How do you check the oil level in the rear axle of a 1995 GMC K1500 Suburban? I can find no plug or inspection port.

Hi, your basic symptoms will be. Your brake pedal. Will be very hard to push. When the pedal is engaged there will be a large vacuum leak, usually causing the engine to be very ruff or stall. If its bad enuff, youll hear the the air leak when pedal is depressed, hope that helps.

Have you checked the temperature sending unit to the computer?

possiable pinion bearing in front axle

its called a QUARTERLIGHT........

Hello, there is a fill pluf on the passenger side of rear end to check the fluid level and to add fluid. here is some help on this.

Remove the rear axle fill plug.

Inspect the lubricant level. Specification
The lubricant level should be between 0-10 mm (0-0.4 in) below the fill plug opening.

If the level is low, add lubricant until the level is even with the bottom edge of the fill plug opening

Where is the leak? Toward the middle or at the right or left sides near the rear wheels?

The axle probably lost a keeper ring on the inside of the differential and the pieces may be going through the differential and ring&pinion gearing making the noises you hear. You will need to drain the oil out, find the broken pieces, and inspect all gearing for broken/damaged teeth, and for any noisy bearings. Flush the case out with cleaning solvent. Re-insert the loose axle after cleaning and inspecting it well--especially the interior end. Replace the keeper (new) on the axle end inside the differential spider gearing. Inspect the brakes on the loose axle side for any oil deposits and for any damage that might have been caused when the axle came out. If the differential is badly damaged, it might be cheaper to find another rear end in a wrecking yard. Hope this helps!

the rear axle takes 85-140 gear oil if you have limited slip you have to also add a friction modifier to it. you have to fill it from the level check plug about halfway up either on the differential cover or on the front of the third member depending on the axle that you have

Inspect Brakes and Traction Control Evaporative Emissions System (E) Inspect all the fuel and vapor lines and the hoses for proper hook-up, routing and condition. Ensure that the purge valve works properly, if equipped. Replace the components as needed. Exhaust Gas Recirculation (E) Fluid - Differential Inspect front/rear axle fluid level and add fluid as needed. Check constant velocity joints and axle seals for leaking. Lubricate Steering and Suspension Lubricate the front suspension, ball joints, steering linkage, transmission shift linkage, transfer case shift linkage, parking brake cable guides, and brake front axle. Ball joints should not be lubricated unless their temperature is -12 degrees C (10 degrees F) or higher or they could be damaged. Replace Air Filter Element (E) Engine Oil (E) Change engine oil and filter as indicated by the GM Oil Life System (or every 12 months, whatever occurs first). Reset the indicator. Never drive the vehicle more than 16 000 km (10,000 miles) without and oil and filter change. The system will not detect dust in the oil. If the vehicle is driven in a dusty area, be sure to change the oil every 5 000 km (3,000 miles) or sooner. Fuel Filter (E) Oil Filter, Engine Rotate Tires

You are correct, it's not brake fluid. Check the level in your rear axle, it sounds like you have bad seals in the axles allowing the rear differential gear oil to leak inside the brake drums.
This is a heavy weight oil, 80 or 90 weight. This leakage will ruin your brake pads, and if enough leaks out, your rear differential will blow. The seals aren't expensive, but it's a lot of labor to pull everything apart to get at the seals, plus new rear brakes. My Ford ( and I'm sure your GMC) require removal of the rear axles to change the seals. Good Luck! countrycurt0