brake pedal still soft, new master cyl, no leaks

[loud92CB7]

if it was the booster it would be a super hard pedal to push in. from what little bit i have heard....

[CB7_213]

hmmm..this is really weired.... ive read the whole thing twice and i still couldnt figure it out.. i'll check at alldata for you tomorrow....lucky you im taking a break class..

[CB7Luver]

Not completely true. The brake booster runs off vacuum. If it's leaking or has a certain problem inside the booster it could create the spongy pedal. I would look towards two things. The first i would check would be the rear brakes are adjusted properly, about 90 percent of spongy pedals are due to improper brake adjustments. If they are ok, i would look at the abs system. Some systems that have abs have to be bled in a certain way by going in thru the abs computer to open certain internal valves that control the abs operation. With that wiring going to that certain front wheel missing due to the axle not being right one, there is no information going to the computer saying where the wheel is at relative to slip. And no abs master cylinders also only have two lines coming off from them as well. Trace the lines, on this particular model, it is a non-integral system and will have the two lines going into a box which is the modulator. You should see either three or four lines coming out from there. Sometimes the rear wheels are controlled by one channel and seperate channels in the front. Or independent all the way around.

[TomQuick]

The brake has been mushy from the day I got the car. When I first got it, the rear rotors were torn up, and the ABS light was coming on every time I moved the car. I disconnected the ABS computer, and replaced the rear rotors. Wile doing the rotors, I noticed that the calipers were also in very poor condition, so I changed the calipers as well. The brake pedal was worse after changing the brake calipers, and bleeding them out, and seemed in addition to being mushy that it would creep towards the floor if I maintained steady pressure on it, like you would braking down a hill, or sitting at a traffic light. That made me believe that the master cylinder was at fault, and I changed the master cylinder. The pedal doesn't seem to creep now like it did before, but the mushy feeling is much the same.

The two lines from the Master go directly to the ABS modulator. From there, four separate lines exit for the four wheels. Because of that, the only way to fully remove the ABS system would be to get the correct bits from an non ABS car, which either means a Master Cylinder with four ports on it, or a separate proportioning valve. I'm not certain which system is employed, however I'm fairly confident that my problem isn't in the ABS system. When the computer is hooked up, the pump primes properly, and the ABS light goes out, meaning that the system is passing self check. The light only comes back on when I start moving the car because of the missing signal. Additionally, the computer has nothing to do with this, as it is disconnected, it isn't getting, or interpreting any signal, it's shut off.

I know about weight transfer, and how you don't get nearly as much on a slippery surface as you do on a dry road, however I've NEVER had any car in which I couldn't lock up all four brakes on a patch of dirt, and all of my previous cars have had drum brakes in the rear. I would think that a car with disc brakes in the back should be at least equally capable of locking the rear brakes with the brake pedal on the floor.

As for adjusting the rear brakes, I know about adjusting drum brakes, but I've never heard of disc brakes with an adjustment system. I'm waiting for a bottle of brake fluid to arrive so that I can go at the back brakes again, and hopefully I'll get this fixed today.

[TomQuick]

I'll throw a little update here, I bled the crap out of the brake system, and hooked the ABS computer back up, and bled the ABS modulator as well. It made no difference.

When the engine is off, the pedal is firm a short distance down, and stays firm, no chance of pushing it to the floor. When I start the engine up, the pedal travels perhaps half way down before it builds up any resistance, and then I can fairly easily push it the rest of the way to the floor. I'm every bit as lost as before.

[loud92CB7]

Not completely true. The brake booster runs off vacuum. If it's leaking or has a certain problem inside the booster it could create the spongy pedal. I would look towards two things. The first i would check would be the rear brakes are adjusted properly, about 90 percent of spongy pedals are due to improper brake adjustments. If they are ok, i would look at the abs system. Some systems that have abs have to be bled in a certain way by going in thru the abs computer to open certain internal valves that control the abs operation. With that wiring going to that certain front wheel missing due to the axle not being right one, there is no information going to the computer saying where the wheel is at relative to slip. And no abs master cylinders also only have two lines coming off from them as well. Trace the lines, on this particular model, it is a non-integral system and will have the two lines going into a box which is the modulator. You should see either three or four lines coming out from there. Sometimes the rear wheels are controlled by one channel and seperate channels in the front. Or independent all the way around.

hey man where are u in nashville? maybe u could come help me out and get this problem fixed.

i didnt get a sponginess till i took out my abs computer. since then it has only gotten worse. if i get the time im gonna get the prop vavle from a teg and then go about taking the abs completely off. but im pretty stuck on its the abs system or master cylinder....

[TomQuick]

loud92CB7db18, I can tell you with absolute certainty that disabling the ABS is not the cause of the spongy pedal. I honestly don't know what the cause is yet, but I know it isn't the ABS.

Yesterday, I hooked the ABS back up for long enough to bleed the ABS system, and verify that the brake pedal was still spongy. I also bled all the brakes on the car again, running an entire 32 oz bottle of brake fluid through the system. That didn't help either.

Today, following instructions I found from Mighty Auto Parts, I tested for air in the system. Basically, you have someone pump the brake pedal 20 times, on the 20th stroke they hold the pedal down firmly, while you remove the cover from the master cylinder (I also removed the strainer for an unobstructed view) and observe the fluid. Have the helper sidestep the pedal to allow it to pop up. If there is a geyser of fluid that spurts up in the reservoir, then there is air trapped in the system. If no fluid spurts up, then there is no trapped air. There was no fluid spurting up, it didn't move at all.

Additionally, I observed the fluid as my helper was depressing the pedal. Any swirling of the fluid would indicate that fluid was getting by the piston seals in my new master cylinder, but there was no motion in the fluid.

On to the main task of the day, which was replacing the two front lower ball joints. During that job, I also took the opportunity to replace the drivers side CV-shaft with the proper ABS unit. When I got everything back together, I hooked the ABS computer back up. The ABS is now working properly. The light comes on when I start the engine, then goes off after self check, and stays off, so I know that the ABS is working properly, and I fully bled it yesterday. The brake pedal still sucks though.

I'm now waiting to hear back from a friend of mine who is a mechanic, hoping that he can shed some light on the situation for me. If he finds the problem, I will post back to let you know what it was.

[loud92CB7]

loud92CB7db18, I can tell you with absolute certainty that disabling the ABS is not the cause of the spongy pedal. I honestly don't know what the cause is yet, but I know it isn't the ABS.

Yesterday, I hooked the ABS back up for long enough to bleed the ABS system, and verify that the brake pedal was still spongy. I also bled all the brakes on the car again, running an entire 32 oz bottle of brake fluid through the system. That didn't help either.

Today, following instructions I found from Mighty Auto Parts, I tested for air in the system. Basically, you have someone pump the brake pedal 20 times, on the 20th stroke they hold the pedal down firmly, while you remove the cover from the master cylinder (I also removed the strainer for an unobstructed view) and observe the fluid. Have the helper sidestep the pedal to allow it to pop up. If there is a geyser of fluid that spurts up in the reservoir, then there is air trapped in the system. If no fluid spurts up, then there is no trapped air. There was no fluid spurting up, it didn't move at all.

Additionally, I observed the fluid as my helper was depressing the pedal. Any swirling of the fluid would indicate that fluid was getting by the piston seals in my new master cylinder, but there was no motion in the fluid.

On to the main task of the day, which was replacing the two front lower ball joints. During that job, I also took the opportunity to replace the drivers side CV-shaft with the proper ABS unit. When I got everything back together, I hooked the ABS computer back up. The ABS is now working properly. The light comes on when I start the engine, then goes off after self check, and stays off, so I know that the ABS is working properly, and I fully bled it yesterday. The brake pedal still sucks though.

I'm now waiting to hear back from a friend of mine who is a mechanic, hoping that he can shed some light on the situation for me. If he finds the problem, I will post back to let you know what it was.

hmmm so could u tell me if maybe unpluging the abs computer would sumhow affect the master cylinder and causeing it to go bad? if i have a bad master cylinder then hell thats an easy fix from what i hear.... but yes as soon as one of gets this figured out we need to post the cure. this makes a car unsafe and we need to keep the cb's on the road and running like tops

[TomQuick]

No, unplugging the ABS has no effect on the Master Cylinder. The master cylinder is quite similar to the cylinders in your engine. There are rubber seals (instead of the metal rings in the engine) that seal the plunger to the cylinder bore. Over years of use, the rubber wears out, and begins to allow brake fluid to leak past it. When this happens, instead of the plunger pushing brake fluid into the lines to apply the brakes, the fluid leaks past the seals and back up into the master cylinder reservoir. Because of this, you can usually identify a bad master cylinder by watching the fluid in the reservoir while someone is pushing the brake pedal down

Generally a mush brake pedal is the result of either a bad master cylinder, a fluid leak in the system, air in the system, or a weak brake hose that is bulging under pressure.

What's aggravating in my situation is that I can't identify any of those problems in my braking system, yet the pedal still sucks.