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Avoid This Mistake: Leaky Rear Main Seal
Common mistakes made when building or restoring a classic Mustang, #6: rear main shaft seal
This is the sixth installment of our Restoration Mistakes series, dealing with common mistakes made when building or restoring a classic Mustang and how to avoid them. As we said at the beginning of this series, “We’ve been horsing around with classic Mustangs for more than four decades and have come to the following conclusion: we’ve never stopped learning from our mistakes nor have we stopped making them. When you’re restoring a classic Mustang or building a hot restomod it is important to see the pitfalls before you find them, not after stumbling and falling into them. Silly stupid mistakes we make time and time again. Whatever your reason for screwing up, we’re here to remind you we have been there ourselves and know how not to make the same mistakes again.” Our newest tech tip deals with:
Seal The Deal
Isn’t it something how we don’t give enough thought to the most obvious elements of a restoration project? We’re reminded of this when there are oil spots on the floor from a fresh restoration—so irritating! Seal and gasket installation requires the tender touch and close attention of a neurosurgeon. Gasket contact surfaces must be hospital clean and milled perfectly—irregular surfaces will leak no matter how much sealer you slather on them.
As a rule gaskets do not require sealer except at joints, yet we watch engine builders use excessive amounts of sealer on them. It is redundant and unnecessary. The gasket itself is a seal and doesn’t need any help. Fel-Pro’s composite steel/silicone gaskets don’t require any sealer. When you apply sealer to gasket surfaces, lay down a hair-thin layer. If it is oozing out of joints you’ve used too much. Word to the wise — stop wasting your money on cork gaskets. Step up and spend the money on high-quality one-piece oil pan and valve cover gaskets. When you rebuild your small-block Ford opt for a one-piece rear main seal conversion. Nearly any machine shop can do it and it is worth every penny for improved durability.
There are two basic types of shaft seals: garter spring and conventional lip. When you install a garter spring-supported seal, keep in mind the spring can pop out when you are driving the seal in. Without the garter spring a seal doesn’t seal. Take a big wad of assembly lube or wheel bearing grease and pack the garter spring cavity. This keeps the spring in place during installation. Seal lips should be generously lubricated to where they are wet during start-up, especially if an engine, transmission, or rear axle is going to sit for a while before operation. Dry seals and spinning shafts don’t mix. A dry seal will tear and then leak.
Now where did we put that bag of Speedy Dry?