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Topic: 427 rear main seal

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427 rear main seal (1/25)
6/14/14 10:14am

rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed

Joined: 7/24/2012
Posts: 134

Do you have to remove the engine from the car to replace the rear main seal on the engine?

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Re: 427 rear main seal (2/25)
6/14/14 11:18am

Adams' Apple

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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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No...it can be done in the car. Need to drop the steering linkage, and remove the pan. Thumbs Up

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Joel Adams
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Re: 427 rear main seal (3/25)
6/14/14 11:31am

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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Thanks. I am getting some diffferent answers on the procedure. I just had the engine overhauled and it is leaking fresh oil from the general location of the rear seal. I would hate to have to pull the engine back out of the car. I am going to continue to look into the problem. Hopefully between my mechanic and the overhaul shop they can find the leak.

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Re: 427 rear main seal (4/25)
6/14/14 1:30pm

F4Gary

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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.

Joined: 8/26/2006
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Sounds like whoever put your engine together needs to have it fixed. Not you.

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Re: 427 rear main seal (5/25)
6/19/14 8:57pm

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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The engine has a couple a hundred miles since overhaul. I have been driving it to get some time on the engine. Will the new rear main seal start to seal better after I drive it more or should there be no leaks?

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Re: 427 rear main seal (6/25)
6/19/14 10:27pm

Adams' Apple

It's not going to stop leaking if it's leaking now. The rear main seal is a rope type seal originally, but replacement seals are rubber. If not installed properly, either type will leak. To replace it, you'll have to remove the oil pan, the oil pump, the rear main cap, and loosen all of the main caps, to allow the crankshaft to drop down just a smidgeon. This will allow the upper seal to be replaced. I sure hope it has the rubber seals....the upper rope type seal is a major pita to replace...
The trick to making sure the seal doesn't leak is to off-set the ends of the seals, so that the seam between the upper and lower seals are not split at the same place as the main cap/block....one end should protrude from the engine side, and the other end of the seal should protrude from the main cap side. Don't know if that makes any sense without a visual aide....

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Re: 427 rear main seal (7/25)
6/20/14 9:31am

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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Thanks for answering my question. I am going to have to keep after my mechanic and the engine shop that did the rebuild to make it right.

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Re: 427 rear main seal (8/25)
6/27/14 1:32pm

nosal1
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Dunedin, FL - USA

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1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

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Joel, It sounds like the builder did not "Offset" the hard rubber seal (sold in the gasket set's these days) or not installed it with the seal "lip" forward to retain the oil into pan..

I hate that when it happens...Big job on a big block,albeit can be done as you have stated by slightly dropping crank to get the upper seal to rotate..Trick is to be sure to install new rear main seal correctly without hurting the seal going into upper rear main cap with each half offset,also tricky..

Good luck... Sal C

|UPDATED|6/27/2014 10:32:29 AM (AZT)|/UPDATED|

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Re: 427 rear main seal (9/25)
6/29/14 2:13pm

rep69
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1969 convertible 427 4speed

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The engine shop said they would look at the engine and determine the leak and replace the seal if needed.

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Re: 427 rear main seal (10/25)
10/1/14 9:29pm

rep69
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1969 convertible 427 4speed

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Update on the oil leak. It has been a very long summer of dealing with different people about the oil leak. Very frustrating dealing with people that do not follow through with their work. I finally got some answers to my questions . The rear main seal is NOT leaking. I have the car at a new mechanic and he told me after putting the car up on the lift that the oil pan is where the oil leak is. I am thinking that when the engine was put back in the car that it was damanged. I am going to have my new mechanic fix this after he finishes with installing the new carburetor.

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Re: 427 rear main seal (11/25)
10/2/14 5:13am

Good Morning,If I may suggest,to have your new mechanic to check valve cover bolts,and the spot where the oil pressure sensor is connected.The oil pressure sensor,in most to all cases on Vettes, is on the side of block just above the oil filter location. I have found that most mechanics state the oil leak is a rear main seal ( more money to repair)than checking the pan bolts,valve cover bolts,and sensor area.In any event glad to hear it may be the pan and not the rear main seal..Have a great day.. Sal C

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Re: 427 rear main seal (12/25)
10/2/14 10:33am

rep69
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1969 convertible 427 4speed

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Thanks for the information. I will ask him about those areas on the engine. Bobby

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Re: 427 rear main seal (13/25)
10/2/14 12:52pm

Adams' Apple

The '69 should have a brass oil pressure line fitting in the block, with a metal line going up to a junction fitting in a bracket. From there, it should have a plastic line into the interior for the gauge.You could certainly have an oil leak at any of the junctions for the oil pressure lines. Wink

I'd be leaning to it being the pan gasket, tho....especially if someone thought it was the rear main leaking to begin with. Prolly leaking from one of the corners of the pan back there.

|UPDATED|10/2/2014 9:52:57 AM (AZT)|/UPDATED|

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Re: 427 rear main seal (14/25)
10/2/14 10:06pm

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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Thank you for the information and diagram. The bottom of the pan is bent in , probably damaged when the engine was reinstalled in the car. I want to keep the original pan and hopefully get it repaired.

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Re: 427 rear main seal (15/25)
10/13/14 2:34pm

rep69
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1969 convertible 427 4speed

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It was determined that between the damaged oil pan and the original muncie 4 speed leaking that we finally found the oil leaks . I am happy to know where they coming from. Now I can get these two things fixed. This will be a good winter project. I want to save the orginal oil pan and have it repaired, and then have the muncie gone through completely

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Re: 427 rear main seal (16/25)
10/13/14 3:19pm

Adams' Apple

The only place a Muncie could leak up front is the countershaft, where it fits(snuggly) into the case bore. That area should have a thin layer of silicon spread around on it to keep it from leaking. Originally, just the tight fit kept seepage to a minimum, but over time, the case bore distorts, and it will start leaking some. The silicon will prevent that from becoming an issue. The input shaft has NO seal at all on it....and it rarely leaks. The only way for it to leak up that high is if the oil level is too high. Also, a leak from the input shaft will get gear lube onto the clutch...not a good thing.... Unhappy

Hope they got the engine Thumbs Up

oil leaks fixed, anyway....

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Re: 427 rear main seal (17/25)
10/13/14 3:47pm

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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Thanks for the info. I will update when we get the oil pan fixed and transmission out of the car and open it up.

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Re: 427 rear main seal (18/25)
10/13/14 3:49pm

Hello All, and congrats on them finding the leaks and your plan on sealing up the culprits. Joel is right about the leak between trans and bell housing etc..I wanted to ask if your Muncie trans is aluminum or like the Saginaw trans( Oh yes Muncie did have some cast iron cases) .. I have a Aluminum Muncie "Rock Crusher" in my '68 Camaro for over 20 years and have never had a leak,however I have had friend with a cast iron trans who also had a small leak and repaired just like Joel recommended..Again Great finding the problems and good luck on the repairs. Sal C

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Re: 427 rear main seal (19/25)
10/13/14 10:51pm

rep69
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1969 convertible 427 4speed

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Pic- Oil pan leak

(modified life-size image to link-aapple)

|UPDATED|10/13/2014 7:51:50 PM (AZT)|/UPDATED|

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Re: 427 rear main seal (20/25)
10/13/14 4:39pm

rep69
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I believe it is aluminum

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Re: 427 rear main seal (21/25)
10/13/14 10:49pm

rep69
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1969 convertible 427 4speed

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Pic of leak at trans

(modified large pic to link-aapple)

|UPDATED|10/13/2014 7:49:33 PM (AZT)|/UPDATED|

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Re: 427 rear main seal (22/25)
10/13/14 10:58pm

Adams' Apple

Dang! They bent to pee outta the pan, right at the drain plug! Yeeeesh! No wonder the thing is peeing!
Also...I see that the bellhousing has been welded....sure hope it is a good weld job.
The trans is aluminuminum....never seen a cast iron case on a Shark era Corvette...from the factory, anyway. If the countershaft is leaking, it will leak from between the bellhousing and the trans case. The gear oil will run both forward, down the bellhousing, and back onto the trans case. An input shaft leak will normally only run out the front side of the bellhousing, close to the engine side.

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Re: 427 rear main seal (23/25)
10/14/14 11:00am

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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Thanks for info. The oil pan is going to be fixed. The weld on the bell housing has been there for years. I am trying to keep the number matching drive train. This winter the transmission will be taken out and over hauled.

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Re: 427 rear main seal (24/25)
10/14/14 12:51pm

Adams' Apple

Be SURE, when you do have the trans worked on, to remove that small metal tag on the bottom of the shifter cover and hide it....that is the factory part number. Very rare to see one still attached to a trans because they usually get lost, or thrown away when having trans work done.... Ouch

Once you get the trans finished, re-install the tag in the same place.

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Re: 427 rear main seal (25/25)
10/18/14 11:38am

rep69
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Suffolk, VA - USA

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1969 convertible 427 4speed

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Thanks, I will be sure to keep the tag.

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