Hello,

A few days ago, the brake warning light came on, and I noticed that the brakes feel less powerful, though they’re still working. When I checked the brake fluid reservoir, the smaller compartment was nearly empty i reffiled it.

I have an appointment at the shop next week, but I’d appreciate any insights.

Could it be just old fluid (last changed 10 years ago) or maybe air in the system? Or is it likely I’ll need to replace the master cylinder and brake booster?

The issue here in Germany is that it takes a while to order parts from the USA.

BR alex

 

You have a leak which caused the plunger in the combination valve to slide to one side cutting off 1/2 of your braking system and lighting the light. Inspect for and repair faulty wheel cylinders and or calipers.

 

thanks, so that the rear tank war empty may in the rear circut, to identify this i could jack tha car up and try to rotate a wheel while braking?

is that cutoff process safe to drive to the shop 50 miles with the 50% brake power or not?

 

You need to troubleshoot the leak in the rear and inspect the front for possibly a similar future failure. Driving the car as is can be dangerous to you and others.

 

It’s interesting that the brake warning light turned off after topping up the rear tank. This could suggest that the brake fluid level was low enough to trigger the light initially, but now that it's refilled, the system is operating normally. It’s encouraging that the brake feels better, too. Checking for any leaks before heading to the shop is still a good call—especially around the reservoir, lines, and brake calipers. If everything seems stable and no leaks are visible, it may have just been a simple low-fluid alert.

 

There is no "low fluid alert" function. The BRAKE warning light comes on for one of three reasons: 1) the lamp test function when the key is in the START position, 2) the emergency brake pedal is not in the fully released position, or 3) there is a pressure differential between the front and rear brake systems. In your case it sounds like the latter, but that is not the only possibility. IF the rear reservoir in the master cylinder was very low, you have a leak somewhere in the brake system. This leak has caused a loss of pressure in one half of the brake system, which is why the light comes on. Refilling can recenter the piston that triggers the light, but this is only temporary. Once fluid leaks out again, the light will come back on. This is NOT a drill, this is a real problem. Fix it.

 

The first thing I would do is just look and see if there is a spot of brake fluid under the car somewhere. That would show you that there is a leak and where it is.

But I’m going to guess there isn’t because you likely would have already noticed it. So you have a slow leak. It’s not just a “normal loss” of fluid over 10 years because, if it were, you would expect to see a loss of fluid in both reservoirs, not the just the rear one.

Check around the master cylinder and the lines connected to it. Check where the lines from the master cylinder connect to the distribution valve. If everything is dry, jack up the rear and remove the wheels and brake drums. In all likelihood you will see dampness around the top of the brake housing where the wheel cylinder is because you likely have a slow leak from one (or both) of the cylinders. The repair is to replace both cylinders (replace both, even if only side is leaking), reassemble the brakes, and then bleed the system.

You will need new wheel cylinders, and if those aren’t available where you are, you will have to order them from the U.S.

While the brake drums are off, be sure to inspect them for wear, and check the brake shoes. If they’re worn at all, you might as well replace them while you have the brakes taken apart.

Now, here’s the real question. Have you ever disasssembled and reassembled a brake drum assembly? I’ve done it a number of times, and each time I’ve added to my repertoire of swear words. There are videos to show you how to do it, and there are special tools made to help with this and that aspect of it, but it still takes a little intestinal fortitude, at least in my experience. It really helps if you have five or six hands.

I see from your avatar that you have a ‘73 Delta 88. It just so happens that I have one of those, too, and I redid the brakes on it last summer. Here’s some before and after photos of the left rear. New drums, adjusting wheel, wheel cylinder, and shoes, and I reused the old return springs because the kit didn’t include them. The kit did provide new brake shoe hold down springs, and I used those.


Before. Note how dirty and ugly it is. Expect this when you remove the drums.There was still some life left in the shoes, but I replaced them anyway with something made in the 21st century. And look at that star wheel. It probably hasn't worked since Ronald Reagan was president. Yet the brakes still worked ok. It always amazes me how resilient the braking system can be.






After.







Also, keep in mind that, if the brakes have not been worked on in many years, it may be difficult to remove the brake line from where it connects to the wheel cylinder. In my case, it was so corroded and dirty that the entire line twisted when I tried to loosen the nut. It did this on both sides, so I ended up cutting the brake line back a bit from the cylinder and “splicing” in a short length of new line.

Here's my repair on one side. Yes, the tube going out to the right is tilted slightly, but it is sealed and hasn't leaked in the past year. The line is also supposed to go under that little clip attached to the axle just below the new joint, but it can't fit there because of the joint. I could probably put some kind of strapping or even a tie-wrap to hold it against the axle, but I haven't done it because the line is stiff and holds it's place, so I've left it as is.