Brake questions

[tcrist]

Very interesting.

You would have to remove the whole assy and change the piviot point (for a CR I believe that would also move the clutch pedal)and relocate the attchment point for the brake rod. Moving the pivot point could also help the clutch ratio also. As long as you moved the cable/rod attachment also (you would have to).

[MaSnaka]

Here is the problem with changing the ratio or geometry of the pedal(s). Right now my brake pedal measures 12" from the pivot to the pedal pad. If I drop the pivot down 2" then I need to raise the pad 2" which shortens my pedal to a 10" stroke from the new pivot point to maintain the pad location. That would change my ratio to 5.7/1. Still way short of the 6.5 or 7/1 recomended. Although it should be an improvement, I am guessing and checking and that scares me. I only have one pedal box. It seems that installing a booster or smaller bore MC or both is the way to go.

Terry, You mentioned your brakes are good, big discs and a booster, what are your pedal dimentions? Pivot to pad and pivot to rod. And do you know your MC bore size?

John

[tcrist]

John,
My pedal length from pivot to the bottom of the foot pad is approx 13". The distance from the pivot point to the master cylinder rod is approx 4". The master cylinder is Wilwood P/N 260-8556. which is a 1 1/8 bore.

Edit:
I would say that our pedal boxes are close to the same depending on where you are actually measuring to. It is hard for me to get under the dash to measure real close. The differance is probably me having a brake booster.

[bobcowan]

Although I built a Classic Roadster, that was quite a few years ago. And I don't remember how the pedal box is put together.

You will need to shorten the pedal, but that's at the top. You need to move the pivot point down about 2" or so. If there's a hole there in the box, then that's how much it should be shortened. The attachement point for the brake rod, and the pad stay in the same place.

That makes the total pedal length 11.75, and the pivot to rod length 1.75.

11.75 / 1.75 = 6.7

Still not perfect, but a dramatic improvement.

My car has a pedal ratio of 6, and 3/4" MC's.

I started out with stock Mustang and T-Bird components, and I had no trouble locking the brakes at any speed less than about 40. Now I have Wilwoods for track use, and braking is even better. But the stock components were more than adequate for anything less than high speed track abuse.

If you're going to modify your pedal (and it really sounds like you need to), then you should also consider making it a dog leg. Put a 7* angle just below the pivot point. I did that to my pedal during the initial build, so I can't say it made any improvement. I "borrowed" this idea from Richard Oben.

http://www.norcal-cobras.com/project...rake_pedal.htm

[MaSnaka]

Thanks for the details of your mods. I will be out of town for a couple days but expect to pick this back up next week. I really appreciate the detailed explinations. Thanks guys. There may be hope for me yet, but I'm sure others are learning a lot as well.

John

[mickmate]

Measure a couple of factory cars. It's important to keep the pedal pad the correct height from the floor and the right distance above the gas pedal. If your moving stuff like that around make sure it finishes up in a comfortable and quickly and intuitively accessible position. The brake is also positioned to work first if you accidentally hit both pedals.

[MaSnaka]

Ok, got the brake pedal modified. If the pictures (before and after) don't show up here they are in my gallery. I re-installed the pedal in a lower hole on the pedal box, the MC rod position did not change nor did the pedal pad height. However the depth of the pedal in relation to the other pedals has changed with it being in a more depressed position at rest. I am not able to correct this because I have no adjustable rod on the MC, and was unable to remove it from the MC piston to change the length.

In flushing the old brownish orange hyd brake fluid I found a lot of gunk and sludge in the MC and so I removed it and cleaned it thouroughly. BTW it's 15/16" bore. I re-assembled and flushed the brake lines starting with the passenger side rear, driver side rear, passenger front and then driver front. I have clean clear fluid throughout. Now pressing in the pedal I feel that there is hyd pressure again, but the pedal does not feel completely restored. It does not return as crisply as I think it should. It feels kinda dead.

Thoughts on this please...do I need to purge more air that is still in the system? Do I have some other foreseeable problem like bad springs in the brakes? Disc front, drum rear. I'm not really sure what causes the pedal to return.

Thanks, John

[mickmate]

It should be pulled back by a spring not just rely on hydraulic pressure. The main reason to pull it back fully is to expose the port allowing the brake fuid supply in to the master cylinder. Any kind of a good extension spring mounted out of the way of your feet should do it.

[bobcowan]

Yes, use a light spring to bring the pedal back. But, make sure that there is a return stop so it doesn't get pulled back too far. It sounds like it won't pull the rod out of the MC. But it will create a dead zone in the brake pedal.

See if the clutch pedal is adjustable. Maybe you could move it foreward to match the new brake pedal.

[MaSnaka]

Mick and Bob,

There was no spring for the pedal return before and so far the only change has been the pivot location and fluid replacement. Admitedly I am pretty novice at this but it seems to me that a spring shouldn't be required now if it was not required before.

I will bleed the lines again and see if that helps before I start changing anything else.

Thanks for the advise, I do find it quite helpful.

John

[Double Venom]

John,
It Should NOT require a spring. How ever I have put springs in on the cars my customers raced or the ones that I have raced just to make sure the pedal was that much quicker!

[CobraEd]

Isn't the spring built into the inside of the master cylinder???? Maybe the pedal is binding somewhere.


.

[MaSnaka]

Bled the brakes again today, I'm pretty sure I saw a couple bubbles bleed out as I'm using clear tubing into a plastic bottle. I tapped each caliper and MC to help dislodge any air. The peddle is still too soft and requires pumping to actually stop the car. My MC was in pretty bad shape with a couple spots of rot inside the cylinder but I figured if it was in a criticle area it would have given me trouble before. Maybe it was but the peddle was not soft. I may have pumped a lot of air into the lines trying to reprime the MC after I cleaned it out. I also have a fitting in the MC where the front brake line connects that won't stop dripping. It is tight as I dare go. So now I'm beginning to think I may need to replace the MC and re-flare the brake line. I was really hoping to find out exactly how much improvement from just the pivot ratio change. I hope to get this solved, it's really frustrating.

John

[mickmate]

Remember you've mechanically increased the leverage and pressure. If that's on the same hydraulic components and they were questionable I think your exposing the weak links.

[Double Venom]

John,
If you have any kind of leak on a fitting, everytime the pedal returns it is putting air in the system. Doubt if it's your MC at this point but you may have to take it off, fix the flair and re-bench bleed the MC. Pedal is soft.....and it will pump up a little it has to have air in the system somewhere.

[MaSnaka]

Took master back off today. Getting faster at this... Fitting is screwed, I don't believe by me either. Anyway stay tuned, shopping for new MC and I will get the fitting and flare nut replaced. I really appreciate the help and support here.

John

[Double Venom]

John,
Maybe a hint for you.......I don't know if your car is done or not, but If you have installed the left vent per the manual with silicone, just work the vent out of the car and it is really easy to reach through to the MC and to replace it!

[MaSnaka]

Reporting in...MaSnaka has brakes! For those who have been following I hope this is the end of my saga. I replaced the MC. I took the old one to the local NAPA auto parts store and the nice folks there were able to cross reference the part number and find a replacement (made in USA). It is from a late '70s Mustang II. I paid $75 for the new one. There were instructions on bench bleeding which I followed and the install was a snap. I replaced one of the 3/16" brake lines that had a bad fitting, NAPA has them already flared in a variety of lengths, 12" long for about $3.50. I modified the push rod to make the length adjustable for the perfect pedal height (picture included). I have noticed that with every little change there comes a handful of related project tasks. After spending days/hours working on this I am able to say changing my pedal ratio made a big difference (that was great advice). So far I have about $200 in this total with the pedal mod and new MC plus incidentals. I still plan to upgrade pads, resurface discs and clean and lube. Today was a day I could actually get my tires to lock up at about 45-50mph. I still look forward to a total four wheel disc upgrade (when my stimulus check arrives) but for now it's good enough to stop as one would expect. For some reason my brake light switch lost power, it never ends...Thanks you guys for the help and support.

John

[bobcowan]

Yaaaa for you! It's good to get a tough problem resolved for very little money (comparativly speaking).

[James Stern]

John, Congratulations for seeing it through. Now that you no longer are driving the Toyota/Cobra you should get a lot more joy and less of that butt-clenching feeling. Enjoy yourself.

Jim