brakes
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June 11, 2012 06:24 AM - 1273 Views
Trying to get brakes on the 34. Can't get a good pedal. Any suggestions?
Here is what I have, master cylinder under floor, 2 lb & 10 lb residual valves in lines, new S-10 rear drums in rear, GM calipers in front, all new, new lines. No leaks. Thought I had a bad Master cylinder, bought another one, same problem.
Here is what I have done, bench blead the master, blead the lines 4-5 times - no air.
I just can't get a good pedal that I like. Feels spongie & goes away when I push on it.
- Newest Post: July 13, 2012 07:56 AM
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I went through the same with my roadster. Went to 1 1/8 master cylinder and 8 in.dual booster. Gm calipers require more volume. Stops great now.
make sure brake pedal is coming back all the way or it will never bleed properly. probably needs a strong return spring.i found this out the hard way.make sure the rear drums are adjusted up real close too.
sam
Another thing to check, there are some through the frame fittings that tend to form air pockets that are all but impossible to push through the fitting into the caliper/wheel cylinder. Art Morrison is one place to get a "new & improved" frame fitting that eliminates the traps - http://www.artmorrison.com/brakes.php
Thanks guys, keep them coming.
Sam, pedal is coming all the way back up, positive of that.
Roger, no through the frame fittings on this "Quad Rod".
Gbfab, no booster, 1" master.
Do you have crush washers at the ends of your brake hoses? Sometimes air can get in if not.
I have had bad calipers that would suck air but not any leaks. Here is how to check :
Pinch all the flex lines and press the pedal. Should be hard as a rock. If not problem in master. Release furthest line clamp and push pedal. If it goes down that is your culprit. Do each wheel one at a time and find out which one's are the problem.
I have corvette calipers and they are famous for going bad from sitting. Have had to replace a few sets over the years.
Good luck
Bad left front caliper. Called Speedway to get another one, bought 2 years ago. No CHARGE!! Can you believe that?? Will be here Monday/Tuesday.
I've had nuthin but good luck with Speedway customer service.
Same here good cutomer service from Speedway.
Replaced caliper. Still do not have a good pedal until half way down. Any more suggestions.
you will never have a good pedal at the top with the brakes in the floor. the geometery is just wrong .
My buddy's 40 chevrolet ( fresh build ) had the booster under the floor . Bled it numerous times , tried other suggestions . Even sent the booster & master cly. back to the vendor for replacements , residual valve , nothing worked .
Finally gave up & put a used booster off a truck on the firewall . Has all kind of brakes now .
you have to increase the distant from the pivot point to the rod for the booster. or use a larger dia mastercylinder.
Had 2 buddies over tonight to help bleed, insteat of wife. NO LUCK!! Pedal does not move when bleeding front, goes to floor when
bleeding the back.
Shine, no booster, 1" bore Master cylinder
What size lines should be going to the front & rear???
the larger the bore the more fluid it moves, same with lines. small bore gives more power but moves further to fill the cylinder..
I have under floor master cylinder and no booster 1" bore cylinder believe I used 5/16 line size, getting old can not remember for sure. Have a good hard pedal pushed 2 to 3 inches down. Stops fine but takes little more foot pressure to hold it at idle, booster probably would have been better. I had trouble bleeding the rear and thought it was because the lines are a little higher than the master cylinder. Pedal going to floor never will get air out so I used a cheap vacuum pump on end of line plus pedal bleed and that did it. I got the vacuum pump from Speedway but have seen them at parts stores. Seems the pump was $25 or $30.
Lynn, your problem sounds exactly as I had. After I could not get it bled with the pedal and got that vacuum pump I Vacuum bled the cylinder closest to the master a couple times then did the other but still was getting some air. The cheap vacuum pump is not real strong and does not hold vacuum for very long--So, I pulled vacuum on the one further from the master cylinder and hurried and pumped the pedal a couple times. Think I did that a couple times and Waa Laa I had a good pedal. No mess pump has bleeder hoses and I did not need a helper.
Sorry, typed that line size wrong I used 3/16 not 5/16. As said, getting old I guess. Sorry.
Typical master under floor would be mid '70s Corvette. what is master cylinder ? Don't use crap adjustable prop valve for rear brakes.
How far are residual valves from master ? They hold slight pressure in wheels cylinders/calipers so fluid does not drain back in to master.
Spongy and then no brakes sez poor bench bleed ??
Jim, School of Hot Rod Hard Knocks, 1957
Mid 70's Mustang/Fairlane master.
Residule valves are about 12" from master.
30 A PU........ditto on our '33 SD. But also have a OEM fixed equlizer block. No booster. GE silicone fluid............for over 72,000 miles.
Double check the flow direction of the residual valves.
Lynn, when I put all new stuff in mine, including running new lines.. everthing in the rear was higher than the master cylinder and of course wheel cylinders/lines were completely dry being new. I simply could not get the pedal to push it all full. Once I vacuumed fluid through which basically filled everthing the pedal would push fluid fine but not when all the lines and wheel cylinders were completely dry. I tried pedal bleeding the rear umpteen times with no luck, once vacuumed it pedal bled fine.
is the master cylinder for drum/disc ? a 79 chev pu master works. corvett is disc/disc just a thought good luck
Well, I got some brakes, not the best! I switched the lines on the master cylinder, front to back, back to front. I think it still has air in it. I will vacuum bleed it this week when I have time.
Thanks for all the suggestions, Lynn
had sorta the same trouble years ago and it drove me crazy . after replacing all parts others suggested i still had soft pedal so i then had a old timer mechanic tell me to make sure the front wheel bearings where lubed and tight like they should be . long story short the old timer was right when he told me to check . all ok now . the rotor being loose bearings would push the pistons in on the calipers and it just made it that much more travel of fluids to push them into a clamp like mode . good luck