Possible Worn diff?

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JezHall

RCTalk Basher
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RC Driving Style
  1. Bashing
  2. Crawling
Hi,

Is it possible for the internal cogs inside a diff to wear and fail?

It all looks ok to the untrained eye but once assembled only one of the cups moves when the main shaft is turned…..

This is from an FTX Outlaw so it does take a battering…

Thanks in advance…

BFAD923A-4FAB-4F7F-BD31-B1A4BD141FDE.jpeg


image.jpg
 
Hi,

Is it possible for the internal cogs inside a diff to wear and fail?
Yes it is.

It all looks ok to the untrained eye but once assembled only one of the cups moves when the main shaft is turned…..

This is from an FTX Outlaw so it does take a battering…

Thanks in advance…
Can you take all of the gears out and lay them flat on your work bench and take clear pics of them for us to look at? Maybe we can see if they have excessive wear or something.

When you have the diff assembled and you turn one output shaft does the other side rotate?

Did you check and make sure all the bearings are in good working order and spin freely?
 
Yes it is.


Can you take all of the gears out and lay them flat on your work bench and take clear pics of them for us to look at? Maybe we can see if they have excessive wear or something.

When you have the diff assembled and you turn one output shaft does the other side rotate?

Did you check and make sure all the bearings are in good working order and spin freely?
When I turn one output shaft the other does turn. The bearings turn OK.

I did notice that when assembled and the wheel nut is tight it seems worse. When its driven with a loose nut it is better........If that means anything, or is that a seperate issue?
 
I did notice that when assembled and the wheel nut is tight it seems worse. When its driven with a loose nut it is better........If that means anything, or is that a seperate issue?

That almost sounds like the wheel nut (or something behind it) is pressing on a bearing and not letting it spin freely.
 
That diff looks awfully dry, there's supposed to be silicone "diff" fluid in there that wants to grab at all of those spider gears and trying to turn the whole diff as a whole including spinning both diff cups at equal rates. The reason why when you assemble it and only one cup spins is because the transfer of torque from your hand is going to the cup with the least resistance. Clean up the housing good and throw some 30k diff oil in it and your should be good. The level should be 3/4 of the way up.
 
That diff looks awfully dry, there's supposed to be silicone "diff" fluid in there that wants to grab at all of those spider gears and trying to turn the whole diff as a whole including spinning both diff cups at equal rates. The reason why when you assemble it and only one cup spins is because the transfer of torque from your hand is going to the cup with the least resistance. Clean up the housing good and throw some 30k diff oil in it and your should be good. The level should be 3/4 of the way up.
Thanks. I will oil it......does it need grease or fluid??

I cleaned out a lot of old solidified grease which can't have been helping......
 
Judging by the picture it seems that there is no gasket on that ring gear, so I believe that's style takes grease. I'd find the tackiest grease I can find to help with the 1 wheel peel. Is that front or rear? Rear I'd get tacky and if its front I'd use a normal grease, front axle needs the tires to spin at different speeds so it can turn without causing the tires to hop and fight the turn.
 
Look at the back of your wheel hexes that are behind the wheels. Show us pics. If one of them has crushed, and the hex is resting on the inner and outer race of the bearing, then it will cause that bearing to lock up when you tighten the nut. Also, if there are worn parts in the drivetrain behind the bearing, or the bearing journal the bearing rests in is worn, tightening the wheel nut will put the bearing in a bind. Both wheels need to spin freely when the wheel nuts are tightened. So pics of all the drivetrain parts on the side that is seizing up when you tighten the wheel nut may reveal some answers.

Your spider gears look to be ok, but blurry pics don't help. But you need some diff fluid in there. Not familiar with FTX. Searching for it I see it says it is a rock crawler, desert buggy, etc. Depending on how fast it runs, and what you do with it will determine the best diff fluid. If it is pretty fast and you do a lot of racing around, taking corners at speed, I would say it needs at least 100k diff fluid in the rear, but no idea really. If it is like a rock racer, 500k would be better.

This is what the axle assembly should look like. The only thing the wheel nut should be doing is clamping together the axle, inner bearing race, wheel, and wheel hex.
Axle Assy.png


If there is no gap here, it will bind up the bearing.
Axle Assy 2.png
 
Last edited:
Thanks. I will oil it......does it need grease or fluid??

I cleaned out a lot of old solidified grease which can't have been helping......
Any kind of generic synthetic automotive grease will work. Tacky or regular isnt going to make much if any difference.
 
Look at the back of your wheel hexes that are behind the wheels. Show us pics. If one of them has crushed, and the hex is resting on the inner and outer race of the bearing, then it will cause that bearing to lock up when you tighten the nut. Also, if there are worn parts in the drivetrain behind the bearing, or the bearing journal the bearing rests in is worn, tightening the wheel nut will put the bearing in a bind. Both wheels need to spin freely when the wheel nuts are tightened. So pics of all the drivetrain parts on the side that is seizing up when you tighten the wheel nut may reveal some answers.

Your spider gears look to be ok, but blurry pics don't help. But you need some diff fluid in there. Not familiar with FTX. Searching for it I see it says it is a rock crawler, desert buggy, etc. Depending on how fast it runs, and what you do with it will determine the best diff fluid. If it is pretty fast and you do a lot of racing around, taking corners at speed, I would say it needs at least 100k diff fluid in the rear, but no idea really. If it is like a rock racer, 500k would be better.

This is what the axle assembly should look like. The only thing the wheel nut should be doing is clamping together the axle, inner bearing race, wheel, and wheel hex.
View attachment 155003

If there is no gap here, it will bind up the bearing.
View attachment 155004
Thats great information. I'll check this later.

Thank you!
 
Just an update.....

I got a brand new diff but it does the same thing! Only drives one wheel.

I also got new metal Hex's too.....

Any ideas??

TIA
 
It's an open diff with no grease or fluid to cause resistance on the spider gears which is allowing 1 wheel to spin due to the path of least resistance. If you want both tires to turn you need to put something in it so the Torque doesn't get to pick what tire it wants to spin.
 
It's an open diff with no grease or fluid to cause resistance on the spider gears which is allowing 1 wheel to spin due to the path of least resistance. If you want both tires to turn you need to put something in it so the Torque doesn't get to pick what tire it wants to spin.

Thank you.

What should I put in? Its a new sealed diff.

Or is it doing its job as it should? It looks to be 3 wheel drive at the minute :oops:
 
It's a crawler right? I think it is doing what it's supposed to, in the real crawlers they are able to engage and disengage diffs at will depending on the conditions so it most likely is doing its job correctly.

Since it's not ment to have "fluid" I'd say a very thick grease will help if you want to go that route.
 
It's a crawler right? I think it is doing what it's supposed to, in the real crawlers they are able to engage and disengage diffs at will depending on the conditions so it most likely is doing its job correctly.

Since it's not ment to have "fluid" I'd say a very thick grease will help if you want to go that route.

Its an FTX Outlaw truck buggy thing. Its the front diff causing the issue.

.
c1.jpg
c2.jpg


On full left lock at full speed it lifts the left front wheel off the ground, On full right lock at full speed it doesn't lift the right wheel.....Obviously because there is no drive to the other wheel........If that makes sense??
 
Do you crawl or bash it? Since there's no seals o ring for silicone diff oil your pretty much limited to grease.
 
Without being able to get eyes and hands on your kit it sounds to me like the diff is functioning normally out of the kit. If you're having an additional issue with power delivery to one wheel when its in the kit then you need to thoroughly go through that corner of the kit and make sure bearings are good and not being pinched like discussed above. Make sure everything is assembled correctly etc. Thats my best guess
 
Without being able to get eyes and hands on your kit it sounds to me like the diff is functioning normally out of the kit. If you're having an additional issue with power delivery to one wheel when its in the kit then you need to thoroughly go through that corner of the kit and make sure bearings are good and not being pinched like discussed above. Make sure everything is assembled correctly etc. Thats my best guess
Thinking about it.......I used the same bearings from the original diff.....

I may have made a schoolboy error here....

🙈
 
Thinking about it.......I used the same bearings from the original diff.....

I may have made a schoolboy error here....

🙈
If your bearings spin freely and dont feel gritty or anything then they should be fine. That being said a couple of bearings isnt that expensive if you wanna give that a try.
 
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