Conversion of Rear drum to Disc Brakes

[tfowler9]

I have a 1971 coupe - 351 C  It came with front disc and rear drum. I installed a rear disc LEED conversion kit.  When it was completed, I called and talked to the tech guy at LEED and told him I expected a bigger change in braking. He recommended disabling the proportioning valve, He said with the disc brakes and the radical tires there isn't a need for it and it would improve the rear brake performance. Has anyone completed the rear drum to disc conversion? What was your results? Do you recommend disabling the proportioning valve?

Thanks Tom

 

[turtle5353]

You could probably do away with the stock proportioning valve, but I would definitely run an aftermarket adjustable one. That way you can dial it in to your needs.

 

[Jeff73Mach1]

That is what I did as well.

Rear brakes provide less braking than front. When you brake, weight shifts forward onto the front tires. Without some ability to adjust rear brake line pressures, you may end up with a brake system that is prone to locking the wheels which can cause the rear of the car to swing out and possible loss of control.

You could probably do away with the stock proportioning valve, but I would definitely run an aftermarket adjustable one. That way you can dial it in to your needs.

 

[tony-muscle]

I removed the spring and plunger from the factory proportional valve but kept the valve's housing to keep functionality of the idiot light, which is useless anyways. I installed an adjustable proportional valve and adjusted it so the fronts lock at the "same" time as the rears. I think the adjustable valve is an important add on. Dont expect to feel a huge change, since all the weight gets shifted to the front during braking anyways.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[tfowler9]

Thanks for all the feedback. I will replace with an adjustable valve. 

Tom ::thumb::

 

[Tnfastbk]

I have a 1971 coupe - 351 C  It came with front disc and rear drum. I installed a rear disc LEED conversion kit.  When it was completed, I called and talked to the tech guy at LEED and told him I expected a bigger change in braking. He recommended disabling the proportioning valve, He said with the disc brakes and the radical tires there isn't a need for it and it would improve the rear brake performance. Has anyone completed the rear drum to disc conversion? What was your results? Do you recommend disabling the proportioning valve?

Thanks Tom

I have ran a disc brake conversion from Right stuff brakes for about 6 years now "without" a proportioning valve with zero issues. I drive my car a great deal, so is it the best set up? Who knows but it has worked for me.

 

[will e]

The biggest difference with disc brakes is less fade and no issues when they are wet.

 

[Hemikiller]

70-73's did not use a proportioning valve, it's a distribution block and place to put the brake warning switch. The "proportioning" was built into the master cylinder starting in 1970. The distribution block has a shuttle that moves to one side when there is an extreme pressure differential, like when a wheel cylinder fails or a line breaks, triggering the brake warning light on the dash.

If you didn't replace your master cylinder when you installed the rear disc kit, then you probably should, as it's only getting the factory drum brake spec'd fluid volume. A common size cylinder bore M/C along with a Willwood adjustable valve should do the trick.

 

[tony-muscle]

70-73's did not use a proportioning valve, it's a distribution block and place to put the brake warning switch. The "proportioning" was built into the master cylinder starting in 1970. The distribution block has a shuttle that moves to one side when there is an extreme pressure differential, like when a wheel cylinder fails or a line breaks, triggering the brake warning light on the dash.

If you didn't replace your master cylinder when you installed the rear disc kit, then you probably should, as it's only getting the factory drum brake spec'd fluid volume. A common size cylinder bore M/C along with a Willwood adjustable valve should do the trick.

I am confused with your post. I thought the distribution block has a built in proportioning valve. Please look at this diagram. In my case I removed the piston and spring indicated, and left the shuttle valve to actuate the idiot light. My block looks just like the one in this diagram inside and outside. Could it be that different blocks came with different models?

 

[Tnfastbk]

70-73's did not use a proportioning valve, it's a distribution block and place to put the brake warning switch. The "proportioning" was built into the master cylinder starting in 1970. The distribution block has a shuttle that moves to one side when there is an extreme pressure differential, like when a wheel cylinder fails or a line breaks, triggering the brake warning light on the dash.

If you didn't replace your master cylinder when you installed the rear disc kit, then you probably should, as it's only getting the factory drum brake spec'd fluid volume. A common size cylinder bore M/C along with a Willwood adjustable valve should do the trick.

I did use a new Wilwood M/C that I failed to mention but still no proportioning valve. I had purchased a Wilwood adjustable one but after some debate and talking with a few local builders decided not to use it. My car is also a manual brake car BTW.