1995 K3500 rear brake reservoir keeps losing fluid. No sign of a leak yet. Is the rear reservoir for the front brakes or rear brakes? Have front calipers and rear drums. Thanks

if you have a hydraulic clutch ( no transmission offered) check the slave cylinder for leaks ( some cars use the brake master cylinder as a reservoir for the hydraulic clutch)
check the brake booster to master cylinder mounting for leaks or the rear seal of the master cylinder may be faulty allowing fluid to pass to the booster chamber
check for a leak under pressure at the rear flexible rubber hose from the body on

Did you by chance add power steering fluid to the brake reservoir instead of brake fluid?

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

The front reservoir (the small one)is for the rear brakes.Have you pulled the rear brake drums and checked the wheel cylinders for leaks?
Is the rubber seal on the reservoir cap in place?
Follow the lines carefully to the rear brake hose and on the axle to the brake cylinders too.
Lastly,it can be leaking from the front section of the master cyl internally to the rear section of the master cyl but not likely.

When you bled the system was fluid coming out the bleeder valves?
Where the bleeder valves closed off with the brake pedal fully depressed?
Is the fluid reservoir cap ok?
Is the master cylinder ok?

The front portion of the reservoir has fluid used for the front brakes which provide the majority of the vehicles stopping power. There is a valve that is supposed to shift to isolate the front and rear brakes when this occurs but it doesn't always work as designed. You have lost all the fluid in the front brake system. This is due one of these possible issues:

Broken brake line
Broken brake hose from line to caliper
Leaking caliper seal

You need to find and repair the leak, refill and bleed the front brake system to get the vehicle back in service. IT IS NOT SAFE TO DRIVE IN ITS CURRENT STATE!!!

most common bleeding sequence is furthest from master cylinder to closest.right rear left rear right front left front may need to be repeated.be sure to keep fluid topped off. also check brake lines for leaks

hi from the uk this warning light has two functions 1st it comes on when park brake is on then goes off as p/brake released the other function of this light being on ? is a warning that the brake fluid level in the reservoir is low the sensor is on the fill cap however! low level may be a fliud leak ? orsimply the level has dropped over time due to as the brake pads and rear shoes wear down then the fluid displaces from reservoir and compesates for the wear and fluid keeps the w/cylinders always topped up automatically may i suggest you check your b/pads and shoes are not too low for safety if so then renew asap also make sure there is no sign of fluid leaking on brakes especially the rear cyl's and actual b/pipes hope this helps?

Hi:
All modern cars have a dual brake system, this way if you would happen to spring a leak in your rear brakes, your front brakes still work. When one system fails, you get a brake light. In your case, the first place to start your troubleshooting is to check the fluid level in the brake reservoir. If either the front or back of the reservoir is empty, you have a leak. If both are still full, the most likely problem is your master cylinder failing. If you think you have a leak, look at the inside edges of all 4 wheels, and look for signs of brake fluid .

I have changed brake pads before and did not lose any fluid but air can get in the lines. Brake fluid is not compressible while air is, so if you get air in your lines it compresses when you hit the pedal there fore the pedal goes down to floor and your brakes dont grab that good. You can either bleed the brakes your self by starting at the wheel furthest away from the brake fluid reservoir and unscrewing bleeder hose and letting the fluid just bleed out. (get something to catch it and dispose of it properly). Make sure you keep the reservoir under your hood full of brake fluid while letting the other stuff by tires bleed out. Work your way from the furthest tire first and the closest one to the reservoir last. GOODLUCK!

hi from uk if you are saying that the brake master cylinder reservoir fluid is falling in level? and that there is signes that fluid is leaking from the ABS hydraulic master cylinder ie fluid is leaking from the arpeture where the electrics wiring loom enters then there is probably one of the piston/valve seals leaking within abs assy ? or is leak from somewhere else? not had this problem before with fluid passing from abs assy resulting in reservoir losing fluid in this way?