Transmission sealant additives

They're basically solvents that soften crud deposits in your tranny, hopefully disolving them. They also soften seals that are 'semi-hardened' from age, but if they're hard from overheating, they won't work on seals. Because it's a solvent, it might actually make your tranny fluid thinner and increase leaking. If your tranny is really gooey inside, they can knock loose globs of junk that can lodge in passages and make the problem even worse.

Not that they're never any good. I put some in a couple cars (Trans-Medic) years ago and it completely fixed my shifting problems in all 3 of the cars I used it in. None of these trannys leaked, they just shifted very hard or wouldn't go into high gear. In each case, TM fixed the problem, but that doesn't mean it'll work for you. Having it inspected by a pro is a good idea if it's leaking. You may only be looking at a few seals that are easy to replace - or a complete tear down. Either way, bad leaks can't be fixed with a can of anything. God luck, - Jeff G

We don't know if your just buying a little time or what, GS. However, with most problems, diagnosis is the key. Know your enemy. Try to determine where the transmission is leaking. A front seal requires trans removal. But a rear tailshaft seal is fairly cheap to replace. And sometimes you can have a bad leak from the o-ring where the speedo shaft is attached and that's a quick fix. Don't let your transmission die from lack of fluid because of this leak.

Most of them work by softening and slightly swelling the polymer-based seals in the transmission. They seem to work (at least to a degree) but my experience is that the softening additives are somewhat volitile and tend to leave the fluid fairly quickly, at which point the seals shrink again.

The above is assuming that the seals are intact and just shrunken/hardened... if the tranny has a seal that is failing (torn, cracked, etc) then the additive may mask the symptoms for a while, but the seal will continue deteriorating and the problem will be back with a screaming vengeance in the future.

Now, I've found them much LESS effective in terms of sealing external leaks than in terms of improving shifting by reducing internal leakage. I think the difference is that even if the additive reduces external leakage, there's still SOME leakage. But reducing internal leaks can make a difference in shift quality without achieving a perfect seal.