Temporary Rear Main Seal Leak Fix

[chezhed]

I have a leak in the rear main seal and until I get my gearhead buddy to fix it  I would like to use the thing a bit....short trips but hate the oil leak idea.  I ran across stuff called White Shepherd that was recommended...anybody ever try it?  Claims to fix such leaks.

[RV Mech Tech]

chezhed- your rear main seal is one of two styles -the earlier is a two piece seal without a garter spring (old style Chev) or the newer one piece double lip seal with a garter spring that requires the removal of the transmission to replace- officially G.M. did not us the one piece seal in 86 on passenger cars but I have seen a few of them on truck engines as early as 1984- the additives  to cure oil leaks work and don't work - if the seal  is not damaged  then the additive will soften the material in the seal and make it swell and may stop it from leaking for a while but eventually it will have to be replaced- if the seal is damaged then nothing will work and replacement is required - I have found that these additives work better on the newer seal material but again its a gamble so if the additive is not expensive then its worth a try to get you through - different applications may have different gasket material/seals such as the difference between cars and light trucks and heavy duty applications such as motorhomes - rear main seals included- MHomes are considered extreme heavy duty application and the actual engine temperature will vary depending on usage so heat and wear and tear take a toll  more so in these cases - I have used these additives with moderate success in similar situations - when your mechanic has the rear main cap off (two piece seal ) have him check the rear main cap  surface behind the bearing shell - pull the bearing half out of the cap to inspect) - I have found more than one with a cracked main cap in this area that will leak oil out after the new seal is installed - many of the Chev small block 400 c.i. had this problem and some of the higher c.i. truck and marine blocks cracked as well.   Hm?

[Froggy1936]

hi mech  is this true on the 4 bolt main caps as well Since i replaced all my bearings rods & mains & 2 piece rear seal (offset) i have a small oil leak from that area  Frank

[RV Mech Tech]

Frank - sorry -never saw your post!! - did you use sealer between the cap and block surfaces? - Loctite has a special sealer for this - the parting surfaces can be a passageway for oil if there are any imperfections including any warpage in the cap -even a thou would do it- the 400 small block Chevys were bad for that including cracked rear main caps - that sealer or any comparable sealer would do and is applied at the rear parting surfaces of the cap and block and on the two halves on each side of the two piece seals - and the racers used to offset (the same as you have )  the seal ends- in other words rotate the seal so the ends would not be open at the parting  surfaces of the cap and block but would   be inside the the cap and block area - and the parting surfaces would have the solid part of the seals - also you have to check the surface of the crank journal where the seal rides for both the rear main and the front harmonic balancer neck - any imperfections will ruin a new seal - later Chevs have the one piece seal at the rear - there are repair sleeves available for a harmonic balancer  neck and for the crank rear main surface on the one piece seals - and don;t forget your PCV system (Positive Crankcase Ventilation System)-  if its plugged oil will be forced out of any opening it can  find including out the seals.   

[Froggy1936]

Thanks for comments, I did not know about the sealer compound being necc. The crank looked perfect, Even the old 90K bearings were in very good shape. after seeing the old parts i attributed the loss of oil pressure to oil breakdown after extreme high temp and high RPM operation in Texas ambient temp was 110 and RPM were pushed to 4000+  after which pressure dropped noticeably. Though now with new bearings and oil pump pressure is higher than it was before Will have to check for cracks at overhaul time Whenever that is  Frank

[RV Mech Tech]

Frank - that sealant is Loctite #515  Flange Sealant - it comes in a small tube and is colored red- I use it only at the rear parting surfaces of the cap and block - this sealant is meant for machined parting surfaces and  is used both as an auto and industrial  sealant- one other leak area is the rubber seals on the ends of the pan where they meet the block and main cap (rear main cap0 surfaces - for that area I use a dab of Permatex aircraft sealant .

[Oz]

I tried some rear main seal additive.  It's supposed to swell the seal.  It's supposed to work within driving 250 miles after putting it in.  I drove that distance.  It was still leaking the same amount by the end of the trip.

But, I have to say that I'm sure it depends on how shot the old seal is too.