Thread: BRAKES, again!

Tweet

'48 Ford cdan, 4WDisc with booster under floor. Will lock up rears but not
front. Wilwood pro. valve. Thanks for any help.

Are you sure that you don't have the front brake output going to the rear, and vice-versa? Do you have 2 lb. residual pressure valves in both lines?

Thanks for reply. Port next to booster to frt. Don't have r valves.

You need 2 lb. residual pressure valves in both lines. On under-floor MC installations, the fluid can back away from the wheel cylinders. Another method is to use a non-vented cap on the MC. I prefer the RP valves, though. RP valves may not be the whole problem, though.

Do you have the proportioning valve in the line to the rear? If not, you have no hope of adjusting, since the prop valve only reduces pressure.

Also, I believe you have the lines reversed. Mounting the MC under the floor reverses its normal position. That means that the foremost port (nearest the booster) needs to go to the rear of the car, and the rearmost port (furthest from the booster) needs to go to the front.

The attached photo shows the MC in my A-bone. It's not power, but the same theory applies.

The MC in my current project is mounted on the firewall, The front port goes to the front, and the rear port to the rear.

I'm not sure if this would make all the difference, but they set them up that way for a reason.

yeap , Henry is right there dude

Thanks for the help guys. I will instal the valves & change the lines.

Final note: Make sure you bleed everything, including bench bleeding the master cylinder.

Henry Rifle is right about the front/rear brake lines if you have a Corvette style m/c. If you have a Ford m/c, you have them right. You can tell by looking for the reservoir with the larger capacity. The Corvette m/c is tricky to see, because the cap is symmetrical, but look for the bulge in the sides of the casting. The larger reservoir goes to the front brakes. This is because the front disc brakes need to draw fluid from the reservoir as the pads wear, and the pistons move to compensate for the wear. Front brakes wear faster than rear brakes, too.

Originally Posted by Henry Rifle

You need 2 lb. residual pressure valves in both lines. On under-floor MC installations, the fluid can back away from the wheel cylinders. Another method is to use a non-vented cap on the MC. I prefer the RP valves, though. RP valves may not be the whole problem, though.

Do you have the proportioning valve in the line to the rear? If not, you have no hope of adjusting, since the prop valve only reduces pressure.

Also, I believe you have the lines reversed. Mounting the MC under the floor reverses its normal position. That means that the foremost port (nearest the booster) needs to go to the rear of the car, and the rearmost port (furthest from the booster) needs to go to the front.

The attached photo shows the MC in my A-bone. It's not power, but the same theory applies.

The MC in my current project is mounted on the firewall, The front port goes to the front, and the rear port to the rear.

I'm not sure if this would make all the difference, but they set them up that way for a reason.

Why does it matter where the lines go on the master with 4 wheel disc? I know it matters with disc/drum.

Thanks Jim

It matters because most of the braking power is applied to the front.

Originally Posted by Henry Rifle

It matters because most of the braking power is applied to the front.

When you step on the pedal, somehow the front gets priority? If so, how?

On most duel reservoir master cylinders the reservoirs are two different sizes. The larger one is for the front disc brakes. Larger pistons in the front calipers than in the rear drum wheel cylinders require more fluid volume. When you hit the brakes the weight of the car is transfered forward so the front brakes do most of the work. If you have a master cylinder and both of the reservoirs are the same size and a little on the small size it is probably a drum/drum master cylinder.