About a year ago I changed the gear oil in my truck's rear axle. I filled it with AMSoil 80w-90 synthetic gear oil and made a seal using Black RTV for differential cover. A couple of days ago searching AMSoil's website for some oil information on some other model year Blazer's; there was an interesting post about on AMSoil's website about NOT using synthetic oil with differentials with RTV gaskets. After doing some looking on the internet there is some talk about how some sort of chemical in synthetic oil eats at RTV seals.

Well, after nearly a year of no rear differential leaks I found a small leak right at the bottom of the differential cover and traced to the cover gasket. I had to buy a $4 gasket at Autozone, and when I recovered the old oil to be recycled I got back about 2 quarts of gear oil (the starting fill of a rear differential service) so the leak is pretty recent.

My question is, has anyone esle had this same problem of using synthetic gear oil with rear diff covers sealed with RTV only later to have a leak?

 

I believe all 2nd Gen Blazers and S-10 pick up trucks came from the factory with synthetic gear lube. I can remember there were problems early on with the synthetic lube deteriorating the axle seal material over time and there were quite a few warranty claims. So, I would think the AMSOIL synthetic gear lube will not hurt your seals or cover gaskets. If you used all rtv for a gasket and it leaked I'm a bit surprised because I thought rtv was suppose to resist just about everything.

 

I run plain old dino 80W90 and a cork gasket so I'm no help to you.

 

After getting the truck on the lift I found another leak on the rear axle, this time it's the pinion seal. I replaced the rear diff cover a while back and won't know for sure if the rear axle is sealed for good until I replace the pinion seal. I have to wait until monday to do the work, because my truck's drive shaft broke last week and it's stuck at the school until then I am going to get some de-greaser to get garbage off the bottom of rear axle. Hopefully the rear axle holds oil after this, I have a 1000 mile trip in april and everything esle on the truck has been fixed.

 

Good luck with that! I got an estimate done on my rear axle seals not that bad but they did not want to remove bolts as they are very rusted out. Said if break bolts would be a few grand to fix it then yikes. So I have to drive it with it feeling like grabbing of brakes and is making me very nervous indeed. If I cannot get anyone to fix this will maybe sell it as is.

 

First off the this thread is 3.5 years old!!!

You should find a new shop if they said it would be a couple grand to fix a broken bolt. Broken bolts are part of being a mechanic and should only be charged the hourly rate for the time it takes to extract them and on an axle that shouldn't be very long as there is good access to every bolt on an axle. I'm not even sure which bolts you are referring to either. If its that big of a deal find another axle for a few dollars at a junk yard or on Craigslist and swap it in.

 

Ok new to this forum did not realize the date of the message. Yes now I brought it to midas muffler and they fixed the rear axle seals and the pinion seal was leaking as well so fixed that 500 total. Now I drive it out and is doing the same thing! I will have to bring it back have them test drive it so they know what I am talking about very frustrating here.