alot of brake pedal travel

[choppedtop]

Ok Fletch, I think that I understand now. To be honest, it was a hydraulics guy that told me about changing the line on the sidecar. I did try a proportioning valve first, to no avail. I also believe that is why my friend has poor brakes on his hot rod, due to the change of line size between the two front disc.
Thanks for your explanation. Didn't mean to barge in on rubicons thread.
Maybe I missed it, but is the m/c under the floor. If it doesn't have residuals built in, it must have them in the lines, or the fluid will drain back to the m/c. This would for sure cause problems in bleeding, even more after traveling down the street a few blocks

 

[fletcherson]

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.

Good point, I am going off of wilwoods site, and another hydraulics site (I don't remember the name) on an Internet search. If I get time later, I will look it up again and try to make sence out of the formula. I guess it would require a physics experiment to prove or disprove the theory, but from what Wilwood said larger line size requires more pedal travel, it seems the larger line and resulting fluid volume also allows for expansion more so than using the smaller line and adds to the issue. I personally wouldn't have thought that would be a consideration. Good discussion, anyways. I guess there are two ways to look at the line volume, one way it is a chamber full of fluid, but it is also a larger chamber, so even if it's full, it's a larger chamber that requires more fluid to move it, the way I see it, and I don't profess to be an authority, the larger line is like having a larger diameter cylinder, so it would require more volume to be displaced to move the piston, hence the additional pedal travel. It is like having a larger diameter wheel cylinder so more fluid is required to move it the same distance. Does that make sence? Again I am not being argumentive either, just trying to figure it out.

 

[409T]

or the fluid will drain back to the m/c.

If your brake system is closed and bled properly, after you release the brake pedal the fluid has to drain back somewhere or the caliper(s) or wheel cylinder(s) can't relax. The only place to go is back to the master cylinder unless you have a leak.

 

[Indycars]

If I get time later, I will look it up again and try to make sence out of the formula.

If you find the article again, please post the paragraph in question and
link to the full article.

but from what Wilwood said larger line size requires more pedal travel, it seems the larger line and resulting fluid volume also allows for expansion more so than using the smaller line and adds to the issue.

Being that the larger line has more material/greater circumference, then
yes in theory it's going to expand more under pressure. But like the fly
that lands on a 10 inch steel I-Beam is also going to defect..... it's not
very damn much.

If the steel lines expand, then how much is the flexible lines going to
expand? Since the flexible lines are acceptable, then I can't see the steel
lines expanding enough to be on anyone's radar ...... except maybe Roger
Penske's radar.

Wonder what they would say about this brake line? hehehehe !!!




Yes, I definitely am not trying to start an argument, but have a great discussion.

.

 

[fletcherson]

http://www.thirdgen.org/forums/brakes/612528-brake-line-size-why.html#post4911851
Plumbinghttp://store.fedhillusa.com/faq.aspx
Sorry so long to reply, busy day. Here are a couple links I looked at with some info, one is a source for lines, fittings, etc that may be helpful. There are several. I am not endorsing any. It seems our discussion is a fairly common discussion among car builders and hot rodders. I found several forums, etc with similar discussions. I didn't want to post links to them because I don't want to ruffle any feathers, etc... I did post a link to one that has the formula relating to this discussion. But you can do a search and find them if it interests you. It seems people have different views related to pressure vs volume, ie line size, but the general answer I got from the folks who seemed most credible was that drum brakes require more fluid volume due to wheel cylinder travel due to brake shoe travel and the fact that the springs retract the wheel cylinder pistons every time applied, requiring more volume, that's why the larger 1/4" line is installed. Larger line = more volume, smaller line = more pressure, more volume requires more pedal travel. My translation of this is if you have disc brakes front and rear, with different sized lines front to rear, the theory infers the brakes with the smaller line would have more stopping power. Disc brakes do typically have larger cylinders, but require less volume because the piston has minimal movement. They also repeatedly restate that smaller line size is stronger and less likely to flex. Again, the majority also think that the flexing or expansion of the hard line is a minimal issue, as do I, but include it as a matter of discussion and consider it to be fact. I think I may have mis stated the source of some of my info earlier, the info was as reported, I just confused the source, sorry! My conclusion is that I don't think the line size would make a big enough difference to actually feel in a light car, unless it is undersized and isn't supplying enough for drum wheel cylinders, but that would be unlikely and would infer other issues such as mis sized master cylinder bore, etc. In a car with disc, drum, I would stick to the manufacture engineers method of running larger rear line to the drums, and smaller to the disc. That allows the proper volume to operate the wheel cylinders, and the pressure for the calipers. Also the proper master must be selected. Another interesting point I read is that the masters are also designed with different sized resevuors on disc, drum equipped cars to supply the required volume to each perspective type.
I am not a mechanical engineer, so please do not take my translation or understanding of this as gospel, I am just trying to understand it and enjoy a good discussion. One interesting thing I read that was posted by a man who professed to be an engineer for ford was that the line size differential related to balance, and changing this could create unbalance, or "twitchy" erratic braking. He strongly advised not changing from what the manufacture engineered as far as line size. I suppose that an adjustable pro portioning valve and correct residual valves would maintain proper fluid position, flow, and allow enough adjustment to negate any real difference created by line size variation, but that's just my sort of educated opinion, lol! If anyone reading this is trying to design their brake system, I would advise researching the components and make sure to select the ones that are compatible to your situation and with each other. Brakes are important, don't assume. I like the kiss theory, as far as why reinvent the wheel? There are already brake system models that were designed by engineers that can be readily adapted to our cause, a little research can save some frustration. This has been a good exercise for me in respect to my project. I had most of the braking system components bought, but the line size issue really didn't come to mind. I know more now...

 

[fletcherson]

If your brake system is closed and bled properly, after you release the brake pedal the fluid has to drain back somewhere or the caliper(s) or wheel cylinder(s) can't relax. The only place to go is back to the master cylinder unless you have a leak.

Yes, I agree, but if the master is positioned low, like many buckets, it is recommended to use residual valves to prevent the fluid from flowing away from the wheel cylinder or caliper. They suggest 2# for disc, 10# for drum. That prevents fluid cavitation, from what I have read. If someone neglected to install them, that could explain excessive pedal travel, I would think. This is my first car with the master mounted under the floor, so I am relying on information obtained from others as opposed to personal experience on this topic.

 

[fletcherson]

If you find the article again, please post the paragraph in question and
link to the full article.


Being that the larger line has more material/greater circumference, then
yes in theory it's going to expand more under pressure. But like the fly
that lands on a 10 inch steel I-Beam is also going to defect..... it's not
very damn much.

If the steel lines expand, then how much is the flexible lines going to
expand? Since the flexible lines are acceptable, then I can't see the steel
lines expanding enough to be on anyone's radar ...... except maybe Roger
Penske's radar.

Wonder what they would say about this brake line? hehehehe !!!

View attachment 11886


Yes, I definitely am not trying to start an argument, but have a great discussion.

.

We share opinions on the expansion topic, I wouldn't have even considered it. They do, however, recomend using braided lines over stock rubber, and to minimize length. Sounds reasonable to me, but I seriously doubt it would be noticeable in a light car. As to the discussion thing, I enjoy it, even if I am not right, it allows me to see different views and makes me think. I now know more about brake lines than I thought I needed to know, lol!

 

[choppedtop]

I think I agree with all of your latest posts. Especially the expansion of rubber versus braided lines. Not sure why anyone would use rubber lines on an exposed front end, just because braided look so much better. I witnessed quite a few internal failures of rubber lines when I had my cycle shop. Cannot remember a failure with braided s/s lines. As far as drums on the rear, I do check from time to time, the adjustment of shoes, just in case the auto adjusters don't do their job as they should.
This has been interesting and enlightening. Thanks for your research.
Lee

 

[2old2fast]

Before this thread went off the rails , Rubicon had a problem w/ a low brake pedal . I'm curious as to whether He's made any progress w/ the problem ???
dave

 

[choppedtop]

Me too, Dave. Hopefully some of this may have helped him some with his problem. Don't think anyone meant to derail the topic, but there is a lot of information here that could help with similar problems.

 

[Larry]

I have learned more about brakes than I knew there was to know. I'm putting new wheel cylinders and brake lines on my wifes '62 caddy with drum brakes all around and I will be studying to this thread for help. I hope Rubicon got his figured out

 

[fletcherson]

I think I agree with all of your latest posts. Especially the expansion of rubber versus braided lines. Not sure why anyone would use rubber lines on an exposed front end, just because braided look so much better. I witnessed quite a few internal failures of rubber lines when I had my cycle shop. Cannot remember a failure with braided s/s lines. As far as drums on the rear, I do check from time to time, the adjustment of shoes, just in case the auto adjusters don't do their job as they should.
This has been interesting and enlightening. Thanks for your research.
Lee

Funny how much I learned about something I thought I understood... I always change the rubber brake hoses when I do a brake job on my vehicles because I have had so many failures with them particularly on the front. they get stuff inside of them where the brass fittings are attached and it gets stuck inside and acts like a check valve. I don't know if it is from the rubber deteriorating or just debris that gets forced in and can't escape through the smaller opening, but I have even replaced calipers thinking they were hanging up and found the issue to be the line... That was a very frustrating lesson. I have had more problems with GM hoses than any others, but I used to work on a lot of GM cars, so not sure if that's a fair statement.

Before this thread went off the rails , Rubicon had a problem w/ a low brake pedal . I'm curious as to whether He's made any progress w/ the problem ???
dave

i don't think it got off topic, it got pretty deep into the topic and things relating to it. I think we covered just about every conceivable cause for his issue. Rubicon, did you figure out the pedal travel issue?

 

[fletcherson]

Funny how much I learned about something I thought I understood... I always change the rubber brake hoses when I do a brake job on my vehicles because I have had so many failures with them particularly on the front. they get stuff inside of them where the brass fittings are attached and it gets stuck inside and acts like a check valve. I don't know if it is from the rubber deteriorating or just debris that gets forced in and can't escape through the smaller opening, but I have even replaced calipers thinking they were hanging up and found the issue to be the line... That was a very frustrating lesson. I have had more problems with GM hoses than any others, but I used to work on a lot of GM cars, so not sure if that's a fair statement.

i don't think it got off topic, it got pretty deep into the topic and things relating to it. I think we covered just about every conceivable cause for his issue. Rubicon, did you figure out the pedal travel issue?

I went back and read to make sure I didn't "derail" the thread, and Rubicon stated that he was not going to be replying for a while because he was working on his jeep, then he stopped commenting. I presume he will chime in when he gets back to his brakes.

 

[rubicon]

I want to thank everyone for thier imput. I found it quite humorus that the discussion got so indepth. I have not had time to work on the T yet but when I do I will let everyone know what I find. Again thanks you guys are amazing. I glad I found this site.

 

[rubicon]

I finally found time to work on my brakes. The problem was I had the adjustment rod set up wrong. I needed to remove the play in the MC before I adjusted the other end of the rod that connects to the brake pedal lever. problem solved. Thanks guys.

 

[Indycars]

Now back to cruising again.....yippeeee!

 

[Tjbucket]

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?

Fletch,
I because it is hydraulic.....I din't think line size really matters, once the lines are filled and bled, you are just adding pressure when applied. I used 3/16 and have minimal pedal travel, but, that is not say if would have not had the same results 1/4 inch line. The project I started with had 2 different size brake lines and I thought that was wrong......so, I used all the same size (3/16) when I re-built it. Granted I have not had a true road test yet, but the pedal travel is acceptable.

 

[fletcherson]

Fletch,
I because it is hydraulic.....I din't think line size really matters, once the lines are filled and bled, you are just adding pressure when applied. I used 3/16 and have minimal pedal travel, but, that is not say if would have not had the same results 1/4 inch line. The project I started with had 2 different size brake lines and I thought that was wrong......so, I used all the same size (3/16) when I re-built it. Granted I have not had a true road test yet, but the pedal travel is acceptable.

From what I read, the master and wheel cylinder bores also play a role, so depending on the combination, it may not be noticeable. I find it difficult to conceive that there is an actual difference between 3/16 and 1/4 line based on the steel line flexing, but they claim there is. If that's true, I would think line length would also figure in, so shorter wheel based cars like ours would be less susceptible to the effects, right? I never realized there was a difference, I just didn't think about it until I, we, started discussing and researching the topic. Let me know how it drives. I think with an adjustable pro portioning valve, whatever the difference is would be negated by changing the bias to overcome it anyways. Especially in a light car. I just never really put that much thought into brake line size before. I know more now than I thought there was to learn, and I still don't totally understand it. lol. Glad you got good pedal, etc... There is science to support the advertised differences and the theory makes sense, I'm just not sure how relevant it is for our purpose. I will say that from what I read, I am going to run a larger line to the rear drums, and smaller to the front discs so it is like the system was originally designed. I am also using a adjustable pro portioning valve. I seriously doubt that there will be any noticeable difference either way, but it will be simpler because of the fittings, etc. I just want to duplicate the ford disc/drum system, they already done the engineering. The bias adjustment should allow me to dial it in to accommodate for the weight difference and the tire contact patch, etc. The T is so much lighter than the car that the system was designed for, there should be ample stopping power... I hope anyways.