Hi -

I have a 1993 S10 Blazer Tahoe 4x4 that I purchased brand new in 1993 from Dennis Fronrath Chevrolet in Delray Beach, FL. I am the single owner of this truck and over the years have done just about all the repairs and maintenance it has needed. Well at this time it now has 185k miles on it and I have never checked the rear axle differential to add gear oil or replace the gear oil. I figured it was long overdue so I purchased 3 quarts of SuperTech synthetic blend 75w90 gear oil at walmart. It is GL-5 approved so it should work fine on this truck. But for the life of me I cannot find the fill plug anywhere on the rear axle. I have the official Chevy owners repair manuals and on page 4B1-9 it in the section labeled *Carrier Cover Gasket Replacement* it clearly mentions that there is a fill plug on the axle. But where? I have seen other online posts for newer model S10 blazers (95 and higher) where the fill plug is in front of the axle pumpkin on the drivers sides but not on my blazer. I do see on my Blazer a vent hose on the right side front of the axle housing that leads away and it bolted on to the under side of the carriage. But I don't know if this is the hole we should be using for refilling the gear oil Can anyone assist? What I want to know the most is where the fill plug is if any exists and/or if these axles were ever designed to have their gear oil replaced. Although it seems unlikely maybe these things were not supposed to have this kind of maintenance done on them.

Thanks,
JC

 

its on the passenger side of the diff housing. right behind the pinion yoke. you will see a round cap with a square head. insert a 3/8 extension into it.

 

Ok thanks. I will have a look at it again this weekend and post the results of what I find here.

JC

 

Chris

You were right. It is in fact on the passenger side on the diff housing. I was looking for a plug facing toward the front of the vehicle but in fact it is off at 90 degrees and faces toward the side of the vehicle. The plug is flush with the axle housing and I had to clear some grime to get to it. As you say a 3/8 inch ratchet and extension bar is all I needed to get it out. Thanks for your help.

JC

 

Glad you got it done. The Rear Axle Service tech article documents this fairly well too.

 

If you have the G80 limited slip option, might need friction modifier in with your lube. I know my Wagoneer has to have it. I destroyed the axle in my 93 when all the lube leaked out on a long trip. It started howling like a banshee and I drove 10mph for 6 hours to get home. Moral of the story? Check & change your diff oil!

Tom

 

Just out of curiosity what color is friction modifier in these oils? Or does it even have any color? As I was topping off my rear axle I noticed that some of the oil spilling out after reaching the level had a little bit of white color in it. I figured maybe it is friction modifier. I only needed a 1/4th of a quart to fill it up (~250 ml) so I don't think the cover plate gaskets have any issues otherwise it would have been lower. My concern is though about the off change maybe some water got into my differential. Any advice is much appreciated.

Thanks,
JC

 

As stated in the tech article I previously linked to, the G80 option does NOT require friction modifier. Regular GL5 rated gear lube is all that is needed.

As far as white in the gear lube, that sounds like water making it froth.

 

I stand corrected on the friction modifier, but I'm sticking to my guns on changing the diff lube, don't top it off, change it. Cheap insurance.

Tom

 

Yeah I also think there might be some water in there also. It was never really changed. As far as I can tell there is no drain plug though. The plate on the back of the axle has a number of bolts around the perimeter but I do not see a drain plug anywhere. I might have to take the whole plate out to drain it and replace the gasket then refill everything backup. Can anyone confirm if a 1993 S10 Blazer has a rear axle drain plug or not?

Thanks,
JC