I have a standard length Imco lower that I purchased used many years ago. It has a 1 1/4 shaft and a blue bearing carrier. I don't believe Imco's came with a blue carrier, so I believe it was rebuilt at some point, and am not sure if any thing else has been changed.

I need to put in a new lower gear set soon, and am not sure what part number I need. I see many different part numbers for a 1.5 ratio,15/19 gear set. How do I know which one I need ?, Should I take it apart first and see what part numbers are on the gears? What differences do I need to know about.

Thanks,
Steve

Is it from an IMCO SC Drive

Yes it is a SC lower. I am not sure if the prop shaft and bearing carrier are Imco though.

Pull it and inspect carrier shaft seals ect .who knows , might have some tbs gears in there

All XR uppers have 16/19 gears. You change ratio in the lowers ie. 15/19 = 1.5 ratio; 15/17= 1.36 ratio; 17/18= 1.26 ratio.

Oh, the part # for the merc lowers gears to get 1.5 ratio is 43-818928A2

I just finished rebuilding an IMCO SC Drive for my customer, it had XR Gears , 1;5 ratio, Bawana listed the part numbers above.

I always heard the 1:50 gears were stronger than the 1:36 gears due to the gear cut, is there any truth to that.

nope

Revd Up,

If your lower has the Merc propshaft you will need to use the XR gear set, (43-818928A2).
If it has the Imco propshaft you can use the B1 lower gear set (43-14063A1) or the XR gear set. The difference is the size of the machined hole in the driven gear. Imco sells a spacer that slides on their propshaft to take up the space on the XR driven gear.
Hope that helps.
Dick