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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: johnnymk on July 04, 2007, 08:25:12 pm

Title: Rear main seal on an '85 305 engine.
Post by: johnnymk on July 04, 2007, 08:25:12 pm
I have this engine in my '83 C10 pickup. The rear main seal is leakng. Anyone know if it's a 1 piece or 2 piece seal?
Title: Re: Rear main seal on an '85 305 engine.
Post by: Blazin on July 04, 2007, 10:04:29 pm
85 It should be a one piece. If the dipstick is on the passengers side it is a one piece seal.
Title: Re: Rear main seal on an '85 305 engine.
Post by: johnnymk on July 05, 2007, 12:33:44 pm
Thanks
Title: Re: Rear main seal on an '85 305 engine.
Post by: 1976Scottsdale on July 06, 2007, 08:48:28 pm
1986 and up are one-piece rear main seal engines.  IF your engine is an 85 or earlier, regardless of which side the dipstick is on, it will be a 2 piece seal.  If you need to know for sure, remove the trans inspection cover and look between the flexplate and the engine.  You will be able to see the back of the crankshaft.  The 2 piece engines will have an oddly shaped rear portion of the crank.  one side will be circular and the other square.  If it is a one piece rear main, it will have a completely circular rear crank portion.  Come to think of it, remove the alternator if you cannot see behind it and then write down the numbers on the pad at the front of the block just in front of the passenger side head.  then go to 73-87.com and follow the link to mortec and decode the number using the small block chevy suffix code page.
Title: Re: Rear main seal on an '85 305 engine.
Post by: johnnymk on July 06, 2007, 09:51:09 pm
So I have to remove the oil pan and loosen the main bearings?
Title: Re: Rear main seal on an '85 305 engine.
Post by: VileZambonie on July 06, 2007, 10:32:02 pm
If you have a 2 piece rear main seal you need to remove the oil pan, the oil pump and the rear main bearing cap. If you have a one piece you have to pull the trans.
Title: Re: Rear main seal on an '85 305 engine.
Post by: Lt.Del on July 07, 2007, 01:01:38 am
on my 79, 2 piece.


(http://www.delbridge.net/seal3.JPG)



(http://www.delbridge.net/seal4.jpg)


 

Title: Re: Rear main seal on an '85 305 engine.
Post by: Blazin on July 07, 2007, 08:37:48 am
I have always thought 85 was the first year of one piece seals. My 84 was built in Aug 84 and it had a 305 with a one piece seal. The 85 305 thats in it now also has a one piece rear seal. Both of them had the dipstick on the passegners side.
Title: Re: Rear main seal on an '85 305 engine.
Post by: VileZambonie on July 07, 2007, 09:03:55 am
The 85 K10 I just pulled the engine out of had a one piece also... so never assume lol
Title: Re: Rear main seal on an '85 305 engine.
Post by: johnnymk on July 09, 2007, 02:57:44 pm
My engine is probably an '84. I checked the trans availability at Autozone and they don't show a 350 trans for '85.But they do show a 350 for '84.

I also checked rockauto.com for crankshaft seals. Both '84 and '85 list one piece seals.
Title: Re: Rear main seal on an '85 305 engine.
Post by: johnnymk on July 11, 2007, 03:34:57 pm
I removed the trans. The flexplate attaches to a 1/2" thick unusual shaped casting at the end of the crank. It doesn't appear to be removable. So it appears to be a two piece seal, since there is no way that a seal would fit over it.

I checked Autozone and they list three diffferent types of two-piece seals for that year and model. I guess I have to take it out to match it.
Title: Re: Rear main seal on an '85 305 engine.
Post by: red4wd on July 11, 2007, 03:44:40 pm
The dipstick changed from left to right in 1980...
Title: Re: Rear main seal on an '85 305 engine.
Post by: johnnymk on July 13, 2007, 03:21:35 pm
I changed the seal. You should have seen how the lower part just fell apart as I took it out. It's no wonder it was leaking.