rear main seal
New User
Joined: Oct 2002
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rear main seal
Ive got oil leaking out of my flywheel cover, Ive been told that means my rear main is bad. Is this true? And if so, is the seal in a 351m a two piece or a one piece? Im hoping to change it out without having to pull the engine or tranny. 
Senior User
Joined: Sep 2001
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From: USA
rear main seal
The rear main in the 351M is two pieces. I don't know if you can do it with the engine in the truck. I'm sure it can be done but it must be difficult. I've done two of them already but the engine was already out of the truck. (First one I did leaked like crazy). Good Luck.
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Joined: Aug 2002
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rear main seal
The rear main seal replacement in the truck is a piece of cake. I did it on my 400 a few months ago. While your in there be sure to replace your bearings and probably your timing chain. Best to do it now while everything is apart 
Depending on your suspension lift, if any, you will probably have to unbolt the motor mounts (one 3/4" nut on each side) and jack the engine up a bit inorder to get the pan off. Once the pan is off the rest is simple.
79 F250 Ranger Lariat 400 4wd C-6 3.55's
Depending on your suspension lift, if any, you will probably have to unbolt the motor mounts (one 3/4" nut on each side) and jack the engine up a bit inorder to get the pan off. Once the pan is off the rest is simple. 79 F250 Ranger Lariat 400 4wd C-6 3.55's
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Joined: Jul 2001
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From: Gainesville, FL
rear main seal
Hold on there Ranger!
Repairing a rear main and rebuilding your motor are two different things.
You'll have to drop the oil pan and rear cap of the crank.
If you've got poor oil pressure consider changing the oil pump.
Dropping the tranny is painful and destabilizes the motor during repair. If your careful and clean, you may very well be in and out without too much trouble.
A timing chain is on the other end of the motor and entails timing chain cover, distributor removal, etc.
If you need to fix your truck, then fix it, but don't break the bank over a rear main seal.
My Way is the Highway,
KingFisher
Repairing a rear main and rebuilding your motor are two different things.
You'll have to drop the oil pan and rear cap of the crank.
If you've got poor oil pressure consider changing the oil pump.
Dropping the tranny is painful and destabilizes the motor during repair. If your careful and clean, you may very well be in and out without too much trouble.
A timing chain is on the other end of the motor and entails timing chain cover, distributor removal, etc.
If you need to fix your truck, then fix it, but don't break the bank over a rear main seal.
My Way is the Highway,
KingFisher
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Posting Guru
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rear main seal
Hey King who's talking about rebuilding the whole engine? You have to remove the oil pan to get to the rear main seal, and remove the rear main cap to get the seal out. I never said anything about touching the tranny. IF you know anything about the 351m/400 bearings are in the copper at 75k causing low oil pressure. Pump may be ok, for $45 bucks who wouldn't change it?? The is pan is off. Anyhow the pan is off, which it would be to do the rear main why not save some money, do what is right and save your engine. Also by this time the factory timing chain is starting to get some pretty good strech! The dizzy doesn't have to be touched, take off the water pump, timing cover, balance, and tada your at the timing chain. It's a lot easier on the bank and your back if you do it while it's apart, NOT doing it over and over again.
Do it the right way, not while laying on the highway
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Joined: Oct 2002
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rear main seal
Ok, yes its true, Ive got dimming oil pressure. but I thought that meant the cam bearings are on their way out or the cam is flattening. You are stating, if I change the rear main seal and the oil pump, the pressure will show signs of life again?.. and I dont have to drop the tranny, just remove the oil pan and the rear main bearing cap to get to the rear main seal. The rest I understand about the timing chain, Ive done that on a different ford and dont expect any problems changing that out. 
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rear main seal
From all my experiences loss of oil pressure is from the main bearings starting to wear. If you change the rear main and pump you may get some pressure back, but not much. While you have the pan off pop a few caps and you'll see what I'm talking about. How many miles do you have on the engine? I had 74000 when I did my rear main, the bottom bearings looked decent, however the tops were all in copper mains and rods. I didn't have any rod slap, or bearing noise.... but take a look you'll be surprised.
You don't need to touch the tranny, just take off the oil pan. You will most likely have to raise the engine a bit to get the pan out from under the engine. You can try jacking up the truck letting the suspension fall getting some room between the front axle and the pan; but probably not enuf to get the pan out.
I see from your other posts your wanting to mod the engine, best to get the bottom end back up to snuff before putting too much money in it.
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Joined: Jul 2001
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From: Gainesville, FL
rear main seal
Greeny,
Swapping bearings without turning the crank is not a recommended procedure. It is a lesser evil than losing your bottom end due to low oil pressure.
Often enough, when swapping bearing without turning the crank, you'll be back to low oil pressure in a few months.
Secondly, doing a timing cahin and a rear seal are two different jobs and have no correlation to one another.
Removing the timing chain cover includes removing all the accessories which do not have to be removed to do the rear seal.
Thirdly, someone else said to remove the tranny, which is a waste of time and effort.
Keep it simple,
KingFisher
Swapping bearings without turning the crank is not a recommended procedure. It is a lesser evil than losing your bottom end due to low oil pressure.
Often enough, when swapping bearing without turning the crank, you'll be back to low oil pressure in a few months.
Secondly, doing a timing cahin and a rear seal are two different jobs and have no correlation to one another.
Removing the timing chain cover includes removing all the accessories which do not have to be removed to do the rear seal.
Thirdly, someone else said to remove the tranny, which is a waste of time and effort.
Keep it simple,
KingFisher
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rear main seal
Yes I completely agree removing the tranny is a complete waste of time. Bearings on the other hand are not. I read in one of your other posts you have 130k on the engine your gonna see copper. My dad did a bearing swap on his 351m in a 78 bronco back in 82 74k miles, didn't turn the crank. Ran great with 50 psi oil pressure until 1998 when the stock timing chain started skipping teeth 135k mi. Yes keep it simple, if you have to tear it apart do everything once, not again and again and again. It's a lot easier. All the parts you need will be under $175 from napa, thats rods+mains bearings, all the gaskets and seals, timing chain and oil pump. The only corrolation between timing chain and rear main is you have the pan off, simple as that. But then again who doesn't love taking out all those oil pan bolts
Elder User
Joined: Jan 2002
Posts: 525
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From: Mansfield, Texas
rear main seal
Not to throw coal in. But I replaced my main bearings ( which only cost about $10-20) when I was down there replacing my two piece seal. Even after three or four parts counter gentlemen told me it would be a waste of time. Had no oil pressure when she got warmed up. Now , with at least 4,000 good miles of mainly pulling a 20' boat around. she still stays up in the 20-25# range at an idle of about 625rpm. So, my two cents are if you're down there anyway. pull your caps and replace. It's not going to hurt anything in the long run.
Senior User
Joined: Nov 2002
Posts: 204
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From: Shirley USA
rear main seal
just to throw my 2 cents in, my 400 block had do be put down at about 395,000 miles due to... wait for it...do you feel the suspense?... main bearings 1 and 5 failing and losing all oil pressure, they seized and scored the crank and I was 200 miles away from base. had to leave the truck behind and come back two weeks later, scrape metal shavings out of the oil pan, change the two sets of bearings, change the filter, and drove it 200 miles keping it over 2000 RPM to maintain oil pressure. My suggestion, if you value the motor and dont want to do a swap and plan to keep it for a long time, pull the engine and freshen up the bottom end if it has a significant amout of mileage on it(you don't say how many miles it has) if your only planning on keeping the truck short term(or it only has 30,000 miles on it) then just slap the seal in, they're easy on that block.
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Joined: Oct 2002
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rear main seal
Ok, Ranger250 Im going with you advice for now. Ill worry about hp.s another day. So, Ill changer the rods and bearing seals gaskets timing chain and oil pump. Maybe when Ive got more money, Ill do a complete overhaul. :-)