Losing Brake Power
 

Just replaced the front drum components & shoes on my 1970 C10, bled them, and drove for a little. Worked good, stopped good, and I was happy.

But then while driving and taking a sharp corner, lost all brake power, no braking until the end of the pedal. But then I put it back in gear and power was back. This happened a few times that day, even without turning, sometimes just in a straight line.

Manual drum brakes, any ideas?

Re: Losing Brake Power
 

Did you top off the master cylinder after you bled the brakes? Check the fluid level in the MC.

Re: Losing Brake Power
 

If you have a brake booster check to see if you are losing vacuum...

Re: Losing Brake Power
 

If the previous suggestions aren't the problem, I would put on a new or reman master cyl.

Re: Losing Brake Power
 

Check MC, fluid is fine, no need for top off (as it was filled prior to driving), no booster, just basic manual drum, any other options? Is there some way I can check the MC for problems before replacing? Although I trust all of your opinions, I don't want to blindly replace parts without truly knowing it's what it needs.

Re: Losing Brake Power
 

I had the exact same problem till yesterday. About 2 weeks before I parked it last year l replace my front passenger side wheel seal and it was all good no problem for a week then I would have to pump twice to stop sometime's not always though.Blead the brakes multiple times but the brakes would never go soft in the garage only when I moved and then not always. Put on my new tires Friday so I pulled all the drums off just to have a look and there it was a broken pin and spring on the back brakes. Never thought of the back figured it was something to do with my work up front.l have the same set up as you with no braking assistance so it's a pretty simple system it baffled me. Got a spring kit for all four wheels pads where all good so I freed up the adjusters and no more problem .l hope you're problem is as easy

Re: Losing Brake Power
 

I will check, thank you

Re: Losing Brake Power
 

You can hook a pressure gauge to a master cylinder to see if it's actually working. First I would also check inside the drum for any moisture.

Re: Losing Brake Power
 

If moisture is found, what is it from? How is it prevented?

Re: Losing Brake Power
 

Brakes are a mystery to me if it isn't apparent yet, they confuse and scare me

Re: Losing Brake Power
 

Are the rubber hoses going from the hard brake lines to the brakes new? Did the peddle have resistance or did it drop straight to the floor. Brakes are actually pretty basic once you know the method to the madness.

Re: Losing Brake Power
 

I would check your rear wheel cylinders. They will definitely leak if sitting around for too long.

Re: Losing Brake Power
 

Moisture can leak out your axels (oil from diff). It can come out your wheel cylinders(brake fluid). Or if someone is sloppy the can use to much brake grease and it can get on your brake shoes. Even a small amount of brake fluid could leak out causing weak brakes, by small I'm mean too little to notice by looking at the mc.

Re: Losing Brake Power
 

Replaced both rubber lines, pedal goes pretty much to the floor.

Re: Losing Brake Power
 

I did not replaced the wheel cylinders in the rear when I did the rebuild. I'll double check those aswell, what a pain to have to take them back apart to replace the wheel cylinder.

Re: Losing Brake Power
 

Ok if you replaced the front rubber lines, did you bleed the brakes again? If not you'll need to do this...ed :chevy:

Re: Losing Brake Power
 

It's always easy to generalize what the problem might be with brakes, and much harder to pinpoint the issue. Pedal travel distance is directly related to pad/shoe distance to rotors/drums, and fluid level or air in the lines. You need to check for any cracks, bad bends, or even minor leaks. If fluid can get out, air can get in, especially with pressure systems. Re-check wheel cylinders for even the slightest moisture around the rubber seals and line connections.

Furthermore, how old are the wheel cylinders, master cylinder, and brake lines. Also the intermediate soft line that joins the front to the rear axle can be in bad shape.

Re: Losing Brake Power
 

I did all of the work and bled the brakes after working on them and before driving, I've only had the truck for a year so as to when or even if the other parts were replaced, I have no idea

Re: Losing Brake Power
 

Make sure if you haven't replaced your master cylinder, buy a new/remanufactured one, stay away from rebuild kits, they always leak, almost as cheap to buy new any way. also, bench bleed the new master cylinder (they come with plastic fittings and hoses to feed the brake fluid back to the reservoir while bleeding the air out) this will help you when you go the bleed the lines out.
HTH,
Ben:metal:

Re: Losing Brake Power
 

I know this sounds dumb but maybe readjust the brakes or at least see is they have the slight drag they need. Your master cylinder might have a bad seal some where also.

Re: Losing Brake Power
 

my vote is rear wheel cylinder(s). sounds like they are the weak spot, if you replaced the fronts already