Safe, Efficient F/R Brake Bias

[GoreMaker]

I'm planning some brake upgrades for my '77 Trans Am with 400/4-speed. I'm staying with OEM-sized 15" wheels, so my options are somewhat limited. My current plan is for 12" front rotors with Wilwood dual-piston D52 calipers (I'm installing Pro-Touring F-Body tall spindles that accommodate 12" brakes). I'm debating a bit on the rear. I'm definitely planning a Wilwood rear disc conversion, but I'm torn between 11" Dynapro Low Profile and 12.19" Dynalite kits. I'm concerned that the 12.19" would be too much brake compared to the front and shift the bias too far back. The calipers for each kit both have the same piston diameters, though the 11" kit appears to use slightly shorter pads. It's kinda hard to see what the actual pad surface height is for each caliper from the diagrams, so there's a bit of guessing in my calculations, but I doubt the differences are big enough to cause much error.



Whats a safe brake bias for these cars that still maximizes the rear brake efficiency? I was planning to try to stay near or above 70% front, which it looks like the 11" rear kit would achieve, while the 12.19" kit would bring me to about 65% front, which seems inadequate considering how front-heavy the car is. I can get away with 65% on my Buick Roadmaster wagon because its weight balance is about 50/50, but that's definitely not the case on this Trans Am.

Yes I realize I could "fix" the ratio with an adjustable proportioning valve, but I'd like to get it as close as possible using just brake hardware and a regular, stock-looking disc/disc proportioning valve.

[Jk918]

I believe they make the D52 with a couple different piston sizes I would get the largest size for the fronts and get the dyna with the smaller piston size for rear.

[Jonathonar89]

From what I’ve seen on the good ole internet, you won’t be able to fit the bulky Wilwood calipers with a 12” 1LE rotor in 15” wheels. The guys who run 15” wheels with the 12” disc use the factory iron caliper as it has more clearance to the wheel barrel. I’ve gotten that 12” and Wilwood caliper to clear my 16” WS6 wheels but it’s tight.

Unless you’re upgrading the wheels, just do the 12” front disc with good pads and to some braided hoses. You’re probably best just leaving the rear brakes as is if you’re using stock 15” wheels.

[GoreMaker]

Good point, I'll have to confirm that the Wilwoods fit. I run them on my '93 Roadmaster wagon with OEM 15" wheels, so I can swap one over to confirm whether the 15x8 snowflake wheels still fit before I order another set of Wilwoods. If they don't, there's really nothing wrong with the cast iron D52 calipers, they technically have more piston area than Wilwood dual piston calipers anyways.

[Jonathonar89]

Good point, I'll have to confirm that the Wilwoods fit. I run them on my '93 Roadmaster wagon with OEM 15" wheels, so I can swap one over to confirm whether the 15x8 snowflake wheels still fit before I order another set of Wilwoods. If they don't, there's really nothing wrong with the cast iron D52 calipers, they technically have more piston area than Wilwood dual piston calipers anyways.

You will have to swap the calipers over to check. The B-Body you mention has a 5x5 bolt pattern and the F-Body (WS6) wheel is 5x4.75. That wheels won’t swap for checking unless you swap on the 12” 3rd Gen F-Body 1LE rotor onto your B-Body spindle.

[GoreMaker]

I can just grab the D52 caliper from the Roadmaster and put it on the trans am's new spindle to see if its wheel still fits properly. They both use the exact same caliper and mounting. I don't need a brake rotor to test, I run KORE3 billet hubs.

[GoreMaker]

Some added details:

OEM cast-iron D52 calipers on 1LE spindles fit fine in OEM 15x7 or reproduction 15x8 snowflakes with room to spare. Wilwood aluminum D52 calipers do not, unless a bit of grinding is done to them. The rubbing is caused by the fact that the wheel barrel narrows toward the outside edge, thereby reducing clearance diameter enough that the thicker D52s rub against the barrel. It's possible that wheel spacers would allow them to fit without grinding, I'm still working that out.

Technically the OEM D52 calipers have more clamping force than Wilwoods anyways, but the Wilwoods spread their clamping force more evenly across the pad. So I'm thinking of just sticking with the cast-iron calipers. That way I'm stuffing the maximum possible amount of braking force into a stock-sized 15" wheel.

[jetmech442]

Just gonna throw this in here for you...
A bodies disc conversion kits run the D52 in front (like you) and a D154 in back . wilwood makes a version for both. My old setup ran those and the bias seemed to be right. D154's are known as "metric calipers, or Eldorado calipers". The version with the parking brake is trash and now I run the version without it.