# Aurora Rear Gear Sizes



## Grandcheapskate (Jan 5, 2006)

warnergt said:


> That agrees with what I've seen. I used to hate getting cars with the white
> gear. I thought somebody had replaced them because I never bought a
> new T-jet with a white gear back in the 60's. But these gears kept showing
> up in older cars. It became obvious that there was a trend to what I was
> ...


 I copied the above from an old thread but need to ask about the original Aurora gear sizes for the rear.

As I understand it, there were three T-Jet pinion gears - 9 tooth (standard), 12 tooth (Hop-Up?) and 14 tooth (Tuff Ones). Were there then three crown gears all with 15 teeth and just a different rear collar size?

And how about AFX/MT? Just one pinion and crown gear? Is the crown gear the same as any of the T-Jet crown gears? I can see it is a slightly different shape than the short-collar T-Jet crown but the collar size seems to be about the same.

Lastly, how about the crown gear on the G-Plus, Super-Mag and Super-Mag variations (Blazin' Brakes, etc.)? A unique crown gear or the same as...?

Thanks...Joe


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## AFXRICK (Dec 6, 2008)

The Super II used a 19 tooth axle gear, versus the normal 15 tooth on A/FX and Magnatraction.


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## vaBcHRog (Feb 19, 2003)

So how does a 4 gear Chassis crown gear compare?


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## Grandcheapskate (Jan 5, 2006)

In looking at a Tuff Ones crown gear and the crown gears from a Hop-Up kit, it looks to me as if they have the same size backside collar. The only difference I see is the Tuff Ones crown gear also has a collar on the tooth side of the gear (as does an AFX crown) whereas the standard crown and Hop-Up crown do not.

Joe


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## alpink (Aug 22, 2010)

the "collar" on the inside of later 15 tooth crowns, primarily for AFX, is there to help grip the axle.
4 gear crowns tend to be smaller in diameter and thinner because of the limited space in side the rear of the chassis


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## Grandcheapskate (Jan 5, 2006)

So, would you use the same crown gear for the 12 tooth and 14 tooth pinion gear? If the measurements in the OP are correct, there's only a .005" difference between a Hop-UP and Tuff Ones collar.

Joe


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## Bill Hall (Jan 6, 2007)

Visually ... assuming you are holding the crown gears in your hand, it's pretty easy to eyeball things.

9 tooth uses the full outside shoulder 
12 tooth uses 2/3 of the shoulder 
14 tooth uses 1/3 shoulder on the outside and 2/3 shoulder on the inside.

Both the 9 and 12 tooth have an outside shoulder only.

The 14 tooth has an outside and an inside shoulder. 

The Slimline uses the 12 tooth crown gear with a 9 tooth pinion because the axle box is .... uh.... slim. 

During the golden age we just did the home grown hop up, by recycling the 12 tooth armature gear and used it as the pinion. The standard crown gear shoulder was nipped back to fit. 

The 14 tooth mod, while available, wasnt reliable due to lack of available shoulder area after you nipped it back, (we're talking pre Super Glue LOL); until the factory jumped on with the inside shouldered Tuff Ones crown gear.


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## Joe65SkylarkGS (Feb 15, 2010)

Bill Hall said:


> Visually ... assuming you are holding the crown gears in your hand, it's pretty easy to eyeball things.
> 
> 9 tooth uses the full outside shoulder
> 12 tooth uses 2/3 of the shoulder
> ...



Wow, simply put Bill ??


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## Rich Dumas (Sep 3, 2008)

As an added note I have not seen any aftermarket crown gears that are made to mesh with a 14 tooth drive pinion. In a T-Jet, A/FX, Magnatraction or X-Traction that combination is going to be too tight. I just built up an X-Traction car and I had to shave the hub of an RT-HO crown gear, made for a 12 tooth drive pinion, to just under 0.04 inches (if I remember correctly).


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## Grandcheapskate (Jan 5, 2006)

Rich Dumas said:


> As an added note I have not seen any aftermarket crown gears that are made to mesh with a 14 tooth drive pinion. In a T-Jet, A/FX, Magnatraction or X-Traction that combination is going to be too tight. I just built up an X-Traction car and I had to shave the hub of an RT-HO crown gear, made for a 12 tooth drive pinion, to just under 0.04 inches (if I remember correctly).


Rich,
Which combination is going to be too tight?

Because both T-Jet Tuff Ones and AFX use 14 tooth pinion gears, isn't the crown gear the same for both? Therefore any NOS AFX crown gears should mesh with a T-Jet 14 tooth. Right, or am I missing something?

In my new parts box I only have the crown gears for the 9 tooth and 14 tooth pinions. Still on an Aurora card I have Hop-Up gears (pinion and crown combination). I have to look closely at those carded parts to insure (1) the pinion is 12 tooth and (2) the size of the back collar/shoulder of the crown gear is midway between the crown for the 9 tooth and the crown for the 14 tooth. I know the carded crown gear has no inside collar. When looking at them while still on the card, it sure looks like the crown gear has the same size back collar as the crown for the 14 tooth pinion.

If the back collar is three different sizes as pointed out by Bill, I should be able to see that by eye.

Right now, the carded parts are in the garage which is cut off from civilization due to the snowstorm.

Thanks...Joe


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## Rich Dumas (Sep 3, 2008)

I was speaking of the RT-HO crown gear that was made to mesh with a 12 tooth drive pinion. That was a little too wide to mesh properly with a 14 tooth drive pinion. I am fresh out of A/FX/Magnatraction crown gears. Maybe I will remember to order more of those.


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## Ralphthe3rd (Feb 24, 2011)

Joe, believe it or not, there IS a difference in the OEM Aurora Crown Gears designed to mate with the 12T or 14T pinion....it's slight, but they're different and necessary. That is, if all other things are up to spec, sometimes- some chassis are not. 



Grandcheapskate said:


> Rich,
> Which combination is going to be too tight?
> 
> Because both T-Jet Tuff Ones and AFX use 14 tooth pinion gears, isn't the crown gear the same for both? Therefore any NOS AFX crown gears should mesh with a T-Jet 14 tooth. Right, or am I missing something?
> ...


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## Ralphthe3rd (Feb 24, 2011)

PS to Joe, btw- some aftermarket Race suppliers, now even make 10T, 11T & 13T drive pinions. But it's up to you to Spec the Crown gear mesh spacing.


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## Grandcheapskate (Jan 5, 2006)

I don't doubt there is a difference, I just can't see it.

Still on Aurora cards I have the standard T-Jet crown gear (for 9T), the Hop-Up combo (12 tooth pinion and crown) and AFX crown gear (for 14T). By eye, the Hop-UP and AFX appear to have the same backside collar, with the AFX also having a front (teeth) side collar. I have not removed any from the card yet.

Once I get around to removing them I will be able to get measurements for each.

Thanks..Joe


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