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Discussion Starter #1
I'm splitting the case again after only 3500 miles since a fresh overhaul because a couple of the gears in the transmission decided to self destruct.

This time I plan on looking at each and every tooth of every gear before putting the case halves back together.

Is there anything in particular I'm looking for besides obvious chips or cracks? This trans is going on 30 years old and I'm wondering if there are internal stresses that aren't apparent until they bite you on the road.

991258
 

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You’re going to see a polished looking wear pattern on the teeth if everything is ok. Everything should fit and slide together, no roughness or play as you’re pushing gears back and forth on the shafts. If there is a “ step” between worn and unworn areas , that’s not good. Galling , which looks like dull spots , but you can feel them with your nail, not good.
Any wear on shaft splines, or chips, not good.
Take pics and post them of what you find. You’re lucky, there are a couple of complete trans gear sets on eBay right now.
 

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Discussion Starter #3
Thanks! I have one on the shelf that was original to my bike but the shaft that houses the clutch through-rod broke on one end. I bought this "newer" one off eBay at the time.

I'm going to disassemble both, select the best of the two, and put back one perfect set (I hope.) I would ask if the individual pieces are available if I have one gear that is not up to snuff, but I think the answer will be that I can buy a whole transmission off eBay for a fraction of the price I'd pay for one Ducati-bagged gear. :)
 

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Discussion Starter #4
One of the eBay transmissions had some great pictures. On one of the gears, I saw some pitting. (See attached photo with the red arrow.)

I want to avoid pitting like this correct? I'm worried that more often than not, these used transmissions are going to have these defects. Or maybe not.

991266
 

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yes avoid pitting --also you want to look at all of the shift dogs you want nice sharp corners not rounded off or nicked---look at everything after you have cleaned it really well very slowly, If you have a magnifying glass use it. If anything at all looks abnormal post pics of it & let others who know more give you advice. --If something does not look quite right chances are it's not
 

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Discussion Starter #6
Ugh... As if I don’t have enough to worry about with replacing the transmission.......

Does this mean my engine case is toast? Looks like the output shaft bearing took part of the housing with it when it disintegrated.

I’m starting to think I might also have an oil pump issue, though the oil pressure light never lit.

991281
991282
 

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Might I make a suggestion, Find a good used engine somewhere, by the time you deal with repairing that & a new gearbox & whatever else you find that may be bad you may come out spending less money.
 
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Discussion Starter #8
I hear you. I've got a lightened and balanced crank and flywheel, 944 kit, ported and polished heads, race cams, etc., so I'd have to transfer those parts to the new engine.

I did see a bunch of 900 cases on fleaBay. What engine cases fit? Only 90 to 98? Or are there other years, models?
 

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Discussion Starter #9
Also, I may as well ask here. I've been told not to use gaskets between the case halves and on the right side cover, but do use a gasket on the left side cover (alternator side.)

Is this good advice? Last time I used a liquid gasket.
 

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I would not use any paper gaskets .

It appears you do not care if the bike is original so I would use later 900 cases from a injected bike as they are stronger. you will find motor mount holes larger but that is a easy fix. At the same time i would play ebay roulette and grab another transmission until you get a good one. most likely wither the bearing failed and the floating shaft caused the gear damage or the gear chunking got into the bearing and blew it up. hard to say at this point. in about 23years of doing this full time I have still seen less than 5 broken transmissions that were due to defects as opposed to a outside something damaging them. I would buy a ebay gearbox and inspect it well I would not use anything from the damaged gearbox as it is simply not worth the risk.

The erosion of the gear is due to spauling which is from inferior oil, many people have a favorite oil but never see what that oil does in the gearbox which is where you usually see oil breakdown results. This is why I have relatively few oils I recommend simply because most of the time you do not get a motor that has been run exclusively on one oil and then torn down to inspect things like transmission gear faces. Race shops do tear motors down often so as long as they are looking they will always be where I ask opinions on oils.
 

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That case can probably be saved if you wanted to go that route, but you need to find the right guy to do it. I’d look into another motor and transfer parts to it. Probably the easiest and cheapest and you don’t have to worry about why it happened to avoid a repeat.
 

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Discussion Starter #12
@ducvet I've used Motul 10/40 exclusively since I've bought this bike in '98. Thanks for the info on the fuel injected cases. What years? 99 through ??
 

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Ducvet - if he goes with later cases, won't he have to swap the crank also, or is that just a case cover issue?
 

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Discussion Starter #14
I found a really low mileage (11K) case from a '95 that had new cylinder studs installed. I've already got new cylinder studs so I guess I'll have an extra set that I will hopefully never use!

And I do kind of want to keep this original. It's a Mk 1 SuperLight. Every original part that has come off of this bike is in a box so that I can restore it to bone stock. I've even got the Marvic's hanging in the garage while the SL wears a beautiful pair of carbon fiber wheels.

As long as the engine looks relatively stock on the outside, who cares what's inside. (But.. guess what... I have the original cylinders and pistons in a box!)
 

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Seeing he has a superlight he should have a short stub crankshaft on the left. He should be 88mm from bearing surface to surface on the crankshaft. This is the same with most big block crankshafts so he will simply need to re-shim with later style (thicker) shims. Transmission shift drums will also be different as the later cases will use a smaller right side with a second shift detent . Yes IIRC the 99 cases have both more internal webbing as well as a stronger front motor mount area.

To be honest if I had a superlight I would swap in a later motor and hot rod that motor while re-freshening the early correct cases and motor for the day the bike returns to stock. A later 900ie motor with your 944 kit and a freshened original superlight motor with correct cases sitting pretty for the day it is worth more selling it than riding it.

If you are seeing spauling running the motul 10/40 I would not run it anymore.
Was that gear from the original transmission or the ebay motor?
if it was the ebay gearbox are you sure it was not there before?

I have a few bikes running Motul and other than it being a dirty oil I have not seen spauling before.
 

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Discussion Starter #16
@ducvet I put in an eBay transmission from a ‘94 Monster 900 in it when the case was apart 3500 miles ago. (Ugh!) The old transmission failed on the input shaft side right where the clutch push-pin enters the case. When we cracked the case, we determined that the guy who rebuilt it last about 15 years ago had not shimmed it properly and it eventually failed.

I made the mistake of not thoroughly examining the transmission before putting it all together again. I won’t be making that mistake this time.

Wasn’t the Motul’s fault.
 

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Discussion Starter #18
I've found a few 900 transmissions from 900ss, 900 monster, the aforementioned 748/916.....

What years will fit the '95 case that I just bought (that was in impeccable shape!)

I know '91 through '98 will fit. '99? '00? '01?
 

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The shift drums may be different diametersat the case but I believe the transmissions themselves will interchange between all dry clutch 900..... although...... IIRC there may be the odd output shaft that is a different length possibly on a monster 900 2000-2002 and the early 900's may have had a short box as well like the 620/750's make sure it is from a 900 or 916,st series and you will likely be fine. Watch for different gear ratios if cross pollinating. Not that it would be bad just understand the changes.
 

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I've found a few 900 transmissions from 900ss, 900 monster, the aforementioned 748/916.....

What years will fit the '95 case that I just bought (that was in impeccable shape!)

I know '91 through '98 will fit. '99? '00? '01?
I'm hoping that the case you got for the 95 is both half's --I cant swear on the Ducati but most bikes the cases are matched & line bored at the factory. if you got both L & R matched your fine but If you only got 1 side I dont know---Belter or Ducvet will know the answer to this for sure
 
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