Hello,
Looking for a little help/direction on my 67 RS/SS 350. My brakes suddenly felt spongy so I checked the master cylinder and saw it was a bit low. I added fluid but the pedal still went to the floor. So I thought some air had gotten into the system. I bled the brakes and the rear (drum) bled out fine..little to no bubbles. The I go to the front (disc) passenger and got foamy fluid..same on the drivers side. No matter how much the pedal was pumped the foam (air) never stopped coming...both sides. Why would this occur on the fronts only? I read somewhere that you need to hold in the metering valve pin on cars with front disc brakes. I don't see it. Does anyone have a picture of one? Are they located on all cars with disc? Thanks for any help/pictures. Rob

 

Check all your lines, fittings and bleeders and make sure you don't have a leak somewhere. Does the fluid in the reservoir look foamy too, or just when coming out the bleeder?
What kind of brake fluid are you using? If it's Dot 5 (silicone), that could be the issue.

 

Switch is Item #7 - turns on BRAKE light if an axle has a major leak.
Normally, general bleeding will not push the valve to one side.
If the switch is pushed to one side, then pump up brakes and hold firmly, open bleeder of the other axle and with a firm pedal pressure, the valve should center. Repeat as necessary. Shown here are regular drum brakes and J52 - disc brakes.

You might unscrew the bleeders and smear grease about the threads to seal from the atmosphere - as 69 suggested, might be the source of air bubbles.

 

Camaro 69 the fluid in the reservoir does not look foamy but there appears to be a few bubbles. All fittings are tight and I'm using dot 3-4. I'll try your idea Everett and report back.

 

Was it spongy or did it go to the floor? Those are two totally different issues. Adding fluid to a low master cylinder will not get air into the system. If you some how managed it you would need to bled the master cylinder itself. You could spend a week trying to get air from the master cylinder down to the calipers with the petal method of bleeding. There is no way for air to enter a system that has no hardware problems, Even if the car sat for 30 years, unless a seal failed or a line rusted Air would not get into the system. The fluid would separate and over heat and boil very quickly but it would go back to being a fluid once it cooled back down.

First thing I would do is power or vacuum bleed the front caliper until I had nice clean fluid. Next stomp test the brakes as hard as you can. If they are power then do it with the car running. Hold it at least a minute. Then you should be able to track down the leak. If you have gone over the whole system and can find no leaks, replace the master cylinder.

Brake Bleeder and Vacuum Pump Kit

 

Ok, so I think I've found the problem. The front passenger side disc brake caliper piston seal appears to be leaking. Fluid is running down the outside of the caliper way more now that I took it out on a test drive after I bled the brakes. Question, is it possible/advisable to repair/replace the piston seal? Will I have to also replace the pads? Is this an easy task or should I attempt?

 

Just replace the whole caliper, they're cheap enough. One cause for a leak can be a pitted rust area in a cylinder, which happens when a car sits a while. But you won't know if yours is easily fixable or not till you get it all apart. If it is that bad, the caliper would have to be re-sleeved, which isn't a diy job. I'm restoring my old Vette. It's been sitting a number of years, brakes didn't leak when parked. But I'm throwing on new (rebuilt) stainless steel sleeved calipers just because it has been sitting so long. Brakes are something you don't want to cheap out on, if you value your car, and yourself.

 

Chance are if one is bad from sitting then the other one is not to far behind it. I would do both calipers. On older cars if one front caliper blows out then you loose front brakes. Last thing you want to try is stop a heavy car with nothing but rear drum brakes. I did a Vet one time, customer just wanted the leaking side fixed. The other lost pressure during the test drive. I told my service manager next time I will do the single caliper but he was doing the test drive.