Brake line pressures

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Dustin at Wilwood said pressures aren't that off for the calipers, not sure why the rear is reduced unless the MC has some internal metering.Theri MC do not but some factory ones do. Suggested a larger to get less travel but may be at the expense of leg effort.

So with a long weekend looks like I wil be trying a few things out in the heat of the garage. Might try swapping front and rear ports and see if the one port still is putting out less pressure

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From Wilwood's site on their master
CALCULATING EFFECTIVE PISTON BORE AREA TO DETERMINE PLUMBING
To determine the effective piston bore area of any caliper, you must first calculate the area for each piston bore found on one
side of the caliper. Use the formula " Area = (bore x bore) x .785" for each piston bore size. Then, add the areas of all pistons
on that one side of the caliper to determine the total effective piston bore area. Compare the difference between the front and
rear calipers and attach the line from the primary outlet "A" to the calipers at the end of the vehicle with the greater total
effective piston bore area.

So where do they get the .785? I though area sq in was pi(3.1416) x r x r with r being 1/2 bore

Their masters do have different volumes for the different ports so maybe that is the issue with mine.

[silver69camaro]

So where do they get the .785? I though area sq in was pi(3.1416) x r x r with r being 1/2 bore

0.785 is pi/4. They just rearranged the equation.

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Matt thanks I see that now that you point it out,any thoughts on the ordeal here?

In looking at Wilwood's site their MC do have the same pressure but also one end only moves half the volume. I would assume the Vette one does also. Maybe why the rear isn't building the pressure the front is.

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From Strange's site on their MCs Mopar style so pressures in the ball park for lockup but reversed. Still alot of travel to get.
PEDAL / HANDLE RATIO
1.032” bore master cylinder: Pedal ratio- 5.5 to 1 / Handle ratio- 11 to 1
1.125” bore master cylinder: Pedal ratio- 6.5 to 1 / Handle ratio- 13 to 1
The 1.032” master cylinder is recommended for systems using single piston or two piston calipers up front, and four
piston calipers in the rear.The 1.125” master cylinder is used with four piston calipers in both the front and rear. Brake
pressure should always be checked with a brake pressure gauge before use. In disc brake applications used for drag
racing only, front brake pressure should be 550 to 650 lbs. and rear brake pressure 1,000 to 1,100 lbs.These pressures
should be achieved with a lot of effort since they are at “lock-up”of the tires and the actual normal stopping pressures
will be lower.

Question for you all if most of these aftermarket MC have a 2:1 volume output difference why have the same size reservoir? And if pistonsizes are the same(4 piston front and rear liek many aftermarket and early Vette) does it matter if the small is on the front or rear?

[andrewb70]

From Strange's site on their MCs Mopar style so pressures in the ball park for lockup but reversed. Still alot of travel to get.
PEDAL / HANDLE RATIO
1.032” bore master cylinder: Pedal ratio- 5.5 to 1 / Handle ratio- 11 to 1
1.125” bore master cylinder: Pedal ratio- 6.5 to 1 / Handle ratio- 13 to 1
The 1.032” master cylinder is recommended for systems using single piston or two piston calipers up front, and four
piston calipers in the rear.The 1.125” master cylinder is used with four piston calipers in both the front and rear. Brake
pressure should always be checked with a brake pressure gauge before use. In disc brake applications used for drag
racing only, front brake pressure should be 550 to 650 lbs. and rear brake pressure 1,000 to 1,100 lbs.These pressures
should be achieved with a lot of effort since they are at “lock-up”of the tires and the actual normal stopping pressures
will be lower.

Question for you all if most of these aftermarket MC have a 2:1 volume output difference why have the same size reservoir? And if pistonsizes are the same(4 piston front and rear liek many aftermarket and early Vette) does it matter if the small is on the front or rear?

I wouldn't pay much attention to what is said on the Strange website because the majority of their customers are drag racing. ON a drag car the rear brakes do a lot more work than the front brakes because the rear tires are massive and the front are puny.

For a car that is set up for handling and overall performance you want more brake pressure in the front. I did a pressure test with my system, you can read the results here:

https://www.pro-touring.com/showthre...ion-2.0/page10 Post #189

I am using a 15/16" bore MC. My set-up at the wheels is not slightly different, but not much. I used to have the Wilwood billet superlite 6 calipers with 14" rotors on the front. I now have the C6 Z06 brakes which also use a 14" rotor and the caliper piston area is very similar. I've never measured the pressure at the rear, but my prop valve is fully open and the rear brakes don't lock up before the fronts. However, the rear braking system uses a smallish C4 single piston caliper and a 12" rotor. Eventually I want to swap to the matching C6 Z06 set-up from Kore3.

Andrew

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Andrew thanks for the input-on disclaimer this car is for the time being(my project swap duties) going to be mainly a drag car, but most of the drag guys if it stops well enough to make the last turnaround that is OK,so maybe not the ideal for their car. I think the folks here have a better handle on brake stuff. Dustin at Wilwood did also say the pressure weren't that bad.

So you have a fixed caliper on the front(so only use 1/2 the sq in) and a small floating on the rear. The C4 rear is much smaller than the 2.5" metrics I have so they need a little less volume to move. No reason why a GOOD 1"(just a hair bigger than the 15/16" you have) shouldn't have made over 1000psi with as much effort as I used to the Wilwoods on the front. There is nothing for a restriction but the line loc acting as a T for the front brakes and the port for the pressure gauge.

Most of the master seem to use the larger 9/16 port as the "secondary" port-I assume the rears. That is how this MC is plumbed right now,it is on the rear port. An extra 81 TA 4WD master I have has the larger on the front port, as do most of Wilwoods, but the front reservoir is slightly smaller so I assume that it the rear(although I think I have my 78 with an 81 MC plumbed that as the rear and it is well balanced).

My biggest issue is the excessive travel with little effort to get low pressure, with alot of effort at full travel you only get moderate pressures. So with little effort and alot of travel seems like needs a bigger MC. The low drag calipers may be the biggest fly in the ointment also, and may need to be swapped out-heck maybe the actual ratchet E brake TA calipers might do better.

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Well swapped the front for the rear lines at the MC and removed the prop valve-pain finding all the right fittings on a weekend. Too hot to bleed it out (99 degrees) over the weekend so will try later this week-got too much air in it doing it. The Strange MC I have is 1 1/8 and has a very small reservoir for the secondary port, that is going on next as a trial if this MC looks good just too much travel.

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OK for you brake experts-new data for you. Took completely out the prop valve. Plumbed rear brakes(2.5" Gm metric calipers 11" rotor) to the "front" brake port of the GM 1" Vette MC. Plumbed front Wilwood 4 piston 1.75"Dynalite to the "rear" port. 6.7:1 pedal ratio.

Previous alot of pedal travel,little effort fronts would develop 1000psi , rears 500 at full pedal alot of leg pressure. Both would got to 400 at the same rate then the front would keep climbing.

Doing some research some of the early GM MC had about a 60:40 output front/rear. All the Wilwood tandems have 2:1 output volume their new aluminum or their Chrysler aluminum.

So after swapping the lines, gravity bleeding and pressure bleeding all 4 corners and both gauges the rear now goes to 850 and front 800.But both slowly drop 100-150 psi. Pedal is better as far as effort but still takes almost all the travel to build that psi.

I'm still thinking especially now since the pressure slowly drops it's a bad MC.

[andrewb70]

If the pressure is dropping the MC is bad or the linkage is overcentering and loosing leverage.

Andrew

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Andrew it is dropping with the pedal near the floor and not moving my foot. Going to swap on a Strange MC I have laying around this weekend to see what I get and will keep you all posted.

I'll probably use the "front" for the rear bigger piston calipers. All else fails may have to swap on some of the new Wilwood D154s with the small dual pistons.

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Update for you all. Put on the Strange 1.125" MC after bench bleeding the crap out of it. Got hard when plugged like it should Tobin. Had to make a new pedal rod out of a long 3/8 fine thread bolt. The Stange rod has a rubber sleeve in a groove to help retain it but the hole is 3/4" deep, so I would think pretty deep. I guess I can have a friend chuch the rod in a lathe and cut a groove.

Pressures both go up the same and go up to 1100 stomped hard near the floor. 200 comes real quick with maybe 2-2.5" of travel. Definitely a firm pedal and less travel than the bad 1" was. Definitely alot firmer and more effort than my power brakes on the GTO I just drove to dinner(fajita night ) So not sure if another good 1" would still be too easy and too much travel to move the volume of fluid to start building pressure or if a 1 1/16 would be the ideal ticket. I guess a slight decrease in pedal ratio would move the piston more per pedal travel as well as give better feel for the 1", but that involves pulling the pedal out and drilling it between the upper and lower power stud.

So any of you with a pressure guage what is it reading while actuall stopping and engaging the brakes? I want to think the Wilwood guy said around 400 or so is generally operating pressure.

I haven't added the ajustable prop valve back in yet, not sure I need it with skinnies on the front and big tires on the rear. I do have the rear plumbed to the rear, which probably moves 1/2 the volume as the front port if it is like the Wilwood "Mopar" style. Not sure if the bigger low drag rears would do better with more volume.

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New update for you all. Plumbed the adjustable prop valve back in the rear. No drop in pressure when wide open-so it wasn't an issue before. Cuts pressure almost in half when all the way shut.

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Also some numbers from another guy with a gauge.
"Sitting still - 200 PSI
Regular stops - 400-700 PSI
Staged, 1500 rpm - 800 to 1100 PSI (depending on light/dark, etc)
Absolutely to-the-floor, both feet on the pedal and standing up in the car - 1450 PSI"