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Discussion Starter #1
When changing the lube in my GTA close ration gearbox I found a broken tooth on the drain-plug. No choice but to pull the box and disassemble. The culprit turned out to be 3rd gear – on the mainshaft. I now have another 26 tooth NOS 3rd gear but the hole for the bushing is different. It has a step in the bore for the bushing. The ID changes from approx 37 mm (as per the old gear) to 39.5 mm. Each portion is about 15 mm deep.

I am thinking of having a collar made and shrunk into place o hold the new bushing. Any expert advice would be appreciated.

Any thoughts as to why the new gear is different? It has 6500753 written on the gear.

First picture is the old gear, second new gear, third is both and the forth shows the difference referenced to my caliper. Sorry for the shadows, the built in flash is not for macros...

Thanks for any help,
Don
 

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Check that the tooth angle is the same on both; Bacci gears have a step for a needle roller bearing but also a different tooth angle, so can't be used with original Alfa gears.
Vince.
 

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Discussion Starter #3
Re 3rd Gear

Thanks Vince, not the news I wanted to hear but at least now I know. The angle of the bevel gear does appear to be different.

Any one know of a 26 tooth GTA 3rd gear for the mainshaft for sale?

Regards,
Don
 

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Discussion Starter #4
Next Question

Assuming I will not be able to find a GTA 3rd gear could a 3rd gear from a spilt-case 4 speed be made to work? Tooth count and other dimensions seem to be compatable. The rest of the trans is the moly synchro type so those parts will have to be changed.

Any thoughts as to why it won't work?

Don
 

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Contact Richard Jemison, Alfar7 here on the BB. He does all my GTA CR transmission work.
His suggestions or work will not disappoint.
 

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Don If you find 3rd gear from a split case 4 speed will work, I have a couple of 4 speed gear boxes for parts, however I am still in Arizona untill the 1st of april.


OFRACER,(AKA Denny Pillar) Email: [email protected]
 

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Richard Jemison
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Gears

one of your gears is from an aftermarket gearset, the other from a Alfa gear set. Teeth will have different tooth designs and OD. They wont fit together with the layshaft gear.
You will have to make a matching pair from a 4 speed set to repair it and have the same 1.25 ratio.

If you want to send me the layshaft I can do the modification and have the gears to repair it with a matching 3rd gear for the mainshaft.
 

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Problem solved. Thanks RJ.
 

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Discussion Starter #9
Trial Assembly

This morning I did a trial assembly with the 4 speed third gear and the original GTA layshaft. It went together easily and turns freely with no sign of binding, the Bacci gear does obviously not mesh correctly. Now it is off to the machinist to change the bushing and engagement dogs...

Thanks,
Don
 
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