Rear main leak options

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68conv4sp

New Member

Oct 24, 2005

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Nov 3, 2008

#1

• Nov 3, 2008

• #1

My '68 has a '68 block and a TKO 500 trans. About 6 months after installation oil began to drip off the bottom of the bell housing. I did not do the install so I don't know what kind of seal was used or what orientation. The leak is about 4 or 5 drops per night, so really not a ton in a month's time. But it is annoying.

Would I be able to reach all of the bolts that compress that seal? Would it be helpful to back them off and retorque them ( I have a high qual torque wrench). I don't have the skill or dollars to do it right (R and R). What do you think?

 

rhyno9

Founding Member

Oct 30, 2002

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Oswego Illinnoying

Nov 3, 2008

#2

• Nov 3, 2008

• #2

If it didn't leak before the tranny install I would guess is that it's not the rear main.

My guess is you had a new flywheel put on at the time of the tranny install? They probably didn't put sealant on the flywheel bolts. The threads for the flywheel on the 302 are open to the crankcase. Oil will wick up and out the thread in the amount that you are seeing. The fix is to pull the driveshaft, tranny, clutch and then remove and apply sealant to each flywheel bolt and then torque them down to 90 ft lbs. reinstall clutch, tranny, and driveshaft.

 

6

68conv4sp

New Member

Oct 24, 2005

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Nov 3, 2008

#3

• Nov 3, 2008

• #3

I think you diagnosed it well. There was no leak before the new flywheel/trans. If it is unsealed bolts, the amount of leakage should remain constant (assuming I still use 15W-40 and don't change to someting thinner). Can that oil get onto the clutch surface and do any damage?

 

rhyno9

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Oct 30, 2002

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Oswego Illinnoying

Nov 3, 2008

#4

• Nov 3, 2008

• #4

68conv4sp said:

Can that oil get onto the clutch surface and do any damage?

Click to expand...

It could....... but truthfully the path of least resistance would indicate that as soon as the oil reaches the crank snout it will gravitate down between the flywheel and the block. I don't think it would be able to wick it's way to the face of the flywheel and clutch disc.

With a helper the job should take an afternoon if you have all your tools and parts lined up. Don't forget to have a cap for the trans and an alignment tool for the clutch. I have found it's easier to align the trans when you align and then put tension on the throwout bearing.

I use permatex 2 to seal the bolts.

 

R

rc4mike

Member

Oct 10, 2006

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Nov 3, 2008

#5

• Nov 3, 2008

• #5

i have the same problem with my rebuilt 408W. During breakin on the dyno, the builder claimed no leaks. Now with the new flywheel and trans installed i have a similar leak. Looks like coming from rear seal, but could be flywheel bolts. I did not seal the bolts.....didnt know you had too!! Does the 351/408 have the same condition? ie needing sealant on the flywheel bolts?

thanks
mike

 

rhyno9

Founding Member

Oct 30, 2002

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Oswego Illinnoying

Nov 3, 2008

#6

• Nov 3, 2008

• #6

rc4mike said:

Does the 351/408 have the same condition? ie needing sealant on the flywheel bolts?

thanks
mike

Click to expand...

Everything I have read would indicate that the 351w flywheel bolt holes are blind so oil should not get past. I haven't checked my stock late model crank. I have a leak from somewhere back there so I am at least going to drop the pan and then I can check for sure.

RV

 

R

rc4mike

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Oct 10, 2006

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Nov 3, 2008

#7

• Nov 3, 2008

• #7

i got rid of my original 94 crank so cant verify if the holes are closed. Wish i still had it. Let me know if you find anything. Sure would be a pain to drop trans. only to find out bolts are closed. I suspect my pan is not sealing properly. Have an occasional leak at front seal as well. Both front and rear are brand new.


Mike

 

R

rc4mike

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Oct 10, 2006

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Nov 3, 2008

#8

• Nov 3, 2008

• #8

i got rid of my original 94 crank so cant verify if the holes are closed. Wish i still had it. Let me know if you find anything. Sure would be a pain to drop trans. only to find out bolts are closed. I suspect my pan is not sealing properly. Have an occasional leak at front seal as well. Both front and rear are brand new.


Mike

 

418mach

New Member

May 24, 2008

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Sydney

Nov 4, 2008

#9

• Nov 4, 2008

• #9

68conv4sp i am assuming from your post that you haven't had any recent work done to your motor if your leak is from the flywheel bolts that could come out on the clutch surface or the front of the flywheel if you drop your starter you may get a good enough look inside to determine where the leak is. what about the front seal on the box.
with my 418 aftermarket stroker crank the flywheel bolts are open.
i have a two piece rear seal which has leaked from start up the aftermarket cranks i have been told have a smaller slinger and need a one piece seal and preferably to use a racing seal ? and increase pcv vacuum if possible i only have -8.5ins at idle. i will be having the motor stripped down and machined for a one piece seal

 

rhyno9

Founding Member

Oct 30, 2002

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Oswego Illinnoying

Nov 9, 2008

#10

• Nov 9, 2008

• #10

rc4mike said:

i got rid of my original 94 crank so cant verify if the holes are closed. Wish i still had it. Let me know if you find anything. Sure would be a pain to drop trans. only to find out bolts are closed. I suspect my pan is not sealing properly. Have an occasional leak at front seal as well. Both front and rear are brand new.


Mike

Click to expand...

Just an update in case someone ever does a search.

I finally got around to pulling the trans and flywheel. I can say that my stock 94+ 351w crank has blind holes so no sealant is required. Once I pulled it apart I could see that my leak appears to be from the oil pan.

Good luck chasing the leaks