GB32 transmission questions

[Knot Lost]

So, I have my 32 and happy as a clam at high tide.... until the transmission oil pump failed and killed the input shaft and ahead clutches. Long story short, I’d spoken with a guy back East who told me I had the wrong tranny, that it should be a Velvet Drive 72C, not the 71C. But everything in the thorough documentation and manual that came with the boat shows the AS3-71CR and serial numbers as original to the boat back to 1972.

So the question is, did American Marine at some point realize they needed to move up to the beefier 72C? Or is what I have the true, correct unit?

TIA

 

[SteveK]

If your engine is more than a 182 HP engine then use the 72C, not 71C
You say you have AS3-71CR which outputs in opposite rotation to the 71C or 72C
My 71CR spins the prop counter clockwise as viewed from the rear.

What is your prop rotation?
"a guy back east said" may refer to your prop rotates clockwise going forward which would need the CR to run in reverse to go forward. running in reverse for long time is not good, is that what he was talking about?

 

[Knot Lost]

Yup 71CR

Hi Steve. Actually, I don’t really know what he meant? He seemed to imply that the 71s were too small for the Ford Lehman engine and that they’d burn up - which mine did. But I don’t know which was the chicken and which the egg: did an overloaded clutch pack heat up the oil too hot and compromise the pump over time; or did the pump simply fail and cause the rest. Dunno.
Either way, it took me finding a rebuilt unit to figure out where the “R” is stamped, as on mine it was corroded away. Seeing the new one, I can now just barely make out the remains of the R. And knowing that the manual identified it as the LH counterclockwise 71CR, it seemed to make sense. In referring to it in my earlier post I just meant that it was a 71 series, not 72. Definitely turns ccw to go forward, and yes, trying to go forward by putting it in reverse is never a good idea. So maybe that’s what he meant? Thought I’d been pretty clear to him, but oh well. Moot point now, as a new unit is on the way. Crossing fingers it works! I figure the original lasted 40 years, so... AS3-71CR it remains. Thanks for your help! Scott

 

[SteveK]

I figure the original lasted 40 years, so... AS3-71CR it remains

 

[Xsbank]

A couple of misconceptions here...40 years to kill it? What other stuff in our lives last that long?

Many twin engine installations have one engine turning "backwards" which, with a standard wheel means the gearbox goes forward in reverse. The transmission doesn't care, the pitch of the wheel compensates for any ratio issues. The other way is to run both engines the same way, one in reverse gear with a reversed wheel. There is nothing wrong with this except the odd engine and trans were not as numerous as the standard set so parts are more elusive.

 

[SteveK]

Xsbank, both my Lehman turn the same way. The CR tranny spins the prop opposite from the C. The CR is 2.1 to 1 and C is 1.91 to 1 to compensate and turn the prop at the same speed at the same rpm.
Or I misread it all.

 

[Knot Lost]

Thanks everyone! Great info and feedback. Picking up the new one today so will let you know how it all goes.

 

[Marinex]

We have a 1967 GB 32, it runs the AS3-71CR. It wasnt until i cleaned all the paint off the model plate that you could see the hand stamped R at the end of the model number. 54 years and still going!

Oil levels should be checked and set warm and just after engine shutdown otherwise the oil in the cooler flows back to transmission and makes it look overfull.

 

[SoWhat]

A 71C would be properly matched with a Lehman 120. More interesting question is why oil pump failed. The gears wear so after 40 years it is possible it was not putting out enough oil so clutch plates overheated but prior condition of plates is unknown so no conclusions there. Input shaft would likely be scored over over 40 years but low oil pressure would overheat the bearings.
I would remove old oil pump for failure analysis.