What to use for Booster/Master Combo...disc/disc conversion

[Colin70ta]

Hey Guys, new to the Pro-touring forum, thanks in advance for the help!

Here is my situation. Car is a 1970 Pontiac Trans Am, all numbers matching and stock appearing other then new 18" rally style rims
I am upgrading the tires/brakes and suspension as my wife drives the car and we have a one year old daughter that I would like to also take in the car and I just don't trust the stock braking system from a safety stand point.

Since the car is stock otherwise and I would like to keep it as close to stock appearing as possible.

With that in mind what do you think I should do for the master and brake booster? I am changing to 4 wheel disc over the winter, have already purchased the front disc brakes (Wilwood, 6 pistion, 12.8") and will probably go with something more basic out back unless someone recommends otherwise?
Is it possible to still use the 11" booster and just change the master and proportioning valve? I could hide an adjustable valve somewhere too if needed.

I want the car to brake like a new car so if it does mean I just change all of it, please let me know.

Thanks!
Colin

[69L48Z27]

Colin,

Nice car and welcome!

You didn't mention what you have currently. I would think TA would have had power brakes? I'm not a TA expert, I'm not sure what they had.

I run a 9" dual diaphragm booster with Detriot Speed brackets. Then issued a C6 master cylinder, 1" bore. I used a proportioning valve and re-ran at 3/16" lines and used braided lines to each caliper. Then big Wilwood brakes all around.

I don't think you need to go to this extent. Key is the 1" bore master cyliner. The booster is more about what will fit and how much assist it will give. I think 11" single vs. 9" dual is probably the same. I had to use the 9" so it would fit on the LS swap. Prop valve is nice to have if you need it but most things I've read say you really don't need it. I have mine cranked in the whole way.

You should be able to get a 'stock' booster and master (1") from companies like Right Stuff that will bolt in and use existing lines and distribution blocks. Keep it looking original.

Good luck, don't over engineering it.

[Skip Fix]

The 79-81 Firebird factory 4 wheel discs used about a 9" dual booster and a 1 1/8" MC. The 79-80 used a cast iron MC with a smaller register than the 81 aluminum MC(bigger for the stepped MC for the "quick take up" calipers). They also used less pedal ratio than the single 11" boosters for disc/drum as they provide more assist. I would think a 79-80 would be a bolt on if you want to go dual.

[Colin70ta]

Thanks for the help and recommendations! Skip I totally forgot about the late 2 gen 4 wheel disc cars. I think I will first try it with my existing booster and just change the MC to the factory set up and see how I like it. I think it will come down to what feel I like so I might as well not throw a whole bunch of money at it right off the bat.

Thanks again both of you.
Colin

[NOT A TA]

I believe the late 2nd gens with 4 wheel discs also had a different pedal with a different mounting point for the clevis you will want if you try the stock 4 wheel disc master. You can modify the pedal arm http://transamcountry.com/community/index.php?topic=31184.msg284780#msg284780. Need a disc/disc combination valve or an adjustable proportioning valve for rears. There's some math involved to determine the correct piston size master based on caliper piston surfaces etc. Maybe someone will chime in with the equations.

That said, the 2nd gen stock disc/drum setup can work well for street (even spirited driving) if set up with good components.