I had a previous post on here about my brake pedal going to the floor erratically. i dont lose all my brakes but seeme like there is no pressure. I bled the brakes and eventually changed out the mc. i thought the problem was fixed but now its back. any idea what could be wrong?

 

weird, I just posted the exact same problem, this is happening on our 1993 Del Sol Si.

I recently did the brakes, I didn't bleed them, I would think if it was just air in the line the brakes would be spongy, but this is a complete loss of pressure. Only happens at stop lights, and not all the time. If you figure it out let me know my g/f is scared to drive it.

I have a Haynes manual and see if this is covered in the brakes section and post back.

 

Fill the brake reservoir and park the car on a dry spot of pavement. Keep pumping up the brakes over and over again dozens of times. Check to see if the fluid level drops. If it does, move the car and check for fresh brake fluid on the ground. There should be plenty if you have a leak.

mason rocket, you probably have air in the lines. When you replace the Master Cylinder, you have to bleed it, sometimes extensively, and THEN bleed your brakes. Follow your service manual for bleeding instructions, but in layman's terms, start at the farthest wheel from the cylinder, get a friend to mash the brakes as you crack the bleeder screws until no air comes out at each wheel, and once there's no air, move one wheel closer to the master cylinder.

If you don't bleed the master, you may need to go through the contents of the brake fluid reservoir a few times to get it all out. Don't let it run dry while you're doing it or you have to start the process over.

If there's no air in it, and it's not leaking somewhere, the pedal will not fall. If you can't find leaked fluid, and the pedal still falls, keep bleeding it.

 

Is it going to the floor with little to no braking force or is it just gradually sinking as you're coming to a stop, but the car stops fine?

If it's the latter it could be several things. Sticking calipers or worn pads because of the tendency to overheat (a combination of those two would make it more likely to happen). Even water in the brake fluid.

That's if you aren't low/losing any fluid of course, you'll check that first obviously.

 

I replaced the master cylinder and bled the brakes according to the manual, pass side rear, driver front, driver rear, pass front. Got all the bubbles out, nice and solid pedal.

I didn't bench bleed the master cylinder which would have saved me lots of time and brake fluid, but over all everything looks good to go.

Will report back in a week and let you know if the pedal stopped traveling to the floor at stop lights.

 

The pedal just drops to the floor but i still have a little brakes which allow me to stop over a long distance. no mo ridin othere peoples bumpers. I bled the system twice properly before i even changed out the MC and also monitored the fluid level for months as this problem got worse. There was no fluid loss whatsoever. After i changed out the mc i bled the brakes twice also and it seemed to work well for a week and then it happened again. No fluid leaking and no air in the lines. They function just fine most of the time and then randomly the pedal goes to the floor with no resistance. I just cant understand how the brakes can work just fine and out of the blue do thi, then work just fine at the next stop! gremlins i tell ya! or maybe the underwear knomes.

 

Keep bleeding it. I tell ya, if you can't get any more air out of it, pull the drums off the back brakes and make sure nothing's wet in there. You won't see fluid dripping out if the rear cylinders are leaking inside of the drums.

 

Its disc brakes all around. So what your saying is I should be able to see if the calipers are leaking?

 

I wasn't assuming that you had an si. My bad. Yeah, if it's leaking from any one of the calipers... or in the case of drum brakes, leaking from a wheel cylinder, there will be wet fluid in that area. Especially if your pedal ever falls all the way to the floor as a result of a leak. That's actually a lot of fluid if that happens, and you will see it. You'll have brake fluid slung all over that wheel well and will be leaving oily spots where you park.

If you made a mess bleeding the brakes, get some brake cleaner and spray it all over that area. It will dry everything up again and make finding a leak easier.

If everything is dry including the lines, your car brakes in a straight line when you mash the pedal, and there's no fluid leaking inside the car down the firewall & the fluid level in the reservoir stays the same... then the ONLY thing it could be... is air in the lines. Probably in the master cylinder since it was replaced... and it can frequently be a bitch to bleed it all out. Some cars are worse than others. Try bleeding a '63 VW Beetle if you don't believe me.

 

now that you mentioned it the old MC seemed to be leaking where it mated with the booster. it was only enought to bubble up the paint and then cause the booster to start to rust. it was a very slow seep and didnt cause much fluid at all to leave the system. I figured when I changed the MC this would stop that leak and so far it seems to have worked. Could that leak have meant for sure the old MC was bad and caused air to enter the system? If thats the case then the new MC should be good and it sound like i need to rebleed the system once or twice and see what happens. I just cant figure out why it doesnt happen all the Time. I would think if there definitely was air in the system it would happen all the time.