Rear brakes locking up after Double MC/Booster install

[Backpayne]

My truck is drum/drum.

I just finished installing this mc/booster combo: http://piratejack.net/chevy-truck-19...er-brake-unit/ I bench bled the mc and bled the brakes properly.
I did install rear brake like to front port and front brakes to rear port (read that is proper?)
Issue: Rear brakes lock up when slowing down. I know front brakes are working as I lifted front up, spun front wheels, and watched them stop when brake was applied.

I know the link says that a drum/drum setup needs a metering valve but I thought it was a misprint and meant disc/drum.

Do I need a metering valve? If so will any work?

[jayoldschool]

On drum drum setups on our trucks, stock 67-70 dual reservoir setups plumb the FRONT port to the front brakes. No metering needed. I would confirm that the master in that kit is the correct one for drum/drum.

[PGSigns]

The link is for a disc drum setup. Also with drum/drum I had mine front to front and back to back. Also with a split system I found that the adjustment is more important. I had a rear drum locking up early nor long ago on my disc/drum setup on my 66 and I had a brake drum out of round.
Jimmy

[Backpayne]

Originally Posted by PGSigns

The link is for a disc drum setup. Also with drum/drum I had mine front to front and back to back. Also with a split system I found that the adjustment is more important. I had a rear drum locking up early nor long ago on my disc/drum setup on my 66 and I had a brake drum out of round.
Jimmy

The description says for disc/drum or drum/drum. I will be ticked if they listed it wrong.

But with a prop valve could I make it work?

[Captainfab]

The factory drum/drum braking systems did not have a metering valve. All they had was a distribution block with the brake light switch in the middle. If you were to use a '67-'70 truck master cylinder as I typically recommend for a drum/drum system, all you have to do is connect the front brake like to the front port and the rear line to the rear.

The master cylinder in the pic appears to be the same master that all of the big parts sellers supply with all their power brake conversions. That master resembles a '77-'82 Corvette master cylinder.....Corvette's came with a disc/disc brake system.

[vince1]

With the 67 dual cylinder are the pressures at front and rear ports not the same? I know some M/C's have different bore diameters for front and back but probably not for the 67. With mine plumbed the opposite way, which I plan on rectifying, I notice no difference between front and rears than with the single original M/C.

Could it be that with the power brakes you are just putting on a lot more pressure than before. With all shoes front and back the same size it seems logical that the rears would slide first. It is a compromise between a loaded or unloaded truck. If your truck is never needed for hauling maybe an adjustable proportioning valve would help in that situation.

[HackJob65]

Captainfab correct me if I'm wrong but on the 67-70 drum/drum dual pot master cylinder trucks the distribution block containing the brake switch internally have a piston. This piston will actuate if a leak develops in a front or rear line. When actuated it will block fluid flow to the line which is leaking. Internally master cylinders typically have a center floating piston which requires fluid on both sides/ in both reservoirs to work correctly. Thus the real safety component of any dual reservoir master system in actually in the proportioning valve / brake switch block. I believe this is a majorly overlooked component.