hey guys just ordered the topcad ball dif an guess what! the fricking shafti s too thick to fit through the ballbearings i have on my motor mount!!!! that sucks. beware of this hopup and which kind of ball bearing you get. if anyone knows what imdoing wrong with this ball diff then please e-mail me @
Quite a few Members use TopCAD ball-diffs without any trouble.
They are a little roughly finished, but it's nothing that a bit of maintenance can't sort out. At a much cheaper premium that the Kyosho units, they are a bargain.
I sanded the anodizing off the shaft to get the diff to fit my bearings... its supose to be a snug fit, but not so snug it wont fit...
the 90degree areas were its machined to a smaller diameter are often squished sort of, and can easily be filed to a cruded radius or chamfer to get it to fit... with out any loss. If the shaft slides in realy easy its a bad thing. but you dont want to have to use a tool to get it in.. or you might damage the bearings.
You could put the empty shaft in a dremel tool and spin it.. to file the areas needed, just make sure its in the dremel straight and dont take all of the anodizing off at first... test fit it then if it needs more go for more. most likely only the little corner on the non spur gear side needs a trim.
I wouldn't recommend filing it.
I used a Dremel and some fine sandpaper with light oil on my TopCAD unit.
What I discovered was (like Drac said) a build up of anodising on the shaft. Once this was removed, it worked just great.
I've been trying to make my topcad (or TOP) fit kyosho plastic motor mount.
I think I've spotted the problem.
The left hand side drive element.
It is 1.5mm thicker than kyosho's. (see picture)
TopCad shaft is 1mm longer than kyosho's, probably to compensate.
I think I'll file the drive thingy to make it fit, because shimming the diff won't help as then the shaft won't be long enough to enable lock nuts to stick.
A bit of a bummer as the only file I have at hand is the one in the backbround.. my trusty Victorinox
I ran the TopCad ball diff with the keyosha stock pod for a while with no problems. It was definitly a little snugg going on the first time. Just use some fine sand papper on the shaft( that sounds bad!) . Dont get to caried away with it...you want a snug fit!
Originally posted by W-tone Well.. my problem wasn't the shaft not fitting through the bearings, but the left wheel sticking out more than the spur gear side.
I had that same problem (one side sticking out more than the other)... but the differential still worked. I solved it by putting spacer washers on the opposite side and "evening" out the sides.
The car runs fine... I don't know if I'm losing something... I haven't noticed any problems. AND the differential works great... I hardly spin out anymore.
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Since i couldnt find a small enough HEX thingie for my Z i used a small precision scre driver set to put the screw driver in the hex find a grove and turn till its loosened about 10 minutes and it was off lol. Damn Im ghetto!
Another problem that I noticed with my topcad is that it sticks out too far on the side opposite the diffential! And it makes the car spin on that side!! what to do to even out the diff?
If ur havin' problems with ur Top cad diff. get it replaced from the place u bought it at. I guess stuff made in China isn't as good as stuff made in Japan.
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All I have to say is I'm glad I bought the GPM ball diff....no probs wot-so-ever!! Just about all the hop-ups I have on my Z are GPM. Alittle more in cost than Topcad, but no probs like this
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