discs in the back, drums up front..what did i do!?!

So I got a puller on lend and couldn't get the hubs on my tapered d44 to budge. So I called up R&P and ordered a 71 d44 with an OX locker and discs. I'm done playing with this old arse axle, going to buy I once and cry once...but here's the deal.

I have the stock axle up front with a 11 Drum upgrade on it, also from R&P. So am I going to need to wait to bolt in my rear with discs until I can get discs up front? Will the prop valve be able to handle this set up instill I can have the front d44 I want built up? Any advice would be great.

Thanks

 

Is the proportioning valve adjustable?

You will have to wait tell you got disk up front.. Front does majority of braking.

 

Not adjustable...figures I would have to wait...crap!

 

What prop valve, if you didn't put it in, the factory had no prop valve on the early jeeps only a distribution block.

My 71 has disks up front and the rear 10" drums and still has no prop valve after 8 years.

 

Hydraulic brakes work on a very simple principal: Load is applied to the brake pedal, which creates pressure using hydraulic fluid that is directed through high-pressure lines to either a drum wheel cylinder or a disc brake caliper. For disc brakes, this pressure (in pounds per square inch—psi) is applied to one or more pistons that squeeze brake pads against a rotating disc. For drum brakes, the pistons in the wheel cylinders push outward to apply shoes against a rotating drum. Drum brakes benefit from something called self-energizing action where the leading shoe uses the rotating drum to help push the larger trailing shoe into the drum with additional force, requiring less hydraulic pressure to apply the brakes.

Fixed proportioning valve:
After disc brakes began appearing on production cars, the factory came up with a device called a combination valve. This valve is placed downstream of the master cylinder and performed both as a proportioning valve to reduce the pressure to the rear brakes while also acting as a failure warning device to trigger a light should a loss in hydraulic pressure occur. Factory combination valves are carefully engineered to reduce pressure to the rear brakes to balance the braking effort for maximum braking efficiency. Unfortunately, this device is not adjustable, which means any change to brake or suspension components may create a premature rear-brake lockup problem. Ideally, the front and rear brakes lock up at the same time.
If you are running front disc and rear drums, or has four-wheel discs, hydraulic pressure should be reduced to the rear brakes for several reasons. The single most important reason is because even under moderate braking, natural weight transfer reduces weight on the rear tires and moves the weight to the front. This unloads the rear tires, which makes it much easier to lock up the rear brakes in hard braking. Once the rear brakes are locked, the tires skid, which immediately causes loss of control.


Adjustable proportioning valve:

Since we deal with modified Jeeps, even something as simple as adding taller rear tires can have a drastic effect on braking performance. Taller tires increase the distance between the rear axle centerline and the ground, increasing the leverage of the brakes over the tires.
Most adjustable brake proportioning valves are very simple devices designed to fit between the master cylinder and the rear brake line. The valve offers a range of adjustment that decreases master-cylinder pressure down to a preset minimum. Most valves reduce the master-cylinder pressure by turning the valve clockwise.

A properly installed and adjusted brake proportioning valve can dramatically improve stopping distance. When it comes to stopping safely, nobody wants to be slip sliding away.

 

If you actually look closely at the system in your 71, the brake line diameter to the fronts are larger, the distribution block chokes down the volume somewhat also. The MC on the 70 and 71 has a stepped piston to also control volume, that is why the large bowl (back) goes to the disk brakes and the small bowl (front) goes to your drums. if you hook the small bowl to your disks, they won't stop squat, ask me how I know?

 

Mike.........that's a great example of how the engineering dept at Willys did the math on brake fluid volume & pressure calculations................taking into account all aspects of the system including line size, distance, a stepped piston in the Master Cylinder ,larger reservoir volume for the discs only , Caliper piston and brake cylinder size & volume notwithstanding the correct Pedal ratios to apply the pressure............Basically a system engineered for the specific equipment.

Anyone looking to add aftermarket Disc brakes, larger drums, different Master Cylinders should take note, there is a correct formula & way to do this.

I have a simple excel Program that I built a while back that helps to get close.

 

I love this board! Lot of guys and gals more knowledgeable than I am keeping me from doing stupid things! Thanks everyone!