[Greg Reid]

Originally Posted by Scarebird

Correct. Mid-70's GM did a flip-flop on the reservoirs for simpler valving.

Some masters are still being made for the older style but more expensive and less effective.

Drum/drum work fine too but watch the fluid level.

How do you recognize that by looking and if I used the pictured master, front reservoir is for the rear and visa versa?

[RocktimusPryme]

Originally Posted by JLMounce

factory type master cylinders are fairly cheap. It's more work than anything to try out the smaller bore master. You might consider changing out the brake pads at the same time as part of a brake service and see how you like it. If you hate it, you've still got the old stuff.

I'm assuming you have the D154 calipers for the rear?

Its also a right stuff kit in the rear, but Im told they are basically factory equipment for early 70s A bodies.

[JLMounce]

More than likely the metric rears (D154). They probably look mostly the same as the front calipers, but are on a roughly 5" hole to hole mount vs a 7" hole to hole mount? May also have an integral parking brake.

[Scarebird]

Originally Posted by Greg Reid

How do you recognize that by looking and if I used the pictured master, front reservoir is for the rear and visa versa?

Bigger rez is for fronts.

[Greg Reid]

Doh!... Why didn't I catch that?

[Murf]

Originally Posted by Scarebird

Bigger rez is for fronts.

I’ve got a couple more basic questions if you have time.

1. What exactly is the difference between disc / disc vs disc / drum master cylinders?

2. Is there any correlation between the fitting sizes on the master cylinder and where they go? I.E. does the bigger fitting always go to the rears, which usually have a larger line?

Thanks,
Murf

[Scarebird]

1. Not much that I have seen or know - maybe spring rate between the 2 pistons?

2. All I have seen have larger lines to the rear. Some have the same size.

[punkin]

I went manual Wilwoods some time ago as well. I did end up going with their master mostly because their proportioning valve set-up was nice and clean when packaged up. No regrets.

The car was always a manual set up and way back it was my daily driver. Manual brakes was never a concern because I didn't own anything else that had power, I just didn't know any different. Now that I'm older and have been driving modern cars it does take a little reminder how it will behave but very solid performance.

Jason, question if you don't mind. I recall seeing one of your videos where you replaced the rear lines with a smaller diameter. Did you do this to optimize the manual setup and/or to avoid the use of an adjustable prop valve?

[JLMounce]

Yes I went with a 3/16” rear line over the factory 1/4” line. Disc brakes don’t necessarily need the same volume of fluid as drums. My research suggests that this reduces pressure drop to the rear calipers.

Whether that’s actually happening I don’t know, but I haven’t had any issues. The smaller OD line was a heck of a lot easier to snake through the chassis, that’s for sure.

[Murf]

Originally Posted by Scarebird

1. Not much that I have seen or know - maybe spring rate between the 2 pistons?

2. All I have seen have larger lines to the rear. Some have the same size.

Thanks man!

[twov8sandat4]

As a brake system novice here, can you shed some light on this? How did you bolt the master to the firewall? Did the factory pedal work? Does it feel like manual vs power steering, where you get way more feedback for a bit more effort? Trying to figure if I have to look into this vs the Chinese knockoff factory disc/disc booster/master that I have on mine now.

Thanks.

[68WarDog]

Originally Posted by JLMounce

Call me a believer.

For 10 years or so and specifically in the last 3 years I have really chased performance issues with the braking of my Firebird. It had basic stock type components on it to create a 4 wheel power disc system.

It consisted originally of a single 9" diaphragm power booster which clamped GM D52 calipers on 11" rotors in the front and GM Metric calipers on 11" rotors in the rear. In this configuration, the braking was adequate. It would stop decently, but never really wanted to lock up the wheels.

In 2022 the power booster failed and the decade + aged calipers had started to leak and really just looked like crap.

Last year I replaced the calipers with Wilwood variants of the D52 and Metric calipers and had a rough time with it. This is what led me to discover the power booster was failed/failing. I had determined through speaking with several different people that the booster just wasn't adequate for the type of vacuum I was pulling. On the edge, so the single 9" diaphragm just wasn't adding enough pressure to the system.

I opted for a TuffStuff dual 9" designed around the C3 braking system. With the massive 6.28" front and 4" rear piston areas, combined with the larger power booster, the car stopped very well, now able to lock the wheels when needed. However the pedal feel as atrocious. The booster worked so well that it slammed all the pressure into the calipers as soon as you touched the pedal. Very little firmness from the pedal and zero feedback. It was like the first time you try left foot braking and your foot is asleep at the same time.

You can imagine, in traffic this was pretty terrible to deal with. You were going or stopping, not really anywhere in between.

I've been wanting to change the wheels and tires on the car for a while for a bit different look and figured if I was going to do that, now would be the time to re-engineer the brake system, in case my track widths changed.

With a bit of trepidation, I opted to go with an upsized Wilwood package in the front and rear and matched it with a 15/16" manual master. The system consists of a 12.88" front rotor with the Forged Narrow Superlight 6 piston caliper in the front and a 12.19" rear rotor with the Forged Dynalight 4 piston caliper in the rear.

I was able to get the system bled out and the pads bedded in yesterday and got some drive time in. I can tell you, I should have done this years ago.

Yes, the pedal effort is increased, but not in a bad way. It's nothing like a hard pedal with a bad power booster where it's just needless hard with no stop. You feel the pads come on to the rotor and you can feel the adhesion of the tires to the ground. It's super easy to modulate what you want the car to do. Actuation is quite linear and the pedal is always doing what you expect it to do and how you expect it to feel.

If you're on the fence about going with a manual setup over a power setup, the only thing that might sway me away from manual at this point is if the car is daily driven in stop and go traffic. The increased pedal firmness isn't that much of an increase. In fact I don't think my pedal is much firmer than the pedal on my wife's '13 Corvette. The feel is just so good as to override any issues with the firmer pedal.

As an added bonus, I now have zero vacuum accessories that I need to worry about having an engine support.

What size wheels are you able to use with the new rotors? I will soon be getting the Willwood manual brakes system,. However I will retain my 15" Rally 2s.