Put on your thinking caps. Oil leaking

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MG2936

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I bought my 1970 M35 in 2002 with 29000 on the speedo.
In 2006 I replalced rear main oil seal at 36000 miles.
In 2017 it went from leaking a few drops to a major leak in one day, I couldn't beleive it, when I stopped the engine it drained out of the bell housing vent in a stream, not drops.
So in 2017 I replaced the rear main oil seal at 49000 miles... I then took the truck for a 50 mile ride on the X way at 55mph. When I pulled in my drive and shut off the engine oil poured out the bellhousing vent in a stream. (about a cup of oil) Being tired of the whole thing I said to heck with it and drove it a couple of years that way. You didn't have to worry about the bottom of the truck rusting. Tired of the mess, in 2019 I again replaced the rear main oil seal at 50000 miles. This time I put a speedy sleave on the crank sealing surface where the oil seal contacts it. I rubbed my hands with glee, I thought I had that sucker fixed. I took the 50 mile test drive and it leaked as bad as ever. Through all these prloblems the clutch has never slipped, the engine starts good and runs as strong as the day I bought it. I have checked for excessive pressure in the crankcase and at 55mph the gage read 0 pressure and a good oil seal should withstand up to 10psi. I drove it very little in the last couple of years because I don't trust it. Does anyone have any ideas on what the heck is going on with this engine?
PS I also checked the oil drain back hole which drains excessive oil that has collected in the seal housing to the crankcase and it was clear.
 

davidb56

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2 things.check the crank horizontal end play and make sure the lip of the seal is riding on a good surface. Then there is a problem I just encountered with a 460 Ford I rebuilt last month. The rear main seal (felpro) was manufactured .060 oversized and even being clocked 3/8 inch, poured oil out. I ordered a new one (felpro again) but it was a different color and was .018 oversize, which is the correct "crush" when installed and "clocked. So check your seal and dont assume its correct. I would have never known about the .060 oversize until I read different Ford building forums that had the same problem. I reread your first post and see you installed a speedy sleeve.....I would definitely mic everything when you do it again. As others have stated, at least check the trans oil level too.
 
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rustystud

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Did you ever check the cam plug ? It can rot out and then start to leak. Also there are several NPT plugs back there that could possibly be the culprit.
Could it be your transmission oil leaking ? The rear oil seal is not the only thing keeping back oil.
 

gimpyrobb

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Are you sure its motor oil?

Many of us have had the trans puke oil out the input shaft.
 

glcaines

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I had a rear crankshaft seal leak on another vehicle. After replacing the seal with a new one (Chinese), the leak was much worse. I replaced the seal again with an American made seal and no more leaks. Make sure you have a good quality seal, if the leak is indeed from the rear seal.
 

MG2936

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I'm 83 and in no hurry to tear it down again but I will ck the crank end play if I do. I always ck the oil seal size because people do make mistakes. Rustystud, Cam plug was not leaking. Even if an oil passage plug was leaking, how could the oil get into the bell housing? This is not a tranny oil leak, I use 80w90 and it has its own smell which is bad. doghead, no fuel contamination in motoroil.AjaxMD, your thoughts got me thinking, If I lost a cup of oil in 50 miles I woulld have been down 5 qts. the last 2 years I drove it.(1000miles) It didn't come close to being that low, maybe a qt. or two. I am at a loss to where it is leaking but its sure a mess and there is way too much motor oil getting into the clutch housing. When I did the oil seal jobs I simply washed the clutch disc with break cleaner and put it back together. It has been a very forgiving clutch but I feel that my days are numbered, some day it is going to start slipping.

e.
 

cattlerepairman

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Just from reading this, two things stand out:

- the leak occurred repeatedly, despite taking steps to "do the job right" (good seal, ensuring size and fit, speedy sleeve to be sure)
- the indicated loss of crankcase oil on the dipstick does not seem to match the observed volume of continuous oil loss from the leaky seal

Oil that is mixed with diesel fuel has low viscosity and seals start to leak when this occurs. I understand that MG2936 says "no fuel contamination in motoroil" but unless the Deuce is refilling its crankcase with fresh motor oil when no one is looking, the discrepancy between drop in oil level and observed oil loss may be a strong reason to take a sample and send it off for an oil test!

Of course, it could just be yet another damaged/cheap/wrong seal.....what are the odds?
 

rustystud

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. Rustystud, Cam plug was not leaking. Even if an oil passage plug was leaking, how could the oil get into the bell housing?
.
The oil passages in the block are drilled from the front to the back of the block. They where drilled out when the block was first made. The manufactures just use NPT plugs to seal off the passages. Some are used for pressure gauges and other things like Turbo oil feeds.
 

MG2936

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The oil passages in the block are drilled from the front to the back of the block. They where drilled out when the block was first made. The manufactures just use NPT plugs to seal off the passages. Some are used for pressure gauges and other things like Turbo oil feeds.
Thanks guys for all the imput. I guess I'll just keep driving it untill the clutch starts slipping. Oil is cheap, its just the mess that bothers me.
 

WillWagner

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If it were mine and it had been done multiple times, I would check for a blocked blow-by tube. The valve cover to tube is a cork gasket, IF someone sealed it with silicone or the cork expanded, there would be no place for the pressure to go and would find the easiest way out, in your case, the rear main. Pull the goodie off of the valve cover, look at the gasket and hose to make sure it isn't blocked/collapsed and pull the tube to make sure no wasps or other critters have at one time or another, made a home in it.

Also could be that there is too much CC pressure, but simple things first and check the exit for crankcase gasses.
 

rustystud

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If it were mine and it had been done multiple times, I would check for a blocked blow-by tube. The valve cover to tube is a cork gasket, IF someone sealed it with silicone or the cork expanded, there would be no place for the pressure to go and would find the easiest way out, in your case, the rear main. Pull the goodie off of the valve cover, look at the gasket and hose to make sure it isn't blocked/collapsed and pull the tube to make sure no wasps or other critters have at one time or another, made a home in it.

Also could be that there is too much CC pressure, but simple things first and check the exit for crankcase gasses.
Good call ! Totally forgot about crank-case pressure.
 

CMPPhil

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Another odd possible cause

Hi Will

Good question / possible solution with the crankcase preasure idea.

Another possible cause (had this with another MV not M35) dipstick wrong so that an extra 1 to 1.5 quarts of oil. The truck in question would always leak after oil change when the truck was filled to the full line. One the oil level dropped to the middle of the safe zone it would go the next 1000 miles without leaking or needing oil.

Cheers Phil
 

MG2936

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Lapeer, Michigan
Another odd possible cause

Hi Will

Good question / possible solution with the crankcase preasure idea.

Another possible cause (had this with another MV not M35) dipstick wrong so that an extra 1 to 1.5 quarts of oil. The truck in question would always leak after oil change when the truck was filled to the full line. One the oil level dropped to the middle of the safe zone it would go the next 1000 miles without leaking or needing oil.

Cheers Phil
been there. On the last seal job I changed the oil and left it 2 qts. low just in case. No differances. I'm starting to think improper oil seal. Talking with the SKF people. Let you know when I hear from them.
Robert
 

texas30cal

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My money is on fuel in the oil, when I got my truck and drove home 100 miles and shut it off it dumped a large amount of oil out of the bell housing hole upon shutdown. Being a long time gas engine mechanic I immediately thought the rear main seal was the culprit. A few days later I changed the oil/filters and it stopped leaking. After driving daily for a few weeks I noticed it was leaking bad again but the oil level in the crankcase had not dropped accordingly. I changed the HH o rings, eliminated the flame heater and re sealed the boost pump, now 2 + years later and I have zero issues with leaking or making oil .
 

davidb56

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everything on my truck that holds oil leaks. Engine, transmission, transfer case, differentials....all seal leaks. The FP also weeps a little diesel under it too. Not bad, but I don't have to worry about rust under it. I run the truck with a load in it on fire roads, so it works pretty hard. It doesn't see much asphalt at all. If it isn't pouring out, I'd leave it alone until it does.
 

MG2936

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Lapeer, Michigan
My money is on fuel in the oil, when I got my truck and drove home 100 miles and shut it off it dumped a large amount of oil out of the bell housing hole upon shutdown. Being a long time gas engine mechanic I immediately thought the rear main seal was the culprit. A few days later I changed the oil/filters and it stopped leaking. After driving daily for a few weeks I noticed it was leaking bad again but the oil level in the crankcase had not dropped accordingly. I changed the HH o rings, eliminated the flame heater and re sealed the boost pump, now 2 + years later and I have zero issues with leaking or making oil .
I got rid of the flame heater 18 years ago. I have the truck torn down again. I suspect bad seal. I am replacling it with a seal GM used on their 10.4 liter turbo diesels. It will withstand higher internal pressures plus will withstalnd twice the heat of a standard nitrile seal.
 

rustystud

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I got rid of the flame heater 18 years ago. I have the truck torn down again. I suspect bad seal. I am replacling it with a seal GM used on their 10.4 liter turbo diesels. It will withstand higher internal pressures plus will withstalnd twice the heat of a standard nitrile seal.
Do you have a part number for this new seal ?
I will be replacing mine this up-coming summer.
 

MG2936

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Lapeer, Michigan
Do you have a part number for this new seal ?
I will be replacing mine this up-coming summer.
SKF 49927 There is much information on it on the SKF web site. A standard Nitrile seal is good for a temp of 250 degrees, the seal temp will run 30 degrees hotter then the engine temp because of friction. If your deuce is running 200 on a hot day, you are pushing the seal close to the max. The 49927 seal is good for 400 degrees. It is also twice the cost of a standard M35 seal.
 
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