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Old 2002.02.12, 09:33 AM   #1
bobman
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Exclamation Ball diff problem

Hi all,

yes, another ball diff problem... and yes, I have read pretty much every post on this forum that relates or even mentions ball diffs

ok here's the problem... I have bought a Topcad ball diff, and it is now installed. However, there is a problem with the spur gear assembly. The action is very smooth, much more so than the gear diff, but there is a lot more resistance. If I turn one wheel, the other turns in the opposite direction, but it requires much more effort than with the gear diff.

Now, I examined the spur gear section, and I think I can see the problem. The plane that the spur gear assembly is in is not perpendicular to the axis of rotation. i.e. there is not a 90 degree angle between the axle and the spur gear. This means that if you rotate the diff the spur gear appears to "wobble". This prevents the spur and pinion from meshing correctly, and makes my car very loud.

In my hunt through previous posts I found this thread about ball diffs. Butler and RS172 both mention problems that sound similar to mine, but I do not understand how to go about fixing it.
RS172 said:
Quote:
Look very closely at the ball race that sits in the spur side hub, this is the key to everything. Is it sat absoultely square ?
Is the ball race the spur gear assembly? how do I go about setting this so that it is square?
My problem doesn't sound exactly the same as there are no "tight spots" as described by butler, and the action of my diff is very smooth.

Any help or suggestions would be much appreciated

bobman

PS. other topcad ball diffs seem to be anodised blue... whereas mine is gunmetal. I like it tho
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Old 2002.02.12, 09:45 AM   #2
Mondo
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Bawl-Duff?

Bobman,

What brand of ball-diff did you buy?

If it's the TopCAD, they are finished a bit rough and require some work to run smoothly. I was fortunate enough to have a choice at my LHS and I dug through about 5 or 6 before finding one that was really smooth.
Even then, I stripped it, did some light sanding on the bad anodising, greased and re-assembled.
Also, the TopCAD ball diff required one washer to be used on both alloy and standard motor mounts, this went against the threads on the tension adjustment collar side (Spur Gear) to prevent the threads from possibly digging into the bearings.
Bobman, I also assume you have bearings.

The Kyosho ball diff (at three times the price) never gave me any crap what so ever, just fitted the babe and it worked.

If you get stuck, mail me and we can get together and sort the beast out

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Old 2002.02.12, 12:43 PM   #3
bobman
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Mondo,

cheers for the reply and yup, it's a topcad. sadly mine was sent mail-order and I did not have a few to choose between.

The action of the diff is very smooth, it just requires more force to turn than the gear diff.
I don't yet have any bearings, i'm still on the plastic bushings. Bearings will be in my order to the mini-z shop tho I am using a washer between the bushing and the adjusment thread.
I should point out that I dont think its a bearings/bushings issue, as the diff is stiff even when not installed in the car.

what specific part of the spur gear assembly would cause it to be out of shape?

cheers,
bobman
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Old 2002.02.12, 01:25 PM   #4
Mondo
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Bobman,

I have both the TopCAD and the Kyosho units and they work fine.
That doesn't resolve your problem though..

I am still to come across a ball-diff that runs as freely as a standard plastic helical-gear diff. They are tighter and adjustable.
There is a knurled collar that sits upon the threads of the ball diff shaft, that adjusts the tension. Played with that yet?

The only thing I can assume is worn bushings, remembering that the ball-diff shaft is aligned by the bushes.
I recieved a some spare pinion gears with my TopCAD unit. Have you tried another pinion gear?
Also, ensure that you use the correct motor spacers as per the Mini-Z owner's manual.

I would dissasemble it and give the inner anodised parts a good sanding. "le-manz" and "Butler" (I think) had to do this.
I did the same thing as I always strip, examine and re-assemble any mechanical part/s before fitting it/them, Kyosho ball-diff included!!
Although the TopCAD diff I chose was smooth, I still found traces of poor anodising on the inner flush areas of the ball-diff.

Mondo
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Old 2002.02.12, 03:09 PM   #5
Joe
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I've also got a small problem with my topcad ball diff. When it is on, it does not align fully with the pinion, i have to pull the pinion out a little to get it to have full contact. Is this ok?
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Old 2002.02.12, 03:11 PM   #6
Mondo
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Pinion alignment

Joe,

As long as is makes 75% contact, it should be A-Okay

Mondo
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Old 2002.02.12, 03:21 PM   #7
Joe
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Ok, thx.

Thx 4 the bearing help too. My miniz is cool!

I just messing with my z now, high speed turns are a little tricky with power on.
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Old 2002.02.13, 02:22 AM   #8
butler
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Joe,

Just incase your still having trouble. Mondo's posts are legendry detailed. One of the hubs comes with a bearing in it. Take that bearing out and grind/scrape/poke out the anodising around the bearing seat. Replace the bearing back in and thats it. Thats all I had to do.

BTW my pinion line up is the same too, so don't worry about it!

Cheers,

Marc

Last edited by butler; 2002.02.13 at 02:24 AM.
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Old 2002.02.13, 03:13 AM   #9
bobman
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thanks for the replys ppl

there are still a few questions I have tho...

1) how do I make sure the spur gear assembly is is totally square on the axle?
2) do I just take it apart and put it back together again and hope its better? or is there somthing in particular I should be looking for?
3) butler, you said:
Quote:
One of the hubs comes with a bearing in it. Take that bearing out and grind/scrape/poke out the anodising around the bearing seat. Replace the bearing back in and thats it
where is the bearing you speak of?

thanks again for the help

bobman
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Old 2002.02.13, 04:36 AM   #10
butler
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Bobman,

1) 2) and 3) are all related to this bearing. Unfortunately I don't have a digi camera.

I will try to describe it as best as I can.

You have 2 metal hubs that fit either side of the spur gear. One hub fits over a small metal pin that goes through the axle.
The other contains a ball bearing. Can you see it?

That bearing will come out.

If the bearing is square in its seat the whole assembly goes together "wonky"

Good Luck!
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Old 2002.02.13, 05:05 AM   #11
bobman
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butler,

so the bearing is in the side of the ball diff that is held together with the small c-clip? i will have another look when I get home tonight - lets hope this fixes it

thnx again for the help

bobman
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Old 2002.02.13, 05:30 AM   #12
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You got it Bobman.

Be careful taking that c clip off. I did it and heard ping from across the room. Never to be seen again. I took a replacement off a old 1/10th scale shock absorber.

Let us know how it goes...
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Old 2002.02.22, 02:03 PM   #13
runtracer
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i was following this thread because i had a topcad diff on the way when i read it, mine too wasnt square when it arrived. the problem was that the bearing just inside of the c-clip wasnt seated all the way. i had to remove the c-clip and tap it into its race with a punch and a mallet (gently). once seated all was good.

tom
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Old 2002.03.01, 08:40 PM   #14
Scoobaru
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wheel alignment?!?!?

have any of use noticed that the wheel on the spur gear side sticks out a bit more than original?.... i find that my rear wheels are not aligned with the front now...... i would estimate that they are off by around 1mm-1.5mm..............any solutions found to this?

thanx,

scoobaru
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Old 2002.03.01, 08:48 PM   #15
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Scoob, did you install the spacer? The wheels should line up as stock.
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