Hi All!
HELP! Purchased a '48 Chevy with a power brake booster already installed. Brakes are soft. Bled them in sequence & still a soft pedal. What is next to try to get this fixed?
Thanks in advance,
Mack
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Hi All!
HELP! Purchased a '48 Chevy with a power brake booster already installed. Brakes are soft. Bled them in sequence & still a soft pedal. What is next to try to get this fixed?
Thanks in advance,
Mack
How are you bleeing the system? Does it have residual valves?
Are you starting at the right rear? Then the left rear? Then the right front and lastly the left front?
Also, are you using a pressure bleeder? Or, a vacuum pump? Or are you pushing fluid backwards into the system from the wheels? Or do you have an assistant pump the pedal? If an assistant, are you pumping more than 2 "strokes" of the pedal, this may induce aeration in the fluid! Are you also keeping the reservoir full after each wheel?
So many questions.. and I'm sure others will come along and offer more ideas. Keep trying, you'll get it!
Thanks 34-40!
Yes, sequence is correct. Am using an assistant to press the brake pedal for me. He was pumping it.... many times. fluid always checked in the master cyl. Sounds like we'll try and do it with pumping.
Also, If the power booster is not working properly bleeding would still stiffen the pedal yes?
Mack
Then I would offer, DON'T pump it Many Times! Twice with the bleeder closed and don't rush! Pumping fast and often will / can cause the fluid to aerate, or trap air bubbles! Sometimes it's better to let it set overnight if you have trapped air in the fluid. Are you also using a catch can with a hose from the cylinder/caliper? This will let you see if there is air caught in the fluid when caught in a glass jar or clear plastic container.
A malfunctioning booster will make things "hard" yes.
Didn't get the air out of the master. I never do either.
Try this: press the pedal down very slow. Then release quick. Watch the master, keep doing it until you see bubbles. Then, keep it up till they stop.
how do you bleed the master? with the cover off push the pedal slowly and look for bubbles?
Another thing to consider - do you have through the frame fittings with a boxed frame? There are types of through the frame fittings that have air pockets in the middle, and getting them out can be all but impossible. You can find tech articles on them in several of the monthly's from a few years back.
Hi all!
Thanks for the input! I've found that the vacc line from the booster is not attached to anything. I have an edelbrock intake & am not seeing a port for the booster? This could be causing the brake issue or at least a contributor yes?
I bled the master & each wheel again, pedal slightly better.
Rspears, just seeing your post - will check it out! Thank You!
If you have nothing on the base of your carb to hook that big old vacuum line to, you can buy an adpter plate for under your carb that has that fitting on it. Or if you have a spot in your intake for a fitting you can just put one in there. If you do not have the place for a screw in fitting you can always drill and tap for one. The base plate is an easier solution, if you have the hood clearance.
Adjust the brakes, too much clearance in the brakes can give you a spongy pedal that seems like it needs bleeding
Thank You Bob,
I adjusted the rears and got a little more pedal! Prob need a bit more... How do I go about adjusting the fronts? Drums all around.
Its been so long since I worked on a chevvy that I don't recall exactly but I think the fronts & rears adjust the same way
Both front & rear backing plates should have the oblong rubber plug centered at the bottom, which fills the slot for the brake spoon access to the star wheel. Same process front & rear.Quote:
Originally Posted by Mack57
For drum brakes I always ran the star nutz out until the drum won't quite go on, then bank the adjuster off a couple clicks, and slide the drum on.
Then, the final step of the bleeding process, drive out o the end of the driveway, and punch it in reverse; bring the car to a stop by jabbing the brakes two or three times. This lets the self adjusters put the drums in perfect.
To answer your previous question on the master cylinder:
With the bleeder screws tight, and the cover off the master, just slowly pump the pedal, and quickly release. Any residual air will bubble out.
Thanks guys!
Will let you know how it goes!
Ok,
front brakes are way out of adjustment(why the pedal stayed soft) and the rears were closer but, still not great. Working on that and will re-bleed. I did find through frame junctions in the brake lines (mentioned earlier)....what's the best way to get the air out of those little buggers?
Mack,Quote:
Originally Posted by Mack57
If it were mine I'd get the shoes adjusted and see where you are. Through the frame fittings (the one's for boxed frames about 2.5"-3" end to end) are not a problem in themselves, but there were a bunch on the market a few years back that were machined such that they formed an air pocket in the middle that was just about impossible to get cleared out. Can't recall for sure, but I think they were a larger tube tapped on each end for AN fittings, and the large ID trapped air. I think Street Rodder did a tech article on them? Might have it in the barn stash of old mags, but not sure.
Yes Roger, Street Rodder did do an article about those frame fittings 4 or 5 years back I think. I don't think anyone still made them like those anymore but what would I know? Or if this is an older assembly, it could still have a set in there.
And I'll disagree on the adjustment making the pedal "hard". Air in the system will cause a spongy pedal. An out of adjustment set of brake shoes will cause a low pedal! These are 2 different issues.
Do the adjusting (front & rear) and re-bleed (front and rear). I would suggest adding a hose from the bleeder to a bottle and let the discharged fluid collect under the surface of some new brake fluid. This will prevent air being "sucked" back in should the assistant raise his / her foot before you close the bleeder and you can visually see if your getting air out of the system.
Lastly, is this with all new shoes? Are they high performance type? if so, have they been "bedded".?.?
Mack sinse you bought this with sytem already in place, you might want to remove the master cylinder and measure the stroke of the piston when you push it in all the way while being bench bled, then install and see if you get the same measurement at the rod when the pedal is pushed in, maybe a little short on the stroke which you never get the air out. Another questin arises, is this a dual master cylinder and are the front brakes connectd to the rear port and the rear brakes connected to the front port, are you running a factory style propotioning valve...? Also does this master have check valves in the ports...?
406 Rich, 34-40,
Today is a car day & hopefully will have some good news this eve. Never thought about the piston length.... Alright, time to get at it!
Not knowing what system you have, when they installed the booster/master some systems require that during install that the pedal pushrod be moved down 1.25 inches further down on the pedal arm, two reasons, alignment and it gives the rod alittle further travel, this means drill a new hole for the push rod. Just something else to consider..:LOL:
Hey guys,
The cyl on the dr side is not working properly but, I did get some adjustment on it. Ordered 2 new for the front. The pedal is significantly better! Also, plumbed the booster vacc line & the booster is operational. I have not checked the rod length yet... Back to it. Thanks guys!!
Hi All,
Have been bleeding & re-bleeding these brakes....pedal still soft. The weird part being, the pedal has been VERY good at times only to be lost.... Using a Mityvac 8020 now and with bleeder open - Nothing but bubbles. What on earth am I doing wrong here?? 406 Rich, I will check that piston position but, I think I should have a consistent pedal even if it is low - yes?
thanks all!
I'm not familiar with the vacuum bleeder you are using, but if it hooks up to the bleeder screws, then the bubbles are the air being pulled past the threads on the bleeder screws. There are special bleeder screws available which will prevent this. Or, you can through - drill a bleeder screw, vacuum bleed that cylinder, then swap it out quick. Follow up with a quick standard pump - and - crack bleed, in case any air gets in the servo when you swapped out bleeder screws.
Yeah, I agree with firebird on this one, as I had the same experience with the vacuum bleeder. The fit of the hose on the bleeder is critical, and the instructions on the one I used warned that a small trail of bubbles would be from thread leakage. The drilled out bleeder is a pretty slick idea, but I'd say you've got a bad master cylinder. Nothing else explains having a good pedal, working fine and then the pedal going soft. You've got an internal problem on the MC seals.
Hey Huys, Thanks! I also gravity bled this AM and still no pedal..... Does that confirm the MC seals?
It does in my mind. You also need to be sure that your pushrod adjustment allows the MC to fully retract with a small amount of free space, like less than 1/16" is OK but you don't want it engaged with the pedal retracted.Quote:
Originally Posted by Mack57
Thanks Roger, Will post how it turns out. Thanks,
Mack
I gotta agree with Rspears. If you can occasionally get a decent pedal, then it goes away. It sounds like the master is failing. Even if the shoes are out of adjustment, you should be able to get a firm pedal. Low, but firm. Once you adjust them then the pedal will be right at the top AND firm.
Hoping to hear good news soon!!
When I put in the new mc in my 74 Vega, I had the same issue - hard then soft pedal.
As usual it was my inept attempt at bench bleeding the mc. It took at least three attempts to persuade the bubbles out using the slow pedal down, fast up technique.
Good morning all!
First...Thank You! I have a lot to look into on this & have also checked the pedal ratio & come in at 3:1. So, along with the MC rebuild how do I go about changing the ratio? It was posted to move the shaft down approx 1.25" yes. But, Do you move the pedal assembly up to do this? wouldn't the MC shaft be at an angle if I just drilled a new hole in the pedal arm? I would love to post a pic of what I have here but, as of yet am not able to post pics.... any ideas on that? lol!
I think I've got the MC bled completely... no bubbles in the last few attempts. I was using the slow dwn/fast up tech each time I bled the lines also. It was an improvement for sure.
TGIF & have a great weekend!!
Sounds like your Master is bled fully. Regarding the pedal ratio, no you wouldn't move the whole assembly down. The ratio is the distance from the hinge/pivot of the pedal arm to the master cylinder push rod. I think before changing the ratio, you should get a good firm pedal feel first.
ok, so, next step is to rebuild the MC. The pedal height is 17(pivot to pedal) & 5.5 MC push rod to pivot.
Mack,
Like Mike says you need to concentrate on solving one problem at a time. Get your MC problem fixed, then you can assess your overall braking once they are working as designed. From the measurements you've given your pedal ratio now is 3.09/1 (17/5.5 - your 17" being from pivot center to brake pedal center where your foot engages). To change your ratio you'll have to move your whole MC assembly closer to your pivot point which means some fabrication work. Using your 1.25" example, you'd move the MC mounting point up 1.25", and then drill a new attachment hole in your pedal assembly at 4.25" from the pivot to keep the rod straight. This would give you a 4/1 ratio. Again, I'd try it with the MC problem fixed first, and be sure you still have a problem.
Just went back and re-read your post #1 and realized you're talking power assisted brakes here. Why would you consider changing your pedal ratio? I would think nominal 3 to one would be fine for power assist. Also, unless you already have a hone with good stones (and probably even if you do...) I'd strongly consider buying a new or rebuilt MC as opposed to re-building it yourself. I haven't put a kit in a MC for thirty years.
Hey Guys,
Ok, replaced the MC & have bled fully. The result is a "reasonable" pedal, still soft....about back to where I started. Roger, I went with a new MC, it was $23 - well worth the money! Thanks!
So, any thoughts on what to do next? The pedal ratio isn't something that would help?
If the pedal isn't firm now, it won't be firm after changing the ratio... did you look to see if you had those through the frame fittings?
They were known to trap air!
Good morning!
Ok, no through the frame fittings that I find, I was mistaken earlier.... it was a junction I was seeing. So, that is good news. God news on changing the pedal ratio also - wasn't certain how to accomplish that short of lowering the MC.
That brings up the question, how about the rod length on the booster? If it's too short that cause a low pedal yes? I'm getting a decent pedal at this point. it responds about 3 inches from the floor is all. I read that it is adjustable also... threaded...
Mack
A short rod length could be the source of all your issues. Someone mentioned to you to check for that.
You'll need to make sure the master cylinder is going through a full stroke.