Rear brakes will not lock up

[Honest Ernie]

Hello again everyone. Build 10314

Another brake problem question. Please help.

The rear brakes will not lock up, they will only put a good amount of pressure but will not totally lock up and hold. The car is still up on jack stands. I am using a long torque wrench on the axel bolt to turn the rotor.

-Willwood MC
-Front brakes are separate from the rear brakes and work well and lock up.
-11.65" stock FFR rotors and calipers.
-IRS
-Changed MC with no different result
-Bled brakes twice with no different result
-changed up bias and adjusted with no different result
-Both sides are doing the same thing and not locking
-e-brake is working fine and locks up.

What am I missing here?

Photo's attached to show what the set up is and how I am turning the rear rotor.

Thank you

[Railroad]

I would first extend the push rod on the rear master cyl to max length AND maybe shorten the front push rod.
Even then with new rotors and pads not bedded, you may not be able to hold the rotors, while torquing the nut.
An option, I have not used, but would consider. Using some thick leather or rubber pads, clamp them on the rotor with a large set of vice grips or c-clamp. When the rotor bottoms out on the caliper, it should stop.
If those are vented rotors, you might drop a tapered punch down into the vanes of the rotor, using the caliper housing as a stop.
Good luck,

[AC Bill]

Calipers should be adjusted when new, or new pads are installed, to lessen the space between the pads and the rotor. You may require a special tool to turn the caliper piston in or out, as they are rotated to adjust them. Properly adjusted the pads should have less than 0,030" space between them and the rotors. Once set as the pads wear down the caliper's internal sprag will adjust the piston automatically when the E-brake is applied, to the correct distance.

[Hoooper]

Are those the right calipers and pads? Looks like the pad is only making contact with a tiny part of the very outer edge of the rotor

[MB750]

If the E-brake can lock it but the hydraulic can't, that's your problem.

As mentioned, make the rear MC pushrod longer than the front, then try again. If you're really into throwing money at the problem, put a pressure gauge somewhere in the line for the rear calipers to see. If your MC is 3/4", you should be getting somewhere north of 700 psi.

[AC Bill]

Are those the right calipers and pads? Looks like the pad is only making contact with a tiny part of the very outer edge of the rotor

They do look like smaller calipers than what I would expect.

[CraigS]

Your front to rear adjuster is centered in your pic. You can tell that because the length of the exposed threads on each end is about the same. You need to turn that shaft so you have more threaded length showing on which ever side is your rear MC. That may help your test results but, if it doesn't I would not worry about it at this stage. Qs above do make me wonder about the rear calipers. But if your system is common in FFRs I am confident it will work. Also pad brake-in will help a lot. Tell us exactly what calipers you have and what pads too.