alot of brake pedal travel
- Thread starter rubicon
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fordsbyjay
Active Member
Are they new calipers? One thing I used to do wrong is pumping the pedal too fast. You need to pump it slow.
Are the bleeders at the top?
Is the pushrod adjusted properly? I had to put a stop for how far my pedal pulls away otherwise it creates a lot of pedal travel before the piston in the m/cyl actually starts moving. How well do the brakes work once they grab?
Are the bleeders at the top?
Is the pushrod adjusted properly? I had to put a stop for how far my pedal pulls away otherwise it creates a lot of pedal travel before the piston in the m/cyl actually starts moving. How well do the brakes work once they grab?
I had the same problem until I finally realized that my bleeders wern't at the top. I have to take the calipers off the front wheels and rotate them so the bleeders are at the top to get them bled. Another thing that helps me is a vacuum bleeder. Not the kind you get from the discount auto parts store that have a squeeze handle, but a vacuum unit that runs off the air compressor.
The GM disc/disc master cylinders are a bit tricky to bleed out completely.
Make sure the master cylinder piston is being fully retracted and bottomed out! and the pedal is not hitting the firewall before that happens.
The power bleeding is really the only way to get that particular cylinder bled out and have a good firm pedal.
The only other way involves having the front system open while bleeding the rears and vice versa (lots of long hoses hanging from the ceiling)
Make sure the master cylinder piston is being fully retracted and bottomed out! and the pedal is not hitting the firewall before that happens.
The power bleeding is really the only way to get that particular cylinder bled out and have a good firm pedal.
The only other way involves having the front system open while bleeding the rears and vice versa (lots of long hoses hanging from the ceiling)
fletcherson
Well-Known Member
I found bleeding with a tube on the bleeder going into a can, jar, whatever of fluid works well, remove the bleeder and put Teflon on the threads so it won't suck air. Then bleed one at a time, farthest from master first, normally rr, lr, rf, lf. Install the tube on the bleeder, it must be submerged in fluid in jar, crack bleeder open, and slowly pump the pedal until no air in that wheel. Check fluid level each time. A clear tube works best because you can see air bubbles. Works great, one man job. If that won't work, I get out the power bleeder. Are you sure the master cylinder is good? It could be blowing by internally.
rubicon
Active Member
I have Wilwood calipers with bleeders top and bottom. Wilwood directions say to use the ones on top for bleeding , which I did. I also use a clear hose into a glass jar with fluid in the jar. I started in the front farthest from the master cylinder. I also put a remote reservoir up on the firewall. I will try adjusting the push rod to make sure it is correct. the rod does seem to come out quite far. I will bleed again. I'm working on my jeep right now so it may be awhile before I respond. Thanks for the info.
EX JUNK
Moderator
I always thought that you were to start at the right rear then to the left rear than right front and finish with the left front. All this is to be done after bench bleeding the master cylinder. I might also add that if you are using DOT 5 fluid you must pour it VERY slowly into the master cylinder so as not to make any bubbles which are difficult to remove from the system.
Jim
Jim
choppedtop
Well-Known Member
That should be true Jim, unless for some reason, the rear brake line was run down the right hand frame rail. I have seen stranger things in some builds. Oh, btw. what are thoughts on mixing 3/16" and 1/4" brake lines? In my mind this would cause a problem volume wise.
Lee
Lee
fletcherson
Well-Known Member
I think the only time you should change line size is when the fluid path splits, for example, 1/4 from the mc to the T on the rearend, then 3/16 to the wheel cylinders. That makes logical sence to me to equalize volume, pressure. I am interested to hear any thought on this too, I am going to be doing this soon.
old round fart
Well-Known Member
That sounds reasonable but I have never used 1/4" line on anything.
choppedtop
Well-Known Member
To add to this question. I have a friend that has 3/16" line everywhere, except where the two front calipers join. One has 3/16" feeding it, then 1/4" joining the two. His brakes are not the best. I tried to tell him I thought this may be a problem, but I may as well talk to a fence post.
fletcherson
Well-Known Member
I know from basic plumbing that reducing line size increases pressure, but I don't think that would necessarily hold true in a braking system because volume is required to move the caliper, cylinder, etc. perhaps to regulate more volume to one and less volume to the other, ie disc/drum it may be a consideration. It seems that a smaller line would inhibit if the master was large enough to push adequate fluid volume. I plan on using a adjustable pro portioning valve and not worrying about line size differential. I " think" that running a larger line from the mc to the splitter, or "t", would enhance response. I've noticed that's how it's done on heavier vehicles that I have worked on. I am not sure if it would be noticeable in a light car like a T bucket. Time for me to do some internet research on hydraulics and fluid dynamics maybe? Lol.
fletcherson
Well-Known Member
Ok, after a quick study session, it seems the big factor is mc bore vs wheel cylinder bore, not so much line size. Rear drums require more fluid than do disc, so larger lines are typically ran for them, the down side is it takes more fluid, ie more pedal travel to do the work, also they say larger line size can allow softer pedal due to fluid and line expansion. Wilwood recommends 3/16" hard line all the way the the flex lines, the flex lines should be as short as possible to minimize expansion, spongy pedal.
choppedtop
Well-Known Member
So, the line change to larger, wouldn't make any difference? How about the extra volume needed to fill the 1/4" versus the 3/16" when the 1/4" is the jump line between calipers? No argument, just wanting to understand. Once when working on a motorcycle with a side car with disc brake on all 3 wheels, the side car wheel would lockup. I changed the 3/16" line to the side car to 1/4", and it solved the lockup problem. Front wheel and side car wheels were fed off front brake on bike.
fletcherson
Well-Known Member
From what I read, the larger line requires more volume, and thus requires more pedal travel. There is a formula, I dont remember it right off. I think it would depend on more than just the line size," think", because there are variables, such as the master bore, wether it's disc or drum, pro portioning valve bias, etc. from what wilwoods site said, they recommend 3/16" and stated it provided firmer pedal feel and less pedal travel. Another site I looked at explained that cars with rear drum brakes used 1/4" line from the master to the " t", then 3/16" to the wheel cylinders. They explained that the drums required more fluid to move them than disc, so the larger line provides the volume, again that is from the master back to the split. Wilwood stated that larger line size allowed softer pedal due to fluid expansion and line expansion, I wouldn't have thought that would be an issue, they also instruct to use the shortest possible soft or braided line for the same reason. Also larger line requires more pedal travel because you are moving more fluid. I believe Wilwood was speaking more to disc than drum brakes. So the example of your side car proves the theory, sort of, if you think about changing the line to a larger size after the split, you in effect created a larger area, which required more volume, so the brake reacted less aggressively. That was a smart fix! I purchased a master designed for disc/ drums, so I plan on plumbing my brakes as the manufacture did with larger line to the rear drum split, then smaller to the wheel cylinders and small line to the front calipers. I hope the adjustable pro portioning valve and the residual valves are enough to make it workout..... That brings another thought to mind, could the excessive pedal travel be caused by not having residual pressure valves installed and allowing to much fluid travel?
Indycars
Well-Known Member
I have to respectfully disagree with the notion that a larger line requires
more fluid from the MC. Ok I will agree that there is more volume in the
line, that is obvious. But the displaced volume is completely depends on
the MC size. If one inch of pedal travel displaces 1 cuin of fluid, then 1 cuin
of additional fluid is in the wheel cylinders, no matter the size of the lines.
A larger line will slow down the velocity of the fluid as it moves thru the line,
but nothing more.
more fluid from the MC. Ok I will agree that there is more volume in the
line, that is obvious. But the displaced volume is completely depends on
the MC size. If one inch of pedal travel displaces 1 cuin of fluid, then 1 cuin
of additional fluid is in the wheel cylinders, no matter the size of the lines.
A larger line will slow down the velocity of the fluid as it moves thru the line,
but nothing more.
