Diff rebuild with homemade gaskets

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savagechiken

savagechiken

Member
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43
Location
BC, Canada
Rebuilding my Savage X alloy diffs and couldn't find anyone local who had gaskets so I decided to try and make my own gasket using Permatex Blue Gasket Maker. I am using heavy duty wheel bearing grease to fill the diffs by the way.

So the gasket maker stuff worked on one of the diffs, the cups spin very smoothly with almost no chatter, but on the other diff after I tighten up the screws the cups will not spin. I think what might be happeing is that without the gasket the spacing for the gears is too tight, thus not allowing the gears to spin freely. So I have now experimented and tried putting a homemade cardboard gasket inside and I think this will solve the problem it is now just a matter of getting the right thickness for the cardboard gasket.

I just think it is very odd that one diff had a perfect fit without a paper gasket and the other needed a gasket to get the right spacing and gear mesh.

Has anyone else had experiences like this with HPI diffs? Any input or experience would be welcome. Anyone else have gear mesh issues?
 
Welcome to the forum!
Yes it is critical that you have a gasket there for correct spacing as you said.
Needs to be 0.20" thick too. There is an excellent article at this link, look at left for diff gaskets.
http://www.sickhobbies.com/Main.html
And I don't know why HPI made it so you have to buy cups just to get the gaskets.
Heres another link to a great company that offers them alone. There may be other ways of getting them but I'm not sure. Maybe they are called washers for a Hellfire???
http://www.innovative-rc.com/product_info.php?currency=USD&cPath=21_30&products_id=93

Dave
 
Thanks for the welcome,

That first link is a good guide to making your own gasket. I will prob go down that road unless my LHS brings in the HPI replacement gaskets #86099(also for the Hellfire and they decided to call them washers).

I'd still like to know how my other diff has a good mesh without the gasket, however it does seem to have about 1-2mm of side slop, but the mesh is so good I think I will just leave it.
 
savagechiken said:
Kind of like the thing this guy is talkg about in this thread https://www.hpisavageforum.com/forums/showthread.php?t=4451
and this video http://www.youtube.com/watch?v=xgMNRTG5ybY

I can move the drive cups side to side a little bit, but it doesn't seem to have an effect on the gear mesh.

Can you can explain to me exactly how I know if the spiders are binding?
Click to expand...

Well if it's like in the vid the whole case needs shimmed, not the drive cups internally but shims added between the side bearing and case and this WILL effect ring and pinion mesh!

On the spiders binding-I would think with the absence of the diff gasket it may allow spiders to bind and also lead to the case moving from side to side.
To check for binding-with the diff fully assembled, hold one cup still and turn the other to check for feel and or binding.

Dave
 
Pineapple said:
Well if it's like in the vid the whole case needs shimmed, not the drive cups internally but shims added between the side bearing and case and this WILL effect ring and pinion mesh!

On the spiders binding-I would think with the absence of the diff gasket it may allow spiders to bind and also lead to the case moving from side to side.
To check for binding-with the diff fully assembled, hold one cup still and turn the other to check for feel and or binding.

Dave
Click to expand...

Ya my diff case doesn't move like that, only my drive cups can move in and out about 1mm or less, there is no play between the bearings and the case like shown in the video.

The diff that I assembled and sealed using only gasket maker is showing no signs of binding. It is ready to go in the truck. Totally smooth when I do your test Dave.

I would like to know why my other diff refuses to be assembled the same way? Are HPI tolerances that bad?

LHS got replacement gaskets in today so I will pick them up and try assembling the remaining diff with them to try and get the right mesh.
 
MMMM... maybe the cross pins aren't in correctly???
And it's easy to get confused here on what gear mesh we are talking about-either spider gears or ring and pinion gears.

Good luck-keep us updated.

Dave
 
Pineapple said:
MMMM... maybe the cross pins aren't in correctly???
And it's easy to get confused here on what gear mesh we are talking about-either spider gears or ring and pinion gears.

Good luck-keep us updated.

Dave
Click to expand...

All four spiders and cross pins were flush and turning fine when the screws were not in, it was after I tightened the screws down when the gears locked up, which is why I think it is a spacing issue between the two halfs of the diff. Thus the need for a gasket.

And the gear mesh we are talking about would be the spider-gear mesh inside the alloy diff case.

Stay tuned.......
 
Assembled the diff and sealed it using a gasket and some gasket maker and sure enough once the screws were tightened it was turning just as smooth as the other diff in which I did not use a gasket but only gasket maker.
 
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