as far as you can.   That will allow you to remove the front driveshaft.  If you have it in 4wd and turn the wheels, the rear coupler on the front diff should be turning.

 

It's fairly common for the splines to strip on the front driveshaft, specifically at the engine end where it goes into a coupler.

[cdyoder 5]

Ok, I'll look at it. If the splines aren't stripped then I guess the motor might be bad. I don't know how common that is. Should i be able to hear it engage? Thanks

[jeepwm69 7,674]

The front diff has an electromagnet on the back.  When you hit the switch, the electromagnet is supplied with 12V and connects the rear input of the front diff to the rest of the diff. 

 

Not common for a front diff to fail without making a lot of racket while moving, so much more likely it's stripped splines on the front driveshaft.  If your front driveshaft is good, we'll try jumping 12V to the front diff actuator next.

 

It's very quiet when actuated, just a faint click, and IIRC the engine has to be running to put it in 4wd, so not something you'd hear with the engine running.

[shadetree 5,943]

word from the wise: unless you put the engine in gear , and put the front into 4wd ?, the front diff will never work !. i found this out the hard way on an older trx450fm !. i did the same thing you are doing..light on dash would light up, but no movement on front diff ?..after buying a control unit..plugging it in ?..same problem !. it was by accident that i was able to see why the front diff was not working ?..i was checking out the transmission , to make sure it shifted through all the gears ?, low and behold, the front 4wd light stayed lit..no flashing, and the front end was working !. sooo..in other words..the atv has to be in gear..like ..1st ?, turn switch from 2wd to 4wd..then watch to see if the front end works ?. also..keep in mind..most of these atvs that have a electronic front diff, they have not 1 ?, but 2 speed sensors !. this is how the front diff works !. sooo..until you put the atv in gear..and the front output drive shaft is spinning ?, the first speed sensor at the front side, input side of the diff can not see any movement on the drive shafts pinion gear ?, sooo..the electronic part of the pinion gear will not engage from pinion gear to ring gear. the second speed sensor is on the very front, top side of the diff..right on the middle of the differential,  its covered by a metal plate cover, same goes for the first speed sensor at the drive shaft input side, left side when viewing from seat.

[shadetree 5,943]

8 hours ago, jeepwm69 said:

The front diff has an electromagnet on the back.  When you hit the switch, the electromagnet is supplied with 12V and connects the rear input of the front diff to the rest of the diff. 

 

Not common for a front diff to fail without making a lot of racket while moving, so much more likely it's stripped splines on the front driveshaft.  If your front driveshaft is good, we'll try jumping 12V to the front diff actuator next.

 

It's very quiet when actuated, just a faint click, and IIRC the engine has to be running to put it in 4wd, so not something you'd hear with the engine running.

you never mentioned anything about the speed sensors grasshopper !...lol.

[cdyoder 5]

On 5/20/2024 at 7:04 PM, shadetree said:

word from the wise: unless you put the engine in gear , and put the front into 4wd ?, the front diff will never work !. i found this out the hard way on an older trx450fm !. i did the same thing you are doing..light on dash would light up, but no movement on front diff ?..after buying a control unit..plugging it in ?..same problem !. it was by accident that i was able to see why the front diff was not working ?..i was checking out the transmission , to make sure it shifted through all the gears ?, low and behold, the front 4wd light stayed lit..no flashing, and the front end was working !. sooo..in other words..the atv has to be in gear..like ..1st ?, turn switch from 2wd to 4wd..then watch to see if the front end works ?. also..keep in mind..most of these atvs that have a electronic front diff, they have not 1 ?, but 2 speed sensors !. this is how the front diff works !. sooo..until you put the atv in gear..and the front output drive shaft is spinning ?, the first speed sensor at the front side, input side of the diff can not see any movement on the drive shafts pinion gear ?, sooo..the electronic part of the pinion gear will not engage from pinion gear to ring gear. the second speed sensor is on the very front, top side of the diff..right on the middle of the differential,  its covered by a metal plate cover, same goes for the first speed sensor at the drive shaft input side, left side when viewing from seat.

Thanks for all the info. I do have a loose wire up at the front that i don't know what it goes to. It's red, and I don't think the speedometer works either. Maybe it goes to a speed sensor. I'll dig into it today

[jeepwm69 7,674]

2 hours ago, cdyoder said:

Thanks for all the info. I do have a loose wire up at the front that i don't know what it goes to. It's red, and I don't think the speedometer works either. Maybe it goes to a speed sensor. I'll dig into it today

 

The 4wd won't engage if the speedometer isn't working.  Both speed sensors have to be reading the same speed for the 4wd to engage.

 

That said, doesn't look like there's a red wire going to any of the front diff stuff.   The front speed sensor is on top, at the front of the diff.  The rear speed sensor is on the right side at the back of the front diff.   The actuator is on the side of the front diff on the right side right next to the rear speed sensor. 

 

 

 

 

[cdyoder 5]

This what my speed sensor on the side looks like. Pretty sure I have shavings inside the actuator. The drive shaft going to front dif turns ,but the wheels don't. Thanks !

[cdyoder 5]

Can you remove the four wheel drive motor without removing the whole dif?

 

 

[jeepwm69 7,674]

7 minutes ago, cdyoder said:

This what my speed sensor on the side looks like. Pretty sure I have shavings inside the actuator. The drive shaft going to front dif turns ,but the wheels don't. Thanks !

 

While I don't think that the shavings from that speed sensor (plastic) will hurt anything in the diff, the condition of the sensor is concerning.   It appears to be melted/ burned, correct?   If so, you probably have a short/wiring problem somewhere leading to the sensor.

 

If it appeared ground off instead of burned, I'd say you had a bad pinion bearing, but that thing looks melted to me. 

 

See the green plug?  That's your front diff actuator.  

 

I'd say you definitely need a new speed sensor, but I'd be trying to figure out exactly what damaged that one first, because you don't want to have the same problem and ruin another sensor.

[cdyoder 5]

I think it's ground off not melted . I think I should take that motor off.

[jeepwm69 7,674]

11 minutes ago, cdyoder said:

Can you remove the four wheel drive motor without removing the whole dif?

 

 

 

You have to pull the front driveshaft to get the actuator off the front diff.  

 

14MM bolt on the bottom of the front diff, accessable from the right side.   Bolt and spacer on the top of the front diff, bolt through bracket on the front of the front diff.  3 bolts total.  Remove those, and grab the axles and pull the whole front diff forward.   You don't have to remove wheels, hubs, or any of that.  Just unbolt the diff and pull it foward.  Then you can remove the front driveshaft (and check the splines) and you should be able to unbolt the acutator and remove it from the front diff.   It won't be easy, and I wouldn't do that just yet, as I don't think it will address whatever problem you have.  Those actuators are sealed, so no way to really "fix" them.  They are $$$ too

[jeepwm69 7,674]

Just now, cdyoder said:

I think it's ground off not melted . I think I should take that motor off.

 

My guess is you have a pinion bearing that's gone south then.

 

Once you start looking at replacing parts on these front diffs, the cost of new parts gets up there pretty quickly.

 

You can pull the front diff forward, remove front driveshaft, and then unbolt the actuator and pry it off the back of the front diff for inspection.

 

Depending on what you find, I think you'll find you're better off buying a used complete front diff with actuator and speed sensors than trying to replace that actuator alone.

 

05-11 Foreman footshift and ES, 05-14 Rubicon, and  Rincon front diffs should work.  The only differences in any of those is male/female plugs differ from year to year, and it's simple enough to either buy a pigtail from Honda or cut/splice the wires to correct.

 

Let us know what you find.

[cdyoder 5]

Will do. I'm working on taking the front diff loose now.  Will the drive shaft pop out once I move the diff forward?

[jeepwm69 7,674]

Yes.  Pull it all the way forward.  You might have to pull and pry on the seal at the front of the driveshaft to get it off the diff.

 

There's a spring between the coupler on the engine end and the shaft itself as well, so you'll have some play there to work with as well.

[cdyoder 5]

I got the actuator off. How do I know if this is bad or not? I see two loose rings inside . The gear going into the dif looks fine

[cdyoder 5]

I've found a couple small pieces in there but mostly like an oily grease

[shadetree 5,943]

4 hours ago, cdyoder said:

I've found a couple small pieces in there but mostly like an oily grease

don't bother trying to take this thing apart !..its a royal pain in the rear to service..been there..done that..lol. better off locating a good front diff. most front diff's used will not be seperated from this part you have in this pic ^^, this means you will need to buy the whole front diff.

[shadetree 5,943]

5 hours ago, jeepwm69 said:

 

My guess is you have a pinion bearing that's gone south then.

 

Once you start looking at replacing parts on these front diffs, the cost of new parts gets up there pretty quickly.

 

You can pull the front diff forward, remove front driveshaft, and then unbolt the actuator and pry it off the back of the front diff for inspection.

 

Depending on what you find, I think you'll find you're better off buying a used complete front diff with actuator and speed sensors than trying to replace that actuator alone.

 

05-11 Foreman footshift and ES, 05-14 Rubicon, and  Rincon front diffs should work.  The only differences in any of those is male/female plugs differ from year to year, and it's simple enough to either buy a pigtail from Honda or cut/splice the wires to correct.

 

Let us know what you find.

i have never bothered to check ?, but is it posb for a front diff ( drive shaft input part )  from a 450fm into his 500 ?. prob the ring gear may be diff ?..but i bet the pinion shaft, the front part that he has out..may swap out ?..they all work the same way.

[shadetree 5,943]

4 hours ago, cdyoder said:

I got the actuator off. How do I know if this is bad or not? I see two loose rings inside . The gear going into the dif looks fine

lol...well..its deff bad...or you would have a working front diff..lol. i'd say that thing is toast.

[jeepwm69 7,674]

39 minutes ago, shadetree said:

i have never bothered to check ?, but is it posb for a front diff ( drive shaft input part )  from a 450fm into his 500 ?. prob the ring gear may be diff ?..but i bet the pinion shaft, the front part that he has out..may swap out ?..they all work the same way.

 

I'm not 100% positive on this, but I know the gear ratios are the same.  05-11 Foreman 500, 05-14 Rubicon, 03-current Rincon, and 02-04 450 Foreman....pretty sure they'll all interchange.

 

 

[cdyoder 5]

You can buy just the actuator too on ebay without buying the whole dif. That should fix my problem correct?

[shadetree 5,943]

6 minutes ago, cdyoder said:

You can buy just the actuator too on ebay without buying the whole dif. That should fix my problem correct?

yes..if you can buy just the actuator ?..but i've never seen many sold this way...they normally do not separate the front diff.

[cdyoder 5]

Ok thanks for all your help!