Hydro mc question

[SteveL]

About to put the hydroboost kit on the 72. Both reservoirs are the same size on the mc. Running 4whl disc. The maker of the kit said it didn't matter on the port front or rear on the mc. I put the same kit on the 66 and the rears hook up pretty easy on a panic stop so this time I'm using a proportioning valve on the rear. I also have lbs valves on both broncos. So my question is is there a preference on which port to go to front or rear on the mc? The vendor was a real a-hole so don't trust his opinion and figured I'd get a better answer here. He's not one of our regular vendors so I don't post his name. I have warned a few members that mentioned ordering from him.

 

[pcf_mark]

I usually go front port to front brakes, rear port to rear brakes if they are 4 wheel disk because it should not matter. Usually if it does matter one port on the M/C has a different thread size than the other one. If yours are different things get complicated unless you know the car it came out of. If it is he Corvette M/C it does not matter - they regulate pressure by different pistons in the rear calipers not the M/C.

 

[thegreatjustino]

Reservoir closer to the firewall goes to the front brakes.

 

[Broncobowsher]

Reservoir closer to the firewall goes to the front brakes.

Correct.

4 Wheel disks? How big are the rear calipers compared to the front? That is a better way to bias braking forces. Adjustable prop valves can do a little to cut pressure to the rear, but once locked you have to back off the brakes enough so the pressure is lower in the master cylinder than the (choked off) calipers for them to back down the braking forces. With a lot of prop valve that means that if the rear locks you have to really get off the fronts in order to unlock the rears. By balancing caliper sizes (front large than rear) you can do a better job of modulating the brakes.

 

[SteveL]

It has caddy calipers in the rear and if I think I put t-bird calipers up front. I know I put the bird calipers on one of em and have a second set on the shelf for the other. As far as the mc it looks like a corvette mc but it's aftermarket and has ports on both sides for the lines. If I remember right they're all the same thread. Th 66 doesn't lock up bad with the hydroboost just never did before with the vacuum booster.

 

[Broncobowsher]

Sounds like a good match. Is the back of the Bronco light?

 

[Apogee]

The C3 Corvette master cylinders are front/front and rear/rear with respect to the outlet port configurations. Any aftermarket version will typically use the same piston and seal design, so should also be front/front and rear/rear.

 

[pcf_mark]

As I said Corvettes balance with piston bores in the calipers the M/C ports are not location specific. That does point to the calipers on your 66 as possibly being unmatched but the prop valve should even it out. Be sure you have some control over brake dive to the front or the prop valve will not be able to adjust. If you have a lot of dive it unloads the rear suspension and you get lock.


For reference Corvette front caliper pistons are 1 7/8, rear are 1 3/8 - 26% difference. But they use the same pad size front and rear. If your pads in the rear are bigger than front and / or your pistons are larger in the rear you may have a configuration problem.

 

[Broncobowsher]

But a Bronco is not a Corvette. Short wheelbase, high center of gravity, very wide F/R weight bias depending on how the rig is built up. Very different then a Corvette.

Just the higher CG changes the dynamic axle loading. If you have good enough tires for it, a hard brake stop will really put a bronco on it's nose. With a lift, heavy front and light back, you can almost get the rear axle to lift off the ground. In something like this you need something like 80% or maybe more of the braking up front. It will be extremely difficult to keep the rears from locking. Lower it and lower the CG, you now run a lot more rear brake as there is more weight on the rear tires for the same braking.

Broncos are probably the hardest vehicle to get the brake bias correct. No two are built the same, and the wide range of parts that are used make the one combo works for everything impossible. Take off the hard top and spare tire and add a winch can totally change the braking forces, That is before you get into any suspension or brake parts differences.

 

[Apogee]

Weight transfer is a fact of life, and as stated above, will determine the amount of rear brake your rig can tolerate. Deceleration rate impacts weight transfer, so the purpose of a proportioning valve is to allow more pressure (relative to the 100% front brake line pressure) at lower decel rates and then proportionally less at higher decel rates.

As for comparing piston areas, while useful, you should use the effective caliper piston area for comparison, not just the diameter. While C3 Corvettes do have 1.875" 4-piston front calipers and 1.375" 4-piston rear calipers, if you do the math, you'll find that they have 5.52 and 2.97 square inch effective piston areas, which equates to a 65/35 split front to rear. Rotor diameters are the same and pad area doesn't matter when calculating brake torque.

With EB's in general, due to their relatively short wheel base and high CoG, you almost can't have too much front brake bias, but with that said, it is a little bit more complicated than that.

 

[pcf_mark]

All excellent points relative to factors on brake balance and bias. The dynamics of weight transfer on these trucks is like nothing I have ever worked with. Even if you get the ratio solid front to rear once you get brake dive it goes out the window in a panic stop.

If these was easy they would be called Jeeps!

 

[SteveL]

The 66 stops real good even on quick stops but doing about 40 on a main street a jack ass slammed on his brakes in front of me to let a car out of a driveway. I was sure I was gonna hit him but didnt. When the rears locked I was able to slide it sideways a little and miss him. That situation made me think of trying the rear proportioning valve to change the bias a little when I set up the 72. Also wanted to check the mc lines. I would've ate that car if I still had the vacuum booster trying to stop the 35s.