# 1968 GTO rear main seal leak



## rob40999 (May 18, 2018)

Hello All: This is Bob again: My new #3 mechanic says my rear main seal is leaking, and is getting worse. What is the best rear main seal kit to put in this car???
Engine is a 400cu. I've noticed that they have the old rope seal, and something new? FEL-PRO rear main seal kit?????
Has anyone replaced a rear main seal??? Dumb Question... LOL LOL
You all have a great Ride,
Bob


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## PontiacJim (Dec 29, 2012)

rob40999 said:


> Hello All: This is Bob again: My new #3 mechanic says my rear main seal is leaking, and is getting worse. What is the best rear main seal kit to put in this car???
> Engine is a 400cu. I've noticed that they have the old rope seal, and something new? FEL-PRO rear main seal kit?????
> Has anyone replaced a rear main seal??? Dumb Question... LOL LOL
> You all have a great Ride,
> Bob


Is the leak bad enough to justify pulling the engine and disassembling the bottom end to replace it? Because that is what will be needed to properly fix the leak.

Since you don't seem to have much confidence in your mechanic, I would get a second opinion to make sure it is simply not an oil pan gasket leak.

Your engine could also be building up a lot of internal pressures as you wind it out. Pressure has to go some where and it will find the weak spot. If I am correct, your valve cover has the twist-on/off type oil fill cover. Replace it with a twist-on chrome breather to allow more engine pressures to vent/escape. Your other valve cover should have a tube going up into the air cleaner to help draw pressure out AND you want to make sure your PCV valve is functioning properly and rubber grommet is in good condition to seal it on the valley cover.

I'd do this first and see if it helps, and if not, and a second opinion says your rear main seal is leaking badly, then look into replacement. :thumbsup:


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## curtis.smith68 (May 9, 2018)

If the diagnosis is in fact a bad seal I personally went with this.

https://butlerperformance.com/i-244...-thru-400-bop-rms18.html?ref=category:1234758

It is very similar to the seals I'm familiar with for the high speed shaft in the GE T701D turbo-shaft engines I worked on. Maybe there are better options and maybe the old-school rope seals are good enough but I would hate to have to pull my engine again to replace this seal... The V-grove is directional and allows oil to enter it for lubricating the shaft but because it's directional, while it's spinning the oil is forced back into the engine. It's a little pricey as compared to a rope but if you've gotten as far as replacing this seal you may as well put something in that will give you peace of mind and this seal is it for me. If mine ever leaks I'll post to that affect but I have very high hopes for this design.


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## rob40999 (May 18, 2018)

*1968 gto rear main seal*

Hello All: I like the new rear main seal from Butler. Looks like a very good product. I will talk to my mechanic about it.

Thank you all for the info;
Bob


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## 29585 (Aug 4, 2013)

Hello Bob, ditto on the 1 piece viton seal from Butler, I used it on my last build and zero leaks after about 2 years. Its a a fluorocarbon elastomer seal with only 1 parting line which you put above the centerline of the crank. Much better than a 2 piece, 2 parting line, rope seal. Worth the extra money in my opinion, i'll never use rope again.

chuck


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## RMTZ67 (Mar 12, 2011)

rob40999 said:


> Hello All: This is Bob again: My new #3 mechanic says my rear main seal is leaking, and is getting worse. What is the best rear main seal kit to put in this car???
> Engine is a 400cu. I've noticed that they have the old rope seal, and something new? FEL-PRO rear main seal kit?????
> Has anyone replaced a rear main seal??? Dumb Question... LOL LOL
> You all have a great Ride,
> Bob


I thought I had a rear main seal leak also. But since i disassembled my engine for other reasons the back of the block was covered with oil. Either the distributor gasket or valley pan. did not investigate it much since it was headed for a full rebuild. Might be worth looking into that first. It may be your problem since it runs down the back of the block. easier and cheaper.


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## BearGFR (Aug 25, 2008)

I used the 1 piece BOP seal also on my last build. (Butler just sells these, they don't make them)

I also recorded a 'how to' video on installing it.


Bear


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## rob40999 (May 18, 2018)

*1968 gto rear main seal*

Hello All: Well, since we are all having so much trouble with the rear main seal oil leak?? I'm going to contact Pontiac re-call Department to see if we can get them to pay $$$$$ for the repair's to our GTO'S.... I'll be sending around a pettion to sign... Who's IN.... LOL LOL

Just some old age humor. LOL LOL
I liked it... You all have a great ride...
I'll let you all know how the rear main seal fix goes...
Tks, Bob  LOL LOL


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## geeteeohguy (Feb 2, 2008)

Have used 3 Viton 2 -piece rear main seals in the past 8 years. No leaks, after years and many miles of service on the three engines. Helped a friend install the new 1-piece Viton rear main in his '69 GTO about 2 years ago. No leaks. If you must use a rope type seal, use the Best Gasket one. The stock rope type seals in the Fel-Pro kits no longer use asbestos, and will disintegrate and leak. The one I installed in my '67 in '88 did, right off the bat. The one I installed in my '65 in 1981 never leaked, and still doesn't.....it's asbestos. YMMV.................


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