I'm wondering if I should use synthetic grease to lubricate the chassis and synthetic 80w-90 lubricant for the differentials in our '95 and '97 Blazers.

The AMSOIL instructions say that I should not use a synthetic lubricant in axles that are sealed with RTV sealant. How does one know if the axles are sealed with RTV sealant and would it be worthwhile to remove the RTV compound and use some other sealant?

Thanks,
-- recurve

Yeah, next time you get your fluids in the rear diffy changed, go with a plain old Felpro gasket. It's just a few bucks. Then, use an aircraft quality sealing agent after you have drained and flushed with solvent - and make sure that you get ALL of the old sealing agent and the old paper/cork seal off. The backplate of that pumpkin and the casing face must be *pristine*.

Apply the aviation seal in a *light* coat on the metal surfaces that the gasket sits on, let air dry for 10 minutes until tacky. Put the gasket in place and bolt up the rear cover plate. Using a torque wrench here avoids overtightening, split seal, etc.

Once done, pull the filler plug and give it a good 3 quarts of Valvoline GL-5 80w-90 (or until it runs out of the plug hole). I buy it in a "nipple tube" that's squeezable because you are never going to "pour" gear lube in from a quart bottle. ;) Once done, plug it up and tighten until snug. Forget about it for 25,000 miles...though you still want to check it every 9K or so to make sure it is still full, and not a mixture of oil and water if you do deep water off-roading.

Synthetics are made of a base that is man made, and as a result, the molecular sizes of the chains that make up the fluid are of uniform size. If there is any defect in the RTV seal that many lazier shops do (which is perfectly OK too, I may add) the fluid you put in there will not stay there long. It will leak out pretty quick. Organic oils are made of rather randomly sized hydrocarbon-like bonds. Like a clotting agent, when enough of them pile up around a small leak, they effectively seal it off.

There also may be some minor chemical interaction between standard RTV silicone and the agents used in synthetics as an anti-varnish and detergent ingredient. Perhaps swapping to or using a "Fuel grade", high temp silicone sealant (Also called Red sealant) may allay any fears of using silicone and synthetics in the same place. Food for thought and research!

Should be able to just drop out the old and add the new synthetic without the other changes.

Thanks for the replies wolfox and blazerLT.

What exactly is a "gasket?" Is it a cork like belt that runs around the edge of two metal plates that are bolted together? In the Haynes manual I see them using a chisel-like device called a "gasket scraper" to remove some oily residue. I'll ask the local auto parts store about Felpro gaskets.

I used AMSOIL's online order system. It is a little clunky but kind of cool. I could enter my vehicle's make, model, and year and then they told me what maintenance items they carried for our Blazers. That online order system put up a flag with the 80W-90 lubes saying they might attack RTV sealant. When I called AMSOIL tech support to ask about it, they said to disregard the comment. They said they use some third-party software tool to generate the list of parts and it automatically adds various warnings. The tech support says that all AMSOIL lubes do not attack RTV sealant and are actually safe with them… go figure. Anyway, I'm still a bit cautious.

wolfox, when you get the chance, could you be more specific about the aviation sealant or the "red" sealant? If that's what you use on your truck, and it seems ok, I'd like to do the same. What is the brand and name of the sealant you recommend?

Thanks in advance,
-- recurve

Aviation Sealant - Permatex Part number: 80017 - A bottle of this stuff will last you a lifetime of water pump, head gasket, valvetrain cover and tranny pan as well as oil pan repairs.

http://www.permatex.com/products/prodidx.asp?automotive=yes&f_call=get_item&item_no=80017

For high temp application requiring a little more protection and assurance that the seal will hold under pressure, vacuum and exposure to solvents:

http://www.permatex.com/products/prodidx.asp?automotive=yes&f_call=get_item&item_no=81855

Adding a thin bead of any of the above and then seating your new gastet into it will make pretty much sure that it will not leak. Be sure to treat both surfaces with this stuff *AFTER* a thorough cleaning. Remove all old gasket materials, oils and solvents before brushing or squeezing on these gasket materials.

If you use RTV Silicone, you may press the gasket down into it and bolt up your parts with no waiting. The Aviation seal will work better if the parts are treated, then left to air dry for 10~15 minutes. Lay your new gasket atop of the treated surface and then bolt them back together.

Done right, this stuff will make seals that will go to the grave. Sealed up a buddy's water pump on his Firebird with the aviation seal. Never lost a drop of fluid ... well, not from the new pump anyway.

Just more useless and personal experince type stuff. Grew up using the Permatex Aviation seal on anything that had paper, or cork seals. The Red RTV will replace the use of a formed gasket made from rubber , or if say - you broke the original rubber seal and it was still physically in good shape. A dab of the red over the split area in the rubber seal will make it good once again. Either one, used on the proper application in conjunction with a gasket will assure leak-proof performance. Use your head when applying the stuff - Aviation seal should not go anywhere near say, EGR valves. But the red stuff in conjunction with a new gasket will work beautifully in an EGR application. Remember - a little bit does more good than slopping it on with a trowel... ;)

Now a gasket is merely material that is put in place between parts to help seal and hold them together. Usually used in areas where you find pressure, vacuum, static and dynamic fluid pressure, etc. They just keep air, fluids, etc. in the right places and help cover over the relatively rough mating surfaces. Think of the little red or black grommit in the end of a garden hose. Without it, your hose would bleed like a seive wherever it connects to the tap or your sprayer head. Same thing here really. (Sorry, overlooked answering that for you.)

They are made of a combination of materials, depending on the application or manufacturer. Subaru has some that are basically metal wire or a stamped metal form with rubber coatings. Many older and American made cars today still use alot of paper and cork seals/gaskets. Others are just plain rubber. Places where there is high pressure, high viscosity greases instead of fluids or air will have a metal seal with a rubber face that seats around the bearing race. You'll find these in rear axle bearings where they have to hold oil, etc.

Wolfox, thanks for the garden hose analogy. Makes sense. Metal-to-metal would just leak like crazy.

I'll get some that permatex sealant. That looks like some high quality bonding agent.

Many thanks,
-- recurve