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Author Topic: Extreme Transmission Leak  (Read 8889 times)
bcaddel
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« on: November 28, 2008, 07:07:54 AM »

We purchased a mc7 in Texas last september from my parents. It had not been driven for almost 4 years when be brought it to Reno, Nv. We have put over 3,000 miles on it in the last 3 months with no problems. We headed to Elko Wednesday night for Turkey Day and after about 100 miles the transmission started shifting hard and the bus actually started slowing down. I stopped to check things out and noticed a layer of fluid on the toad. When I checked the transmission fluid it didnt register so I went and got some and put it in (Dextron III). After about 50 miles the same thing, I checked it and it didn't register on the stick again. I drove the next 200 miles stopping every 40 miles and adding a gallon of fluid. The transmission is a Allisno MT 654.

It appears to be leaking from the gaskets at the end of the transmission just before the output housing. I was aware that with it sitting for several years and I might have some gaskets or seals leaking but a gallon every 45 minutes is that possible from a gasket leak. When I look underneath with the engine idling it drips from these two gaskets but not at that rate, I guess it could be under pressure at highway speed and squirt out. I am hoping its something I could possibly fix but I dont think I would  attempt to take the transmission apart to replace the gaskets.

There is a Smith Detroit-Allison shop here in Elko but I dont see any low price guarentee in their ad in the phone book so I am guessing it will be big bucks to have them turn a wrence.

Any thoughts or ideas? Maybe a magic stop leak? Would appreciate any suggestions or advice
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
makemineatwostroke
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« Reply #1 on: November 28, 2008, 07:17:08 AM »

bcaddel, wash the trany good, more than likely it has blown a o-ring where the cooler fitting attach to the transmission or a hose 
have a great day
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bcaddel
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« Reply #2 on: November 28, 2008, 08:02:27 AM »

Thanks for the suggestion, you suggestions sounded really promising but both the hoses are nice and dry. One on the side and one on the top. I did find some antifreeze on the top of the transmission from a hose passing over it, so I guess that will be another project for a later day.

Is there any change some transmission stop leak would do anything? I can see a light flow of transmission fluid coming from where the gasket sticks out. I tried tightening the bolts but they are all pretty tight. It just seems like too much fluid for a gasket that is in place and not missing any material..
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
makemineatwostroke
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« Reply #3 on: November 28, 2008, 08:12:18 AM »

bcaddel ; check the fitting where the hoses fitting connect to the transmission they have a o-ring with a lock nut, I don't think it is leaking from the gasket or you would have a puddle every time you stop, it is your trany but me I would not use a sealer in the Allison,are you having any problems with 1st gear I ask because the 1st gear clutch pack is behind that cover and when they go it will put more pressure in that part of the transmission     have a great day
« Last Edit: November 28, 2008, 08:29:18 AM by makemineatwostroke » Logged
busshawg
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« Reply #4 on: November 28, 2008, 08:17:10 AM »

I wouldn't use a sealer either, sound like your leak is quite bad and the chances of a additive working would be slim to none with my experience anyway. You'll end up having to fix it in the end anyway.

Good Luck

Have fun!
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Have Fun!!
Grant
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« Reply #5 on: November 28, 2008, 08:34:11 AM »

Check to see if your transmission has a vent breather on top of it.
It might look like the same kind you would find on a drive axle.
Make  sure it's clean and not clogged - IF your trans has one.
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luvrbus
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« Reply #6 on: November 28, 2008, 08:43:00 AM »

Bcaddel, a word of advice for you let Smith check and tell you the trouble but if they want to pull the transmission and repair it you will be looking at around 10 grand from them.If you need a rebuild buy one from  www.utexchange.com for around 3 grand been there done that with Smith and you can change it yourself in 1 day with a transmission jack.      Good luck
« Last Edit: November 28, 2008, 08:44:35 AM by luvrbus » Logged
makemineatwostroke
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« Reply #7 on: November 28, 2008, 08:57:00 AM »

bcadell, they do have a vent up by the torque converter housing it will have test ports at the rear check for any missing plugs and check the governor plate at the rear for leaking and spray. have a great day( if you can)
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bcaddel
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« Reply #8 on: November 28, 2008, 09:26:32 AM »

It looks like the breather tube is actually gone. We are going to head into town and try to get one. It may be plugged up and that could be what caused the leak from the gasket. I dont hold out much hope for a fix but it may slow it down on the trip home The Smith detroit allison shop said they would have to order parts and it would be a week, so we will try and do what we can and limp home. Hopefully we can purchase 4 or 5 gallons of fluid in gallon containers so it isnt such a pain stopping every 45 minutes. Really hopefully the breather tube releives the pressure and the leak decreases drastically.

Thanks So Much For all the suggestions, I will check back in a couple of hours when we get back from hunting for a breather tube.
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
Utahclaimjumper
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« Reply #9 on: November 28, 2008, 10:17:31 AM »

All threaded openings on the trans are standard so it should not be hard to make a tube and route it high and down.>>>Dan
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Utahclaimjumper 
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circusboy90210
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« Reply #10 on: November 28, 2008, 12:24:33 PM »

main culprit main seals first front then rear
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bcaddel
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« Reply #11 on: November 29, 2008, 04:56:02 PM »

Thanks for all the suggestions, I had some hope the breather tube missing might have caused the vent to be blocked building up pressure and causing the gasket to leak. No such luck though. We got the breather tube replaced and drove back to Reno this afternoon (300 miles) and it took 5 gallons of transmission fluid to make the trip.

This leak happened so suddenly, it just seems like something is causing preassure to build up and forcing the fluid past the gasket. I think I will try to search the internet for any clues before I take it to the Allison shop as I know that will cost a bundle. We have only had the bus a few months and just love taking trips in it as it really does great on the road. We just got the jake brakes put on a couple weeks ago and installed a tach this week-end so once we get this issue resolved with the transmission leak we will hopefully be able to take off for a short trip and test it out. Thats assuming diesel keeps going down, I probably won't be able to afford to go very far at all after the transmission dudes get done with me.

Does anyone think there is much of a possibility its just a dried out gasket (it set for 4 years until last Sept) and replacing the gasket will resolve the issue or is the general thought there is pressure building up forcing the fluid out and another gasket would just start leaking after a few miles? There is no oil leaking from the front or rear seal or the cooling hoses just the bottom of the rear gasket....
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
JohnEd
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« Reply #12 on: November 29, 2008, 05:36:03 PM »

bcad,

By all means change out that gasket.  You are getting close to taking her in and then "taking it".  I heard advice to get a rebuilt for 3 grand and doing it yourself in a day or two with a rented trans jack.  That would be my "Worst Case" and I would do a lot of work replacing minor stuff, hunting and pecking and disassembling things before I took the plunge.  I still think that Alison/Detroit shop would be your best bet for a diagnosis only effort.  If they say it must be rebuilt then change it out yourself after you limp home and get access to some help.  Possibly a fellow Knut or two. Smiley

God knows I have only seen pics of an Alison Tx so take this for what it might be worth.  Doesn't the 4 speed auto take the same 40 wt oil as the engine?  I know I have seen that said about some trans and it stuck in my mind....or what passes for what is left of it. Tongue

Good luck Buddy and I agree that this is a strange problem.  I thought one of the most telling observations was that the thing works normally in all regards except leaking.  Doesn't sound to me like a candidate for a replacement unless the case is cracked. Shocked

john

I may not be an expert but I can tell you this:  DO NOT USE THAT TRANNY STOPLEAK.  That WILL result in a worst case.  Don't ever put anything in there but the recommended fluid.  Don't ask me how I know this or why this is such a SORE SUBJECT....spoken through clenched teeth. Grin

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makemineatwostroke
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« Reply #13 on: November 29, 2008, 06:14:59 PM »

bcaddel;can you tell us when the last time the transmission was serviced that is unusual that gasket leaking and not the output shaft seal.If the bus set for 4 years the rear clutch pack could be deteriorating the dexron III is not good for the older clutch pack materail   

JohnEd; you can use C4 15/40 in the transmission but I never heard of or knew anybody using straight 40W
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bcaddel
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« Reply #14 on: November 29, 2008, 06:39:48 PM »

I dont know when (or if) the transmission was last serviced. My Dad kept pretty good records and I have most of them. I dont see see anything about a transmission service. I do know he purchased the MT654 Allison transmission from Arizona Transmission and Engine Exchange on 8/28/1998 for $9,754. About a year later he then had a Hub Odometer installed when he had the 8v-71 rebuilt by Stewart & Stevenson Power on 5/21/1999 for $9,169.38. I only mention the pricing because it indicated to me they appear to be quality products.

The hub meter now reads 11,771 so my assumption is the transmission has about 12,000 miles on it (3,000 since Sept when we purchased). My dad has lost much of his memory for these type of details (haven't we all) and since there isnt any receipt in the paperwork I assume it has not been serviced since it was rebuilt. I read somewhere they need to be serviced at 5,000 after rebuild so having 8,000 when I purchased it makes me think he may have overlooked having it serviced. Do you think that could be the culprit?

The transmission preforms execellant until it gets about 6 quarts low (that happened on the trip to elko last Wednesday night) and we noticed a loss of power. We pulled over and thats when we discovered the loss of fluid. Everytime we fill it up it works great and then in about 50 to 70 miles I check it again and it will be 4 to 5 quarts low and I fill it up again. Makes for a real messy toad...
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Bob Caddel, Las Vegas Nevada
1971 MC7, 8V71, Allison MT654
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