I may have found some 72 disk brake spindles/calipers/rotors for my 72 Cutlass which is currently drum. But someone told me I may have to switch out the master cylinder and / or metering block valve (proportioning valve). Does anyone have background on that ? I would think that master cylinders are all similar ...

 

Master cylinders for drum brakes and disc/drum brake applications are completely different. Disc brakes don't require as much movement from the slave cylinder as drum brakes; therefore, a proportioning valve is used in the master cylinder. In addition, most disc/drum brake systems I have seen also use a dual chamber master cylinder to isolate the disc and drum brakes from one another.

 

The M/Cs are completely different for several reasons. First, the diameter of the pistons inside the M/C are different between disc and drum due to the different fluid volume and pressure requirements. Second, due to the way disc brake calipers work, the reservoir for the half of the M/C that feeds the discs must be larger than the one that feeds the drums.

The distribution block does not need to change, but you DO need a proportioning valve. On the 67-70 disc brake cars, the factory used the same distribution block as the drum brake cars and added an in-line proportioning valve. Starting in 71, the proportioning valve was incorporated into the distribution block (now called a combination valve) as a cost saving measure. You can go either way, but for a 72, the latter is what came from the factory.

You will also need to change the frame brackets that anchor the rubber hoses that run to the front calipers. They are different for disc and drum hoses.

 

I have just gotten a conversion kit for my 72' Cutlass. With the front end completely apart. My questions are: Should the distribution block on the frame be eliminated? And only use the proportioning valve mounted at the MC that came with the kit?
The instructions say remove it, and feed both front sides individually from the proportioning valve and a single to the back brakes all joined/coupled together were the old distribution block is.
What are you thoughts on that?
Any ticks to bending new brake lines?

 

Be careful in what you call a "proportioning valve". There are two designs. The 67-70 cars used a distribution block on the frame and a separate proportioning valve mounted below the M/C. The 71-up cars used a combination valve that combined the proportioning valve and the distribution block into a single unit to save cost. Some aftermarket disk brake conversions mount this combo valve under the M/C the way the old proportioning valve was mounted.

If you have a combo valve (five pipe connections and an electrical terminal), then yes, this replaces the distribution block on the frame. If you have a proportioning valve with only one pipe in and one pipe out, then you must retain the distribution block on the frame.

In reality, the factory mounted the combo valve on the frame where the distribution block is located, but unless you care about complete restoration correctness, the valve will work fine mounted under the M/C also. In fact, this location keeps it out of the way of headers also.

 

Hello Joe,
I have a 64' Jetstar 88 Convt...What aftermarket
disc-brake kit will convert over...442/Cutlass/F-85 ??? I've read that this B-body shares A-body brakes, spindles, control arms, shocks etc...I also, would like to upgrade my bushings to a polygraphite kit and KYB shocks offered for the 64' Cutlass/442/F-85 by PST (Performance Suspention Technology)
www.p-s-t.com The Disc brake kit is offered by Mattsbowtieclassics on Ebay. Thanks.

Regards, LT

 

CADDYDADDY1

Try Scarebird brakes.com they have a conversion that fits your car. Good Luck

 

If you have not found out yet?
Yes you should get the disc/drum MC.
And "combination valve".
You might need some new brake lines as well and brass fittings (the expensive parts). Brass fittings were over $16 to join the rear brake line to the new lines off the "combination valve".