chigung

AAAGH! Dave :mad
Help!


Since i have purchased my car, a 78, it has has a very, vary soft brake pedal.
I only have about 2 inches of good pedal, and about 5 inches off play, and on top of that only the front two calipers engage. And I never.....never lose any brake fluid. No leaks anywhere.

so...

First, I replaced the Brake Proportioning valve, no change
After a thorough bleeding, I had great pedal.....for about 20 mins, then it gave way to the 2 inch pedal again.

Then I replaced the master cylinder, once again, same deal. Had a good pedal for a bit, then the 2 inch thing. Once again, no fluid loss.

Then i started getting a horrid squeaking sound from the right rear caliper, so i decided to go all out.

I replaced...

all 4 calipers
all new pads
all 4 rotors
all new rubber and SS lines

now... In replacing all of the components, all fluid was drained from the system...

I have bleed the system 2 times now (using the old fashioned pump and bleed method) And the pedal is about 40 - 50% better, but still a little soft. I have about 3 - 4 inches of play with the car running, but a stiff, firm pedal with it off.


A few questions...
When you bleed the system, should you leave the car off, or spark it?

Also, Do you go by the (furthest caliper way from the Master Cylinder, and work your way forward) method?

And, should I go and have the car vacuum bled?
Could my issue be the power booster?

Any tips for this issue would be very helpful
Peace

427V8

Bleed with the engine off, less likely to kill the person under the car that way!

Start with the farthest wheel, the right rear.
Do BOTH bleed screws on each caliper!
bleed untill clear fluid comes out...

Check the runout on your 'new' rotors, they may still need to be trued:U

Sacrifice a valuable Corvette part to the brake Gods, then you will have many happy stops... :jester

chigung

Update!!!


I pulled my Master Cylinder today to "bench bleed" it

I pumped, and pumped and pumped, and i could never get past the "air squirts" In fact, many times, no fluid came out of one, or both sides as well.

I assume this means my Master Cylinder is bad, right?
I just replaced it last year.

The power booster rod only came out about 2 inches or so, is that normal?

Thanks,
Dave

lyonsh

If your car was stopping before you pulled the MC, and now you aren't even getting fluid out of it, I would suspect you're missing something in the bench bleeding procedure. You did attach fittings/tubes to the outlets and route them back into the fluid in the MC chambers, didn't you? If not, then when you release the piston it sucks air back in - so you're not making any progress.

Also, as to your first post, I don't mean to insult you, but I'd suggest you stop replacing parts until you can figure out what your problem is. I suspect, again, something in the bleeding process. If you are "pumping and pumping" you're cavitating the brake fluid, and even after bleeding you've still got air in there. The multi-pump method (called surge bleeding) is to get major air out of the system, and after you do that you need to let the car sit for about 30 minutes to let all those little bubbles collect, then do a manual bleed (one pump, crack bleeder, close bleeder).

Also, make sure when you are bleeding that you aren't just reintroducing air into the system - you do this by attaching a plastic tube to the bleeder and putting the tube into a container of brake fluid (an old coke bottle with about an inch of brake fluid in it works well). Also, after you crack the bleeder open, close it while there's still a little fluid coming out (indicating positive pressure).

And don't forget to hit ALL the bleeder screws.

One more trick and I'll shut up: try jacking the end of the car you're bleeding up (and for heavens sake put it on jack stands before you crawl under there). That will make those calipers a high spot, and help any air in the system move into them and then out when you bleed.

C3 brakes are great when they work, but they are finicky about how you bleed them. You've got to give a bit extra TLC. Good luck. :cheers:

Carl in LA

Here is my version of the nightmare... My car suffers from this symptom as well... I had air in the system REALLY bad when the car first came to me... Part of the overall rebuild was to replace the rear wheel bearings which I believed would solve the air in the system problem... Still sucked air and the pedal went to the floor after 30-miles of driving. I complained to the business that did the rebuild accusing them of selling me a lousy bearing rebuild, ie: excessive runout. They went WAY beyond the call of responsibility trying to correct the problem... Ultimately they replaced the calipers thinking that would solve the air problem. The driver side still sucked air and we agreed that I would pay for a new spindle and they would install for no charge (assumeing that someone in the past had hit a curb and bent the one that was in there).

The results... Still sucks air... I am resigned to bleeding every few weeks to keep the problem under control. About the pedal height... I tried extending the pushrod so the pumping action would occur with the pedal higher off the floor, helped, but still not perfect. Bottom line for me, C3 brakes are a pain in the A**.

bigvette1

Lyonsh post is excellent. Bench bleed out the MC slowly - don't pump or you create air bubbles and that's what you circulate. Adjust the booster rod so you have between 3/4 - 1" of peddle free travel before you touch the MC piston. You can feel it with your hand. Bleed the brakes slowly using this sequence:
RR - inner
RR - outer
LR - inner
LR outer
RF
LF

Make sure you are bleeding into a brake fluid jar with a line connected to the bleeder screw and "burp" the bleeder under pressure to get it all out. A soft peddle is air somewhere in the system. Did you have synthetic in the system before? Synthetic just will not give you the hard peddle that DOT 3 will.

I had one hell of a time bleeding my 73 with all new parts. I came across the Phoenix System brake bleeder. You can power flush, vacuum bleed or do what they call the "reverse fluid injection" where you inject fluid from the bleeders and let the air rise in the MC. Go to their web site and read about the tool and their tips. It is http://www.phxsyss.com
Good luck.

Carl in LA

Bigvette1 - at least your taking the highroad on this one... a follow up would be the speed bleeders... I read a post a while back that swore they were great... perhaps that would be another way to manager air in the lines...
http://www.speedbleeder.com/

chigung

A couple questions....


How do you ajust the push rod...


And about how far should the pedal go before you "lock up" the tires?