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Rear main seal on 305

This is a discussion on Rear main seal on 305 within the Small Block forums, part of the Performance category; Got topics in the technical sub-forum so I thought, why not put one here too. I had a tranny go ...

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    Rear main seal on 305


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    Got topics in the technical sub-forum so I thought, why not put one here too.

    I had a tranny go out on me so I am in the process of replacing that now. But since I have it out I figured I may as well put a new rear main seal on the engine. Fix a problem before it starts you know. So would anyone like to see a how-to on this? Might help others out as they have helped me in my tranny swap. Ill be taking pics so might as well post them right? Be looking for them as they come! Thanks guys.

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    Re: Rear main seal on 305

    What year is it? They changed the rear main seal to 1-piece in '87, but either is fairly straightforward... the downside is you need to drop the pan to do either. The 1-piece seal is easier to replace because you don't have to remove the main cap, the 2-piece you do. The 1-piece you drop the pan, remove an aluminum retainer and change the seal, unfortunately the flywheel/flexplate has to come off for this. The 2-piece is slightly more involved... since your trans is out I'd say go ahead and remove the flywheel either way, easier to work around.
    http://4x4mecca.com/tech_article/rep...ll-block-chevy

    '92 Sierra (TBI 383/Vortecs/Comp 08-412-8/EBL/4L60/3.08s), '78 Malibu (Vortec'd 350/4-speed/2.29s), '87 Pontiac Fiero GT (2.8 v6/5-speed)


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    Re: Rear main seal on 305

    You don't have to drop the pan on the 1 piece rear main seal design. I was in the same boat as you with the tranny out for repairs and replaced the rear main seal. I changed out just the seal, not the gaskets around the aluminum housing. If you look at the seal, they are 3 places where you can use a flat blade screwdriver to carefully pry out the old seal. Carefully tap the new one in and you are good. A buddy of mine bought my old truck and it's still running today, years later and tens of thousands of more miles, still no leaks.
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    Re: Rear main seal on 305

    I have read the article at: 4x4mecca dot com previously posted in this thread...

    AND this guy was fortunate enough to be replacing a fairly new rear main seal; he clearly did not have any trouble removing the upper half of the 2 piece rear main seal ... engine block side...
    Moreover, he did not mention using anything other than a hammer/punch/screwdriver to remove it..

    I DO HAVE TROUBLE REMOVING MINE...

    Mine will not budge, anybody have any tips, tricks suggestions etc?

    Not having much luck with google or youtube on this one...

    thanks in advance.

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    Re: Rear main seal on 305

    Quote Originally Posted by Bohemian View Post
    I have read the article at: 4x4mecca dot com previously posted in this thread...

    AND this guy was fortunate enough to be replacing a fairly new rear main seal; he clearly did not have any trouble removing the upper half of the 2 piece rear main seal ... engine block side...
    Moreover, he did not mention using anything other than a hammer/punch/screwdriver to remove it..

    I DO HAVE TROUBLE REMOVING MINE...

    Mine will not budge, anybody have any tips, tricks suggestions etc?

    Not having much luck with google or youtube on this one...

    thanks in advance.
    Winning tip/trick for you all is...
    ended up buying a 3ft piece of brass round stock 1/8" in diameter which was as close as I could get based on mating side in rear main bearing housing I already removed 3/16" was too big & anything smaller than 1/8" was too flimsy. I also found that W/D 40 made the petrified seal a little bit more pliable. The 1/8" homemade drift cut to 14" gave me room to hit it & wrap around crank It was slow going, I won.

    Major PITA, still better than dropping crank & pulling tranny...

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    Re: Rear main seal on 305

    I believe that the rear main seal is leaking in my vortec 350, it's a one piece seal I believe. How is the best way to replace the seal? I'm gonna try some Lucas engine treatment first though. Used the stuff in high school on a 4.3 that had a front main leaking, stopped the leaking right away.
    93 Chevy S10 ext. cab. 4.3 5 speed 4wd -> 5.3 AWD swap in the works
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    Re: Rear main seal on 305

    dont put lucas in there to fix a seal,even if it slows the leak the seal will just get worse and worse...besides have you seen how thick that stuff is, its like molasses...to each his own about the lucas but i dont trust it especially not to fix a leak...

    but to answer your question the easiest way to fix the rear main is safely jack the truck up and put jack stands under it then, unbolt the driveshaft take it out, un bolt the crossmember leave it where it sits, unbolt the exhaust, torque converter bolts, unhook the shift linkage, bell housing bolts, cooler lines,etc.. now just slide the transmission and cross member back together just enough to get to the flywheel bolts and rear main seal...saves a ton of time instead of removing the transmission completely and you dont have to worry about it falling on you because the crossmember is still under the transmission...
    Last edited by Big Red 1500; 12-30-2011 at 07:59 PM.




    1997 RCSB Z71 5.7 Vortec, 411 PCM , Ultra gauge, SS Headers, EGR Delete, Magnaflow Hi-flow cat assembly, Cat back with flowmaster 40, Transbuilderguy Built 4l60E, Yukon Duragrip Posi 3.73, 33 x 12.5 Maxxis Big Horn

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    Re: Rear main seal on 305

    You should be able to get to the flywheel bolts with a boxed end wrench.

    '92 Sierra (TBI 383/Vortecs/Comp 08-412-8/EBL/4L60/3.08s), '78 Malibu (Vortec'd 350/4-speed/2.29s), '87 Pontiac Fiero GT (2.8 v6/5-speed)


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    Re: Rear main seal on 305

    we used to slide them back as far as the cross member would let us i think a foot or so and it was plenty




    1997 RCSB Z71 5.7 Vortec, 411 PCM , Ultra gauge, SS Headers, EGR Delete, Magnaflow Hi-flow cat assembly, Cat back with flowmaster 40, Transbuilderguy Built 4l60E, Yukon Duragrip Posi 3.73, 33 x 12.5 Maxxis Big Horn

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    Re: Rear main seal on 305

    Quote Originally Posted by JadXtreme View Post
    I believe that the rear main seal is leaking in my vortec 350, it's a one piece seal I believe. How is the best way to replace the seal? I'm gonna try some Lucas engine treatment first though. Used the stuff in high school on a 4.3 that had a front main leaking, stopped the leaking right away.
    I believe the first year of the one piece rear main seal on a small block chevy was 1985, but you can search autozone by make, model etc., and find out for sure...

    IF you have a 2-piece seal it is a whole lot easier than if its a one-piece seal...
    Earlier post in this thread from 4x4 meca details it very well...

    Also, depends on whether you have a 4x4 or not, 2 piece is easier still with 4x4...

    One piece seal ... you will need to slide tranny back to get to it...
    Last edited by Bohemian; 12-31-2011 at 04:58 PM.

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    Re: Rear main seal on 305

    Quote Originally Posted by JadXtreme View Post
    I believe that the rear main seal is leaking in my vortec 350, it's a one piece seal I believe. How is the best way to replace the seal? I'm gonna try some Lucas engine treatment first though. Used the stuff in high school on a 4.3 that had a front main leaking, stopped the leaking right away.
    also, on the stop leak stuff... they all work pretty much the same way... your seals are dried out so they shrink and start to leak... the stop leak or whatever flavor you use makes them swell up a little bit... usually its a very temporary fix, often when it starts leaking again, you will pump the engine dry in minutes...

    so don't wait too long before fixing it right...
    Last edited by Bohemian; 12-31-2011 at 04:58 PM.

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    Re: Rear main seal on 305

    I already put the Lucas stuff in today. When I used it in high school, the 4.3 tbi engine had about 50K miles on it when it started leaking. I drove that truck until I got rid of it, 90K on engine, and it never leaked again.
    93 Chevy S10 ext. cab. 4.3 5 speed 4wd -> 5.3 AWD swap in the works
    42 Ford GT8 1.5 ton truck, military model. 226 flathead I6, granny 4 speed, flatbed
    07 Saturn Outlook XR

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    Re: Rear main seal on 305

    Lucas = slippery. My only personal concern would be ring seal. The 4.3 in mine was a bit of a leaker, but it wasn't too bad. Surprisingly with 230k on it, it didn't really burn much oil if at all. It puffed a little at startup from the valve seals but that was it.
    Last edited by Doober; 12-31-2011 at 09:33 PM.

    '92 Sierra (TBI 383/Vortecs/Comp 08-412-8/EBL/4L60/3.08s), '78 Malibu (Vortec'd 350/4-speed/2.29s), '87 Pontiac Fiero GT (2.8 v6/5-speed)


 

 

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