Advice on rear main seal replacement

[slugish]

Have a 400 sbc with the good ole leaking 2 pc. rear main .Always leaked , just getting worse. Question , even though I know its best to remove engine for this , has anyone ever done it or know of anyone who has done it with the engine still in. Why in the world I didnt do it while the engine was out doing a head & cam upgrade is beyond me ,just not thinking . I really dont want to take engine out again if I can help it.

[Krwright]

It's a really simple job. Done many this way.
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[79Betty]

Don't have to... Drop pan, break loose rear main. Take a punch or flathead and hit out old one o main then one out of block. Put new one in. Feeding around crank. Leave a 1/2" sticking out so if doesn't sit level with pan. Put new one in mean to where it lines up and makes full circle. Retorque and install new pan worh new (i suggest one piece) gasket. Tadaa!
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[slugish]

The mechanic who I was going to get to do this for me said it was a pita to try & get the seal in full circle while engine still in truck > Says it requires a special tool for installation & do you not have to remove your flywheel
to gain good acces to it . Thx for your response

[79Betty]

That i don't know as my motor was out of the truck. But i wouldn't say so. It's not actually hard.
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[mrolds88]

Also when you offset the seal, dab a small bit of RTV on the ends of the seal. Don't have to take the flywheel off.

[geezer#99]

Don't use something solid like a blade or punch to push the old one out. Use a soft wood like a pencil or wood dowel. Unless you like a nicked journal that will never seal.
I've never done a rear main by yanking the motor. No challenge if you can't work flat on your back under your truck. I'm still doing it at 62 too!!
Only reason to pull flywheel is if no room to get the pan out.
Put a little oil on the seal and it'll slide in easy.

[nheller76]

Also I know it may seem like a fun thing to say but I've had ppl do this. Pay attention to what edge is facing the tranny. U can put them in back words and u will not stop the oil leak. It is super easy when u get it all apart. U should also get a new oil pan gasket if your taking the pan off. I would suggest the one peace they are SOOOOO easy to put back in.
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[mud.man.rj]

Lots of great advice here, like the last one on which way the seal faces, installed one backwards many many years ago, wow I remember that one, she really leaks after that. Just takes time and patience, you will get it.

[tucsonjwt]

So, mechanics I talk to say you also need new bearings when you replace the rear main seal - otherwise it will still leak. Is this true? I see different size bearings advertised, I assume to accommodate varying amounts of wear over time.

[79Betty]

I didn't replace mine they looked good. Do you have good oil psi now? If so i'd reuse the bearing. If you replace it it'll wear different then the others.
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[geezer#99]

Originally Posted by tucsonjwt

So, mechanics I talk to say you also need new bearings when you replace the rear main seal - otherwise it will still leak. Is this true? I see different size bearings advertised, I assume to accommodate varying amounts of wear over time.

No you don't need to change the bearings. THe seal rides on the end of the crank. To change the bearings you'd need to pull out the crank. Get a new mechanic.
Different size bearings are for different crank journal sizes. THe journals do wear over time and it's common to grind the journals smaller which requires bearings (thicker ones) to match.

[79Betty]

I'd get a new mechanic.. Sounds like this one is trying to take you for a ride.
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[nheller76]

Agreed!
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[slugish]

Originally Posted by geezer#99

Don't use something solid like a blade or punch to push the old one out. Use a soft wood like a pencil or wood dowel. Unless you like a nicked journal that will never seal.
I've never done a rear main by yanking the motor. No challenge if you can't work flat on your back under your truck. I'm still doing it at 62 too!!
Only reason to pull flywheel is if no room to get the pan out.
Put a little oil on the seal and it'll slide in easy.

Thx Geezer , That should be my name ,Im 66 & still just know enough about this stuff to be dangerous

[slugish]

Originally Posted by nheller76

Also I know it may seem like a fun thing to say but I've had ppl do this. Pay attention to what edge is facing the tranny. U can put them in back words and u will not stop the oil leak. It is super easy when u get it all apart. U should also get a new oil pan gasket if your taking the pan off. I would suggest the one peace they are SOOOOO easy to put back in.
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So one peice will work > wht did they not put one peice seals in originally especially since so much trouble with the 2 peice

[willett]

Never done a 400, but when I've done 7.3's and 24 valves you get a slide hammer and drive a couple #8 sheet metal screws on either side of the output. Use the screws as slide hammer anchors.
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[geezer#99]

Originally Posted by slugish

So one peice will work > wht did they not put one peice seals in originally especially since so much trouble with the 2 peice

Modern technology. Not available back then. Cork on side rails and rubber on the ends wasn't bondable back then. It's progressed quite well since then. THe one piece rear main brought the one piece pan gasket along with it.
At least all these young guys haven't had to replace a rope seal for a rear main. THat was always joyfull!!

[TDS-MN]

I never knew this task could be done with the engine still in the truck. Nice to learn. Related question, how would I know which type of seal I have in my '85 vintage 305? I'm tired of the constant oil leakage and mess in my driveway. . . .

[jjzepplin]

Originally Posted by TDS-MN

I never knew this task could be done with the engine still in the truck. Nice to learn. Related question, how would I know which type of seal I have in my '85 vintage 305? I'm tired of the constant oil leakage and mess in my driveway. . . .

You can tell by looking where your flex plate attaches to your crank. If it's completely round it's one piece if there is one side that a section that is offset and has way more meat it is the older 2 piece. One piece you have to pull the flywheel to get at it. 2 piece you don't. A fella on this board also mentioned to not put the 2piece ends in all the way flush with the block and to leave one side out a bit so when it joins the other side it will be inside the channel and be less likely to leak. Sounds like good advice I could have used a long time ago!
Also... If your block has ever been Align Honed you will need a spacer type seal for the rear main (400 sbc). When I did my 400 sbc Fel Pro had just stopped making the larger one. Wonder if they brought it back yet. Speed shop gave me the smaller one and forgot the spacer and that sucker leaked like it was not even there. Good thing I didn't have to take it all the way back out...

[bnoon]

Originally Posted by slugish

So one peice will work > wht did they not put one peice seals in originally especially since so much trouble with the 2 peice

Originally Posted by geezer#99

Modern technology. Not available back then. Cork on side rails and rubber on the ends wasn't bondable back then. It's progressed quite well since then. THe one piece rear main brought the one piece pan gasket along with it.
At least all these young guys haven't had to replace a rope seal for a rear main. THat was always joyfull!!

You guys appear to be talking about two different things. Slugish is asking about 2 piece vs. 1 piece rear main seal and geezer is talking about a 1 piece OIL PAN gasket. One piece oil pan gaskets are awesome!

[nheller76]

Originally Posted by TDS-MN

I never knew this task could be done with the engine still in the truck. Nice to learn. Related question, how would I know which type of seal I have in my '85 vintage 305? I'm tired of the constant oil leakage and mess in my driveway. . . .

U can almost Bet that if it's an 85 it's a 2 peace. The older motors are one peaces I've never seen a 75 and up with a one peace. It is a little aggravating when mechanics charge an arm and a leg for a rear main replacement in a motor like theses. If u have the parts it won't take more then a few hrs. Have the torque specks and wrench to tighten the rear main cap back on it is a good time too to see how your bearings are holding up. If they look good the don't worry, if not then u gave a choice to make.
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[mud.man.rj]

I have changed an 85 rear seal and it was a one piece, first year I heard, maybe it was a late 85 early 86, can't say for sure. If it is a one piece will have to move trans back and pull flexplate to get at it, hope it is a 2 piece, easier.

[bnoon]

Originally Posted by mud.man.rj

I have changed an 85 rear seal and it was a one piece, first year I heard, maybe it was a late 85 early 86, can't say for sure. If it is a one piece will have to move trans back and pull flexplate to get at it, hope it is a 2 piece, easier.

'86 was indeed the year for the 1 piece rear main seal. '86 was a bastard year for the block though as it still had flat tappet lifters in the Corvette/Camaro/TA. In '87+ those engines went to roller cams. I've never seen an '86 SBC with anything other than the 1 piece rear main seal. Odd that yours was a 1 piece for '85.