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235 rear main seal: rope or neoprene

Discussion in 'The Hokey Ass Message Board' started by Vetteman61, May 21, 2010.

  1. Vetteman61
    Joined: Oct 28, 2008
    Posts: 217

    Vetteman61
    Member
    from Tennessee

    My 235 is freshly rebuilt, however oil leaks out of the dust cover. I believe this oil is also causing my clutch shudder on take off after the car has been driven a while. I assume the rear main seal is the cause of the oil (I don't think it's coming from the rear of the valve cover).

    Has anyone dealt with 235 leaky rear main seals? What's everyone's opinion on the best type of seal, rubber (neoprene) or rope? If I could get this leak stopped (and consequently, the shudder) that would be the end of my major problems, so I'm looking forward to solving this.

    I don't have a rack anymore (the government tore our shop/business down to put up a parking lot).

    brandon
     
  2. terd ferguson
    Joined: Jun 13, 2008
    Posts: 3,646

    terd ferguson
    Member

    It could be the oil is coming from somewhere else besides the rear main seal. In my case, it's coming from the side cover and migrating to the trans dust cover, dripping down to the ground from there. Clean your engine really well and find out for sure where it's coming from. It can fool you. I found out leaking oil will migrate towards heat, even moving UP the engine.

    That said, I think the general consensus is that the N.O.S. asbestos rope seals are the best for the rear main seal.

    Good luck and let us know what happens. It always helps somebody later down the line when searching.
     
  3. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,291

    junkyardjeff
    Member

    I have a 57 235 in my 37 p/u that I rebuilt and the rear main leaked shortly after starting to drive it (motor sat for 10 years before being driven but started occasionally),I eventually tore it down and found that I had one half of the seal in backwards and it could also come from the pan gasket if not installed properly.
     
  4. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,244

    Road Runner
    Member

    Not sure what transmission you have, but with the original 3 speed some gear oil dripping from the clutch cover is normal.
    The throwout bearing is lubed by a 1/4" hole in the main shaft collar of the transmission.
    Excess gear oil ends up inside the bellhousing and drains from the hole in the clutch cover.

    If you swipe the dripping with your finger and smell, you know right away if its motor or gear oil.

    You can get clutch chatter in low gear (1st and reverse), when the main shaft of the transmission is worn and has play sideways, especially if the pilot bearing is worn as well.

    Later 235s are machined for the neoprene seal and work well with it. I got them in both my late 235 and 261 without any leaks.
    I read somewhere the new production rope seals don't have asbestos any longer and don't last as long ?
     
    Last edited: May 21, 2010
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  5. Rrumbler
    Joined: Apr 4, 2006
    Posts: 79

    Rrumbler
    Member

    Your clutch chatter may not be a result of the oil, wherever it is coming from. If you didn't replace your engine mounts, or if they are possibly loose or broken, that will cause clutch problems due to excess movement of the engine in the chassis. As to the seal, my preference is for the old fashioned "rope" seal; ain't ever used a rubber one.
     
  6. Vetteman61
    Joined: Oct 28, 2008
    Posts: 217

    Vetteman61
    Member
    from Tennessee

    Thanks for the replies everyone.

    I believe the shudder is oil related mostly because if the car sits for a while it doesn't shudder, but once I have driven it it starts to do so worse. The longer it sits, the longer it goes without shuddering, making me believe it's the oil.
    I suppose this could somehow be linked to wear in the transmission, but I don't see how (which doesn't mean much with my limited experience).

    When you say "later' 235's, which years does that encompass?

    Do you mean that no matter what, a 235 will always have some type of fluid coming out of the dust cover?

    thanks,
    Brandon
     
  7. Vetteman61,

    I have a 216 in my 48 chev and from what I've read, almost without exception, all the chev 6 cyl. engines develop a small leak where the 2 halves of the rope seal meet. If you go to the VCCA (Vintage Chevrolet Club of America) forum, there are threads on the this very subject. What some of the gear heads have done with some success is to make sure 1 half of the rope seal is just a tad long and use a dab of silicone sealer where those 2 halves meet before assembling the oil pan to the engine. I haven't tried it myself. Those guys recommend using a rope seal. My car has a small drip, no clutch chatter though... I just live with it.
     
  8. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,862

    Truckedup
    Member

    If you use a rope seal buy one from Best Gaskets,all the others are shit except for asbestos NOS.55 and up 235-261 should be machined for a rubber seal.Some crankshafts have a series of small serrations around the area where the seal rides on the crank.These cranks seem to work better with a rope seal.
     
  9. waldo53
    Joined: Jan 26, 2010
    Posts: 837

    waldo53
    Member
    from ID

    There's a good Tech Tip on the stovebolt.com website that describes how to do this right, step by step. I've read somewhere that these seals were designed to leak a little, otherwise they wouldn't last long (forgot where I read that though).
     
  10. 6inarow
    Joined: Jan 24, 2007
    Posts: 2,188

    6inarow
    Member

    Here is what I did - this was on a total rebuild though: 1 piece rear main.......
     

    Attached Files:

    Last edited: May 22, 2010
  11. Kool49
    Joined: Mar 14, 2010
    Posts: 297

    Kool49
    Member

    That looks very nice , how did it work for you ?
     
  12. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    The rope seal will not leak if done right. You must not have to much bearing clearance. The seal needs to be formed in the engine a little smaller than the crank. The ends of the seal need to be cut flush with the block and cap, with a raiser blade. Do this with a round piece holding the seal down and in place.
     
  13. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    Also it could be the expansion plug at the rear of the camshaft. You need to use sealer on that when you put it in.
     
  14. RichFox
    Joined: Dec 3, 2006
    Posts: 9,860

    RichFox
    ALLIANCE MEMBER

    I did much the same thing as 6inarow except I machined the crank flange down .060 (I think. Been a while) and used a one piece seal that did not require setting up the block and machining it. It was covered in the 12 Port news at the time. Last I heard it was working fine.
     
  15. Ryleej3
    Joined: Mar 6, 2006
    Posts: 58

    Ryleej3
    Member
    from Washington

    Thanks everyone. I had the same question. Rope or rubber. I'll go with rope and follow the tips in this thread to get it right.
     
  16. Ryleej3
    Joined: Mar 6, 2006
    Posts: 58

    Ryleej3
    Member
    from Washington

  17. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    I have put hundreds of rope seals in. They will not leak if you do it right. Buick used them long after ever one else switched.
    You have to form it almost to the crank size, just a little smaller. You have to cut the ends flush with the cap and block. Best to use a round piece the size you formed it to , like a socket. hold it in place with that while you trim the seal with razor blade. Use a little sealer at the seal and cap, not much. Put grease on the seal so you do not burn it when you first start it. If you leave the seal long it might not let the cap come all the way against the block. Last the main bearing most be to specks, to loose it will leak.

    My 56 chev with a 265 has the seal from the factory, it has a 140,000 miles on it. It does not leak oil at the rear main. Non of them came from the factory leaking oil.
     
  18. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,552

    sunbeam
    Member

    Rubber seal is for 1955 up.
     
  19. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    Sorry but 55,56,57,58.265,283 V8 still had rope seal from the factory. I think it was about 59 when the V8 changed.
     
  20. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,552

    sunbeam
    Member

    I don't think a 235 was a v8
     
    briggs&strattonChev likes this.
  21. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    Your right of course it was a 6 cylinder.
    But the 6 cylinder had a rope seal through 62.
     
  22. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,552

    sunbeam
    Member

    Chevrolet changed their machining in 55 so rubber seals work. before that it's 'better to stay with the rope.
     
  23. I just had this issue this past weekend, although it was with a '58 283 V8. We had the engine in my wife's 58 Bel Air rebuilt. After I put it in & broke in the cam, I realized it was leaking oil and throwing it everywhere off the flex-plate.
    I thought it could be the oil pan but it only leaked while it was running. Either way, I had to pull the motor. I had suspected that the guy who rebuilt it ma have used a '59 and up neoprene rear seal. We bought a neoprene seal made for 55-58 SBCs to replace the rope seal. When I pulled it apart it had a rope seal.
    It came out really easy from the block side. I just pushed on one side with a piece of plastic until the other side pushed up a little bit. My wife was able to use some needle nose to pull it right out. It came out like butter. I don't know if he didn't put it in right or what.
    Anyway, I put in the new seal & used some Permatex Ultra Copper at the rear of the seal in the rear main cap & where the cap meets the block. I let it sit for 24 hours before adding oil & starting it. Leak fixed. Thank God!

    Sorry for the long ass story. Point is, was it a poor installation of the rope seal or what? Who knows. I'd go with the neoprene seal.


    Posted from the TJJ App for iPhone & iPad
     
  24. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    It was not put in right. If done right it will not come out easy. They use to make a tool that had a screw on it with a handle to pull it out. You had to turn the crank at the same time to get it out. They also made a tool that you could drive a shim in on top of the seal to put more pressure on it..
    If they are done right they work very well. But most of the guys today have no experience with these seals. Another problem is the cranks have to be ground with no more than .0005 run out at the seal dia from the mains. The cranks that I have used are not that close.
     

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