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OMC Upper Housings 72b vs 73b and up

L

l_anthony

New member
"Can someone tell me the diffe

"Can someone tell me the difference between a 72 and a 73 and newer OMC Upper gear housing? What can I bring along from my 72s if upgrading housings to 73-up, the gears, water pump, anything I can't? In other words, will the guts of my 72 120hp housings work with 73 and up upper gear housings? What will and what won't? How can I tell what uppers I actually have? My upper housing numbers as read from the "silver ID tags", can't be found?

tag1 979953 120hp
tag2 979680 165hp

Thanks,

l_anthony"
 
"But all parts will fit and wo

"But all parts will fit and work? I realized the last person to service the uppers replaced an original upper with the 165 and yes the gears are mismatched. But the 72 gears are not something special that cannot be used in a 73 and up upper, correct? I am asking this as most parts places have catelogs starting at 73 and up. Intermediates now had several changes, sometimed many within the same year. But upper then should be the same between 70 and 77 for electric shifts, is this correct then? My units are 1972 GUFM-10S 120hp. So I just need to find a set of 21-18 gears to replace the 165 and I can use my old uppers then?

THX
LEX"
 
"yes you need the correct gear

"yes you need the correct gearset.

but the upper housing will work, with your old lower see all the lowers are the same the upper gearset is the one you have to worry about."
 
So the splines or something ar

So the splines or something are different. How about the main or lower shaft? Sometimes refered to as the water pump shaft?
 
"Your giving me far to much cr

"Your giving me far to much credit for thinking I know what I am doing. Do you mean the gear ratio is different or the actual gears are smaller or different shaped for something? on another note I just looked up the drive shaft for my year (lower)on boats.net. They say my 1972 is no longer available but I go up to 73 and they say "is available" and will sell me one. They have different numbers? I am wondering if there really is a difference or if they just stopped updating written material before 73 and the numbers may have been replaced, and they are indeed the same part or identical?

Sorry?"
 
"Click on my name and will bri

"Click on my name and will bring you to a page with my email, email me and i will email you my phone number i have the book open right now and it's a little strange, they list funny numbers.

I sse where you are confused and please don't be sorry."
 
"One of the biggest things I h

"One of the biggest things I have found is that the '73 and up uses the same Ball Gear configuration, BUT the mounting of the Ball Gears onto the shafts are different.

The later ones go onto a tapered Spline, and are retained by Nuts, whereas the early ones press-on, and friction holds them in place.

I was looking into using later shafts and Ball Gears on my '72 and if I use the earlier retainer, and space the Coupler away from the Flywheel about 3/4", and use the later Coupler, which has a larger diameter spline, then the Intermediate Shaft will fit.

Not sure about the Opposing Ball Gear shaft though, as I haven't one to compare. Got lots of later shafts though.

But, with the Upper Gears, they have to be matching sets, or they will grind themselves to death.

Bruce."
 
"Thanks Bruce. My intermediate

"Thanks Bruce. My intermediates are fine. I actually found 2 shafts "new" for around 150 a piece, one with a brand new coupler. I have been searching numbers and cross referencing them until my brain now is going on strike? I have a planing houseboat, so I want to go with the 16:20 low gears 120HP. I actually have a GUFM-10S which came factory with the 19:20. Most of the other 72 like the C's came with the 16:20. Carberation was different and I think they were high profile? Mine is low profile. I just figured out the water pump shaft is the cheap one that they continued with after 72 on the low profile 120 hp setups. The upper driveshaft was also used upwards of 76. The gear that goes across, that holds the ball gear in he upper is not so easy to find. I can find bolt ons here and there? Originals are press ons. Do you know of any newer numbers or any other years that used this config for this? I have lucked out in that go2marine and others have been trying to sell me vintage shafts for big bucks, boat.net cleared it up for me since once again I have an "S" model or low profile. I thought. I don't think I can regut everything and keep the 16:20 gears though? I think with the 19:20s that continued on for quite some time, I could get away with regutting everythning to this new config? Can I use bolt shafts with 16:20s in place of press on older types? Is there a difference when you put them together? Do you see my delema? Any additional advice?

Thanks,

Lex"
 
"Follow up for anybody interes

"Follow up for anybody interested. Well, I have talked to just about everybody, eg., G2M, Crowley, DLG, Boats.net, local mechanics. My GUFM 10S is a low profile unit, must have been OMC experimenting with these? Some of the GUFM-(S), (S) for short I think, start showing up in 75 again. I was just told by an internet dealer, this is when the shorts or lows started up again? My OMC manual shows a special tool for 72S. I have a 120hp by the way. So, indeed the main shaft is the same number for 72 and 75, the water pump shaft is the same for all electric shorts or lows I am again told? The gears however are bolt on in 75, my gears are press on. Reason for the special tool possibly? My upper shaft or pinion gear, press on is only $150.00 as compared to the new lows (73- on) that start at $320.00 (BRP). THe only concern I have is the book still states there is a special tool for the 72 (S) for setting up the main shaft in the gear carrier? If anyone can shed more light on this subject, please weigh in. Also, since my steering in hydrolic and not OMC, I have been told I can use any housing from 70 through 84? It was Marine.com that set me somewhat straight on much of this, so cudos to them. Not all of this stuff, so don't blame them here, because I have mixed and matched a bit, from the various sources.

Thanks,

LN"
 
"I just figured out what Bruce

"I just figured out what Bruce was trying to tell me a couple of posts ago on my ball gear and shaft. If you will be so kind as to respond as I did not get the full picture until now, faced with this issue as well. Question: If I have a newer shaft with gears "bolt on ball" and match it with a newer ball assembly, will this work without modifiying the engine coupler by 3/4s"? I just discovered the extra shaft and gears I have 16:20 have the bolt on ball. I can redily obtain a new ball assy. as my last mechanic lost this and will replace with what I want?


LN"
 
"G'day Lex,

The Shaft f

"G'day Lex,

The Shaft for the Bolt-on Ball Gear is shorter than the Press-on shaft, not sure why, but the ones I have here in my possession are different lengths.

Plus, the shorter shafts have a larger diameter Spline at the Coupler end, and use a different diameter Bearing Retainer, and Oil Seal.

Maybe the V8 Shaft is shorter than the V6, or lower Horsepower engines. Or the V8 Flywheel/Crankshaft Hub sits further back towards the Intermediate Housing. But, the Bolt Pattern in the Coupler is the same for the GM engines.

But, the Bearings are the same outside Diameter, and width, so all that is needed for the Retainer to fit the earlier housing is to machine the outside diameter of the retainer to the same diameter of the Press-on one, but you won't be able to machine in a new "O" Ring Groove, but that shouldn't present a problem as using a RVT Sealer when installing the Retainer will stop any oil from leaking out, or water getting in.

Will try and post some pictures when I get everything set up.

Bruce."
 
"Interesting Bruce. I have two

"Interesting Bruce. I have two new ball shafts for my GUFM-10s Intermediates and one "like new" for backup, along with two new couplers. Hopefully I am OK here. My latest delema entails the upper assembly shafts. My 72 GUFM-10S's are press-on type gear drive shafts, the waterpump shafts appear to be the same for all short profile low hp's at least through 75? Let me know if this is not true. The big question is; my gufm-10s's use the same upper drive shaft as the 1975A model 120hp low profile, the shaft number is 0907738 (expensive and hard to find). I am entreating the idea of upgrading my drives to a new upper configuration, say a 1975A 120hp with tapered gears, I think? Some of the later 1976 "M" started using a different shaft all together, a 0909121? These are cheap and readily available. These also are used on higher hp models so I suppose the shaft is heavier and or different splines? Also, are 16:20s, the gears I need, still available on the later models? I guess I am thinking, I would be better off going with a system that utilizes the 0909121 shaft system rather than staying with the more expensive original drive shafts and press on gears and balls that are becoming more scarce? My ball gear shaft in my current uppers are cheap if you can find the balls? I have an empty extra upper housing and a set of 16:20 tapered "press on" gears and upper pinion shaft "bolt on ball gear" as well, so I can go either way with one of my drives? The question is, what is the best or most economical way to go under my circumstances? I am leaning at building 2 drives to original spec as I have almost everything needed and then to build my "new" extra outdrive system based on the future? What is the most economical year or system to go with, in an upper assembly then and still be able to have 16:20 gears?

Thanks,

Lex"
 
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