Rear Wheels Lock Up during Heavy Braking

[BillCA63R1]

My R1's rear drum brakes were just rebuilt and now the rear wheels 'lock up' during heavy braking. Does the Avanti have a proportioning valve in the braking system? If not, I could use advise on fitting one. Note: This car has previously had a dual master cylinder/fluid reservoir brake system installed.

[PackardV8]

There is no proportioning valve because the rear brakes are not self-energizing. Was the Shop Manual followed exactly when the rear shoes were installed.?

Most likely you now have an imbalance of front pad and rear shoe compounds. The front pads may be harder than the rear shoes. The answer might be to fit softer front pads so they more than 60% of the work in braking.

jack vines