Rebuilding Allison M-20 transmissions

[TJones]

Have a 74 53'Hatteras MY,when checking transmissions this fall discovered small shavings in one and bearing parts in the other as well as black burned smelling oil in both transmissions. Its my understanding the black oil indicates rear seals on engines are probably bad, I have been re-habing the boat over the last 2 years and unsure of tranny history. Williams Detroit Deisel has quoted me a price of $10,000 to remove and re-install. They ship to Louisianna for re-building - estimate $3,000 per tranny if no gears are involved.One repair shop suggested I replace transmissions with twin disks - rough estimate of $6,000 per tranny. Looking for your expericences with this situation.

 

[Genesis]

I think this one is easy.

$6,000 per gear .vs. $10,000 for both IF there is no gear damage? I'd spend the other $2k and have new gears. No contest. Among other things, if you have bearing carriers coming apart - and it sounds like you do - its a near certainty that the pumps are toast as well as the gears, so add a vickers pump overhaul into the price - which they didn't quote.

Or was that $10k for the R&R plus another $3k per for the overhauls? If the latter then its no contest - toss the Allisons.

I like Allisons on principle, but (1) they're heavy beasts, and (2) parts will get harder and harder to get over time. The overhaul price is roughly correct - there's exactly one source for parts now, and they're in LA. That's where you want to send them to be overhauled, but as you discovered, its going to be stupid expensive to have done.

 

[TJones]

$10,000 is for removing and installation only, which includes new rear mains and checking oil cooler located in engine heat exchanger. Estimating $3,000 per transmission to re-build. Total: $16,000

New twin disk are $12,000 plus the removal and installation cost of $10,000. Total: $22,000.

 

[Capten]

OUCH! Now I'm really nervous that mine might go up and need attention.

Will the $16K include freight to and from LA? Might the TwinDisc guys get competive on the R&R charges in order to move some product?

 

[Liquid Asset]

WOW! that is really outrageous. I think that you can find an independant mechanic/yard to pull them for less and send them to Louisiana to be reuilt and spend less money. I think some of these big outfits like Williams charge way to much money for this stuff.

If it was my boat, I would get some other opinions from some local shops/mechanics. I would definetly concider relaceing the gears too, especially if they are that expensive to repair.

Look at it this way, what if you spend all that money to rebuild and then you have a failure in a part that was not replaced and is not covered by the waranty. You will then have to go thru this again. If you purchase new gears, you will have complete waranty for the entire gear and will have parts avaliable. Just my $.02

 

[Nonchalant1]

I wonder if the old Allisons are worth $1K or more each, as is, to help defray the cost of new ones? Lots of big, heavy, expensive parts in them. I'd think that the place in LA would certainly know and offer you something if they're worth something. I see M20's in Boats and Harbors occasionally.

Doug Shuman

 

[Genesis]

I'd find someone else to pull them.

The only real trick to getting them out is the WEIGHT.

The newer gears (e.g. TwinDiscs) are a LOT lighter than these beasts, and are nowhere near as nasty to reinstall.

One consideration - in most setups on Detroits the gear is the rear engine mount location! This can cause some problems as brackets may need to be fabricated ($$$) to mount the TwinDiscs - but $10k? That's outrageous.

I'd get another quote.

 

[Geoff58yf]

When we had our 58yf in Fla I had the stbd tranny rebuilt in the boat. They wanted an extra $2500 to remove the tranny (pulling up the salon etc). I knew there had to be an alternative and what we ended up doing is having the yard (allied) build and weld an "A" frame in the engine room and hallway to hoist the tranny away from the engine. Total time start to seatrial, 5 days. Total cost $7026.65. Its been perfect since.
geoff58yf

 

[MikeP]

Let me jump on my "do it yourself" soapbox (I keep that one at the very front of my soapbox colection).

It may be useful to understand that these transmissions are EXTREMELY basic automatic transmissions - dramatically less complicated than the simplest automotive tranny. Additionally, and what the tranny people don't want you to know is that rebuilding an automatic tranny is suprisingly easy. I still clearly remember the first automatic I rebuilt. After removing everything I actually looked into the case and said, "That's all there is?"

In those days the typical "fix your tranny" shop charged 350 bucks to overhaul it (which they didn't anyway). The parts to do so cost 36 bucks for a normal rebuild. If you were doing a rebuild/conversion for competition use, the parts were 56 bucks. Sure the prices have gone up since then but the percentage of parts to total charge hasn't. Throw in the "It's a boat so we can shaft 'em" surcharge and there you are with a $16,000 price quote.

On the day I opened my first automatic, I realized that the tranny overhaul business was one of the biggest money-makers in the industry. Now, after rebuilding automatics in everything from US Army Tanks to Toyota's to 18 wheelers to John Deere Combines I can guarantee that if you have the slightest mechanical inclination, you can rebuild that M-20. However just as in an automotive rebuild, the hardest part is removing the tranny. The rest is easy. As Genesis pointed out the issue is weight.

There is no way in Heck (or even in that other much warmer place) I would actually pay someone to rebuild one of these. In the 53MY there are hatches in the salon directly above the engine rooms. The engine and/or tranny can be pulled straight up into the salon. You could do this easily with a sturdy A-frame and a come-along. Once it is in the salon two or three guys could remove it from the boat. Or - and this is what I would do - you could overhaul the trannys in the salon. Set up a workbench and there you go. This may sound like a lot of trouble but it would cost you the price of the parts and whatever interior disruption that's it. Obviously you would need the Allison manual and tools that you probably already have. Pay attention to clearances and torque settings and that's it!

Again, if you do mechanical work at all, you can overhaul one of these trannys. Don't be intimidated by their size. As I found many years ago - there aint much in there!

 

[Genesis]

One thing to be aware of with the Allisons is that the bull gear nut torque spec is pretty insane. If I recall correctly (been a while since I looked at the manual) the spec is 300ft/lbs - THEN you index 90 degrees from there! Aieeeeeee!

But in general I agree - there just ain't much in these things. Its a handful of gears, bearing carriers and a couple of clutch packs with hydraulics to engage them. Really very simple.

The problem with the Allisons is that they're stupid heavy and damn messy to get out, because of the wet flywheel design. Plus the parts are SILLY expensive, because Arcadia owns all of them - Allisons are no longer made, and there's no aftermarket support other than the guys who bought all the stuff.

With that said Allisons are some of the simplest marine gears there are, and are a pretty good basic design. If you had a rear bearing failure (and it sounds like that's what's going on) check your shaft alignment CAREFULLY - I bet you find it to be significantly out. That places nasty loads on the bearings and causes them to take a dump.

BTW, the rear main seal for a Detroit is about $20. The rest of the charge for replacement is for the labor to get to it......

 

[REBrueckner]

I know a 58 YF owner who bought working Allisons about four years ago to keep at home as spares. A few thousand bucks. I like nonchalant's suggestion about Boats and Harbors: I'm pretty sure each time I see a copy I have noted Allisons for sale in there. I would contact commercial advertisers there and pretty soon you'll have identified a source.
From what I've heard, rebuilding them in your salon is very feasible, but likely the real test is having the experience to find each point of failure and near failure to assure that when the unit is reassembled and reinstalled it stays put for another 20 or 25 years.

You can get to Boats and Harbors via:
http://www.boats-and-harbors.com/

Also, I had a minor rear main seal leak a few years ago...as noted it was due to shaft misalignment. I noticed a thin spray of oil on my engine room floor, just enough to feel it, no loss of oil was apparent from the tranny. Getting both issues fixed was under $2,000 during the winter in NY.

Good luck.

 

[SKYCHENEY]

I've got an M20 that turns in neutral and it appears to be a clutch not fully disengaging. I took apart the selector valve and that's not it. Anyway, I plan to have it fixed before spring, but I can tell you that I talked to a Williams mechanic and he said that he has taken M20s out of a 53 without pulling the hatches. He said that three guys carried it out from the ER, up the stairs and out the back door. Why would that be a $10,000 job? I could unbolt it and hire three kids off of the dock to do that for $100 each. I think I would call Arcadia direct first. Then get a quote for reman/exchange. Then you can decide if you need to hire someone to just pull the old ones and reinstall the rebuilds.

 

[Nonchalant1]

I've got an M20 that turns in neutral and it appears to be a clutch not fully disengaging. I took apart the selector valve and that's not it. Anyway, I plan to have it fixed before spring, but I can tell you that I talked to a Williams mechanic and he said that he has taken M20s out of a 53 without pulling the hatches. He said that three guys carried it out from the ER, up the stairs and out the back door. Why would that be a $10,000 job? I could unbolt it and hire three kids off of the dock to do that for $100 each. I think I would call Arcadia direct first. Then get a quote for reman/exchange. Then you can decide if you need to hire someone to just pull the old ones and reinstall the rebuilds.

Sky,

These M20s frequently turn slowly in neutral all the time. Mine do, but just sometimes. I have read here to not worry about it unless it's making the boat move. At 5 RPM, it ain't gonn'a do much. If you do find out and do something about it, I'm sure others would be interested. Maybe call Acadia?

Doug

 

[MikeP]

As Nonchalant suggests, if the tranny will actually move the boat in neutral - it's a problem. Otherwise...

The output shaft of most automatics (and manuals too) will turn in neutral if there is no restrictive load applied to the output shaft. If you disconnect the driveshaft from you car's transmission the same thing will happen. But you can hold the output shaft with your hand, and it will not. The M20s are just exhibiting the same behavior. Since they're bigger, they can turn a much heavier load than holding it with your hand. There isn't anything wrong with this.

Some trannys do it and some don't depending on the internal clutch pack/band clearances and the tightness of the various seals. This can change depending on temperature variation so you may see that sometimes they will turn in neutral and other times they won't.

Since the engine is running, the tranny's oil pump is supplying pressure so there no cause for concern that the unit is turning without lubrication. This IS a concern if you are moving through the water with one engine shut down. The movement through the water will cause the prop to turn which WILL damage the transmission unless the shaft is prevented from turning.

Again, it's quite normal for transmissions and I wouldn't worry about it at all.

 

[SKYCHENEY]

My stbd trans is no problem. I can stop the shaft with my hand. But the port is another matter. I have trouble anchoring as I will run over the chain before it is fully deployed. I have to be careful when docking since I can't even leave the helm to grab a spring line without the boat moving forward. I have handled her like this for the past two seasons and I'm getting a little sick of it. I found a service invoice from the previous owner from 2001 for this transmission. I think that the guy that worked on it forgot some of the springs that release the clutch. Either that or the plate is warped. I'll know after we get it apart and then I'll post it here just in case anyone else experiences similar symptoms.

 

[TJones]

Thanks to everybody for your responses.As suggested I will try Gregory's as well as several others for pricing. I have talked with a guy out of Toledo, owner of Burt's Transmissions who indicated he would do them in the boat but his total pricing wasn't much different. I probably should explore the twin disk option more fully.I will keep you posted - I'm hoping to do this in the next two weeks - thanks again!

 

[Eufaula]

- I'm hoping to do this in the next two weeks - thanks again!

Maybe the fast turn around would be core exchange with your allison M20. Try Boats and Harbor. Another one is not sure if this is correct (scrutonmarine.com). If you decide to open your own allison it should be in a clean emviroment and may need a hyd. press. James

 

[Genesis]

The problem with metal shaving contamination is that the pieces get into EVERYTHING, and if you don't get them ALL out they will eventually go mobile again and trash your rebuild.

It only takes one piece of a bearing fragment (high-grade hardened steel!) to rip up a new bearing race or cage, not to mention doing a real number on pressure plates and the vickers pump.

 

[SeaSwick]

I'm looking at a boat (Hargrave design Daytona 50) that has 8-71 Nats & M20 trannys. The starboard one is toast & needs replace/rebuild.

Do to parts avail, would swapping them out for another brand be a better solution? Besides the before mentioned rear engine mounts needed, is an exchange a "bolt in' proposition, or an expensive re-enginering? What alternative trans should I be looking at?

Thanks FVS.

 

[q240z]

A thread revived after seven years...that's gotta be a record.
It'll be interesting to hear from the regulars how things have changed since 2006 (or not). It might also be interesting to hear from the OP. How'd things turn out?

Cheers,
Q