Kraton Please help! 4s blx replacement diff tight mesh

[quiljw01]

Broke the rear diff the other day when I landed with apparently too high wheel speed.

The internal diff gears are fine, it's the input gear and output ring gear that are both stripped.

I'm replacing the gears now . I'm finding that the mesh is far too tight and I cannot get smooth action out of them no matter how hard I push the bearing onto the input gear and even when I remove the spacer from the diff housing.

My question is, is this normal? Will the plastic gears chew themselves up while driving until the mesh is correct? Or have I done something wrong in the assembly? It seems very simple and straightforward but I suppose I could have made a mistake.

Please somebody with experience guide me! I don't want to burn through another diff!

Jrod

 

[JAM]

Make sure your diff housing is put back together correctly. I’ve never had one be tight after reinstalling the input gear into the housing. Make sure your bearings line up and are good as well On the shaft.

 

[ph47mf]

as above make sure the yokes are put back the correct way, if you look inside the yokes one of them has a little plastic sticking out, that side should be on the opposite side of the gear, keep the spacer on the original gear side, when you tighten the 2 screws make sure it's tight but not too tight, put some grease on gear and it should be buttery smooth.

 

[quiljw01]

Make sure your diff housing is put back together correctly. I’ve never had one be tight after reinstalling the input gear into the housing. Make sure your bearings line up and are good as well On the shaft.

I'll have to make a video because trying to describe with words is always challenging.... I have looked it over for an hour and have found it doesn't come close to fitting together if it's not in the correct orientation. So putting it back together the wrong way seems impossible because you'd have 1/4" gaps at the seams , it just doesn't fit. I've tried putting it back together in every way imaginable and it only want to go together one way so i don't think the problem is that it's put together wrong.

I've tried removing the shim, i've tried moving the shim to the other side, neither seemed to help.

The only explanation i can think of is if the input gear is not seating all the way down against the bearing properly. But i've put almost 150lbs of force trying to push on it to make sure it's all the way down and it doesn't want to go any further. i've probably ruined the bearing by pushing so hard... it's not quite smooth any more. so i'll have to get another on order in case.

I think since the parts are so cheap it's probably worth just trying it as is. If it melts then it melts. Or maybe there's a chance it will wear into place? i'm sure i won't get that lucky but i don't know what else to try.

as above make sure the yokes are put back the correct way, if you look inside the yokes one of them has a little plastic sticking out, that side should be on the opposite side of the gear, keep the spacer on the original gear side, when you tighten the 2 screws make sure it's tight but not too tight, put some grease on gear and it should be buttery smooth.

just tagging you to see my response above. sorry not sure if that's appropriate/ necessary as i'm new to forums. maybe my parts have a manufacturing defect? hmm

 

[Stevenj76]

They don’t go all the way down , there’s a small lip at the bottom .

 

[quiljw01]

They don’t go all the way down , there’s a small lip at the bottom .

Yes, agreed. For pressing the new bearing on the input gear, I did actually install input gear backwards into housing and push down to verify it was all the way down, up against the lip. it seems to be all the way down. comparing with how it looked before it came apart.

 

[ph47mf]

Could you take some pictures of it and see if we can advise from there? Just lay it all out on the table in a way like how you're going to put it together and maybe some close ups too.

 

[quiljw01]

Thanks for your help guys... i made a video... sorry for all the talking and long video, maybe you can watch on 2x to save time but i tried to cover everything.

One thing i didn't do was try to rotate it with a flexible piece of zip tie so i could show how difficult it is to turn.

 

[razorrc]

Thanks for your help guys... i made a video... sorry for all the talking and long video, maybe you can watch on 2x to save time but i tried to cover everything.

One thing i didn't do was try to rotate it with a flexible piece of zip tie so i could show how difficult it is to turn.

What if you run the diff without the input shaft, does it spin freely? What if you remove the diff and only run the input gear, does it spin freely?

From the video, that gap between the two halves without the screws seems like it's going to put extra tension on the bearings when it's tightened down, that's my best guess. I've had that happen with transmission halves that cranked down on the bearings not allowing it to spin smoothly.

 

[metalboy4]

as above make sure the yokes are put back the correct way, if you look inside the yokes one of them has a little plastic sticking out, that side should be on the opposite side of the gear, keep the spacer on the original gear side, when you tighten the 2 screws make sure it's tight but not too tight, put some grease on gear and it should be buttery smooth.

What grease? What kind? Anything?

 

[ph47mf]

What grease? What kind? Anything?

I use marine grease made for cars and it seems to stay on pretty well and can keep water out. Not to mention it's much cheaper and comes in a massive tub.

Thanks for your help guys... i made a video... sorry for all the talking and long video, maybe you can watch on 2x to save time but i tried to cover everything.

One thing i didn't do was try to rotate it with a flexible piece of zip tie so i could show how difficult it is to turn.

To be fair I think you have put it back together correctly like you said, to my knowledge they don't spin as freely as you might have expected it needs a bit of force, I see you didn't need to put a lot of power on the input gear to move the whole gear, with a bit of grease and a few runs I think it will be okay.

Mine seems to be only slightly looser than yours when without grease and before I put it in for a few runs. So yeah a slob of grease, go bash and report back, my money is on it's okay, try to avoid standing back flips. ?

 

[jondilly1974]

Plastic gears aren’t machined as well as metal gears and sometimes need ran to break them in.

 

[OLIVERH]

I am having the same problem, it’s a smooth mesh until I tighten down the screws for the diff case? Did you have any luck solving it? Think I’m just going to put them back in and hope for the best?‍

 

[jondilly1974]

I am having the same problem, it’s a smooth mesh until I tighten down the screws for the diff case? Did you have any luck solving it? Think I’m just going to put them back in and hope for the best?‍

Don’t over tighten the yoke screws. Back them out an 1/8 turn until there’s less binding.

 

[OLIVERH]

Don’t over tighten the yoke screws. Back them out an 1/8 turn until there’s less binding.

Hi thanks for the reply, I have to have like a slight gap in the diff casing for it to mesh nicely is this ok?

 

[jondilly1974]

Hi thanks for the reply, I have to have like a slight gap in the diff casing for it to mesh nicely is this ok?

Are there any shims on your main gear? May try removing these or attempting to push the bearings on a little deeper on the diff cup.

 

[OLIVERH]

Are there any shims on your main gear? May try removing these or attempting to push the bearings on a little deeper on the diff cup.

Iv tried everything with the shim like op and the bearings are deffo all way down, I will loosen the yoke screws slightly like you said and hope for the best ?

 

[quiljw01]

I am having the same problem, it’s a smooth mesh until I tighten down the screws for the diff case? Did you have any luck solving it? Think I’m just going to put them back in and hope for the best?‍

I haven't tried yet but that's my plan too. Won't be able to test until this weekend.

Thanks for all the responses guys!

I'm using clear silicone grease in mine. Stock grease appeared light grey.

 

[OLIVERH]

I haven't tried yet but that's my plan too. Won't be able to test until this weekend.

Thanks for all the responses guys!

I'm using clear silicone grease in mine. Stock grease appeared light grey.

I will hopefully be trying either tomorrow or Thursday so il let you know how I get on, I ordered some of the red n tacky grease as a few people recommend that for the plastic gears.

 

[jondilly1974]

I don’t think different greases makes a huge difference. I have used SilGlide brake grease in the past. I recently bought a tube of Lucas RnT and am using that now.