Optima Mid Transmission Reliability
 

The rear transmission gears seem to be a weak spot of the Optima Mid. Most cars I got second hand came with either a worn out diff gear, and center gear, or came with an extra new unused front diff housing, showing that the rear diff had already been replaced.

What is the best way to prevent this? Is the Thorp center gear much better than the stock one, and will this make the diff gear last much longer? And how about a belt conversion? So replacing the metal gear on the spur gear shaft by a pulley, that fits over the metal pin that goes through that shaft. And replace the gear half of the diff with one that fits a drive belt. It seems that only 3 custom parts would be needed, the pulley to replace the metal gear on the spur shaft, a short belt (maybe the one from the Lazer ZX-R might fit) and the new diff half to replace the gear half.

Has this already been attempted? Are there better options?

Not seen it but I do remember a guy years ago at our club converted a Rocky from chain to belt

Chain to belt is not what I had in mind. The Optima Mid already has a drive belt to transfer power to the front wheels. I am referring to the internal gears in the rear gear box of the Optima Mid. These seem to wear pretty fast, so a solution is welcome.

Sorry I misunderstood your post :blush:

Im not 100% au fait with the car in question, but it certainly seems feasable from what you describe

Maybe you can ask Rama (Alcyon) and the other guys in this thread ==> http://www.oople.com/forums/showthre...ghlight=optima

I have been considering the same thing for the Mid
It would probably be easier to adapt a Lazer transmission

All the mids I have seen that chewed up the rear gears were due to debris getting into the "sealed" system. Since there isn't really a great way to seal it up and still be able to maintain it, one option is to get the debris deflected instead of allowing it to climb into the gears. Take a look at a Stinger rear gearbox, it has a shield that blocks and deflects the debris, and all they had was a silly cover on just the bottom. They didn't chew up gears and it was basically an open system

I posted in that thread, thanks for the suggestion.

It seems to be feasable, hardest part is probably creating a new diff half to replace the one with the gear teeth. But if succesful, I think it will put the Optima's maintenance needs on a much lower level.

Maybe a Lazer gear box can be made to work, but this approach will be less invasive, and should be a drop in replacement, with no changes on appearance.

In the old days, I used to chew up a lot of center gears and diff gears. But these days, my center gears last a lot longer. The biggest difference is sealing the belt covers. When I was in my teens I would had missing parts of the belt covers, especially over the motor, and under the top deck. When people started making repro covers, I sealed everything properly and found that no dirt gets in. Of course it also helps that I used a low friction delrin center gear and a B4 layshaft that softens the blow to the gears.

So the delrin center gear (by Thorpe, or different source?) makes big difference, along with paying attention to getting things well sealed?

I was told BITD that the problem was rather a bad gearing mesh between the center gear and the differential. So maybe a slightly bigger diff gear would do the trick?

There were also belt conversion kits made in the late 80s... You should check RC10Talk.

Yes the thorp one is good, but I have also made my own, but in black. Mine was installed last year and still holding up. Jopp3 is also using them. I also have a PEEK hard gear but a Taiwanese guy says it caused his gears to overheat and melt. I will test the PEEK gear myself soon when I finish rebuilding my SWB Mid.

As far as I remember, no one made a twin belt optima mid. That belt drive conversion is the hyperdrive , which only replaces the spur and the pinion. Inside it was still 3 gears for driving the rear wheels.

Hmmm,my Optima Mid Custom never scoffed any gears,though I did
blueprint it when it was built with all such covers and seals carefully
made sure that they,well,covered and sealed.

It was thrashed pretty hard on dirt,tarmac and indoors with a range of
motors from a 27t stock down to a 12x4.