Diff cup or more?

Jerold

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I was doing some speed runs and went from AWD to RWD. I was thinking it was a blown front diff because if I spin one wheel, the other one spins the same direction... which is not normal for an open diff. @LicketySplit and others said the grub screw from the on the diff cup may have let go and if there is nothing holding the pinion it's normal.

So I pulled it apart and found the grub screw intact, but the inside are now outside.
IMG_4998 (2).jpg


That is the pinion bearing (AR610019), outside the case. The input shaft/pinion (AR310468) does wiggle about, but if I stop it from moving the diff operates correctly.

1674440255038.png


Just to check the grub screw, which was very tight, i reseated it and it looks like about the same depth as before.
IMG_5002.jpg


I can probably clean it up and push the bearing back in, but I' wondering why it's all wonky and thinking I spun the bearing in the housing (AR310854). Which means at least the housing toast and I need to do some major surgery.

Also why are there no shims between the diff cup and the bearing? Like duh Batman.

Thoughts?

1674439912025.png

A bit more data. I poked around inside the bearing seat and found some bits of the bearing. It looks like the outer seal and a snap ring?
IMG_5003.jpg
 
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LicketySplit

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Looks like the input cup was too far forward. With the bulkhead off the chassis I like to hold the pinion forward with a flat head while I slide on the input cup. Push it against the bearing and tighten grub.
 

Jerold

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Put some 608/639 retaining compound on the OD of the bearing so it doesn’t float or run 8x12mm shims between the bearing and cup 👍🏼
That's a thought, but I'd rather spend the $50-75 for parts if that's what it takes. Although I'm not looking forwards to tearing it apart.

I guess what I'm looking for is to see if someone has seen this and is it the entire diff replacement or just a housing, bearing, etc?
 

Jerold

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Bulkhead -> AR310854
I will replace the bearings too.

Any chance of damage to the pinion/spur?
Looks like the input cup was too far forward. With the bulkhead off the chassis I like to hold the pinion forward with a flat head while I slide on the input cup. Push it against the bearing and tighten grub.
I'm assuming there should be no gap between the outer pinion bearing and the driver cup?
@K-BASH, Since I have to tear is down anyway, are these the F/R drive cups you were talking about for Limitless? AKA these are NOT spool drive cups.
https://www.amainhobbies.com/tekno-rc-steel-differential-coupler-tkr5075/p231747
 
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real_name_hidden

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Bulkhead -> AR310854
I will replace the bearings too.

Any chance of damage to the pinion/spur?

I'm assuming there should be no gap between the outer pinion bearing and the driver cup?
@K-BASH, Since I have to tear is down anyway, are these the F/R drive cups you were talking about for Limitless? AKA these are NOT spool drive cups.
https://www.amainhobbies.com/tekno-rc-steel-differential-coupler-tkr5075/p231747
Scorched. Don’t cheap out. End up doing it twice.
 
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