'75 Duster B body front brake upgrade impressions wanted
I'd start by seeing which brakes will lock up first.....front or rear. Then get an adjustable proportioning valve and get it to where both ends lock up a the same time. That should shorten your braking distance about as much as you're going to get IMO. Going to bigger brakes will just keep them from wearing out as fast and keeping pedal fade from happening as easily. Going to a tire with a better traction rating can help on your stopping distance too.
Big brakes don’t just increase fade resistance and wear. Yes, the swept area is larger which improves both cooling and wear. But the caliper being further away from the hub also increases the “lever arm” used to calculate the braking force. It’s a direct increase in braking force. About 9% in this case, which doesn’t sound like much but it makes a big difference. I’ve run these cars with both the 10.95 and 11.75” rotors, the 11.75’s make a noticeable improvement.
The OP is already running more modern tires, so he will benefit from the larger brakes.
As for the prop valve, all that does is reduce the pressure to the rear. It does not change pressure in the front. And since the front brake do more than 70% of the braking, it’s really hard to go wrong with larger front brakes. Even if currently his rear brakes do lock up first, adding the larger rotors up front could very well solve that balance issue.
The 11.75 setup up front is a good idea. Mopar never put the big brakes on the A body car but no reason you can't. Don't forget the rear brakes. If you a big bolt pattern rear axle then you should be able to swap over to the biggest B body drum brake. Just have to search around to find the correct backing plates. Not sure if anyone is reproducing them or not.
Totally agree. I found the stock combination valve worked fine on both my Challenger and my Duster using 11.75” disks up front and 11x2.5” drums out back. There are also two different wheel cylinders available for the rear drums, so you can dial it in even closer. I’m sure an adjustable valve can get you closer than my cars were, but they were better balanced than what the factory sent out.
I didn’t have much trouble finding 11x2.5” rear drum set ups. You just have to be careful if you’re only buying backing plates because the 11x2” and 11x3” backing plates have different axle flange offsets, so you actually need backing plates for an 11x2.5” drum. Buying them or finding them all together makes that a bit more certain, some sellers may not know that there are different plates for different drum/shoe widths.