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brake ratio?

Posted By: Anonymous

brake ratio? - 02/06/07 01:34 AM

My dad has 37 ford street rod,it has a brake pedal with 6 to 1 ratio,for his brakes to work with his new abs system he needs a 4 to 1 ratio,does any know how to change the ratio? Cant find anyplace that makes different pedal,the people at abs said cut the one he has,and make it a4 to 1, anyone have any experence with this?
Posted By: moparx

Re: brake ratio? - 02/06/07 02:04 AM

pedal ratio is detirmined by dividing the length of the arm [the pedal pivot to the pedal pad center] by the distance from the pivot to the master cylinder pushrod hole. the FARTHER away from the pivot point, the lower the ratio. you maybe able to fix this by just drilling a new master cylinder rod attaching hole in your pedal. the thing to watch for, however, is that you don't bind the rod in the master at full stroke. hope this helps.
Posted By: poorboy

Re: brake ratio? - 02/09/07 08:14 PM

OK, I need a clearifacition on this. I bought a brake pedal "kit" that included the brake pedal assembly, the dual 7" brake booster, and the "corvete" style master with the brake line fittings on both sides of the master. Its suppose to work on disc/drum brakes. I also bought a "GM" style poroprting valve. This is installed on my 39 Plymouth and I have a disc brake conversion with Volari rotors and chevy truck calipers. The rear brakes are 9" drums from a Dakota. It has all new lines (3/16") and all new hoses, the calipers were rebuilt (napa) and there are new rear wheel cylinders. The master was bench blead before being installed and gave good fluid supply from both fittings.

Pretty much, these brakes suck. The pedal pushes real hard (motor has 17" vacume at idle) and the rear brakes do not work. With the rear axle off the ground, at idle in gear (auto trans) you can have to push with both feet to stop the rear wheels from turning! The car stops with front brakes only. The brake pedel is firm and is not bottoming out, if you open either a front or a rear bleeder screw the brake pedal goes lower. There is no air in the system, and I can see the rear wheel cylinders move when the drums are off (least the driver side).

The pedal bracket is mounted to the firewall with 4 bolts and extends to the bottom of the dash where it is also bolted. The brake arm is 15" long from the pivot to the center of the brake pad and there is a master cylinder arm that is 5" long from the pivot to the center bolt for the master. There is about 1/4" to a 1/2" of deflection in the firewall when you push the brake pedal (need to add some bracing).

Things I have done that have made no difference: put washers between the master and the brake booster thinking the master wasn't returning all the way. Just got a lower pedal. Adjusted the bolt between the booster and the brake pedal-both directions. Blead the brakes (many times). Checked vacume source and amount of vacume. Swapped the positions of the brake lines off the master. Adjusted rear brake shoes (many times). I'm pretty much at a loss here guys, short of throwing the whole mess out and starting over. Summer is coming and I'm not going to drive it this way another summer.

I've been told my brake booster is bad, when you step on the pedal and start the motor, the pedal does not move. That should not have an effect on the poor rear brakes. I'm wondering if the 9" drums and the corvete master are the problem or maybe the porporting valve is defective (its burried in a hole). I would like to get this right on one try, money is a little tight, I'll buy what ever I need....once more. I can live with out the power long as the brakes all work.
What ya think?
Gene
Posted By: RodStRace

Re: brake ratio? - 02/10/07 12:57 AM

Poorboy, sounds like you have a couple issues; hard pedal that does not 'sink' when vacuum assist starts, and little or no rear brakes.
1. Make sure there is vacuum to the booster, and that there are no leaks. Pull the hose off and hook up a vacuum gauge. Start the motor and let us know how much vacuum there is. Next note the idle with the hose still plugged, then connect it to the booster. Same idle after a minute? If not, it's leaking. Also lay under the dash and operate the pedal. There should be a slight vacuum sound when the pedal is pressed.
2. Before you go out and buy expensive pressure gauges, try to cobble up a bypass for the proportioning valve. A couple of double female fittings and a line with fittings should do it. Try that carefully to see if the rears work better.
Posted By: moparx

Re: brake ratio? - 02/10/07 01:49 AM

poorboy, what size is the master cylinder bore ? the wagner book i have shows most corvettes have a 7/8 or 11/16 bore. this should be ok for your application. is it possible your rear flexline[rubber hose] mite be partially collapsed ? i would be concerned about that firewall flex. also, i agree with rodstrace you should remove the proportioning valve & see what happens. is there any possibility of binding in any of the pedal assembly ? brakes can be a real pain sometimes...........
Posted By: poorboy

Re: brake ratio? - 02/11/07 11:21 PM

Sorry it took so long to respond, life got in the way...

There is vacume to the booster, as far as checking the rest, the car is sitting outside in a snow bank right now, the joys of running a business out of a 2 car garage. It will also be pretty hard to listen for a vacume noise under the dash, the car's exhaust dumps under the running boards and even with mufflers, it will be too loud to hear a vacume noise, unless its huge. I can tell you that when you lift your foot from the brake pedal, it takes a few seconds (like across an intersection) for the pedal to return to the top stop (and shut off the brake light switch). If you hook your foot under the pedal and lift, it feels like there is some resistance to it returning. I'm pretty sure the brake booster is junk. According to the web site I bought the brake assembly from the master is suppose to have a 1" bore. Frankly, I didn't measure it, but I will also be doing that. Another thought, the disc brake calipers are from a Chevy pickup, I'm wondering if they have a larger diamiter piston then the Corvette would have had. I also have no idea what size the rear wheel cylinde diamiter is, maybe everything is just sized wrong? (I've been reading a little) Life was sure a lot easier when I used to get all the stuff from the same car, stupid "kits" anyway.

I remeasured (as best I could) and the pedal from the pivoit to the center of the brake pad is 15" long and the arm that applies the pressure to the master is 3 1/2" long from the pivoit to the bolt hole center. If I figure it right, that would give me a pedal ratio of about 4,2 to 1? Wouldn't that require some extra foot presure to apply the brakes? I will be pulling the car into the garage in a week or so to get things ready for summer, so I will be pulling the pedal out to reinforce the firewall and will get a good measurement then. Until a few weeks ago I didn't know the firewall was flexing. My car still has the bolt in floor pans so there is little support at the bottom of the firewall. I plan on welding the top floor pan in instaed of having it bolt in and I think I can add a 1/8" x 1" strap standing at 90 degrees to the floor/firewall joint and still clear everthing. That should give me the stiffiness I will need.

I know its not a sign that things are right anymore, but all the brake hoses were put on the car new last spring when I put this mess together.

As I understand it, the porportationing valve also has the brake residual valve in it, if the guy sent me the wrong valve and I got one from disc/disc instead of disc/drum, could that be my whole problem with the rear brakes?

As you see, my mind is trying to cover too many variables. I have over $1000 in these brakes and I sure can not afford to do all that again!

At this point, I'm thinking I will reinforce the firewall, modify the pedal ratio to somewhere around 7 to 1, and trash the booster (its ugly anyway). I'm going to measure the bore diamiter of the master, the wheel cylinders and the brake calipers, and see how those look. I may also go to a junk yard and get a porportationing valve from a 5Th Ave and trash this one I have now. I do plan on doing one thing at a time, so I know and can let you know what the cause of the problem is.

I would still like your imput on where to begin. The firewall is a diffinate, the rest is speculation right now.
Thanks guys. Gene
Posted By: moparx

Re: brake ratio? - 02/13/07 01:23 AM

from your discription of the pedal action[slow to return & showing some resistance] i think the booster has problems. as for the pedal ratio[4.28 : 1] it is in the ball park for power brakes. 7:1 would be a good ratio for manual brakes. not sure on the chevy truck calipers, but if they are close to the vette [4 piston ?] area size wise, this shouldn't be a problem. if the proportional valve also has residual valves in it, that could be a problem for two reasons. one, with your master mounted on the firewall, you don't need 'em[residual valves] as they are for use when the calipers & wheel cylinders are above the master mounting height to prevent fluid drainback from the cylinders & calipers into the master. 2nd, if in fact they[residual valves] are for a disc-disc setup, they would be[should be] a 2lb. valve[s]. are the brakes retaining heat, as in not releasing fully ? this could have glazed the pads & linings. just thowing out things here that may be of help. brakes can SURE be a pain at times......
Posted By: poorboy

Re: brake ratio? - 02/24/07 04:24 AM

Man, I finally got caught up with work a little and we got a short break in the weather earlier this week. I played a little with the coupe.

First thing I did was pulled off the master and redid a bench bleed, just to be sure both ports were delivering fluid. Seemed like there was a little air trapped in the port closest to the brake pedal, but after a few pumps both ports delivered good fluid. Uppon reinstalling the master I noticed that the vacume to the booster was cocked a little and was binding against the master. I had the vacume port entering at the top of the booster like Mopars do. I was able to flip the booster 180 degrees, so the vacume port is now under the master and it now clears the master compleately. All I was able to do after that was tighten the lines (working alone sucks sometimes) and hope for another day to rebleed the brakes with some help. Out of courisity I fired up the motor to check if the pedal pulled away when in motor started, it does not. I also varified that there is indeed vacume to the booster, and if the pedal is depressed there is a noticable change in engine rpm. That change remains until the pedal is released.

The thing I call a porportationing valve they call a "combination valve" It is for a firewall mounted master with disc/drum brakes, but the place I got it from also offers a "combination valve" for a disc/disc brakes. I don't remember any numbers on the one I have....and I sure can't see a number on it in the hole its in.

Not sure if I have accomplished anything or not, but at least I was able to do something. Unfortunately, its snowing outside again and they are calling for 7"-14" of snow over the weekend. That will put the screws to working on the coupe until at least mid week. Gene
Posted By: moparx

Re: brake ratio? - 02/25/07 10:54 AM

can you hear any vacuume noise inside the car when the pedal is depressed ? the rpm shouldn't change when the pedal is depressed unless there is a problem with the diaphram[induced vacuume leak]. not any progress on my humpback lately due to the cold-i just can't take unheated garages any more..............we're supposed to get another blast of snow & sleet today.....stoopid groundhawg........
Posted By: poorboy

Re: brake ratio? - 02/26/07 02:36 AM

With the mufflers right under the running boards, there is no way I could hear a vacume leak unless it was whistling, which I don't hear. The motor was cold and the choke was on because the motor was just started (it was about 30*) and there was a deffenate rpm change when the pedal was depressed. The motor was on fast idle and it increased in rpm probably a couple hundred rpm change that remained increased until I lifted my foot from the brake pedal. (sorry didn't even think of looking at the tach. ) Once I lifted my foot off the pedal, the rpm dropped the couple hunderd rpm it had increased, back to the original fast idle. I know the carb on the motor has some issues and a rebuilt replacement is sitting on the shelf waiting for mother nature to cooperate. I'll have to try it again when I can run the motor until it reaches opperating temp and then get down where I can put my head near the brake pedal, maybe I can hear any vacume leak.

Probably won't happen this week, we got 6" of very wet snow and then it rained and is snowing again now. The car is once again burried in a mound of snow. This winter sucks. Gene
Posted By: Fig

Re: brake ratio? - 02/26/07 09:28 PM

I went thru some of this same stuff on my 37. I ended up taking off the 7" booster and making manual brakes. I changed the ratio from 5 to 6. In retrospect I don't think that the 7" boosters do the job (mine was not a dual). I also ended up taking off my adjustable proportioning valve.
Posted By: moparx

Re: brake ratio? - 02/27/07 01:20 AM

i agree that maybe the 7" boosters aren't what they are cracked up to be. another thing that i think some forget is that the larger the rear tire[diameter & width],the more rear brake is needed to stop. sometimes an adjustable prop valve is a waste of time.fig, do you know what size[diameter]master you used ? what size front & rear brakes ?
Posted By: moparx

Re: brake ratio? - 02/27/07 01:30 AM

Quote:



Probably won't happen this week, we got 6" of very wet snow and then it rained and is snowing again now. The car is once again burried in a mound of snow. This winter sucks. Gene



we got only a couple inches of sloppy wet stuff but i still hate it......no wonder ron left new york for california...........
Posted By: Mopar Ron

Re: brake ratio? - 02/27/07 02:36 AM

Quote:

..no wonder ron left new york for california...........




we had some really bad weather here this week, we got .18 of an inch of rain
Posted By: poorboy

Re: brake ratio? - 02/27/07 04:15 AM

Fig, Did you have the Corvette master also? How did you do the push rod into the master when you dumped the booster, was the master cylinder plunger deep enough to hold the rod or did you change out to master to something different?

Ron, Really sorry to hear about all that bad weather you had to endure. Been to California twice, rained nearly all the week I was there both times. Sunny California? yea, right. We only got about 6" of the really wet heavy snow over the weekend, but now they are calling for another rain/snow mix this Wed.
Gene
Posted By: Fig

Re: brake ratio? - 02/27/07 06:17 PM

Yes, I used the Corvette m/c, I think that it was 1 1/8". I don't remember exactly how I did it but I made up a plate for the rod to go thru so it wouldn't fall out. I can take a picture of it this weekend if you want me to.

I live about two hours north of Ron, we had horrible weather last night. We got close to 1/4" of rain
Posted By: moparx

Re: brake ratio? - 02/28/07 01:54 AM

Quote:



I live about two hours north of Ron, we had horrible weather last night. We got close to 1/4" of rain



i don't know about you guys............maybe we should start a "search & rescue"..........
Posted By: poorboy

Re: brake ratio? - 02/28/07 02:55 AM

Fig, Would much like a picture if you would be so kind. Gene
Posted By: Fig

Re: brake ratio? - 03/07/07 09:05 PM

Sorry it's taking me so long to take the picture, I have to jack up the car because the m/c is under the car. I keep forgetting to do it . Sorry
Posted By: poorboy

Re: brake ratio? - 03/08/07 05:52 AM

That's OK Fig, The car is still sitting in the snow bank! Its suppose to get into the 40s this weekend, maybe I can dig it out then.....Gene
Posted By: poorboy

Re: brake ratio? - 04/08/07 04:09 AM

Just putting out an update. I got the master reinstalled and have varifiedthat indeed the master is delivering fluid flow from both resivors while it bolted on the car. One posibility is eliminated. blead out the lines and took the car for a short drive. Not much change. The brake pedal pad bolts to the swing brake arm, I modified the pedal and added an inch and a half to the over all arm. Finally got a chance to drive the car a little, before it got cold again. The longer pedal greatly improved the feel of the brakes, power wise. I'm going to modify the pedal assembly to improve the way it sits, but the concept worked. Pedal effort is much better, but the brakes still have room to improve.

Next up is to bypass the porportationing /combinnation valve thing for the rear brake line. I have the fitting, now its a matter of getting in there to remove the lines from the fitting. I will have to pull off the front fender to be able to get my hands in there, so expect another delay to the information train.

I'm taking this one thing at a time so I know what solves the problem. At least at this point, it looks like it's not going to be one big, real expensive fix, but posibaly several small (cheaper) fixes. Gene
Posted By: moparx

Re: brake ratio? - 04/08/07 12:30 PM

glad to hear you are making progress ! of all the systems on a vehicle, brakes are [in my opinion] the most important ! they can be a real pain sometimes to figure out. remember : it's not speed that kills, it's the sudden stop that does ya in ! keep us posted gene.
Posted By: Fig

Re: brake ratio? - 04/16/07 10:12 PM

Sorry to take so long to post these links for the pictures. Glad you are getting it figured out.

http://www.timothynewton.com/teamnracing/Pictures/DSC00914.JPG

http://www.timothynewton.com/teamnracing/Pictures/DSC00915.JPG

http://www.timothynewton.com/teamnracing/Pictures/DSC00918.JPG
Posted By: poorboy

Re: brake ratio? - 04/18/07 04:01 AM

Fig, Thanks for taking the time to take and post the pictures.

I managed to get the porportioning valve bypassed. Made no difference. I did jack up the rear end so the tires were off the ground, started the motor and put the trans in drive. If I push HARD on the brake pedal, the rear wheels will slow and finally stop turning. Pumping made no difference either. At this point I'm thinking I need to completely rebleed the entire brake system. After that I will pull off a rear drum and have someone push the brake pedal to see if the shoes are moving. I'm running out of logical explanations, but I don't want to jump to conclusions until I have reblead the brakes and can watch the shoes for movement (or lack of?)

Just for the record, I did a test drive on a back hard surface road. From 60 I can push the brakes hard enough to stop the car fast enough to have the passenger seat back flip forward, but I have to push hard. I'm kind of thinking maybe I need to add another inch or two to the brake pedal length. Might be the next step after bleading and watching the shoes. Gene
Posted By: Fig

Re: brake ratio? - 04/18/07 04:41 PM

Is your master cylinder for a disc/drum or disc/disc car? I remember something about a restrictor that you remove for a disc brake car, but you leave it in for drum brakes.

Are you sure that you have the rear brakes plumbed to the correct side of the master cylinder? I was thinking that the rear of the master cylinder was the rear brakes, I plummed mine up that way and had to redo it.

Can you just move the brake rod hole on the arm tio change your ratio? I think that I drilled a hole something like 3/4" closer to the pivot point to change my ration to 6 to 1.
Posted By: poorboy

Re: brake ratio? - 04/19/07 05:47 AM

The master I have is the dual purpose Corvette style master. Both resivors are the same size, it has line fittings on both sides of the master (4 fittings total, comes with plugs to plug whichever side you don't use.) I'd thought about the posibility early on that the lines may have been in the wrong position so I switched them at the master, made no difference.

The brake pedal I have has the pedal on one side and there is an extra drop from the pivot shaft to connect the master cylinder rod to. It off sets the master to one side of the pedal by about 2" for what I presume to be steering column clearance. It was a street rod manufactured piece. Relocating the master's connecting rod hole may be something I will look into once I figure what I need, but it may put a bind on the rod to master angle. The pedal is designed to have a pedal pad screwed into the arm, so its real easy to alter the length of the arm itself, least for now.

I think I may have discovered my problem today, but I have yet to test drive the car, once I can be sure the problem has been corrected, I will tell all. Stay tuned. Gene
Posted By: moparx

Re: brake ratio? - 04/20/07 12:44 AM

after you re-bleed the rear, take the drums off & make sure both pistons in the cylinders are working. i have seen one freeze up where only one piston was working. this also had a very hard pedal effort.
Posted By: poorboy

Re: brake ratio? - 04/20/07 03:56 AM

OK we have brakes!

When last I left you, I had bypassed the rear line portion of the brake porportioning valve. I want to note here I had very good fluid flow at this point, almost emptied 1/2 the resivor in the time it took to connect two lines to the union fitting. Bypassing the valve made no difference but I thought maybe I had air in the lines. Yesterday I put the rear on jack stands and pulled the rear tires (makes it easier to reach the bleader screws.) I opened the bleeder screw on the driver side rear cylinder to allow it to gravity bleed.

For those of you that may not know what gravity bleed is, on cars (or trucks) where the master is higher then the wheel cylinders, you can open the bleeder screws and gravity will draw all the air out of the lines, you leave the screws open until the fluid is flowing without air boubles, then close the bleeders. This works best by opening one bleeder at a time, per axle. Start with the bleader closest to the master. When the fluid flows air free, close that bleader and open the other bleeder screw on the same axle. Be sure to watch the fluid level in the master as it can empty very quickly and if the master goes empty you have to start all over. You can do one bleeder from the front and one from the rear at the same time or you can do just one at a time. It is a very effecent way of bleeding the brakes, but can be somewhat slow.

Back to the story. After opening the bleeder and leaving it open for 1/2 hour, I had very little fluid! Should have almost emptied the master in a 1/2 hour. I made sure the bleeder screw was not pluged, it wasn't. So I closed the bleeder and moved forward to the brake line connection on the master side of the rear brake hose and seperated the connection. Great fluid flow, closed it back up. Went to the axle end of the brake hose and disconnected the line going towards the wheel cylinder that I had very little fluid flow from. Got great fluid flow from the hose! Disconnected the other end of the line from the wheel cylinder. The fitting was tight, but the line fell off after only a turn or two! Sure enough, the last two threads were almost stripped off the line fitting! Must have been cross threaded. At this point, I'm not taking a chance on the wheel cylinder. I pulled off the brake drum and the shoes were soaked with what I first thought was gear lube! Didn't smell like gear lube, and there were no tell tail signs the axle seal was ever leaking. Called my favorite auto parts house and ordered a new brake line, wheel cylinder and new shoes. One of the perks with owning your own shop is the parts store deliveres the parts. After cleaning everything up I reinstalled the new brake line and wheel cylinder (making sure it it NOT crossthreaded) I opened the bleeder screw while I reinstalled the brake shoes. As I am finishing up the shoe installation, I noticed brake fluid running inside the backing plate. Closed the bleeder screw and the fluid flow stopped. This is where I add that I have gravity blead many brake sysyems and have never encountered brake fluid on the inside of a backing plate! Now I knew what was likely on brake shoes. So I checked the other side and sure enough, those shoes were wet also, not as bad as the first side, but wet none the less. I replaced those shoes and cleaned everything up (on both sides), and buttoned it back up. The threads on the inside of the wheel cylinder were rusty (this was a new wheel cylinder last year) so I suspect it has been leaking all along, but just wasn't leaking enough to show up on the outside or in fluid loss.

Today I drove the car, its nice to have 4 wheel brakes! The car stops very good. I still think the pedal effort is still a little high, so some more modification of the brake pedal is on the horizon. I have extended the length of the brake pedal about 2" and may go another inch. Once I get something I like, I will pull the pedal assembly and make a perminate alteration.

So the bottom line to all this was a cross threaded fitting at the wheel cylinder, and the wrong brake pedal ratio. After a year of putting up with poor brakes, boy, do I feel dumb. Gene
Posted By: Fig

Re: brake ratio? - 04/23/07 05:26 PM



I would have to write a book to tell about all of the "dumb" things that I have done while building my car. That's part of the fun , my neighbor calls me do and redo .

I'm glad it's fixed
Posted By: poorboy

Re: brake ratio? - 04/24/07 03:26 AM

I understand that do and redo thing. Been there, still doing it.

We put a little over 100 miles on the coupe this past weekend. Its nice to have functioning brakes. Gene
Posted By: moparx

Re: brake ratio? - 04/25/07 01:11 AM

gene, glad you have brakes now ! it is pretty amazing what a "small" thing can cause unending aggrivation & hair pulling[as well as adding to a guys "vocabulary"]. when you get your pedal length how you like it, it will be interesting to see what you started with & what you end up with. keep us posted on that. again, congratulations on gettin that fixed !
Posted By: poorboy

Re: brake ratio? - 04/25/07 01:46 AM

I think I'm just going to pull the pedal out and see where its at now and will probably just go to the 7:1 manual pedal ratio. I will let you guys know what it originally was and what is is now, before I go to the 7:1, I'm not messing with this thing much more. I will take a few pictures of the pedal while its out of the car.

I have other lesser issues to attack, replacing cracked glass, window weather striping, windshield wipers, squeeks & rattles, the list is still pretty long. At least now its OK to drive while I hash out the details. I want to thank you guys for your ideas, thoughts, and support. Gene
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