I'm pretty sure I have a brake fluid leak somewhere in the rear brakes of my 1979 Catalina's brakes. The pedal sinks to the floor, and the rear chamber in the brake reservoir was low on fluid. The brake warning light was on. I added more fluid today and pumped the brake pedal while scanning under the car for a leak. I noticed the pedal feels a little more firm, and the fluid didn't drop anymore. I also did not see any sign of a leak. Does this mean the system now has a bunch of air inside? I figured pumping the brake would circulate fluid and push it out of any holes, especially since the reservoir wasn't empty.
don't double post please. Give the system time to process your submission.
@Mountainmanjoe Sorry about that! Phone service must have glitched and posted twice. I noticed it stopped responding
If you previously lost pressure then you would have air in the system now and you would need to bleed it out. If you didn't see anything leaking then it was probably caused by either a bad booster or a bad master cylinder.
Well if you don't see leaks coming out anywhere it has to have air trapped inside somewhere unless the brake master cylinder is leaking inside in which case it will leak in the booster and you won't see it
Did you remove the rear drums and pull back the dust boots on the wheel cylinders? You might have a slow leak in one or both.
I took a few minutes and pulled the driver's side rear drum off earlier today, well, more like pounded it off, haha, and there was a weird black substance around that wheel cylinder. It almost looked gooey/ greasy. I changed the drum brakes in my 1999 Ranger a year and a half ago and I don't recall any black crud like that being in those drums. There was brake dust galore, but that's it. Carb cleaner took the stuff off, that was all I had handy at the moment. I didn't have time to pump the brakes with the drum off. Could that be a sign of a blown wheel cylinder? Nothing was actually wet.
Don't pump the brakes with the drum off, you'll pop the pistons out of the wheel cylinder! It sounds like it may be seeping brake fluid and mixing with particles of brake dust. (Either that or you have a leaky axle grease seal.) What you want to do is pull back the dust boots on the ends of the wheel cylinders. There should not be any wetness from brake fluid visible - if there is, you have a leak.
Wheel cylinders are inexpensive, might be best to just replace them if you don't know how long they've been there and how long it's been since brake fluid was flushed.
I'll check them out, I didn't know that about the pistons with no drum. I figured they were somewhat self retaining and the tension on brake shoe springs would keep everything together. Thanks for the heads up. Wheel cylinders are only $13.99 from the AutoZone down the street, so it's probably more time and cost effective to just replace the wheel cylinders anyways.
Without the drums to retain the brake shoes, the shoes can extend out far enough for the pistons to leave the brake cylinder when you hit the brake pedal. (Been there!) The main thing to be careful of replacing the wheel cylinders is the brake line fittings being rusty. You'll want to soak the fittings in a good penetrating oil a few times a day for a few days, and have a good-quality line wrench to attempt removal. Since you'll be replacing the wheel cylinders anyway you can use some heat if needed. If you're not careful you'll wind up having to run new hard lines on the rear axle.
you shouldn't use carb cleaner on brakes. It'll leave oil residue on your braking surfaces.
@MountainManJoe, good point on the carb cleaner. Brake cleaner that leaves no residue is readily available and inexpensive.
Since everything has to be taken apart to get the wheel cylinders off, now is a good time to install new shoes and brake hardware, and lube the shoe contact areas on the backing plates with caliper grease.
Not sure what your local prices will be, but Rockauto lists a set of AC-Delco "Gold" brake shoes at about $25 for that car, and complete hardware kits (springs and adjusters etc.) for about $4 to $5. Might as well replace that rear brake hose that might be over 40 years old for $7-$8. (Of course with Rockauto you have to watch shipping charges and try to order parts that come out of the same warehouse. A search will usually turn up a 5% off coupon code.)
I didn't think about residual grease from the carb cleaner. I figured I'm going to probably replace everything in there anyways, it doesn't matter if carb cleaner leaves residue, the parts are coming out anyways. The adjuster gear is seized up, soat least that needs replacing. I had brake cleaner and couldn't find it, lol. I'm not sure if it has a rubber hose back there or not. The line felt like metal all the way to the backing plate, unless it becomes rubber behind the cylinder. I've never serviced those before, so this will be new.
There will be a rubber brake hose between the frame and the rear axle. There has to be due to the up and down movement of the axle. It should be located on or near the "pumpkin" in the middle of the axle.