This page updated:
- In-line: engine, transmission, shaft, propeller in one line.
- V-drive: shaft makes U-turn (V-turn ?) inside transmission.
Saves space by moving engine aft.
- Stern drive / sail drive: most of transmission is outside hull (on transom)
and can rotate.
Great maneuverability, can tilt up, more compact,
engine/shaft alignment less critical, propeller is horizontal,
can use soft engine mounts (less vibration and noise).
But more drag when sailing, more stuff exposed to collision,
more dissimilar metals in water can mean more corrosion,
generally not available for higher than 75 HP.
"Stern Drive Realignment" article by Harry Swieca in issue 2002 #2 of DIY Boat Owner magazine.
SailNet - Mark Matthews' "Breakdown in Paradise" (fixing transmission)
- More transmission problems are caused by cable
malfunctions than anything else.
- Transmission problems can be caused by being over-propped.
- Transmission oil leak can be caused by leaking seal, or by
loose nut holding seal-flange on.
- After replacing leaking seal, make sure engine mounts
and alignment are good, or the seal may break again.
- From "Offshore Cruising Encyclopedia" (1989) by Steve and Linda Dashew
(on Amazon - paid link):
"Nothing will ruin a transmission faster than a misaligned shaft."
- Apparently, whether your transmission should be in or out of gear
when sailing is specific to each type of transmission; see the
manual for yours. The important factor: do the bearings
get oil (or maybe, does the oil get cooled)
when engine is off ? In general: if cone-clutch, can let propeller
free-wheel; if hydraulic, don't free-wheel. [But my Borg-Warner hydraulic says
okay to free-wheel for 8 hours at reasonable speed.]
Free-wheeling gives less drag, but increased wear on cutless bearing.
- If you have a 2-blade propeller, put paint marks on
the shaft so you can align the blades with the keel while sailing.
From Foley Tech Tip 27:
Extend life of transmission by:
- Using an oil cooler (especially if transmission is used
near upper limit of its capacity or in heavy duty).
- Using proper fluid.
- Having a good damper plate.
- Using a flex coupling (reduces vibration and noise,
acts as sacrificial link if prop hits something,
and prevents electrolysis).
From Tony Ardito on the Morgan mailing list:
I have a 25 hp Volvo MD2B. Last year my transmission stopped going forward
(reverse still worked). I drained the engine oil, and disconnected the
transmission from the shaft and the engine. It consisted of removing 8
bolts. The only difficult part was hanging upside down while doing it. I
took the transmission in to be examined and was quoted $1000 for parts and
about the same for labor. Needless to say, I wasn't pleased. At that
price, against the mechanic's warning, I decided to attempt the repair
myself. I ordered a tech manual and began disassembling. Inspection of the
forward gear revealed a torn asbestos friction ring (similar to a brake pad
on a car). When I went to a local shop to order the part I was told I had
to order the entire gear for $600. I have a Swedish friend who contacted
a Volvo factory in Sweden for me. I got the friction pad for about $15
(and a few beers). I glued it in as the factory suggested and reassembled
the gear. Including new gaskets and the tech manual the whole deal cost
less than $50. Nothing I encountered while disassembling the
gear was very difficult. I just took my time and as an added precaution I
took pictures during different stages and marked each part and EXACTLY where
it came from.
Things may or may not go as easily for someone else but it may be worth
investigating before you hand over a few grand. And as an added benefit I can
now repair one more piece of equipment at sea if I need to.
From Ed Kelly on The Live-Aboard List:
I am not sure which transmission I have,
but know it is a Hurth unit. Maybe the 50 or 100.
We had been having intermittent failures to shift into forward.
Reverse was fine. Linkages were not the problem. It would seem
to slip when in forward. We finally figured maybe our plates had
been glazed and maybe in the past the boat was sailed without
being shifted out of forward gear into reverse. That is said to be a
cause of the problem that damages transmissions in some cases.
Anyway, we have no shops in Central Iowa to address the issue and
had our clutch on the transmission going bad, maybe because
of it being glazed. A friend on my dock found an article that
helped us troubleshoot the problem though. We found a
possible temporary cure to get a little more life out of the transmission.
We emptied the fluid and filled it with 9 oz of Mineral Spirits.
We then ran at idle and shifted between neutral and forward
80 some times, which cleaned the unit somehow. Then we changed
fluid and ran it and changed fluid and ran it (repeating this procedure
a total of 5 times to get all the mineral fluid gone). Now it runs and
will go into gear better than it has during our time with the boat.
We intend to get a rebuild kit and try to further address the problems
as we may be on borrowed time. The article we read said
it worked for the writer as well, but that Universal did not endorse it.
From Hugh Brock on BoatDiesel forum:
Re: leaking transmission:
Make sure the propeller shaft is properly
aligned with the engine. A shaft out of alignment will sometimes cause the seal to leak. Run your
hand under the transmission. Sometimes oil leaking from the front seal will run under the unit and
drip off the housing that holds the rear seal. Also have an oil analysis done. One of the first
signs of a gear going bad is leaky oil seals. The unit starts leaking internally and not as much
of the oil being circulated by the pump goes to the cooler. This causes the temperature of the oil
to increase which is hard on seals.
In 12/2004, we took out the Borg-Warner transmission from the trawler "Union Jack" in Miami harbor,
while it was at anchor, had it repaired, and put it back in. Some lessons learned:
- It can be done: you don't need to hire a mechanic, be at a dock or a boatyard,
have a crane, etc.
- Having 4 or 5 people was really nice: when someone got tired or wanted a break,
there was a fresh person ready to pitch in. When we lacked a tool,
it was available from someone else's boat. Although one strong person could have
lifted the transmission, having 3 or 4 to help made it a lot easier and safer.
- There's no magic to getting the transmission out and back in:
unbolt it from both ends and slide it back off the engine. It just slide-mates
to the engine; no real force needed to get it off or back on.
- Good access makes everything easier; this boat had great access through the cabin floor.
- Everything is easier if you don't have to disturb the engine mounts;
this boat had the engine supporting the transmission, not vice-versa.
- The repair was done by a mechanic in a shop; know what your limits are. Cost
$120 or so to have front and rear seals replaced, I think.
- Taking the transmission to the mechanic, instead of taking mechanic to the boat, or taking
the boat into a boatyard, made everything far faster and cheaper.
- Found out later: the seals had been damaged because a failed heat-exchanger had
let saltwater into the transmission fluid. The heat-exchanger and fluids were
replaced, but the damage had been done and was not discovered until later.
Also, the first symptom was complete lack of power transmission (no forward or reverse) because
all the fluid had leaked out; refilling with fluid fixed the problem long
enough to get back to safety.
From Joey Sowell on SailNet's Gulfstar mailing list:
We started by placing a cradle made from 4 X 6's under the engine. We
placed two six-inch hydraulic jacks between the cradle and a supporting 2 X
6 that supported the engine and allowed us to jack it and the transmission
up evenly. Next we fashioned a sling out of webbing for the prop shaft,
secured it to the bulkhead using screws, and disconnected the four bolts
coupling it to the transmission. The sling allowed the prop shaft to slide
back out of the way and provide good support for it while we were removing
and installing the transmission. We then removed the rear support bolts,
loosened the front support bolts, and jacked the engine and transmission up
just enough to remove the alignment shims, which we labeled as left and right
and in the order that they were removed. Next we placed a 2 X 12 under the
transmission and rear support and removed the bolts holding the transmission
and rear support bracket to the engine. Once freed from the engine, we
removed the transmission from the rear support bracket and set the support
bracket aside. The 2 X 12 gave us an area to support the transmission while
we were working and made it relatively easy to slide the transmission to the
side and onto a ramp that we fashioned out of the remainder of the 2 X 12 to
slide the transmission into the cabin. We strapped the transmission to a 2
X 6 and from there it was easier for two people to pick it up and remove it
from the boat for a rebuild. We pretty much reversed the procedure to put
it back in.
My experience 1/2009:
I have a 1973 Gulfstar 44 motor-sailer with a Perkins 6.354 engine
and Borg-Warner Velvet Drive 72C (or 72CR ?) transmission with
2.1:1 reduction gear. Everything is 36 years old; original equipment.
For a while, the transmission had been "creeping" forward while in neutral:
the drive shaft would turn slowly even if the transmission was in neutral,
with the engine running.
One day, I motored for a couple of hours, maybe not getting quite as much
forward motion as the engine RPM warranted, then the engine started choking.
I thought I was low on fuel and maybe gunk from the bottom of the tank had
clogged filters. Sailed back to harbor, added fuel, motored for 2 minutes,
not getting as much speed as I should have,
and then engine stopped suddenly. Sailed to anchorage. Found transmission fluid
is at "L"; should be above "F"; added about a pint of fluid. Changed fuel filters,
ran engine for 5 minutes. Then put the transmission into forward gear,
and the engine stopped immediately. Nothing caught in prop, prop won't
freewheel as it usually does with engine off or with transmission in neutral.
Can rotate drive shaft only a few degrees back and forth before it stops with
a "chunk" heard somewhere in the transmission area.
Transmission is seized.
So, I'll have to take the transmission out and have it rebuilt.
A big complication of the transmission job:
the rear engine-mounts are bolted to the transmission, not
the engine block. So I'm going to have to devise a support for
the rear end of the 1300-pound engine before removing the
transmission. Ugly. I could wedge a bunch of wood under there,
but if the engine settles down at all, it would be a chore to get it up again.
So I guess buying or borrowing a scissors-jack or bottle-jack might be the way to go.
I assume the bottom of the bilge can take the weight, with some added wood down
there to spread the load. I might have to sculpt a piece of wood to fit up under
the bottom of the flywheel bell-housing, so the jack can't slip sideways while the
engine is jacked up. And more wood on the sides to keep the engine in place
when the boat rolls (I'm at anchor), while the rear mounts and transmission are out.
And once I have the engine supported and the transmission out, I
might as well replace the rear engine mounts; they're 36 years old and have needed
replacement for a while, I'm sure.
If I replace the rear mounts, and have a jack available anyway,
then after putting the rear mounts and transmission in, I might as well
replace the forward engine mounts too.
Probably should take the opportunity to have a transmission fluid temperature gauge installed.
Service manual says transmission plus reduction gear weighs 153 pounds.
So, now you see why a serious transmission problem has been one of my
recurring nightmares. I won't mention the others, lest that cause one of them.
Strange: fluid on transmission dipstick looks fine; transmission fluid in
oil-cooler looks dark and smells burnt. And when I took the reduction gear off,
lots of burnt dark fluid poured out. So the dipstick was lying to me; maybe
the fluid pump failed or a filter-screen clogged.
I took the reduction gear off first. I was surprised to find a gear,
instead of a splined shaft, sticking out from the rear of the transmission.
And the big gear and gaskets in the forward end of the reduction gear are
just sitting loose, not held in, so you have to be careful not to dump
them into the bilge.
Made a big stack of 2x4's and 2x6's, fitting them into the bilge,
making them wrap in a U-shape around a small bottle-jack.
Then jacked up the engine and transmission, slid a couple more
boards in, and eased the jack. Now the boards are taking all of
the weight. Wedged a couple more boards down the sides of the
engine blocks, to keep it from moving in this rolly harbor.
Got the tranmission out (had to pound a screwdriver into joint between
flywheel bell housing and transmission to force the joint open).
With help of a friend, got it into the dinghy
and ashore to a repair shop.
Told the repair guy about the "shaft turning slowly even
in neutral", which Nigel Calder explains as worn clutch plates, but the guy said "ahh,
they all do that". That wasn't my experience; my transmission started doing that only
a few months ago.
I explained about the good fluid on the dipstick but the burnt
fluid inside, and how the drain-plug is inaccessible. He asked when the
transmission was last serviced, and when I said maybe never (36 years),
he was amazed, and said they're supposed to be serviced every 4 years (not likely).
I asked him about installing a temperature or pressure sensor, and he says
they're both a waste of money. His shop used to sell them, and stopped doing it.
By the time you see that something is wrong, it's too late. Not sure I agree
about a temperature sensor, but I decided to skip it.
Noticed that Nigel Calder's book says nothing about how to tell if/when engine mounts
The shop did the actual rebuild in about 2 days flat; they're experts, have done
a zillion of them, and have all of the parts on hand.
Got the transmission back to the boat, and then lifted it really stupidly and
hurt my back. That set me back a week or two. Had trouble getting the big gasket
between transmission and reduction gear seated right, and damaged it; had to
get a new gasket. Eventually got it right.
Replaced all of the engine mounts while I was at it. One of the bolts sheared off,
or already was sheared off, inside the stringer. So I had to fill the hole and
replace it with a lag-screw.
I cheated quite a bit on the engine alignment: I left the drive-saver
on. I started by getting the engine mount adjustments to about where
they had started, then used a feeler gauge between drive-saver and aft
coupling. Got it good, rotated the two halves together, checked again,
unbolted them and rotated them relative to each other, bolted them
together, adjusted again. Got it good, motored for a few minutes,
checked again. Motored for half an hour, checked again. Everything looked good.
[And a friend of mine has done a lot of alignments in a boatyard, and said this:
Alignment not too critical on a sailboat, where prop turns at 1000 RPM or less,
as compared to a speedboat turning prop at high RPM.]
[Also, my sailboat has a long run of shaft, 3-4 feet, from coupling to stern tube.
So I figured it's kind of self-aligning anyway. That is, it's hard to get the
alignment so wrong that the angle of shaft through stern tube is very wrong.]
A great feeling when I could run the engine again, and the rebuilt transmission
worked fine ! But it will take a while to rebuild my confidence in it; I keep
checking fluid levels and checking for leaks, and I'm anxious while motoring.
But that will fade.
Bought a handheld IR thermometer, and have started taking termperature readings
of various parts of the engine and transmission while motoring.
The whole transmission-and-mounts process took almost 2 months. I didn't hurry,
every trip to a hardware store took an hour of bus-riding,
I was doing it an anchor in a rolly harbor, I did it almost all entirely by myself, and I hurt my back.
The rebuild and new fluid cost about $1080, and the four new engine mounts
From Steve Painter:
I have a Gulfstar 44 motorsailer, a 1974 sloop "Godspeed".
Last June  about 3 hours out from where I dock the boat I went to the engine room
to check things and found lots of smoke. To make a long story short, my shifting cable
shroud had eroded allowing the inner cable to push through, thus not putting the transmission
all the way in gear. This caused the clutches to burn up.
After checking around I found that�a rebuilt Borg Warner transmission would be
around $5000 so I did the rebuild myself. I was able to do this for about $1000,
but that included a new oil pump and the casing it mounts to which I probably could
have done without ($250 to $300).
The gear reduction section section of the transmission is mounted at the back and
can be removed separately; it will drop the weight about 40 pounds. I built a lifting
frame above the aft engine to hold it up when transmission is removed;
the aft engine mounts are attached to the transmission. I built the frame out of
2 by 4's screwed together in T fashion for two-directional strength.
You probably want to brace this against the forward bulkhead so it can't fall over.
To lift the trans I wrapped it with 3/8 chain and bolted it back to itself, then I
wrapped the chain around a 2 by 4 so the transmission could be lifted by 2 people.
I recommend the 2 by 4 have a small notch in the center to keep the chain from sliding.
I had a Borg Warner manual onboard which did an ok job talking me through the rebuild.
Transmission fluid that has a burnt smell and shows shiny glitter-like flakes under strong light:
clutch plates or drive cone are slipping.
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