So here's where I'm at: My brake pedal does not feel so great. If I keep my foot on it I can push it to the floor... however, I don't think it's always like that. Sometimes it feels firm... I think - not sure why! Anyway, here's my brake system history:

I replaced all the front brake stuff a couple years ago - pads, rotors, calipers and brake hoses. Everything seemed to work pretty well. I did have a little trouble getting the air out of the system but I think I got it pretty good. At this time I also bled the rear brakes. The pedal felt great, and I mean great, up until a few months ago...

A few months ago I started having problems with one of my rear calipers locking up. I tried to fix the problem inside my car, but in the end I developed a significant leak on one of the rear calipers. I then dropped the IRS and changed out all the rear brake stuff - new rotors, pads, and new calipers. I also made new crossover tubes. I bled the rear brakes and they seemed pretty good. Then, as I tested it more, I found that I did not properly tighten the crossover tubes, and I was leaking brake fluid at the rear calipers. After an hour of messing around and testing, I finally got the rear caliper leaks fixed. They do not leak anymore. However, my brake pedal can now be pushed to the floor. The car still stops okay, but probably not as well as it should. I am not losing any fluid.

Any thoughts? Here are some of mine:
1) Bad master cylinder.
2) Air in front brakes was masked by good rear brakes until I had the rear brake problems. Now both the front and rear have air in them.
3) Air in rear brakes is causing the problem with the soft pedal.
4) I did not bleed the brake system properly.

Other things: There is also a groaning "woosh" sound that happens when I push the brake pedal in hard. I think it's coming from the vacuum accumulator. It did this a few months ago but then the sound went away.

As far as bleeding goes, I look at these as two separate systems. I think you can bleed the rears without affecting the fronts, etc.

Also, I installed a teflon/stainless steel/plastic rear brake hose. It is not leaking.

I really hope this is not a master cylinder. What do you guys think?

Also, how hard is it to get the air out of the rear calipers? The crossover tubes are obviously higher than the bleeder will ever be. I have access to a "MightyVac" vacuum bleeder but did not use it on this car.

 

Exercising the master in an old car while bleeding usually tears up the seals because the piston travels far enough in the bore to reach a part of the bore that is slightly rusted. For a firm peddle get yourself a complete series 3 master with the on master reservoir. Also replace the lines to the perporting valve if they have junk in them because it only takes one spec to rip up a master seal. I've had no luck bleeding with a mity vac. Gravity bleeding and taping the caliper while fluid flows through with a hose from the bleeder and inserted into a hole in the cap of used up water bottle worked well for me. Make sure the hose is at the bottom of the bottle and the bottle is higher than the caliper but lower than the master. This is real difficult to do on the rear but easy on the fronts.

 

My money is on the master cylinder.

Good bleeding tips from Iscamerica. Personally I've never had any problems bleeding a Ser III system but, funny thing about bleeding brakes in general: either it works first time around or it takes multiple tries and much cursing. No in between.

Just my experience :-)

Cheers
DD

 

Thanks for the info guys. I went out and tested the car again this morning. I think I overreacted. The pedal does not go all the way to the floor. When the engine is off, the pedal actually feels really good. When the engine is running, it will go down farther, but gradually gets stiffer until I cannot push it any farther. It never really bottoms out. Any thoughts?

I think I am going to rebleed the rear brakes. I have a feeling that some air got into the system through the leaky fittings. Its also possible that I did not get all of the air out regardless of those leaks.

When I was bleeding into a cup, I did not have the end in the cup submerged in the old brake fluid, which let air rise up the clear hose. Not sure if that was causing problems, but it did make it harder to see if I got all the air out. That's a good tip - I am looking forward to trying it next week!

BTW, my car does not have a proportioning valve or bias switch. From what I can tell, the front and rear systems are 100% independent from the time they leave the master cylinder.

 

Yes :-)

"Brake Repair Hyper-sensitivty Syndrome"

I have come across this affliction many, many times. After brake repairs the driver is (naturally) concerned about the performance of the brakes and "pedal feel" often becomes the focus. Typically the driver is convinced that the pedal feels lower or softer than previously when, in fact, it isn't and doesn't.

I have proven this using my own family members as subjects. Upon returning the car to them after service or repairs I tell them that I have bled the brakes or done some other brake repair when, actually, I never touched the brakes or even looked at them.

Without fail....and I've played this trick several times....without fail they will remark the the "pedal seems too low" or "the brakes feel soft".

I *myself* have fallen victim to this syndrome even though I am quite aware of it! Gahhh! With time, though, I eventually learned to suppress the desire to bleed the system "just one more time". :-)





By all means, but be aware of the above!




It was elimnated circa '82-'83

As I recall it didn't serve any function as a proportioning valve. It was simply a shuttle valve used to activate the warning light if brake pressure was lost. "PDWA"--Pressure Differential Warning Actuator or something like that.

Cheers
DD

 

 

When I bleed the brakes, I use a length of clear plastic tubing (so I can see if there are still air bubbles in the fluid being evacuated)
I use a small jar - about 1/4 full of brake fluid, and one end of the tubing submerged in it with the other end attached to the bleeder nipple.
Open nipple.. slowly push brake pedal down as you watch the fluid move into the jar. (having a long length of tubing helps if you are working by yourself - allows you to position the jar where you can see it and still reach the brake caliper being bled
Do not let the reservoir run dry.. Just let the old fluid flow through the tube into the jar and watch the bubbles as they pass through the tubing .
Eventually only fluid without bubbles will be entering the jar. The clear tubing is the key as it lets you see if the fluid still has air mixed in.
Has worked smoothly every time i have used this method. I am not a big fan of the M/C used on these cars - always seem to leak - and destroys the paint under the master cylinder. A lot of XJ6 S3 cars have this paint damage. Next time I clean up the mess,.. I will paint that area with POR 15

 

Wow, Zombie...this thread is back from the dead!

 

It has been a spell, since I bled a set of brakes. the system of using a mate to "pump and hold" usually worked. I merely cracked the bleeder and let fluid out. When I saw no bubbles, I moved on.

One effort involved our 71 Hudson Hornet. In reality, an AMC Rambler !!! Only when I resorted to running the engine to get pedal boost., did I get bubble free squirts.

Carl