ryan22

I've done alot of reading in the forum about this and have found 2 different opinions as to whether or not a proportioning valve is needed when you convert to front disc and leave drum brakes on the rear.

Some who have this setup with no PV say their brakes work perfectly well, don't lock up. I understand how the PV functions. As I understand it a PV may not be needed depending on the compatibility of the brake system components.

I'm converting to front disc now. Please let me know if its worth doing the install without a PV and seeing how it functions or should i install a PV right from the start ?

thanks-

Procrastination Racing

Search again. Most of it depends on what you use for a master cylinder.

If you use a single master cylinder ('65, '64, '63, and back) you need a way to get front and rear pressures different.

If you use a Corvette dual master cylinder, it is set for f/r disks and so the rears won't be right for drums unless you alter the pressure.

If you use a master cylinder form something like the front disk/ rear drum Chevelles, Camaros, etc, then you won't have to change, but they may not be set up ideally for a Corvette's balance.

mashinter

The problem with drum brakes is most are self-energizing (including Corvette rear drums). If you double the input pressure, you will get more than double the output torque. That doesn't happen with disc brakes.

OE brakes are designed so they work properly at both light pressure and high pressure. That requires a PV because the rear drum brakes will "lock themselves up" at high pressure.

If your cobbled system doesn't lock rear brakes before the fronts lock, then the rears aren't doing much at light pressure, but you don't need a PV....and your rear linings will live forever.

Frankie the Fink

My 61 has an original C1 M/C and 1973 Camaro front disc brakes on the original king pin setup with NO P/V and works fine. Probably not tweaked to the very peak of front/ rear balance but after 6 years of driving this setup -- no complaints.

My 67 Chevelle has a front disc conversion by previous owner with original power dual M/C with NO P/V and tries to swap ends on hard stops..so I'm putting a P/V in next week.

Go figure...

Chuck Gongloff

FWIW.....

I converted my 56 Chevy to front discs about a year ago.

I still have the original rear drums.

I bought a pre-engineered kit specifically for 55-56-57 Chevies. It has a dual master cylinder designed for front disc/rear drum.

I do not need, nor do I have a proportioning valve, and my brakes work just fine.

Now, IF you're putting together a system on your own, using parts from here and there, all bets are off. If you purchased a conversion kit specifically for your Corvette, I think you'll be just fine without a proportioning valve.

Chuck

mike16

opinions are opinions.

you need a perportioning valve

ryan22

"If you use a single master cylinder ('65, '64, '63, and back) you need a way to get front and rear pressures different."

What if i'm using a single master cylinder correct/original style for our 62, I assume its the same situation as if a 63-65 MC is used- I still need the PV to get the front & rear pressures different ?

thx-

Pop Chevy

I would suggest putting it together and trying it. You can always go back and make changes. I look at that as no big deal. I put big disc's on the front of my 57 Chevy pickup and ran the stock master, it was o-k. The stock drums sucked especially with a 400 sb under the hood.

C-1 Generation 2

On my 62 I changed the whole front suspension to JMR and used the 70-81 Camaro spindles and disc with a dual master cylinder(non power) and a pv. The pv is set fully open for the rear and has never had a lockup,even on panic stops. Makes me think that on my setup I probably didn't need the pv.

Plasticman

That appears to be the general opinion (including mine). I have had front discs since 2005 (and I do not have a PV), and only once did I feel that the rears locked up before the fronts, but still came to a very controlled stop.

I am changing to a dual master cylinder (old single has an extremely minor amount of internal bleed down due to pitting of the bore), so since I have to revise the rear brake line, I will put a PV in place. I really don't expect to see any change (based on 7 years previous history). The PV will make a nice junction block..........

Plasticman

toddalin

If you use a Corvette M/C of ANY vintage or configuration, yes, you most definately need it!

I did the front conversion using all Corvette parts and at first I didn't include it.

You'll be cleaning the stains off your seat covers the first time you encounter a panic stop without it.

Mine is under the dash (red handle) for adjustment "on the fly." Be forwarned that if you race the car, by rule many sanctioning bodies do not allow the proportioning valve to be located in the cockpit.

Furthermore, I run the valve in position #2, so I'm cutting the rear brakes way down.

Plasticman

I think the OP needs to identify what year Corvette he is changing to front discs. Appears that the C1 folks (me included) don't think a PV is needed, but the C2 folks do.........

And since his profile lists only a 66, he already should have discs all the way around.

Plasticman

1snake

You may "get by" without one but you won't get optimum performance unless you have one and it's properly adjusted. You'll be glad you did when/if you have to make a panic stop that lives depend on.

Jim

ryan22

This is a 62 we're converting to front disc, sorry not have mentioned it initially.

toddalin

What is the weight distribution? It seems that the more percentage of weight on the front, the more you need the valve to reduce the pressure to the rears. The mid-year S/Bs are ~49/51 front to rear.

But it would also depend on the size of the rear drums. IIRC, the 63/64 have 2.5" x 11" drums in back. If the older cars had smaller drums/pads, that could act like a proportioning valve in that there is less material to grab to "lock up"

Regardless of weight distribution and drum size, put it in. You can "fine tune" the system better than without it and the cost is minimal in the grand scheme of things. At it's minimum setting, it hardly has any effect, so you can't really go wrong.

Don't forget that if you use a later Corvette M/C, you also need a 10# residual valve on the rear line.

mrtexas

You might consider one of these:

http://www.speedwaymotors.com/Brake-...alve,8904.html

C1-Curt

I just received the Corvette Central Meyers brake line kit with a new dual master and it came with one of these brake metering valves. I installed it but wondered what it was for. The CC kit did not come with a proportioning valve. It will be another month or so before I get it on the road so will not know how it does until then.

ryan22

I have our 62 at our mechanics shop for the finishing touches on the disc brake swap.

He's having trouble getting the proportioning valve installed.

The PV i have looks very much like this one at Master Power Brakes. See photo on page 2 of this link-

http://www.mpbrakes.com/uploads/prod...60_Rev8_08.pdf

I've seen some of the PV's forum members have used. This one I have looks much more involved. It has 5 inlet ports.

I'm wondering if there's another PV that would function the same & be a simpler installation ?

thanks again-

mashinter

The front disc brake design you use determines if you need a PV.

If the front discs develop more output torque than the front drums did (at all line pressures up to lockup), you shouldn't need a PV.

edit: Ryan, I just saw your post above. I'm not saying you don't need a PV. I'm just spewing theory...

JohnZ

That's a "combination valve", which incorporates the differential pressure warning switch, the metering/hold-off valve for the front disc system, a residual pressure valve for the rear drum system, and the proportioning valve for the rear drum system; they weren't used until the early 70's, and were individually calibrated for each application.

The simple one line-in/one line-out proportioning valve sold by Wilwood, Corvettte Central, etc. will work just fine for your application; if the master cylinder you're using doesn't have a residual pressure valve (RPV) in the rear drum outlet (GM disc/drum master cylinders have them), you'll need a 10 psi external RPV.