'74 Merc 850, lower unit repair

Mercr · Apr 8, 2006

Hello. I'm new here. I've been searching through old posts, trying to find info on lower unit repair. I am buying a "fixer upper" - 15' Caravelle/'74* (*SN 3870380) 850 Merc - from a friend, who has given up on it after going through almost everything else. He ultimately discovered that the lower unit was damaged - & got an estimate of $900, for a rebuild, at the local marine shop. I've used the search function, using "85 HP", "850" and "Lower Unit", but have yet to find a relevant post. I'm an experienced auto mechanic, and think I can tackle this myself. I intend to disassemble the lower unit & determine what's "wrong". I'm trying to locate parts ( don't know exactly which, yet) and/or interchangeable lower units, and "how to" info on the actual process. I've found some bits & pieces, but would appreciate any links, or suggested search phrases, regarding my situation. From the looks of this site, I suspect the info is here. I'm just having a bit of trouble locating it! Thank you! Merc

tashasdaddy · Apr 8, 2006

Re: '74 Merc 850, lower unit repair

manuals are available at oldmercs.com , you may find one on ebay. i did. 71' 1350

Laddies · Apr 8, 2006

Re: '74 Merc 850, lower unit repair

If a online parts manual will help goto BAM Marine.com

Mercr · Apr 8, 2006

Re: '74 Merc 850, lower unit repair

I've got the Clymer Shop Manual (45-225 HP- '72-'89). Is that a good one? What I'm really looking for are some good parts sources, and an interchangeabilty guide. The manual seems to cover the process fairly well. I've been "auto wrenching" for ~40 years ( mostly hobbiest - old Chevies & Fords), but some of the marine terminolgy is a bit "foreign"...( much like automotive manuals - it sounds a LOT harder than it actually is...?) I usually read WAAAY to much about something, before I actually try to do it. The Clymer's directions are still "fuzzy" after a few re-reads. Also - does $900 sound reasonable for a rebuild? Not knowing what is actually wrong, I suspect I could repair it for enough less to be worth my while (?) Thanks, again!

Laddies · Apr 8, 2006

Re: '74 Merc 850, lower unit repair

Most after market manuals are FUZZY. Mercury manuals are by far the best

Mercr · Apr 8, 2006

Re: '74 Merc 850, lower unit repair

Thanks, Laddies! There seems to be an awful lot of "This part is no longer available"... 'guess I better tear into this one, and see what it really needs, and/or start shopping for something newer. Sheesh, I should know better. Old cars, old outboards... I'm getting too old for this! Is there a "for sale" section here? Edit: Nevermind, I found it!

Clams Canino · Apr 8, 2006

Re: '74 Merc 850, lower unit repair

The lower units 70-150hp 1970-1986 will all fit. Ebay will have one.. if not today then withing a week or so. they pop up ALL the time. -W

Mercr · Apr 10, 2006

Re: '74 Merc 850, lower unit repair

Thank you, CC. That's a nice wide range of interchangeables. 'Gives me hope!

tashasdaddy · Apr 10, 2006

Re: '74 Merc 850, lower unit repair

just pickup a merc manual for $44.00 w/ shipping on ebay. it's what you really need.. covers Mercs 1966-1974 Manual # C90-68647. you'll find one on Ebay, or go to oldmercs.com and pay $72.00 + shipping.

Mercr · Apr 13, 2006

Re: '74 Merc 850, lower unit repair

Thanks, once again! I searched "C90-68647", and found one @ www.maxrules.com/fixmercbook.html up to $76, 05/06, PPD (was $51 - 04/06). Please excuse me if this has been posted before - like I said initially, 'new here - just wanted to share! I also stumbled across a neat site - www.repairsdepot.com , with many links to boat & outboard repair (and a bunch of other things).

Mercr · May 4, 2006

Re: '74 Merc 850, lower unit repair

OK, I re-read everything I can find on these ( lower units). I dropped it out, and it seems to be OK in fwd , but I can't get it to shift into reverse. Assuming that this is a (somewhat) simple unit, shouldn't I be able to hand turn the shift shaft and see the prop reverse when I turn the drive shaft? I found a place that works on "older" mercs, but they want ~$500 labor and they're backed up 'til late June ( sooner if I bring in just the lwr unit). & I'd like to be certain that there is really a problem before shelling out several hundred dollars. The original merc manual price jumped to $76 before I ordered one ( still waiting). I know I can't apply 85 HP, but shouldn't I be able to do a cursury check - hand turning the driveshaft & seeing forward, (neutral,) & reverse prop spin when I turn the shift lever? The prior owner said that it spun in both forward & reverse when he tested the motor - just had a "funny" sound - in fwd at higher revs, & metal particles in the oil...From what I've read, neither of those are out of the ordinary, so long as the metal particles are minimal.

AEROCOOK · May 4, 2006

Re: '74 Merc 850, lower unit repair

Originally posted by Clams Canino: The lower units 70-150hp 1970-1986 will all fit. Ebay will have one.. if not today then withing a week or so. they pop up ALL the time. -W

Are the gear ratios the same for the various HP ratings in your list? If there are differences, can you change / swap different gears into the same housing? I have a set of gears for a 74 1150 that appear to be in great shape and I dont need em.

Motor Boater Bill · May 4, 2006

Re: '74 Merc 850, lower unit repair

You will need a tool, like pliers or a socket, to turn the shift shaft. You have to compress a pretty hefty spring to shift it. Then you should be able to turn the drive shaft by hand and see how it works. Removing the water pump impeller will make it easier to turn and to get a feel for the gears.

roger3645 · May 5, 2006

Re: '74 Merc 850, lower unit repair

Send me your e-mail and I'll send you a pic of a good set of 850 gears. You can use these as a reference. I just went over mine. Make sure you turn the driveshaft by hand when trying to turn shiftshaft by hand. rip3645@hotmail.com

Mercr · May 5, 2006

Re: '74 Merc 850, lower unit repair

Originally posted by Aerocook: I have a set of gears for a 74 1150 that appear to be in great shape and I dont need em.

I also believe they should work. How much do you want for "shipping & handling"? Those gears will most likely come in handy! I decided to take the unit in. The shop said they'd do a dissasemble/diagnose for ~ $125, so I opted for that. They said they should be able to let me know in about a week. I got the shift lever to engage, and have a "firm" fwd & reverse, but suspect some kind of problem anyway.(Like possibly 30+ years of wear.) ...and 1 "handpower" can't simulate 85 HORSEPOWER! Also - the impeller was pretty bad - the top ~1/16" or so melted off, & redeposited in the housing. Thanks to all for your help & suggestions!

AEROCOOK · May 5, 2006

Re: '74 Merc 850, lower unit repair

A quick estimate from Fedex indicates around 20 bucks Canadian for a ground shipment delivery within 6 days. Send me a P.M. and we can work out details.

Mercr · May 5, 2006

Re: '74 Merc 850, lower unit repair

'Looks like I'll have to request that I be allowed PM priveledges(?) I'm not seeing the PM icon - mentioned in the FAQ, nor have I found a way to enable them. I feel like such a neub

Thanks for checkin' - 'sounds reasonable!

'74 Merc 850, lower unit repair

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