This is a #!!!^&&*!!# problem! The master cylinder has been bench bled(or so we thought),new brake line,in place,gravity bled the lines then attempted to build pressure while pumping the brakes up. We have bubbles in the rear chamber of the m/c.It seems no amount of bleeding the wheel cylinders will eliminate the air? Any ideas? Thank you in advance!
Sounds like it needs to be bench bled properly ie lines from the outlet into the resevoir, pump full throw until ALL air is out of the lines,, plug fittings install in system & bleed as normal. If still bubbles check the master isn't naffed , pull off the condom from the pushrod end & see if it leaks there, fluid out / air in !!
If it's a made in China rebuild from the parts store, just pull it and tell 'em it's defective and get another one, and save some headaches. Those 8 year olds they have putting 'em together screw up once in a while.
We set the m/c in a vise(no,didn't strangle it) and using good fittings and lines,bench bled it til we didn't see any bubbles.We've both done this on other vehicles a time or two. It's a decent quality m/c,it's just producing air in the rear chamber since after mounting it and gravity bleeding it.
Terryr, It seems this is the case? It's not leaking in the back near the booster,the lines and fittings are all dry,no leaks.This thing has been bled like a blood drive. The chambers are hooked up corrrectly to the front and back and the rear brakes adjusted up. We tried another m/c with similar results. #!!!^&!!# It has to be something simple? Guess we're not smarter than the brakes?
Ryan, try giving the brake pedal very short strokes with everything hooked up and tight. That sometimes will get rid of the air. If nothing else works vacuum bleeding will pull all of the air out, and you can do that with one person. Good Luck Alden
Is the master cylinder mounted under the floor? If it is you need a residual pressure valve in both front and rear lines. 2# disc. 10# drums. Just my 2 cents worth.
We don't have any vibration coils bent into the lines,the master cylinder is under the hood and the highest point of the system.The wheel cylinders are about two years old and the car is garage-kept. We've half-pedalled the pump up process and get really small bubbles then,when full-to-the-floor pedalling we get a steady bubble a second when we let up. Next stop is finding a good vacuum pull setup.The gravity bleed and pump/bleeder deal ain't working. Thanks for the help and ideas! Carl
I've been hearing more and more lately of guys getting multiple defects on rebuilt MC's and only end the tail chasing when they spring for a new US made unit.
31Vicky, No,this has been a conversion from drum over to disc.Apologies for not mentioning this sooner. Everything is new except for the wheel cylinders and they worked great with the drum brakes. I've wiped the entire system twice looking for a break in the deal where air could enter....It's a sealed system. I'll check the other threads you fellas suggested and thanks again for the help! I'll let you know what happens..if it does?
Are you using SILICONE BRAKE FLUID DOT 5 (I think) It entraps air and can be a real headache. I went through this on my 67 Belair that I just put favtory disk brakes up front and SS lines got air for months finally put in regular stuff and NO MORE PROBLEMS. Good Luck
Yeah,just regular brake fluid,fresh outta the plastic bottle. Only new stuff,nothing that's been opened and setting on a shelf. I read "Brewton's" thread concerning his under-floor problem.We've already gravity and peddle bled them too. Having done this deal a few times it's been misery as we've tried everything with no luck.We've carefully replaced parts and borrowed another working m/c.The air has to be "pulled" from somewhere?The consistent purge and leak check has yielded nothing. I'm running out of cuss words...making them up is fun.
Have you rechecked ALL fittings? We ran into this once on my brothers '34, tried bleeding for an hour, still getting bubbles. He went over the firring and found one that took a little turn. bled 'em once more and they were fine. The loose fitting was dry, but it must have been letting air into the line. My brother at the time said he had seen it before.
It is very possible as someone has mentioned to have air being ****ed into brake system thru bleeder screws in wheel cyls. They will NOT fluid out/externally but WILL pull air into wheel cyls. around bleeder screws. When you pull bleeder screws out, you will see that they may have been bent/distorted from over-tightening. You may even see witness marks on bleeder screw showing a distorted seating of the screw in the tapered bore of the wheel cylinder housing.
That's whats perplexing me? We think the wheel cylinders are good. The car is well maintained and garaged.My friend that owns it is particular to a fault about what goes on the carnly good parts nothing discount or junk. As someone stated above,we thought maybe the plunger was nicked and the back/forth motion is churning air into the chambers? I peeled the rubber sleeve back and it's dry. Next step is to fill the mc to the tip top,connect hoses to all the bleeders and let them run.And swear.....a lot. This is a freak for sure.
You and I have (had!) the same perplexing problem. Mine ended up being a combination of two things: Faulty cheapo mc. All 4 wheels had the shoes backed off too far. Adjusting the brake shoes got me a "hard" pedal without pumping the pedal 2 or three times, replacing the master cyl. stopped it from drifting to the floor after it came up. The master cyl cost 14 dollars to replace, I'm using the first 14 dollar as the return "core", so it's cheap to fix.
Whew! 31Vicky,thanks for the ***ist.We've thought all of that too,swearing under our breath the whole time.Check/double check.The coupe is a friend of ours,so we're double picky. We've checked all the flares under a magnifying gl***! No cracks,burrs or ? The rears have been adjusted up,then backed off slightly. We're gravity-bleeding into a jar with the lines submerged.Checking levels frequently so as not to dry sump the chambers. I do not believe it's the mc,but... We're going to walk away from it for a few days,but ****on everything up tight.Other things going on and awaiting the use of vacuum gun and the owner has commitments. When and if we figure out what the #!!!^&!!# the problem is,I'll clue you in. Thank you all for the great help and ideas!
Since this is a fresh disc brake conversion, and a new master cylinder, and since I don't know what the cylinder is off of I would have to guess that it does not have a 10 psi residual pressure valve in it. Add one in the line to the rear brakes and you'll be fine. The reason the rear brakes worked fine with the 4 wheel drums is that the drum brake cylinder probably had the 10 psi rpv internal to the cylinder, and your new one doesn't. What the 10 psi rpv does it keep air from being ingested past the "chevron" style wheel cylinder seals when you release the brakes. I don't know anything about what rear brakes you have but I am ***uming they are the type that do not have cup expanders in the wheel cylinders so you need the rpv. Next time give us more info.
I've had isues with bad master cylinders right out of the box. (Re-mans) I'm beginning to learn my lesson. I have another suspected bad one I am dealing with.. If anyone is looking for decent cheep vacuum bleeder, Harbor Freight has one I have and trust. Sometimes you get **** there, but this is actually a good unit for 27.00. You need a compressor as it requires 90 to 120 lbs of pressure to pull the fluid through. Similar ones are more $$... I had to make a small adapter for my dual master (for the revervoir bottle) as the provided clips didn't work for mine. Took me all of 5 minues. (I drilled a hole and tapped a big 4" diameter metal washer) Everything has to be in good working order of course for a vaccuum bleeder to be of any value but if your system is solid, they can save time.... http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92924 Good luck...
We've gotten a quality Made In Good ol' USA MC and have seen results. After checking the last mc,we noticed that the flared port for the rear chamber on the mc(where the line attaches)was screwed up.The conical shape wasn't consistent. There weren't any leaking issues,but it must've been enough to allow air to draw in and where we kept getting bubbles? No bubbles now and we've bench bled the same as before. Also,the brake line is attached to the top of the rear of the 10 bolt rear-bent and set like factory.At that point(with lowering blocks on the rear)the line is kissing-close to being higher than the wheel cylinder.(The things you notice when you're lying on your back opening and shutting wheel cylinders?) Safe haven for air to reside and be unable to escape or be drawn out. Tonight we're vacuum drawing the system and hoping for success. It's always the little things.... Thank you very much to everyone that gave the great advice! The HAMB rocks!
The Jalopy Journal
