Boat Engine Transmission

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.

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.

Removing transmission:

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.

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 need replacement.

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 cost $300.

I have a Gulfstar 44 motorsailer, a 1974 sloop "Godspeed".

Last June [2008] 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.