Typically, when drives fail, what breaks the upper or lower? I had the lower re-built already this year because the guy that used to own the boat before me beat the **** out of it. The prop shaft was rusted and the vertical shaft had the splines twisted.

Do the upper gear sets usually stay together pretty good, if not, what usually goes wrong with them?

Typical bravo failures are in the uppers....there are always exceptions. Either the upper gears stress and fracture, or the top cap lifts/breaks upward.....but problems can be any number of things!!!!

I don't know if it matters, but it's on a 500EFI

On regular Bravos, the upper is weak link and usually fails before the lower. On the only one I have ever had a major failure on, the upper gears came apart. The lower was fine.

The uppers are the more failure prone.

Most of the failures I've dealt with were
gear failures ( teeth breakage and gear floor
failures)

I have seen bearing failures, but that could be due
to contamination from failed gears

I've never had a lower fail.

Racer,
the B1 is basically a sound drive. Depending on what year your drive is, it can have different weak points. People have been chasing the weak points in the Bravo since it was introduced in 1988.
In the upper, if it is the old style B1, serial number starts with OL or lower then when you increase power to the drive, the floor of the gear would break, resulting in no fwd motion, but typically not hurting anything but the gear. When the OM drives came out, Merc made the floor of the gears thicker, changed a few bearings to accomodate them and made them so they will fit the older cases, hence the X gear upgrade kits, as I call them.
If you add too much power (blower motors), typically the teeth will break off, hence Merc designed the XR gears for the upper.
In the lower the older B1's had thinner vertical shaft and propshaft that was two pieces welded together. If the boat sees any air time it will twist shafts, either the vertical or the propshaft where the prop is mounted. The lower gear set will wear out, in time. More power, the sooner they wear out. They will start to give off metal from the center of the tooth, so if you see flakes or chunks of metal on your magets, that is what is occuring.
So what usually goes wrong with them, depends on the driver, amount of power and maintenance. Also how the drive is setup to begin with. When preload on the tapered bearsing goes away, then you find wear points in the upper case that will allow the gears to move around and then all sorts of bad things happen.. When someone upgrades HP.. they usually dont have enough money to have the drive rebuilt by a performance drive builder, and if it is worn, it will break sooner than later..

Hope this helps..
Dick

Dick,
Thanks for the advise. I have the OL drive and am a little nervous about the upper unit on the drive because it's the only part of the drive train that has NOT been re-built. I bought the boat in March of this year and had to completely re-build the engine (top to bottom) and the lower part of the drive (including both shafts and bearing carriers). The guy who had the boat before me didn't take care of the boat at all.

Soooo at this point should I just stay up on the oil changes in the drive and at the first sign of metal re-build the upper or just this winter have it gone through preliminarily before something comes apart on me. My gut says to try to take it apart before any problems happen (would probably be cheaper that way).
James

Most things are cheaper to rebuild when they still run than to try and fix everything that BROKE. (My XR's are coming apart this winter just for inspection purposes)

James,
For peace of mind, you should have it looked at. If the guy didnt take care of anything, the upper would be included. If the preload in the upper is loose, the case is wearing and will get to a point that it isnt a good canidate for re-use or upgrades.
How much power are you running? And what is your boat weight? What prop, etc.
It is my opinion, that if you dont have enought power to knock the teeth off the X gears you are better off with them. The XR upper gears wear out and have been failing like candy lately. I like to recommend for a B1, the new X gears with a steel tower installed in the upper case and the Merc XR top cap (ribbed). It has a steel tower in it also. The tower I install, goes 2" into the case and it makes for a stable enviorment for the gear stack. I have done many of these upgrades with very good results.
Driven with respect, it makes a very reliable drive.

If you are seeing pencil lead on the magnet in the upper, it is an indication of the preload going away on the pinion bearings, also the input shaft will be very easy to turn, it should have a slight drag on it..
If you have any other questions, fire away..
Hope this helps!
Dick

The deal is if you wait til it pops chances are you'll be replacing the whole upper .....and even though the lower has been done if the upper blows you'll be wise to go thru the lower again ......Pay now ...or pay later ... "Mr Gadgets" knows his stuff ....pay attention ........m