Bravo 3 Chipped upper input shaft gear
 

So - I'm late this year with commissioning, but when I changed my drive oil I noticed some good sized particulate on the upper unit magnet, and a shimmery glittery appearance to the oil. 3 weeks later, after blasting and refinishing the cases I pulled the upper unit apart. It seems my input shaft gear chipped in multiple locations. Obviously I need an upper gearset, but I was wondering if anyone could shed light on root cause of this failure mode. Drive had around 675-700 hours on it. Boat is a 36' Cobalt with Twin 496's, Non HO. 375HP. When I got the boat from the original owner it had 500hrs on it, I added a tie bar and drive showers, and switched to Ams Oil in the drives and motors.

[ATTACH=CONFIG]501171[/ATTACH][ATTACH=CONFIG]501172[/ATTACH][ATTACH=CONFIG]501173[/ATTACH][ATTACH=CONFIG]501174[/ATTACH]

Heavy boat, motors make a ton of torque, a lot of hours, crappy Merc gears. Previous owner may not have been dlligent on changing gear lube.

change the gears those are done,,, you can upgrade the gears to the better XR style if your running a 2.0 gear ratio on the Bravo 3

So I have the serial numbers of my drives. Will that help to determine the gear ratio? Not sure where I stand with gearing. OM179378 and OM179376 The gears in the upper are 27/29 tooth

Both are bravo 3's with 1.81:1 ratio.

http://www.mercruiserparts.com/Show_...O+I%2FII%2FIII

http://www.mercruiserparts.com/selec..._nbr=880951+00

http://www.maxumownersclub.com/forum...cruiser/28.pdf

:Dand switched to amsoil :whistle: Just messing around with you, i'm sure amsoil wasn't the whole cause :evilb::lolhit:

Good luck.:)

Keep that style of gear. They will give you many more happy hours of boating. In most applications the X gears are just as good as XR's and cost almost half as much.

Is there any preload on the pinion bearings? At 700hrs it could be way too loose and causing the pinion to move. That could possibly stress the teeth and cause the chipping. Look at the inside of the snout and look for wear marks from the front bearing, if there is a ridge on that wear mark, it is possible the bearing preload was so loose it has stretched the case. You want to check that before you replace the gears.
Another thought on it, is fatigue of the gear teeth. Not normal to see that, but with the B3 there is a lot of load on the gears and the upper set doesn't hold up as well as when they are used in a B1. And do yourself a favor and don't upgrade to the XR gears, it would be a down grade in reliability, possibly.

Hope that helps.

Lots of great info!! Thank you. I am sticking with the same gearset based on my drive serial number, they are on order. But based on the chart how did you determine they were 1.81:1? Also - since both drives are the same vintage, do you think I should be concerned about the other drive? A little back history on this drive - 2 years ago it blew the upper seal, but I caught it by my drive reservoir sensors. Once the reservoir sensor went off, i hauled the boat and drive. Last year I replaced the pinion bearing due to whining. Is it possible I caused this failure prematurely? I followed the pre-load instructions in the manual, using a snap on dial indicating torque wrench. The gear doesn't show signs of oil starvation. I also torqued the drive shaft nut using a snap on torque wrench, all calibrated by snap on prior to use.

Oh and whats the concern on Ams Oil? I was under the impression all of the new Volvo IPS drives are using Ams Oil under a Volvo name?

Running your serial numbers through mercruisers system shows the info from when they were new. Bravo 3, 1.81:1 Serial No: 0M179378 Model No: 5441400LS


Sorry, There's nothing wrong with amsoil at all, I was just in a funny mood last night is all, I guess I thought it would just be funny to instigate another what aftermarket oil is better than OEM recommended oil.:whistle::)