1968 300 Rear Main Seal Leak

[mgm1986]

Fortunately, after reinstalling the engine, it fired up immediately.

Unfortunately, I forgot how loud an engine is with just headers and no exhaust, so I need new underwear.

Fortunately, after idling for just a short time, the carb kicked down and it seems to run smooth with new main and rod bearings.

Unfortunately, I can't test drive the car because the rear is on the bench for a rebuild along with the front suspension.

Fortunately, I am in no rush to drive her anywhere.

Unfortunately, I am in no rush to drive it because the amount of oil being dumped from the rear main seal area looks like a horror movie; as if I no seal is installed at all.
Sad day in the garage, back to the drawing board.

Vent over.

 

[commando1]

Unfortunately, I am in no rush to drive it because the amount of oil being dumped from the rear main seal area looks like a horror movie; as if I no seal is installed at all

Argh.
I can't imagine the pain.

 

[Big_John]

Fortunately, after reinstalling the engine, it fired up immediately.

Unfortunately, I forgot how loud an engine is with just headers and no exhaust, so I need new underwear.

Fortunately, after idling for just a short time, the carb kicked down and it seems to run smooth with new main and rod bearings.

Unfortunately, I can't test drive the car because the rear is on the bench for a rebuild along with the front suspension.

Fortunately, I am in no rush to drive her anywhere.

Unfortunately, I am in no rush to drive it because the amount of oil being dumped from the rear main seal area looks like a horror movie; as if I no seal is installed at all.
Sad day in the garage, back to the drawing board.

Vent over.

Two things caught my eye.

First is you started it without a rear in the car, so no driveshaft. Was the rear of the trans sealed?

Second "looks like a horror movie" makes me think of blood, red blood that is. If the rear of the trans was open, it would be pumping red trans fluid all over the place.

Honestly, a bad rear seal wouldn't pump that much oil out. It would have to be completely missing to dump what you are describing, and even then, I don't know if it would do that much.

 

[mgm1986]

@Big_John This might be the first and possibly only time I wish the leak was Trans fluid! I am going to move forward with the suspension and rear end rebuild while I contemplate my options. That way if I need to take it somewhere to have it done by a professional it can at least roll up and down a trailer.

 

[detmatt]

Sorry to hear this and I’m very interested to know what went wrong. Other than the main seal itself there are the housing side seals or the slight possibility that it’s coming from up above like maybe the oil sender ports?

 

[65Port]

That sux.. any pics of the install? That is probably where it fell down. Maybe you can get away with an in-car pull of the pan and cap to trim and reassemble? Maybe it wasn't cut short enough and when you torqued everything down it caused a leak. Is the leak worse or the same? Did you check the cam plug on the back while it was out?

Don't lose hope yet.

 

[mgm1986]

That sux.. any pics of the install? That is probably where it fell down. Maybe you can get away with an in-car pull of the pan and cap to trim and reassemble? Maybe it wasn't cut short enough and when you torqued everything down it caused a leak. Is the leak worse or the same? Did you check the cam plug on the back while it was out?

Don't lose hope yet.

The install is absolutely where it fell down!

I am likely going to pull the pan after confirming it isn't something simple higher up, as that would be a nice solution.

I'm not too terribly surprised I have an issue. I went into this expecting I had a 50/50 of fixing it the first time I ran it. First time pulling an engine or doing a rear main so those odds might be generous.

It'll be a bit but I'll post back when I get back to it.

 

[57fury440]

A couple of drops of oil was not bad. When you put the rear seal back in did you put a little sealer where the two ends of the rope seal went together? I assume you replaced the part that was cracked and used the proper length bolts. Did you make sure to put the gaskets on the sides? My 440 has the rubber style seal and thankfully has not leaked in over 40 years. Good luck, rear seals are a pain. If the surface where the seal sits is worn, that adds to things getting sealed properly too.

 

[mgm1986]

A couple of drops of oil was not bad. When you put the rear seal back in did you put a little sealer where the two ends of the rope seal went together? I assume you replaced the part that was cracked and used the proper length bolts. Did you make sure to put the gaskets on the sides? My 440 has the rubber style seal and thankfully has not leaked in over 40 years. Good luck, rear seals are a pain. If the surface where the seal sits is worn, that adds to things getting sealed properly too.

I couldn't agree more at this point, a couple of drops wasn't bad at all just got tired of leaving a trail everywhere I parked. Should have left it alone!

I used RTV for the side seals and followed the Mancini instructions for the rope seal install, cut to length using the tools they supplied.

What I did NOT do, which occurs to me now, is install the "lock pin" they tell you to drill a hole for in the retainer to keep the rope from spinning. Maybe the seal spun around. I do dumb things sometimes.

The rubber seals didn't work I assume because of the knurling on the crank. Two of those leaked with the engine sitting in the stand so I went to the rope seal.

 

[57fury440]

I have had a lot of rope seals that worked very well. I never had to drill a hole for a pin to keep them from spinning. I would contact Mobile Parts on here and see if he has any original seals.

 

[mgm1986]

I wrapped up with the front suspension rebuild so I decided to turn my attention back to the rear main before reinstalling the steering linkage.

Upon removal of the seal retainer the seal indeed spun and there was a gap between the two halves. Obviously kicking myself for not following the instructions from Mancini. I guess with the new aluminum retainer and the graphite impregnated seal being so slick, the pin wasn't an optional step.

Now I must decide if I am going to try and do the job again with the engine in the car or if I am going to pull the engine back out. Leaving it in the car will likely mean dropping the crank to get the upper half back in correctly.

"Never time to do it right, always time to do it twice..."

 

[mgm1986]

I decided to try the one piece rear main from fast fish as it seemed like a viable option without removing the engine. After diligently cleaning everything (and following the instructions this time) I finally got things reassembled.

Initially there was no oil pressure so I pulled the dizzy and primed the pump which resolved the issue.

I ran it for about 6-8 minutes, long enough for the engine to warm up and the "Cold" light to go off. I added UV dye to the oil too.

So far no drips but it is way to early to tell if this is fixed.

She sounds good though!

New video · Monday, May 12 ð¬

 

[mgm1986]

Valve cover and dip stick tube are leaking. Not surprised by either. So far I've run the engine a total of about 20 minutes and no leaks showing up from the rear main area. I'll probably run it another 20 before I call it good enough to reinstall the steering linkage.