Rear Seal or Oil Pan Leak


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By Tough55 - 18 Years Ago
I posted an earlier post on replacing rear seal on my 312' Merc. Today, I took the flywheel inspection cover off and found no evidence of a rear seal leak. The flywheel was dry and the clutch side was dry also. This is a 4-Speed car and I would assume that if the rear seal was leaking with the amount of oil It's leaving on the garage floor that the clutch would slip under load (lugging than accelerating). Am I correct in this assumption?

I had the car on a lift and could see no leakage from the valve covers or the rear of the intake manifold. The road draft tube was fixed a few months ago and was also dry. The front main seal was dry also.

I cleaned all oil off the bottom of the engine, rear of oil pan, flywheel inspection cover and drippings along the frame. Took it out for a 3 mile test drive. Back on the lift....I found oil at the rear of the oil pan and starting to run down the flywheel inspection cover. It looks to me like the oil pan gasket is shot!!!

What is the best pan gasket to use and where is the source to buy? ALSO....does the motor have to be jacked up to remove the pan? All thoughts and suggestions greatly appreciated~~~~~Ron

By Tough55 - 18 Years Ago
Don't quite understand what you are referring to when you say check side seals. How does the oil get outside the engine if it is not leaking through a bad pan gasket or bad rear seal? Sorry for my ignorance...but I don't know!!!!!  Thanks~~~~Ron
By PWH42 - 18 Years Ago
Unless the 312 is different from all the other Y-Blocks, you don't need to raise the engine to remove the pan.  Just turn the engine to get number one at top dead center and the pan will slide out towards the front of the car.  I don't remember 312's being any different than 292's and  272's and I've removed a lot of them.
By Tough55 - 18 Years Ago
Yes....I have a shop manual and now see the seals you are referring to but I still don't understand how the oil can get to the outside of the engine.  You stated.....the rear seal and the pan gasket might not be bad...the side seals could be leaking.  If the side seals are leaking wouldn't the oil seep out the end of the crank into the flywheel and clutch assembly?  As I stated in my post....the area of the flywheel and clutch assembly has no indication of a oil leak and no clutch slippage under load or otherwise.

I'm trying to be hard nosed or bull headed but I don't understand where the oil is coming from and would like to get this problem corrected.     Thanks~~~~Ron

By charliemccraney - 18 Years Ago
The clutch inspection cover of a 3spd manual on a truck does not seal to the back of the engine block.  I'm not certain if it is the same with the others.  In this case the leaking side seal can look like an oil pan leak.  Also consider the oil galley plugs and the core plug behind the camshaft.  Is it dry around the oil filter?
By Moz - 18 Years Ago
g'day ron

i can offer an explanation to what the other guys are saying.  a few months ago i broke my crankshaft.  in changing it i decided to fit a new rear main & side seals.  2 weeks later it started leaking oil out the back a large amount.  on inspection it was all on the outside of the cover.  i pulled the cover.  nothing on the drive plate ( its auto ) or coverter.  i cleaned it up. drove it.  i had a look.  same thing.  i pulled the pan off removed the retainer.  the rear main was dry.  no oil on it.  the side seals were soaked in oil.  i hadnt put enough rtv sealer on the retainer.  the oil ran down the inside of the side seals & onto the pan then onto the cover & outside of the pan hence nothing inside the bell housing as the inspection cover goes inside slightly higher than the pan & pan gasket.  makes it look like the back of the pan gasket is leaking.

By Tough55 - 18 Years Ago
Thanks Moz: It makes a little more sense now. But...........I still don't understand how the oil gets to the outside of the engine if the oil pan gasket is good and the crank rear seal is not leaking. Wouldn't the oil drip back into the pan and stay inside the engine? I sent you an email via this site asking more questions. Please let me know if you get it and respond A.S.A.P.

Thanks for your time and concern~~~~~~if others can shed more light on this subject telling me how to replace these side seals~~~~~~~feel free to jump in and inform me. Y-Blocks are a new challenge for me!!!!

Do I have to buy a complete rear main kit to get these side seals? If so.......where do I purchase the kit?~~~Ron

By Tough55 - 18 Years Ago
YEAH!!!!!  I did a search (replacing rear seal on 312') and found a site that shows closeups of the seal retainer installed in the block.  NOW........I understand how it can leak as the pan gasket does not cover this area. I would appreciate it if someone would walk me through step by step on replacing these side seals.  Do I have to replace the lower crank seal as well?

It feels good when the light finally comes on and you understand what everyone is talking about.  I might just as well order a rear main set and get all the parts I need.  Any suggestions as where to purchase???

Please...someone take the time to walk me through replacing these pieces. Thanks for everyone patience and understanding in this matter~~~~~~Ron 

By Moz - 18 Years Ago
g,day ron

mate i didnt get your pm yet in my inbox the steps to  remove the retainer are fairly easy i will try to walk you through it

1 set engine on top dead centre on #1 cyl

2 undo pick up pipe at oil pump i also undo it where it goes in the pan

3 remove all pan bolts drop pan down & slide forward shouldnt need to raise engine

4 undo 2 bolts holding retainer work retainer forward & backward to remove

5 remove side seals  fit new side seals  aply rtv sealer to corners & sides of retainer  re fit bolts i put sealer around them as well   you should have 2 nails with the new seals fit them between the side seals & the retainer & carefully tap in with hammer  i also fill the holles that the bolts are in with sealer as insurance

6 refit pan & oil pipe.

fairly simple  if ive missed anything check teds post from a few days ago in this section.  parts suppliers i cant help you with but one of the nice guys on this site in the good old u s of a should be able too.

By Moz - 18 Years Ago
ron i forgot 312's dont have the nails the side seals fit in then the bolts go through them.
By Tough55 - 18 Years Ago
Thanks Moz for the step by step instructions.  I'm going to order the seals from Best Gaskets (neoprene).  Got a new oil pan gasket coming from NAPA Auto Parts Friday.  I'll post when I get this thing fixed and let everyone know how it turned out.~~~~Ron
By Moz - 18 Years Ago
g'day ron

mate it sounds good to go dont skimp on the rtv sealer too much is better than not enough

By Town Vicky - 17 Years Ago
The factory RM seal bolts were 3/8 12 points you will need a 12 point socket to remove them
By Moz - 17 Years Ago
dana-dan, town vickys right.  i use a 1/4 inch drive socket thats thin walled as the bolts arent overly tight.  you may need to grind a 3/8 socket a little thinner in the wall to fit in the retainer holes to reach the bolts.