My Jeep is marking it's territory - rear main seal

TerryMason

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Staff member
For about 6 months now I've had a steady oil leak, maybe a quart every 4000 miles. I believe that it's the rear main seal, since it leaks down both the transmission and the oil pan. I've done some research, and I don't think I want to do the rear main seal myself. What's the going rate for this at a normal shop? I've also read many posts where guys replace the rear main seal, drive a couple of hundred miles, then it starts up again - is this common?
 

Looks like we have the same problem my friend!

From what I've heard, the costs for repair at a shop goes anywhere from $300 - $450. You have to remember though, that the part is only $15. Tomorrow I'm going to tackle this job. Doesn't seem to hard, remove engine and replace. I know easier said than done. To answer your question, it probably occurs again because they don't clean all the old sealant and crud off of where the seal sits. You have to clean every single left over sealent or gunked up oil WITHOUT scoring or denting the metal. If you leave sealant or oil behind, you will end up leaking again. Scoring or denting the metal, will cause a permanent leak that is un-repairable. So be careful if you think about doing it yourself. I found a good write up from a fellow jeep forum, Ill post link as soon as I find it :)

If the oil is leaking from the back of your engine to the top of your transmission bell housing, then its your seal. Hope this helped!

Edit: Found IT!: [Repair] Rear Main Seal Replacement
 
Terry, the rear main isnt that hard to do, I would say without pulling the engine the hardest part is getting the oil pan off. Once thats done the job is pretty easy. I have only done them on cj 258, 304 engines but from the repair article in the post above it looks quite the same except for the bearing cap brace. I think they releak when you put the new seal back in, if your not real careful, as you tap the new seal in you can take some of the edge off of the seal and I think that it causes it to leak (did it once) I coat the seal with oil before I install now, helps it slide in.
 
Terry, if your in no rush to tackle this job you can do it. First disconnect the negative batt. cable from the post, drain the oil, remove the exaust Y pipe ( your choice if you want to disconnect the 2 downstream O2 sensors from the plug or remove them from the pipe), remove the starter, remove all the oil pan bolts(11mm) Note: the jeep needs to be lifted from the frame, not the axles to have the room and space to manuever the oil pan out. Tap the oil pan with a rubber mallet if it's stuck on the gasket. Remove the nuts holding the crankshaft bracket rail, remove the rear crankshaft main bearing cap. On this cap you will find half of the rear main seal and the other half will be on the block. To remove the upper half, use a small diameter punch(Blunt tip) and place it as centered as possible on the seal without making contact with the engine block or crankshaft surface and tap it with a hammer until it break loose. Work it on both ends if you have to and you'll see it pop out partially on one end. Use a needle nose pliers to retrieve the seal completely off the engine. Clean the surface with compressed air just in case some debris was left in there with the old oil seal. Pay close attention to the lip orientation of the rear main seal by reffering to the seal thats still on the bearing cap. Coat the new seal with engine oil and slowly slip it in the engine block and crank without cutting the edges, take your time on this, haste makes waste. remove the other half of the seal from the rear main bearing block and coat the new seal with engine oil before intalling it to the bearing block. Place a dab of engine RTV on the surface of the bearing block that meets the engine block by running a small dab on the rear edge by the rear main seal. ( Do not get it on the rear main seal). Re-install the rear main bearing cap and torque the bolts per service manual. If you dont have the specs send me a PM and ill pull it up on my computer. Re install the crankshaft rail bracket and nuts, torque to specs. , Reinstall the oilpan( Place a dab of engine RTV on the corners where the pan takes the shape of the crankshaft on the front and rear, top and bottom side of the gasket. On this i also use a "Form a gasket" brush on type gasket maker on the surface of the factory oil pan gasket on both sides. It's tacky and keeps the gasket in place while you install the pan back into its position, guaranteed leak free. Use it on the areas where the RTV is not required on the oil pan gasket. bolt it on and the rest of the other parts. NOTE: I use a 15mm wobbler socket and a long extension to remove and install the exaust flange bolts from the manifold. I hope this helps. Just PM me if you need more assistance.
 

Also be sure to check the crankshaft for a groove. The static seal riding on the moving crankshaft can cause it to wear a groove and it will leak again. I don't know if this is common with jeeps but I know it is with many makes and models.
 
I thought my CJ had a main leak. Look very closely at the top rear of the engine to see if it's oily. Mine has a 258 that has a replacement aluminum valve cover. My leak displayed just like a rear main, but was really coming from the rear of the valve cover. I took it off and replaced the gasket and applied some silicone goop. Problem solved. No more drip pan needed. Good Luck
 
Terry, I had an 89 Cherokee that was leaking at the rear main. I dropped the oil pan and the bracket around the rear of the crank. I then used a small hammer so I WOULD NOT HIT TOO HARD and a pin punch that I thought was the right size and tapped the old seal till it started to slip out the other side. Then following the curve of the seal pull it the rest of the way out. Clean the channel and oil up the new gasket and slip it in following the curve of the gasket. Replace the outer half and put it all back together.
Now for safety. Drain the oil first. don't drink it. Don't pour it in your eyes. Don't look in the drain plug hole when its draining. Don't cook food with the old or new oil. Don't use a hair dryer in the shower. Don't use the hammer or punch on any body part. Put the pan back up before you add new oil. Don't start it when you have your hands up around the crank. If you hurt yourself when doing this man up and accept responsibility for your actions. Don't sue me if you drop the punch when under the jeep and you poke your eye out.
 

:funny:

This is a project I'm going to tackle this winter on my 360. Found a step by step with photos and I suspect that the shop that replaced it three years ago got RTV in the wrong places on the bearing cap. My primary concern at this point is clearance to drop the pan after I drain it,8177 :lol:
 
If I remember right, on a 304 I just droped the pan, it was tight but came out. On the 6cyl, I had to unbolt a engine mount and jack up one side of the motor to get the clearance needed to drop the pan, both were for rear main seal. All the AMC v8,s have the same size blocks so hopefully the 360 pan will drop out too.
 
I never did anything with mine - it just helps keep the oil fresh :shades:

Actually the leak has slowed quite a bit, almost to the point where it's stopped.
 
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