So my rear main seal finally finished blowing out on me today. It has leaked ever since I rebuilt the engine, I screwed something up when I installed it the first time, but it has popped out almost completely now. The question I have is whats going to be easier; dropping the transmission and doing the work with the engine in place, or pulling the engine out to replace it? I have a two piece seal in there now and there is a chance I could loosen the main cap and pop the seal back in place, but I am thinking that I would be better off by replacing it with a one piece seal. Thoughts? What would be the best plan of attack on this?

Thanks, Brian

 

What trans, what exhaust? Typically, it's a lot easier to remove the trans than removing the engine. Just did one last summer. Somebody put a neoprene seal in, but left the little nail in the bearing cap that holds the rope seal, Boy was that seal a mess.

 

Its a latter model C4, with the larger bell housing. The exhaust is a generic summit brand dual exhaust with long tubed headers made by flow tec.

 

What frustrates me is that
A. I am to blame
B. The engine has less then 10k miles on it
C. Its my fault
D. A new seal was put in when I rebuilt the engine
E. Did I mention I installed the seal that has gone out already?
F. Its not a quick fix for the mistake I made.

I will stop beating my self up about this once it is fixed and I forget about it... Till then.

 

Brian, is this your original 289? if so what you did wrong was to use the 2 piece seal - you need a "rope" seal on the old girl.

 

I had a rear main leak on my 289 20 years ago. I recall pulling the crossmember, oil pan and rear main cap. I think I did it in less than a couple of hours. The only reason I remember this is because the shop mechanic at the time said I couldn't get it done before the sun went down.

My memory isn't what it used to be. Find a manual and check to see if it can be done like I described. Don't forget to retorque the main cap. Do it by the book in stages.

 

I switched from the rope to the neoprene over 20 years ago. Hasn't dripped a drop since.

Much better than two pieces of rope.

 

Use a good neoprene two piece seal. I don't know if you can get the rope seal any more. And if you could, why would you?

There's a "nail" in the seal area of the main cap. That's there to hold the old rope seal in place. Make sure you remove that nail, and fill the hole with silicone, JB Weld, epoxy, whatever.

You do not need to remove the trans. Remove the oil pan and the rear main cap, and there it is. You cannnot use a one piece seal unless the block and cap have been machined for it.

When installing the new seal, carefully slide the old one out, and the new one in. It's real easy, and should just slide right out in a circle. If you have to force it, something's wrong.

When you put the new one in, off set the gap in the seal from the gap in the cap/block by about 1/4". Put a tiny dot of silicone sealant on the edges of the seal. Just a tiny dot. Excess silicone will interfere with the sealing surface of the crank. Also, make sure to add a little bit if silicone where the cap meets the block.

 

No the original 289 is in storage until a later date. I have a 302 block out of a 85 Tunderbird in the car now.

 

By no means has it been machined for a one piece... This engine was quite literally a "back yard build" from when I was in college and on a extremely tight budget.

I have herd that you could replace the seal without taking the trans out, but doesn't the crank need to drop some in order to get the seal out and the new one in? wouldn't the fact that its still connected to the trans prevent the crank from dropping, or will it still allow it to drop enough to do the job?