I'm trying to figure out if the rear differential cover on a 2-door, 4WD, 2002 Blazer is designed to support a diff cover with a drain plug.
From calling auto-part stores, I learned that there are two different sizes of differentials these Blazers tend to have.
Based on what I was told, since my original diff cover doesn't have a drain plug, then I have the smaller gear set of the two.
Finding the right diff cover with the drain plug I want for the smaller differential has been very difficult.
I've even been sold two different diff covers so far that do fit the vehicle, but don't have the drain plug I request.

So now I'm scratching my head wondering if anybody makes a diff cover with a drain plug for the set up I have.
Has anyone else run into this?

 

I've been down this same path doing the same search and have come up with nada. I could not find any affordable diff covers that have a drain in them. There are kits for welding in a drain into a steel cover but I'm not a welder. The only option I've found is to install the covers that are cast and start at about $130. And most of these are the ones with the extra bolts to reinforce the differential carrier.

As for the size of the differentials, I'm pretty sure the ZR2 models are the only Blazers that came with the larger 8.5" rear ends. All of the rest are the 7.625" ones. There are websites that can help you identify which axle you have such as this one: https://www.novaresource.org/axle.htm.

BUT if you do find a source for simple/affordable diff covers with a drain plug, be sure to let the rest of us know! It sure would make changing out the gear oil easier.

Below is an example of what you will find for the 7.625" diff covers.


https://www.summitracing.com/parts/sme-8510400nl

 

Ok....have got to ask...why would you want a drain plug in the diff cover? The diff oil is not something that gets changed very often....like every 75k miles. I know it would make the task far cleaner and save the cost of a new gasket each time....but the gasket is pretty inexpensive. Just asking......

 

It is such a mess to change it out. On mine, you have to drop the spare tire, then I have to remove the brake line bracket and hope I don't bend the brake-lines too much, then I have to work around the rear sway bar. Then you have to get it all cleaned up before putting it all back together.

Also, I don't know if much is gained with respect to taking the cover off to do an inspection of the internals. It is easy enough to see if any metal is wearing off by looking at the oil coming out and if you use a magnet drain plug.

 

I would just buy a weld bung for the cover you have. If you can't weld it yourself, a muffler shop should do it for a few bucks.

 

If one were to do the drilling and welding on a bung, I would suggest removing the original magnet on the inside of the cover and using a magnetic drain plug. Otherwise that original magnet is just going to collect all the ware shavings and you'll never get them out if you never have to bother removing the cover again. At least if they come out on the magnetic drain plug, you can discard them.

My $0.02, there's not much of a reason to go into the diff very often, so it's not an extreme inconvenience to have to pull the cover off, and like mentioned already, it's a great opportunity to give everything a close look.

The only reasons I see to even think about actually changing the fluid is:
1) Regular service obviously, but how often is that actually needed; 50k miles if you're super religious about fluid changing, 60k, 70k, 100k even for normal daily drivers? Heck I just changed mine and I'm fairly certain it's original with 216k miles on it!
2) If you've sunk the axle for extended periods of time in water and suspect that water may have gotten into the diff and mixed with the fluid.
3) Suspected internal issue because of noise from the diff...

I will say that the one thing I like about the cover that Christine linked to earlier is the bearing cap support preload bolts. Although not really necessary on a stock vehicle per say, if you're running oversized tires, it may be beneficial.

 

Why I asked the question to the original poster was to find-out if the vehicle was taken off-road and into water often or if it is just street driven. Curious as to why the need to change diff oil often.

I agree with you Christine, although the spare tire would probably still need to come-out to access the drain/fill plugs in the cover....so not saving that part of the task.
The aluminum cover would also dissipate heat faster.

Takes me back a few decades when covers like these were put on street cars with the rear end jacked-up/front lowered.

 

I had not considered the effect of oversize tires. They would reduce the effective rear end ratio putting more stress on the differential.

I would imagine that it likely wouldn't matter unless the tires are really big, like 35s.

 

My Blazer is mostly highway driven long distance with the occasional dirt/clay road. About 23k miles annually. Currently sitting at 173k miles.
The diff oil was still factory, so I figured at her age and miles I thought it be good preventative maintenance to change it.
My thought on the drain plug was just to have a faster process when next I do it at 250k miles. Since I have to remove the cover this first time, I might as well put another one on that has the drain plug.

 

I replace my front and rear axle oil every 15,000 miles or so. I go this from the owners manual for severe duty since I do short drives in town with it and use it for towing a boat.