Big Block Billy

Konrad suggests the Royal purple gear lube. However a Bravo drive is not a Konrad, it's like trying to make chicken salad out of chicken $#!+ !!!!!!
If anyone has the answer for drive problems it's Konrad ! They are a company dedicated to making tough dependable drives, and are priced reasonably. BBB

PatriYacht

Smitty, a few years ago, one of the tricks people people used to make Bravo's last longer was use 1.36 gears instead of the 1.5's. More stress is pushed to the prop and away from the lower gears. Since you need some new gears anyway, you might want to try that. Someone here could probably lend you a prop to test with. Ian

Big Block Billy

I had great results years back when I changed an alpha from 1.50-1 to 1.32-1 .
Before that I was blowing up lowers. I ran close to 400 Hp through it. Ran for several seasons, still have it and would bolt it on and go. That was on my 21' 454 Baja BBB
Ps.. I think it has something to do with the power coming up gradually (motor has more load) instead of shocking the drive winding up to max Hp out of the hole . This is true even if you drive it sanely !

joee

You are running much more torque on the drive than it has been designed for.

How is the deflection of the shafts under such a big load.

Too much deflection would disturb the correct meshing of teeth.

Have you already tried a tooth contact pattern lacquer (Klüber P39-462 or DYKEM # 80400/80496) in order to verify how the teeth are meshing under load.

Joee

SB

Remember, Gears (if not 1:1) change torque multiplication - not just rpms.

600ft/lbs x 1.5 = 900ft/lbs
600ft/lbs x 1.32 = 792 ft/lbs

After any gear , the following parts will have to handle multiplied torque if higher than 1:1 or fractional torque if less than 1:1 .

The part I have no idea about - is how the propellor effects this. If it does. LOL. SOmeone please let me know - this has been bothering me, but apparently not enough to sit down and figure it out.

articfriends

Thanks for your input,the driven gear (big gear) is preloaded in place with a large bearing to support it behind it,the pinion gear does hang on the end of a shaft and shaft could be deflecting. I'm using max worxs billet shafts,I think a stock shaft would probablt twist off on the first wfo pass. Max worx makes a billet lower case,it has some kind of extra support bearing in it for the vertical shaft to help with shaft deflection,when talking with them they say the case might help but what they say I really need is there stronger 9310 gears they are currently developing so I'm not sure if I spend 4000$ on their case & special vert shaft it would actually help.If I were to pattern in the gears under a load like you suggest would you say to dye them with a permenent marking compound like you mentioned then make some wfo passes?When you look at the gears after they break through the hardness you can see the contact pattern and it looks real even except the fact the teeth start breaking down right in the middle of where they contact, the damage doesn't run off the trailing or leading edge or tooth flank,Smitty

articfriends

My understanding is other than small changes from propellor effieciency the boat should go exactly same speed with a 30 pitch prop at 6000 engine rpm's w 1.50 ratio as it would at 6000 rpm's with a 27 1/4 pitch w 1.35 ratio. How much the load would change I'm not sure.If you take my peak tq of 960 ft lbs X 1.18 (19 div by 16 for the top gear ratio) you would have 1132 ft lbs of twist on the lower pinion gear teeth no matter what ratio you had after that except load theoretically should be about 15% less but once you factor in the fact the prop will be turning 15% faster the load should be the same,but this is all just using the W.A.G method . If anything I would figure the prop shaft would have 15% less twist acting on it,but Ive never twisted one off so it would be a moot point. I do know this though,with these forged,beveled tooth non helical gear sets you pretty much only have one tooth contacting another at anyone time so I'm thinking thats where the problem lies. Strip brought this up a long time ago and it makes sense,aside from deflection that could be occuring,there is just 1 little tooth at any given time transmitting over 1000ft lbs of multiplied tq so it seems for it to last it would take the very best alloy and heat treating or surface conditioning,Smitty

cobra marty

The 27" prop will have less 'resistance' to spinning than the 30" and will transmit less force/deflection to the propshaft and allow the pinion gear to stay better meshed with the vertical?

articfriends

I have seen heavy boats (like patriyachts bt) running 1.36 drives w/26 pitch props so maybe theres some durability merit to this thought,Smitty

Big Block Billy

Also you old school rear end guys would also recommend Prussian Blue to establish gear contact points. And look at old rear end charts, the same basic principles still apply...
BBB