Brake line pressure

Shocks, Springs, Brakes, Frame, Body Work, etc

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Re: Brake line pressure

Post by mk e » Wed May 30, 2018 7:25 am

Ron Gusack wrote:
Tue May 29, 2018 9:04 pm
No transducer technology here, but I did have him measure pedal ratio and either he measured wrong or we may have found the problem because he has 3:1. He said the brake pedal has been cut and welded as if someone shortened it. The measurements were 9 and 3.
Well that's not going to work very well with a 1.125" mastercylinder. It might be ok with .625" or maybe as big as .750", but i wouldn't go any bigger unless the ratio can be increased a whole bunch.
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Re: Brake line pressure

Post by Ron Gusack » Wed May 30, 2018 10:35 am

Thanks Mark, My buddy now thinks the MC bore is 1.0625. I'm trying to get him to 6:1 if he has the space to make a new hole that far up. That should get us in the ball park, right??
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Re: Brake line pressure

Post by tjz450 » Wed May 30, 2018 10:48 am

You should be able to develop 1000 psi line pressure with an average man. 1500 psi in a panic stop. 2000 psi may blow out seals. Pedal force for calculations should be 150 lbs. You have to calc your pedal leverage ratio for force on master cylinder. I suspect that you need a 1 1/16" to 1 1/8" master cylinder.

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Re: Brake line pressure

Post by FC-Pilot » Thu May 31, 2018 8:36 pm

Ron Gusack wrote:
Tue May 29, 2018 9:04 pm
No transducer technology here, but I did have him measure pedal ratio and either he measured wrong or we may have found the problem because he has 3:1. He said the brake pedal has been cut and welded as if someone shortened it. The measurements were 9 and 3.
I don't care if you take a bathroom scale and tape it on the pedal, if you can get an idea of pedal force and be able to put a gauge at the bleeder screw or something then you should get a good idea of what you need. Pedal ratio and MC bore are a balancing act for sure. 3:1 is close to what we run on many of our vehicles with the factory brake systems.

To be honest I don't worry too much about getting close to 3000 PSI as our stuff has never had a problem with seals at that pressure. Granted it is factory stuff (so our quality SHOULD be better than replacement type stuff) and in testing I have seen pressures very close to that. I do agree that you should be able to get to 1500 PSI without much trouble.

Keep us posted on how things progress. This interests me. I play with this stuff in crappy factory cars all day for work so it is fun to hear about this stuff in cool cars for a change.

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Re: Brake line pressure

Post by Geoff2 » Fri Jun 01, 2018 5:17 am

Changing the pedal ratio by drilling a new hole may not help as much as you expect........

To get maximum transfer of force into the m/c or booster, there should be rt angle formed from a line drawn through the pedal pivot/new hole position & the pushrod, just as the brakes apply To get this correct may require welding a piece of metal to the pedal to get the correct angle.

Another option if more pressure is reqd is to reduce m/c bore size; pedal travel will be slightly greater. You meed to check that a smaller m/c has enough volume displacement to work with this system.

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Re: Brake line pressure

Post by mk e » Fri Jun 01, 2018 10:01 am

I was thinking the same thing.....with that pedal ratio .625 is probably the right master. My car is a 4:1 pedal with a .750 master and it seems good, although not tested at any speed yet.

Braided lines reduce pedal travel a lot....I'm like 2" before its a rock and not moving anymore no matter how h ard i push vs more like 2.5 - 3" with rubber lines at the calipers.
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Re: Brake line pressure

Post by Ron Gusack » Sun Jun 03, 2018 2:23 pm

He moved the rod up to the higher hole which works out to be about 6:1. He said it brakes better but isn't great and won't lock up the tires. I'm not sure about the angle of the rod but he confirmed that the bore of the MC is 1 1/16. He plans to call Wilwood on Monday.
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Re: Brake line pressure

Post by af2 » Sun Jun 03, 2018 3:07 pm

He needs a 15/16 MC period.
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Re: Brake line pressure

Post by Ron Gusack » Mon Jun 04, 2018 3:13 pm

My friend called Wilwood and the tech told him he needed more front brake. I asked my friend if the tech knew which MC was on the car and he said the tech never asked and he didn't ask what brakes were on the rear. I asked my friend why he didn't tell the guy what he had and he said it never came up. They talked about the adjustment of the proportioning valve and my friend learned that he's been adjusting it backwards, so he's gonna test drive it again and make correct adjustments to see if it helps. Hopefully he gets a different tech when he calls Wilwood back.
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Re: Brake line pressure

Post by mk e » Tue Jun 05, 2018 8:42 pm

Well, bigger pistons in the front calipers will have a similar effect as a smaller master.....on the brakes anyway, it will have a much bigger effect on his wallet ;)
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Re: Brake line pressure

Post by Ron Gusack » Wed Jun 06, 2018 7:54 pm

Here's the latest, with the valve all the way open the car stops much better but still not like normal. The owner of the shop said that Wilwood sent the wrong MC and that it was supposed to be 13/16.
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Re: Brake line pressure

Post by mk e » Thu Jun 07, 2018 8:52 am

Make sure he can lock up all 4 wheels before you call the brakes finished. That is when you have 100% of the stopping power you're supposed to have.

The rears should take a little more pedal pressure to lock than the fronts....rear lock ups are harder to control so the proportioning valve is set right when the fronts lock first by a little not when the brakes feel a little better.
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Re: Brake line pressure

Post by Ron Gusack » Thu Jun 07, 2018 11:50 am

mk e wrote:
Thu Jun 07, 2018 8:52 am
Make sure he can lock up all 4 wheels before you call the brakes finished. That is when you have 100% of the stopping power you're supposed to have.

The rears should take a little more pedal pressure to lock than the fronts....rear lock ups are harder to control so the proportioning valve is set right when the fronts lock first by a little not when the brakes feel a little better.
Thanks Mark, Yes we've been over this front rear bias many times and I know he understands. Right now he can't lock up any of the 4. When the owner of the shop told him that the MC was not the 13/16 that he ordered but to see if adjusting the valve would get things right, I told my buddy not to waste time doing that because doesn't address the fronts not locking up. They are waiting for the correct MC to arrive before the car goes back.
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Re: Brake line pressure

Post by FC-Pilot » Thu Jun 07, 2018 7:47 pm

That makes a lot more sense as to what is going on. Keep us posted.

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Re: Brake line pressure

Post by Ron Gusack » Tue Jun 26, 2018 6:42 pm

The shop installed a 13/16 MC and my buddy says it stops much better although he doesn't think it's 2,000 dollars better, lol. He still has to work on adjusting the valve to get the backs to lock up after the fronts and to be honest, I don't think he's done a panic stop yet to know if any lock up. I think the whole ordeal has exhausted him but hopefully he'll test it soon. Thanks for all the advice and suggestions. I wish the shop would've given back the parts that came off the car because it's possible that the pedal ratio and the original MC bore were 90% of his problem.
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