weak/spongy brakes

Hi all

I have a question that I hope someone can help with. Has anyone ever experienced a problem with poor braking because the vehicle has 2 different sized lines on the front and back - I have 3/16 on the front, 5/16 on the rear. Everything is new from the backing plates out with the exception of the rear 5/16 brake lines. Would this cause poor brake pressure?

welcome.....i'd say 5/16 is pretty large..my transmission cooler lines are 5/16"..master might not have the volume to move that much fluid.....are the rears drum?.....they take less volume to move than disc....

brake problems

My mistake, the rear lines are 1/4 inch on drums and the fronts a 3/16 on drums. The RP valves are all in place,10lbs on drum brakes. There's a proportioning valve in place for the rear brakes, no leaks, no weeping. Everything is new although new doesn't mean fool proof. I've bled the system maybe 20 different time. The brake adjustment is correct. Man I'm just lost, the lines are the only thing I'm not sure of. The only thing left to do is replace them.

Thankz Man.

First off, exactly what kind of car are you referring to, and is it stock, or has there been any modifications to it? Secondly, 5/16" line sounds a bit large to me as well-are you sure about that?-just asking. Most domestic cars (not all, but most), usually have smaller diameter brake lines on the front and rear, and a slightly larger diameter line going from the front to the rear.
Anyway, the diameter of the line doesn't make any difference to the pressure in the line. The pressure is created by the piston(s) in the master cylinder, and the pressure depends on the diameter of the piston in the master cylinder. At the other end, the amount of force that is generated at the wheels depends on the size of the piston(s) in the brake calipers or wheels cylinders, and the hydraulic pressure that is acting on them.
If you're having problems with spongy brakes, you may have a problem with air in the brake lines, possibly drum type brakes out of adjustment, or a problem with the master cylinder not delivering the proper hydraulic pressure. Hope this helps.

sometimes the flex lines will bloat and you can loose pressure that way.i have had frustrating problems with brakes before but they are as simple as they seem, so it will be something easy

http://ecihotrodbrakes.com/brake_facts.html

i always look at this page when i get into something and need to refresh....good luck

Brake problems can drive you nuts-I just had a similar problem and it took a while but I fixed it.
Question-Is your master cyl on the firewall or below the floor?
-Is it a dual master cylinder?
-what type of fluid are you using?Silicone or DOT 3?
-Is the brake pedal the original pedal?
-Have you checked the pedal ratio?
-Have you checked for proper pedal operation-meaning no deflection in the pedal or master cylinder bracket assembly?
-How much brake stroke do you have?(meaning-how much travel does the master cylinder rod travel into the master cylinder when the pedal is depressed.
-are the brakes adjusted properly?
Lot's of questions but they are all things that will contribute to your problem as I have found out for myself
And yes-I would swap that 1/4 inch line out to a 3/16 to match the fluid capacity.
Spongy usually means air somewhere but I would get the system matched up and note the mechanical operation of the components.(IE-correct pedal ratio and brake stroke as well as line diameter))That way you will eliminate the mechanical aspects of your system and can concentrate on everything else.
Jim

brakes lines

Hey guyz. heres more info. my truck is a 29 ford Roadster Hyboy. 1957- 283 cu.in. 4 wheel drum brakes. Frame mounted dual MC. flowing Dot 3 fluid. Basic Speedway
Motors Brake kit. I asume from the instructions with the kit.that it would be correctly sized for this style of braking system. Brake stroke would be No more than 2 inches. The brakes I beleive are adjusted properly. Spindels and Brakes are 49-54 Chevy. Lots of good info Jim. Thankz Man. I got 9 days B4 the next
show and the boyz want me there. Thankz again. Rock.

Did you bench bleed the MC correctly. You can get away without bench bleeding once in awhile but I find it's quicker and you will get better results.
Plus;; You get to keep your hair

One of the old tricks when bleeding a dual sysyem (remember you are dealing with two seperate brake systems) is to bleed the front and rear at the same time. I know it sounds silly, but try it.... when only bleeding one side (front or rear) the other side isn't allowing full travel in the master.... bleed both together and you get full travel.
We have discusssed brake line size before here... had a buddy with a races car, he went to larger brake lines, and the pedal never felt better than a basket of ripe peaches..... mushy! Brake line size apparently can contribute to the situation.
What brakes EXACTLY are you running front and rear? Wheel cylinder size can contribute also, but I honestly think you have a bleed problem. Systems with the MC low can be a challenge.
How you bleed seems to matter. I bought a little vacum bleeder years ago, and it solved lots of issues. Also make sure the master fully unloads from the pedal (free play).
My 2cents worth....
Clarke

Thankz Guyz

Thankz Clarke Lots of good info there. I will be giving it a try, It's not rocket science, sometimes simple stuff never gets considered. And i am changing the rear lines to 3/16. Thankz again. Rock.

Air can be a real problem to get out of your system
You can try "reverse bleeding"
Here's how it works-Go to your local farm supply like TSC or whatever-get a 50cc syringe (or a little bigger) and some clear hose big enough to fit over your bleeder screw.(about 5/16's should be close)Make sure the other end will go over the syringe-you only need about 6inches.
Open your master and suck up a syringe full-go to the right rear bleeder-put the plastic hose on it-crack it open and push the fluid back in through the bleeder screw -slowly while your buddy watches the fluid come into the master.When the syrine is close to empty-lock the bleeder screw.Do the same at the left rear-then right front then left front.-Push the fluid back slow and it will force any air out through the master and also insures there is no air in the master.If there is air in your system-your buddy will see it come out through the master.
Close it up and see if you have any pedal.If you don't -you have ruled out air in the system

Jim

pontiacguy1/4" lines are fine .The dia of lines has nothing to do with volume. What the dia has to do is the larger a line becomes the walls are thinner in reference to its dia .This causes the walls to flex outward .The most important thing to do is bench bleed the master. Always bleed the furthest wheel first and so on .If at any time while bleeding you happen to run the Reservoir empty you may have introduced air so you may have to bleed it a few more times .As mentioned the front and rear hose's and hose may expand but that usually happens on old hoses but you can feel them as someone presses on the pedal.Also because it is both drums front and back the master should have both Reservoir's of the same size.Make sure both front and rear residual valves are 10 LBS and arrows on them are towards the drums.Make sure the backing plates are installed wheel cylinders on the top and bleed screws on top. (Don't laugh)I've seen it done and even calipers switched with bleed screws on the bottom .Reverse bleeding will not work because of the residual valves unless you can push more than 10LBS of pressure. Sometimes you can't see the trees for the forest.Good luck.

Bob

Don't know if this helps your problem or not, but I'll relate the problem I had. My model A truck has full size GM calipers on the front, ford 8" drums on the back. Was set up by a friend ( almost lost the friendship over this escapade), and he was absolutely adamant that the master cylinder was adequate. It was a 15/16 bore. Notice I said "was".

I did a lot of research on the problem, and figured I either did not have a good enough pedal ratio, or the master cylinder wasn't putting enough volume out to activate the calipers.
I had brakes, but the pedal travel was excessive, almost to the floor before I got good brakes. Everyone told me to bleed, bleed, and bleed some more, but I wasn't getting any more air out of the system.
I decided to check out the bore of a full size GM car, so I headed to the local NAPA store, and asked for the specs on a 70's Impala. I figured I would match the master cylinder to the calipers, like the GM engineers had done on the 70's Impalas that the calipers came from. Turned out to be, I forget, 1.250 inches, or 1.125 inches, I forget, 'cause it was over a year ago. I bought a new one South of the border for about 30 bucks that was 1.250 inch bore. Brought it home, bolted it on, and I had good brakes from that day. The long long pedal stroke was gone. No more mushy feeling. Problem solved.

pontiacguy's break problem SOLVED

Hey guyz, problem solved. Thank you to all of you, but i gotta take credit for this one. I don't no why, but i have the wife pump the brake pedal while i was underneath the truck, just to see what was going on. I found the brake rod was only moving 1/4 inch overall. I double nutted the brake rod spun it in a 1/4 of an inch and the brakes came alive. Probably 70% perfect going to fine tune them in the morning cuz the rears are biting first, but man its nice to drive the little truck again. Once again thankz to everyone that gave me good advice all of it was very helpful. Lets keep hot roddin alive, pass on all you know to someone worthy. Rocke.