# Rear main seal needs replaced



## xconcepts (Jan 4, 2009)

So I just found a rather large oil leak near the flywheel, figure its the rear main thats bad. I've heard that the tranny is the only thing that needs dropped and I've heard the engine needs to come out as well. So which is it? Just trying to see how much work is involved.

-X


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## Instg8ter (Sep 28, 2010)

i used a viton seal, from what i hear the rope seals are hit and miss, and have heard of guys doing it w/o pulling engine but they said they would never try it again that way. tight quarters, wrestling with a 70 lb crank and trying to get it seated with next to no room.


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## jetstang (Nov 5, 2008)

Try mechanic in a can, may buy you some time, probably not.
There is a sticky on rear seal replacement. I had to drop the crank and disconnect the con rods to get the seal in. Good luck!


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## GTO JUDGE (May 14, 2005)

Just last spring I had the car in the shop one of the items was to fix the rear main seal leak. Long story short, after getting the vitron seal and with the motor partially torn apart for the transmission removal it was learned the seal was NOT leaking but I had an oil pan on the verge of busting apart, it was in bad shape. The car was on a lift and motor was jacked up. I had the mechanic replace the seal since that area was exposed. He did it without engine removal. After replacing the seal he left it sit a few days without disturbing it. The rope seal was in good shape. Someone replaced the rope seal with a newer one at some point and it may have been one of those new graphite ones. Its still holding fine. 
When I bought the car both the transmission and engine was leaking oil. I used Bars Leak on both to buy me time and it did a great job. Over the first winter though the puddles on the cardboard were getting larger and larger, from the shrinkage of the gaskets. I just bit the bullet and had the leaks addressed.


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## geeteeohguy (Feb 2, 2008)

Yes, refer to the sticky. To do it once and do it right, pull the engine. The engine needs to come partially apart to do a clean job. It can be done "in car", and tools are available to snake the new seal in around the crank. The success rate for this style of repair is about 50-75% in my experience. Again, you should pull the engine and reseal the whole lower end and clean up the engine bay while you're at it. Just don't do a Too Many Projects and have it stripped to a shell, sitting on crates,with the floors cut out the next day. Engine out, engine in!!!


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## plastic61 (Feb 26, 2010)

I am about to replace the rear main seal on my 69' with a "graph-tite" seal I ordered from "Egge" manufacturing. Earlier threads say the only way to really to do the job right is to pull the motor. I will be removing the motor after the Holidays. Some suggest that you place the rope seal 3/8" off the center line of the main cap and block seam, put a dab of sealant on the ends. This way the seal covers the seam (source of the leak). I will try that method, and report on my results.....


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## geeteeohguy (Feb 2, 2008)

Plastic, I've heard of bad results using that method. If it were me, I would follow the manufacturer's directions to a "T".


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## dimitri (Feb 13, 2009)

The correct way to replace a rope seal with a rope seal with the engine in the car is to remove the cap, dig out the old seal. With the new seal cut it in about four pieces and start packing it in with a wooden dowl. This used to work great with the old style asbestos rope seal. I have never had any luck with the BOP rubber seals. They always end up leaking. I am now using a Best Gasket rear main rope seal. I am real happy with that seal. Before going much further try to isolate your leaks. It could be coming from somewhere else.


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## jetstang (Nov 5, 2008)

plastic61 said:


> I am about to replace the rear main seal on my 69' with a "graph-tite" seal I ordered from "Egge" manufacturing. Earlier threads say the only way to really to do the job right is to pull the motor. I will be removing the motor after the Holidays. Some suggest that you place the rope seal 3/8" off the center line of the main cap and block seam, put a dab of sealant on the ends. This way the seal covers the seam (source of the leak). I will try that method, and report on my results.....


WIth the graphtite, they give you a spacer, 1/16" and a razor knife to cut it off, leaving you enough material to make an interferance fit, no sealant is required, just follow the directions and you should be good. I had to pull the crank to insall, let me know if you can do it without loosening the crank.


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## Eric Animal (Oct 28, 2007)

I hate to say it but.......when loosening and tightening main caps, rod caps, etc., and replacing a rear main seal, you are better off pulling the engine. It is an awkward messy job and you run the chance of causing "other' problems. FIRST !!!!!! verify the source of the leak!!!! It could be something else ie: a bad oil pan/gasket.....X-mission leak....etc. Personally, I would use a Viton seal. IMHO!


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## xconcepts (Jan 4, 2009)

So how do I find out if I need the 3" or 3.25" viton seal?


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## geeteeohguy (Feb 2, 2008)

If you have a 326, 350,389, or 400, you need the 3 inch. The 3.25 is for the 421, 428, and 455.


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## plastic61 (Feb 26, 2010)

Thanks everyone for the advice. I have removed the motor and I will be working on it on the engine stand. I received the "Graph-Tite" seal today, and read the instructions. I will follow the instructions, since I only want to do this job once.....


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## geeteeohguy (Feb 2, 2008)

Plastic, good luck to you, and let us know how it comes out. I've heard nothing but good stuff about that seal, and I hope it SEALS for you!!


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## dimitri (Feb 13, 2009)

Plastic, don't forget to put a small bead of RTV sealant on the bolck from the rope seal leading outward to the edge before you put your cap on. Do not get any sealant on that rope seal.


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## 66tempestGT (Nov 28, 2009)

xconcepts said:


> So I just found a rather large oil leak near the flywheel, figure its the rear main thats bad. I've heard that the tranny is the only thing that needs dropped and I've heard the engine needs to come out as well. So which is it? Just trying to see how much work is involved.
> 
> -X


i dont mean to beat a dead horse but i suspect you have multiple leaks because you have installed an incorrect/ inferior breather. crankcase pressure is causing oil to come out of every weak spot you have. a rear main leak wont cause oil to puddle near the spark plugs. im curious if nobody else thinks this is probable.

just looked at the date on this and i see this thread came first. i just hate to see somebody spend a lot of time and money to try to fix what could be a very simple problem.


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## geeteeohguy (Feb 2, 2008)

TempestGT, I'll jump on your wagon. Years ago, when I first bought my '65, it leaked oil everywhere. Like crazy. I found that the previous owner had plugged off the PCV entirely and installed closed breathers. Installing a PCV system and the proper breathers eliminated the oil leaks entirely. Lots of pressure builds up in an engine, and vacuum, too. Both can oil to blow right past seals and gaskets. When I was a mechanic in industry, I ran into this quite a few other times, as well.


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## xconcepts (Jan 4, 2009)

66tempestGT said:


> i dont mean to beat a dead horse but i suspect you have multiple leaks because you have installed an incorrect/ inferior breather. crankcase pressure is causing oil to come out of every weak spot you have. a rear main leak wont cause oil to puddle near the spark plugs. im curious if nobody else thinks this is probable.
> 
> just looked at the date on this and i see this thread came first. i just hate to see somebody spend a lot of time and money to try to fix what could be a very simple problem.


Well I could try to put another autozone breather on, which they said is correct. The problem with that is it seems to be a one time use breather, since after I remove it the seal is no good and leaks from the breather. The one I replaced it with is not specifically for the gto, but is a perfect fit and doesn't leak from, but it did start to leak bad after I replaced it.


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## xconcepts (Jan 4, 2009)

Also, I spoke to my dad who is more mechanically inclined than I am, I told him where I was leaking and he suggested it was the lower intake that was leaking since its below where the spark plugs are. But it is not from the valve covers.


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## geeteeohguy (Feb 2, 2008)

There is no "lower intake" to leak oil. It sounds like your valley pan, or "pushrod cover" as some call it. Excessive crankcase pressure from no PCV or improper breather type can and will cause this (among other places) to leak oil.


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## plastic61 (Feb 26, 2010)

I removed the crank today, and replaced the rear rope seal with the "graph-tite," as per the instructions with the seal kit. Everything went fairly well with the seal install. I siliconed it in place, used the included 1/16" guide to cut the ends. The only problem I ran into was torque specs for the rod bolts. I went "on line" for the specs, and the source I used listed the connecting rod bolt torque as 63 lbs. I snapped three bolts during the torque sequence. A trip to the NAPA machine shop revealed the spec as 45 lbs, not 63 lbs. I ordered a set of ARP rod bolts today, since I probably stretched the old bolts to a point where they may snap when the engine is running again. Minor set back, but at least I found out while everything is apart. I will post my results when the motor is up and running again...Thanks for all the input..Phil


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## 66tempestGT (Nov 28, 2009)

everything on the internet is true! i might have stopped after breaking the first one. good luck with the rest of the job. :cheers


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## plastic61 (Feb 26, 2010)

Update on rear main seal install. I found the metal plug that seals the rear of the block at the cam shaft opening, had not been installed correctly. It fell out into my hand when I touched it. There was a lot of oil on the rear of the block, behind the flywheel. I guess that was where the leak was, not the rear main seal. Oh well, at least I was able to clean up the motor, and replace some worn parts. Should be a drip free engine.


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## geeteeohguy (Feb 2, 2008)

My fingers are crossed. Sounds like your repair went pretty much like most of mine do-- except I have to agree with '66, I generally stop with the first snapped bolt!!!!


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## Bensjammin66 (May 12, 2009)

geeteeohguy said:


> Yes, refer to the sticky. To do it once and do it right, pull the engine. The engine needs to come partially apart to do a clean job. It can be done "in car", and tools are available to snake the new seal in around the crank. The success rate for this style of repair is about 50-75% in my experience. Again, you should pull the engine and reseal the whole lower end and clean up the engine bay while you're at it. Just don't do a Too Many Projects and have it stripped to a shell, sitting on crates,with the floors cut out the next day. Engine out, engine in!!!


:agree :rofl: :rofl: :rofl:

I know exactly what hes talking about too! Just do THAT job and dont start thinking, well while its apart...


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