Leaky Rear Main Seal

[joker37]

I own a '90 Cadillac Brougham d'Elagance. 5.0L, R/W driven. Has 197K miles on her. Rear main seal is leaking and the type of seal is a "rope" type. Outside of replacement (will cost me $260, parts & labor) what, if anything, can stop or minimize this leak? Vehicle was driven recently from Denver & back to Las Cruces, NM(a distance of approx 1068 miles) and she used 7 qts of oil. Not burning it, no blue or white smoke coming out of tailpipe. I wait to hear from anyone with suggestions..
Joker37

 

[Chris142]

I thought they stopped using rope seals in the 50's?

 

[duaneb9729]

Welcome to the forum!

If you like the car and it runs good, IE not a ton of other problems, that is not a bad price for the repair.

My two cents

 

[Chris142]

I stand corrected. I looked up a rear main for a 307 olds and yup it's rope. I don't think that theres any addatives that will stop a rope seal from leaking. Does anybody make a neoprene seal for it?

 

[Trav]

Good price for the repair.Easy enough to do on that motor,all you need is a couple of hours and a Chinese finger AKA Sneaky Pete to get the seal in.No snake oil on earth is going to stop a 7qt/1000 oil leak.

 

[Scdevon]

7 quarts is a lot of oil in 1000 miles. Usually, they don't leak much when the engine is actually running due to the slinging effect of the crankshaft flange but it's possible I guess. They usually leak the most just after the engine is shut off.

That is a reasonable price to have it replaced. I'd go for it and hope for the best.

 

[Scdevon]

Originally Posted By: Trav
Good price for the repair.Easy enough to do on that motor,all you need is a couple of hours and a Chinese finger AKA Sneaky Pete


I still have one of those in my tool box! They work great. Remove the rear main bearing cap and the old seal halves, loosen the other main bearing caps a turn or two, pack the new seal with grease and spin it in place. If I remember, you need to leave around an 1/8 inch protrusion when you cut the seal to fit to allow the rope to compress into the groove properly. A small dab of sealer at the joint doesn't hurt either.
It's been a LONG TIME since I've done one of these. Find an old timer to do the repair. Most kids now won't even know what a rope seal is........

 

[dickwells]

Another way old timers would fix them is to remove the bottom rear bearing cap and then use a shaped peg to drive the two ends of the top seal up as far as possible, this causes them to swell and fill the space. Next cut pieces of the rope seal longer than needed and in turn drive them into the seal groove. when tight, use a razor blade to cut off the ends flush. Put the new seal in the bottom groove and reassemple. Voila!!

 

[mechtech2]

Packing a rope seal is best - it jams it in there.
Pre lube everything well, of course.


But really watch out for any protrusions of rope seals. The problem is that the cap can not seat properly if the rope gets between the faces of the cap and block. It is easy for the rope to get in the way.

 

[onion]

Originally Posted By: mechtech2
Packing a rope seal is best - it jams it in there.
Pre lube everything well, of course.


But really watch out for any protrusions of rope seals. The problem is that the cap can not seat properly if the rope gets between the faces of the cap and block. It is easy for the rope to get in the way.


Agreed. Except for the odd oldsmobile engine or archaic agricultural/industrial engines (continental & hercules) that I've overhauled, rope seals are mostly before my time. But that's how I was taught to do it. Soak the rope seals in oil overnight, pack them in tight, and trim with a razor. Then put a little sealant where the cap meets the block (not too much).

 

[Scdevon]

Originally Posted By: mechtech2



But really watch out for any protrusions of rope seals. The problem is that the cap can not seat properly if the rope gets between the faces of the cap and block. It is easy for the rope to get in the way.


Yeah. I meant just a little bit of protrusion with a dab of sealer. You have to use common sense. I'd hate to have a rear main bearing failure because the rear cap didn't seat.
I actually need to do this on my 1970 Mustang with a 302 V-8. It leaks probably a pint a year, not 7 quarts in 1000 miles, though. I'm almost 100% sure this engine has a rope seal and it's totally original. Maybe I'll do a pictorial when I do the job???

 

[Kruse]

Check several parts stores and see if you can't get a neoprene replacement. I used to work at a place that had about a dozen forklifts built in the 50s. These forklifts had Continental (the industrial motor, not the automotive motor) flatheads that took rope rear main seals. They were a PITA to maintain and replace. Yes, there is a trick to replacing a rope seal and even if done properly, there is no guarantee that it would still be dry 6 months later.
Good luck. I'm surprised Cadillac would have this in a 90s car.

 

[Kruse]

RockAuto appears to have rope and Viton replacements. I'd check into it.

 

[Trav]

The Viton is for the half ton commercial chassis.
This uses a Chevrolet 305 CI motor.Rock should correct this info,listing it for a 307 CI Olds motor.
Engines designed for rear rope seals cannot use viton lip type seals.

Rope seals installed properly can live many years without issue.
Some folks soak the seals overnight,i like to use graphite impregnated ones with a little assembly lube using just a dab of non hardening aviation Permatex on the cap side where the seal mates.

Parking the car rear end down on an incline will leak like crazy with a bad rear seal,if there is an incline park it nose down.

 

[joker37]

My Tks to all that responded to my request. I looked under the vehicle this a.m. and there wasn't any oil, from same, on the garage floor. Hmmm? I plan to do a little more research, like getting a bright light into the area around the back side of the valve covers, etc....
Again, tks for all the comments. Will post when I find out what the real problem is and how it was solved.
Joker37

 

[mechtech2]

Cleaning everything well, and dusting with baby powder or flour will reveal where the leak emanates from.

 

[onion]

Never tried the baby-powder trick, but it sounds worthwhile. I'll have to give that a try sometime.

 

[Scdevon]

Originally Posted By: joker37
My Tks to all that responded to my request. I looked under the vehicle this a.m. and there wasn't any oil, from same, on the garage floor. Hmmm? I plan to do a little more research, like getting a bright light into the area around the back side of the valve covers, etc....
Again, tks for all the comments. Will post when I find out what the real problem is and how it was solved.
Joker37


Maybe it stopped leaking because the crankcase is empty.

Seriously, dude. 7 quarts in 1000 miles is a LOT of oil even for a failed rear main seal.