Rear main seal on an '85 305 engine.

[johnnymk]

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?

[Blazin]

85 It should be a one piece. If the dipstick is on the passengers side it is a one piece seal.

[johnnymk]

Thanks

[1976Scottsdale]

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.

[johnnymk]

So I have to remove the oil pan and loosen the main bearings?

[VileZambonie]

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.

[Lt.Del]

on my 79, 2 piece.









 

[Blazin]

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.

[VileZambonie]

The 85 K10 I just pulled the engine out of had a one piece also... so never assume lol

[johnnymk]

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.

[johnnymk]

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.

[red4wd]

The dipstick changed from left to right in 1980...

[johnnymk]

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.