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In my search for a hardened pinion for my optima I've come across a few variations of the ot-76. From what I've read, it should be a dull grey but the ones I've come across are not. They are clearly marked OT-76 hard final pinion on the packaging hence my confusion. Are these "shinier" pinions inferior?

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Thorp also made an upgrade gear, I believe made from steel. I managed to score a few of these over the years. Pick one up from this seller (not me) and save yourself a few bucks.

http://www.ebay.com/itm/Vintage-THORP-Dirt-Burners-4738-Ultima-Maxxum-Optima-Javelin-OT76-Final-Pinion-/191756032060?hash=item2ca58cd83c:g:qeYAAOxy7MtRr9fT

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You can also use a 5mm bore Robinson pinion gear. They for great. Can't recall the tooth count but a whole lot cheaper!

Thanks guys. With the hardened pinion, how hot of a motor can these diffs handle? I know that the chain drive won't hold up to today's mod motors but I'm just wondering about the diff itself.

Somebody posted a topic on here about that...I believe it was a great alternative, dirt-cheap...but also needed spacers as the pinion gears were shorter. I believe the final pinion gear is 19T...can someone confirm the pitch?

It's 32 pitch and 19t sounds correct. I don't recall spacing it on mine but I must have

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19 is the correct tooth count as well.

tamiyadan wrote:pitch is 32 metric.

Final pinion is .8 module 19t

Thank you guys. I ended up buying a hardened final pinion off eBay . I know I over payed but who knows what or if any will show up in the future.

Grunger73 wrote:In my search for a hardened pinion for my optima I've come across a few variations of the ot-76. From what I've read, it should be a dull grey but the ones I've come across are not. They are clearly marked OT-76 hard final pinion on the packaging hence my confusion. Are these "shinier" pinions inferior?

The easy way to identify a OT-76 pinion is that the hard pinion has a groove machined into it, as can be seen here.

terry.sc wrote:

Grunger73 wrote:In my search for a hardened pinion for my optima I've come across a few variations of the ot-76. From what I've read, it should be a dull grey but the ones I've come across are not. They are clearly marked OT-76 hard final pinion on the packaging hence my confusion. Are these "shinier" pinions inferior?

The easy way to identify a OT-76 pinion is that the hard pinion has a groove machined into it, as can be seen here.

ot76.jpg

Yes, I made sure it had that ring around it . The one I bought is shiny like the one in your pic. Some sort of hardened aluminum I would assume??

not likely. probably steel, if hardened any significant amount. can be coated about 10 different ways, could be chrome plated, polished, cadmium, chromate, etc.

yes, i recall that the final pinion can be replaced with a robinson motor pinion a lot cheaper.