Rear differential build issues

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Blazemore

Blazemore

Member
Messages
18
Started building a new 5B over the weekend and ran into problems with the mesh of the rear ring and pinion. The meshing is not smooth but feeling like the gears are jumping; best that I can describe it. If I take the front of the trans case and install the pinion and drop the completed diff housing in and hand turn the pinion, its smooth. Once I install the rear housing the gears start to jump. After messing around with this for hours.....I noticed if I unscrew the rear top and bottom screws slightly the mesh gets better but not great. I also removed the pinion shim and it seemed to help some. I'm only hand tightening the screws.
  • The trans case doesn't appear to be damaged
  • Pinion gear is flat and not binding, no damage
  • Ring gear shows no damage
  • Completed diff is very smooth hand turning the cups
  • Bearings are smooth, no binding
Any thoughts? I had to stop and walk away last night.

Also for the front I had to make a shim between the pinion shaft and the coupler. Seems someone else was experiencing the same issue:
https://www.rctech.net/forum/oval-l...osi-5ive-b-rear-differential-build-issue.html

After the shim, play is removed and the pinion doesn't slide backwards and causing the binding; smooth.
 
Blazemore said:
Started building a new 5B over the weekend and ran into problems with the mesh of the rear ring and pinion. The meshing is not smooth but feeling like the gears are jumping; best that I can describe it. If I take the front of the trans case and install the pinion and drop the completed diff housing in and hand turn the pinion, its smooth. Once I install the rear housing the gears start to jump. After messing around with this for hours.....I noticed if I unscrew the rear top and bottom screws slightly the mesh gets better but not great. I also removed the pinion shim and it seemed to help some. I'm only hand tightening the screws.
  • The trans case doesn't appear to be damaged
  • Pinion gear is flat and not binding, no damage
  • Ring gear shows no damage
  • Completed diff is very smooth hand turning the cups
  • Bearings are smooth, no binding
Any thoughts? I had to stop and walk away last night.

Also for the front I had to make a shim between the pinion shaft and the coupler. Seems someone else was experiencing the same issue:
https://www.rctech.net/forum/oval-l...osi-5ive-b-rear-differential-build-issue.html

After the shim, play is removed and the pinion doesn't slide backwards and causing the binding; smooth.
Click to expand...
I had the same issue, it wasn't acceptable. I reached out to Losi, they provided a whole new rear gearbox, that in combination with an aluminum dif housing from China made mine feel good. I never got to the root cause of the issue, but am pretty sure the ring gear was deformed causing binding. I am not sure if the plastic diffferential housing was warped, and that bent the ring gear or what. Mine was smooth, then about a 20degree area it was binding up.
 
moliver said:
I had the same issue, it wasn't acceptable. I reached out to Losi, they provided a whole new rear gearbox, that in combination with an aluminum dif housing from China made mine feel good. I never got to the root cause of the issue, but am pretty sure the ring gear was deformed causing binding. I am not sure if the plastic diffferential housing was warped, and that bent the ring gear or what. Mine was smooth, then about a 20degree area it was binding up.
Click to expand...
Took the diff housing apart again. This time after leaving out the shim and only backing out two of the rear screws some I was able to get a better mess (best its been). No way this is ideal or should be. The mess was ok for about 3/4 of a rotation and the last 1/4 the jumping started. No way the gears would last long in this condition.

I'm thinking your issues are what I'm facing. I didn't look too much at the ring gear, just for damage. Really I didn't want to take the gear off due to the oil and mess that follows.

What China housing did you get? I was think about installing a TLR aluminum housing...but I hate throwing parts. Cost and not really knowing what the problem is.

Not sure on the warranty side. Bought this back in Nov. from DDM and just now got the chance to build.
RcJunkie13 said:
Normal, its just like that
I was also going crazy over mine
Click to expand...
I have a little OCD and this almost needed a beer.
 
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Thanks. I'll give LOSI a call and see what happens. It seems you had success with them.

Thinking about that diff as well.
 
Late update:
Contacted horizon and they agreed to send out a new rear ring and pinion. Replaced with the new the ring gear and the binding stopped. I went ahead and got the mod cups along with the atop housing. Not a bad housing for the price.
Losi_Rear_Diff.jpg

I also noticed, like the front, that play in the pinion would cause binding. If the pinion is pushed back into the diff housing ~.47mm then the mess turns into hard lock binding. To solved the problem was to remove the original pinion shim and install two shims between the pinion shaft and the coupler. This eliminated the movement. As designed, confused how this even works.
 
Blazemore said:
Late update:
Contacted horizon and they agreed to send out a new rear ring and pinion. Replaced with the new the ring gear and the binding stopped. I went ahead and got the mod cups along with the atop housing. Not a bad housing for the price.
View attachment 73382

I also noticed, like the front, that play in the pinion would cause binding. If the pinion is pushed back into the diff housing ~.47mm then the mess turns into hard lock binding. To solved the problem was to remove the original pinion shim and install two shims between the pinion shaft and the coupler. This eliminated the movement. As designed, confused how this even works.
Click to expand...
Can honestly say I had zero binding issues with mine. It has seemed to be an issue with the newer ones though.
 
Out of curiosity, I purchased a new housing and bearings for the pinion to test before the final install. Still had the same movement in the pinion. I'm guessing the older units must had tighter tolerances (?) or something. Really I don't see how the design works without modifications in keeping the pinion in place, but I'm also thinking vehicle rear ends. Its fixed, for now.
 
Last edited:
Blazemore said:
Out of curiosity, I purchased a new housing and bearings for the pinion to test before the final install. Still had the same movement in the pinion. I'm guessing the older units must had tighter tolerances (?) or something. Really I don't see how the design works without modifications in keeping the pinion in place, but I'm also thinking vehicle rear ends. Its fixed, for now.
Click to expand...
Did yours come with shims on it from factory? Both front and rear had shims in place on mine, axial play in the pinion is near zero. I guess that's what's been surprising me the most to hear about diff issues with these.
 
Id say don't stress about it 🤔 if i remember correctly my los 5b the rear assembly was a tad crunchy 😅 and as soon as I bolted it to the chassis it went away 👍🏻 the only up grade I did was the mod bearing kit👍🏻
Blazemore said:
Out of curiosity, I purchased a new housing and bearings for the pinion to test before the final install. Still had the same movement in the pinion. I'm guessing the older units must had tighter tolerances (?) or something. Really I don't see how the design works without modifications in keeping the pinion in place, but I'm also thinking vehicle rear ends. Its fixed, for now.
Click to expand...
 
Seandonato73 said:
Did yours come with shims on it from factory? Both front and rear had shims in place on mine, axial play in the pinion is near zero. I guess that's what's been surprising me the most to hear about diff issues with these.
Click to expand...
One was provided from the factory for the front and rear. There is nothing that prevents the forward and backward movement (~.47mm) of the pinion shaft within the housing.
Shim.PNG
 
dougstar said:
Id say don't stress about it 🤔 if i remember correctly my los 5b the rear assembly was a tad crunchy 😅 and as soon as I bolted it to the chassis it went away 👍🏻 the only up grade I did was the mod bearing kit👍🏻
Click to expand...
No luck here without the shims in place. I thought about that but after a few youtubes of installed crunchy then a few videos later; how to install a new gear set. Maybe this works for some and not others..don't know.

I'll stop..beating the dead horse.
 
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