TheBigBlueBoat

I noticed the one day the pedal was a bit lower than normal, and the brake light came on at the bottom of travel. It got worse in the next few days. It was enough to stop, but if you pushed the pedal all the way down the light would come on.

I pulled the drums off to find out that one of the shoes on the driver's side had all the friction material pop off. Not worn down, it just came off the shoe. I replaced it with new better shoes, did the slack adjuster and shoe bedding procedure and it's no better, but now it pulls to the right.

Master cylinder, lines, hoses, wheel cylinders, and hardware have all been replaced within the last 1-2 years with very little mileage on them. I've checked for leaks and there is no fluid loss. Slack adjusters were working correctly. Naturally everything was bled like crazy when all those new parts were installed.

I'm a bit at a loss on this one. Usually low pedal/brake light means air in the system or a leak. The only thing I haven't replaced is the drums, but I would think even if they were worn well beyond spec the adjusters would take up the slack. Either way I would start with the left/drivers side since it seems to pull to the right, meaning that side is still working well.

classicmuscle442

What year, model, sounds like hydraulic problem, if dual master cylinder would guess back brakes if car still stops okay.

oldcutlass

Go through the adjustment procedure on all the wheels, make sure they are evenly set and that each one grabs the drum.

TheBigBlueBoat

1968 Cutlass 4dr wagon, 4 way drums, power brakes, dual master cylinder. Stopping is sufficient but diminished, which is why I suspect the fronts. The front is also where I saw the shoe failure.

I went through that. Set the adjusters just shy of dragging on the drum, then did several back and forth stops to adjust them. Didn't seem to affect the pull.

classicmuscle442

Check the hoses with someone stepping on pedal. Rear hose is harder to locate and doesn't get changed. If shoe adjustment was out, pedal wouldn't sink.

oldcutlass

Check the wheel cylinders and make sure they are not sludged up and/or frozen. A low pedal could mean the master cylinder is leaking internally and not building pressure.

TheBigBlueBoat

Hoses have been checked and are all relatively new (~1yr), including the rear. The rear hose and lines was actually one of the first things replaced when I got the car.


What do you mean by if the adjustment was out it wouldn't sink?



The wheel cylinders definitely aren't sludged up or frozen. They're relatively new and at least before the pad change I was able to depress the brake pedal and keep the front wheels from turning.


I was thinking of the master cylinder as an issue, but because now it pulls to the right that means at least the right front wheel is working correctly, and an MC failure would impact both sides.


I think it warrants a closer look at the left front in particular. Braking power is noticeably diminished, so the issue is at the front. It pulls right so the right front is working. That leaves the left front, which is coincidentally the one that had the failed shoe. I suppose if I clamp off the left front and it improves I'll have a much better idea.

classicmuscle442

As stated above, if pedal sinks (goes down) with pedal pressure it's a problem in the hydraulics.

RandyS

You may still have air in your line (s), especially the left front. What method do you use to bleed your brakes?

oddball

As usual, debugging at a distance seldom works well. You're probably already headed down the right path.
When I've had an issue with drum brakes the only way to fix it was to pull everything off and start over. I've made more than my share of assembly mistakes with the springs, leading to hilarious problems. Hopefully you replaced the shoes on the other side at the same time.
And FWIW, I've had "new" master cylinders fail within one year. I disassemble and inspect them before installation now. Lots of scored cylinders and bad seals out there.