Weird Brake Problem

[GregWeld]

Are you positive your brakes lines - front and rear - are hooked up to the Master cylinder in the proper position?

Many "ASSUME" that the front line goes to the front reservoir... and in some M/C that isn't the case.

Also - what else is in line with this system? Is the combo valve plumbed correctly?

The brake light is indicating a LOW PRESSURE situation.... could be air trapped where the switch goes in...

I can't imagine a hydroboost of any kind was designed for drum brakes.... I'm just putting my own "thinking" out here - but I would think they came after most OEMS had already upgraded their stuff to disc/disc. Maybe not.

[ProTouring442]

Originally Posted by GregWeld

Are you positive your brakes lines - front and rear - are hooked up to the Master cylinder in the proper position?

Many "ASSUME" that the front line goes to the front reservoir... and in some M/C that isn't the case.

Also - what else is in line with this system? Is the combo valve plumbed correctly?

The brake light is indicating a LOW PRESSURE situation.... could be air trapped where the switch goes in...

I can't imagine a hydroboost of any kind was designed for drum brakes.... I'm just putting my own "thinking" out here - but I would think they came after most OEMS had already upgraded their stuff to disc/disc. Maybe not.

I don't know why I didn't see your reply before now...

Until you asked, I would say that I was 100% sure we had the lines in the correct place. Now I am only 99% sure. Same goes with the combination valve. I'll look into that.

The Astrovans used hydroboost with rear drums, and that's what the unit is off of. Still, someone else mentioned it may be the drums expanding. I'll have to look into that as well. I'm also wondering if larger bore wheel cylinders might help (if they are available).

Hmm...

I'm thinking I need to make a block off for the rear line, and see if the light still activates with it installed. That would eliminate flexing in the rear drums/shoes.

[Vegas69]

If the car is stopping as well as you say, then you may be forcing a non essential problem that isn't a safety issue with excessive pressure at rest.

Your factory proportioning valve may need replaced with an adjustable modern valve where you aren't overpowering the drum brakes. Which end locks up first? If your brakes are functioning properly, your fronts should lock up first.

[rustomatic]

I have to admit to hooking up the lines in reverse on my master cylinder--the whole front-to-front thing is easy to sell. The reality is of course big (pot)-to-front, and small-to-rear. It's really hard to tell in effect, short of your brakes completely sucking . . . The original poster does not seem to have this problem.