Front Brake Selection Help! 1970 Trans AM

[jtwoods4]

Hey Guys,

I am currently restoring my 70 Trans Am I am a weekend warrior road racer at various tracks and events here in the Southeast. I plan on doing the same thing with my 70 Trans Am. Big Engine, Upgraded Suspension, Good Breaks, 17 inch wheels, etc...



So my question... This weekend I installed my freshly rebuilt 12 bolt rear end and the wildwood D154 Rear Disc Brake kit with 12.19 inch rotors (17 inch wheels). The D154 Calipers are the original style "floating" calipers. This should be a nice performance upgrade from the stock Drum Brakes. Anyway, I really want a nice set of front Brakes and Rotors that can handle the abuse and performance requirements of Road Race events. The Rear D154 Floating calipers and 12.19 rotors should do the trick on the rear of the car. However, I don't know what a good selection for the front should be. Does anyone know what a nice "match" for the front brakes would be? They have to be a good match for the rear 12.19 inch rotor and D154 setup Here is a link to the rear brakes I purchased.

http://www.wilwood.com/BrakeKits/Bra...emno=140-13025

[Ron Sutton]

Hey Guys,

I am currently restoring my 70 Trans Am I am a weekend warrior road racer at various tracks and events here in the Southeast. I plan on doing the same thing with my 70 Trans Am. Big Engine, Upgraded Suspension, Good Breaks, 17 inch wheels, etc...

So my question... This weekend I installed my freshly rebuilt 12 bolt rear end and the wildwood D154 Rear Disc Brake kit with 12.19 inch rotors (17 inch wheels). The D154 Calipers are the original style "floating" calipers. This should be a nice performance upgrade from the stock Drum Brakes. Anyway, I really want a nice set of front Brakes and Rotors that can handle the abuse and performance requirements of Road Race events. The Rear D154 Floating calipers and 12.19 rotors should do the trick on the rear of the car. However, I don't know what a good selection for the front should be. Does anyone know what a nice "match" for the front brakes would be? They have to be a good match for the rear 12.19 inch rotor and D154 setup Here is a link to the rear brakes I purchased.

http://www.wilwood.com/BrakeKits/Bra...emno=140-13025

Hey JT,

I'm pretty familiar with these brakes. I have a few questions. They might sound odd, but humor me please.

What are your braking objectives?
What kind of tires will you use for track days?
How long are the sessions you'll run in?
What is your goal when you went from drums in the rear to discs?
Do you have an overall braking goals?
Do you have a single or dual master cylinder set-up?
What size is your master cylinder pistons?
Do you have the stock pedal or an aftermarket pedal?
If aftermarket, what ratio?
Are you planning to go manual or vacuum boosted?

[jtwoods4]

Ron here are the answers to your questions.

What kind of tires will you use for track days? NITTO 555 285/40 x 17 rear 255/45 x 17 FRONT

How long are the sessions you'll run in? 20 to 30 minutes

What is your goal when you went from drums in the rear to discs? Drums Brakes are old technology and there is no performance comparison to Disc brakes.

Do you have an overall braking goals? Must be able to apply brakes very aggressively from speeds of 120 to 130 when coming off the straights at Road Atlanta or other Road courses. Must minimize fade. Must Control Heat. Weekend warrior road racing. I will be running a higher temp pad that is useable on the street but can handle road courses well.

Do you have a single or dual master cylinder set-up? Single Master

What size is your master cylinder pistons? Not sure yet, I have not purchased a master cylinder for this setup. Not sure what the D154 requires.

Do you have the stock pedal or an aftermarket pedal? Stock pedal

If aftermarket, what ratio? NA

Are you planning to go manual or vacuum boosted? Vacuum boosted because I do drive the car on the street occasionally between weekend events.

[Ron Sutton]

What are your braking objectives?
What kind of tires will you use for track days? NITTO 555 285/40 x 17 rear 255/45 x 17 FRONT
How long are the sessions you'll run in? 20 to 30 minutes
What is your goal when you went from drums in the rear to discs? Drums Brakes are old technology and there is no performance comparison to Disc brakes.
Do you have an overall braking goals? Must be able to apply brakes very aggressively from speeds of 120 to 130 when coming off the straights at Road Atlanta or other Road courses. Must minimize fade. Must Control Heat. Weekend warrior road racing. I will be running a higher temp pad that is useable on the street but can handle road courses well.
Do you have a single or dual master cylinder set-up? Single Master Cylinder with 2 reservoirs
What size is your master cylinder pistons? Not sure yet, I have not purchased a master cylinder for this setup. Not sure what the D154 requires.
Do you have the stock pedal or an aftermarket pedal? Stock pedal
If aftermarket, what ratio? NA
Are you planning to go manual or vacuum boosted? Vacuum boosted because I do drive the car on the street occasionally between weekend events.

Thanks JT,

I was asking the what must have seemed like a very silly question about your goals switching from drum to disc in the rear, because this particular disc brake kit from Wilwood has very small pistons & very low braking force. It will have a bit LESS braking force than your drums ... which conflicted with your stated goals of road racing it.

Since they are new & unused, you should be able to swap them for larger piston versions from Wilwood.

I attached a sample brake calc sheet showing your stock braking system on the left, your current set-up in the middle & one of several possible suggested set-ups to achieve your goals.

GUIDELINE:
2500# = Average passenger car
3000# = Performance production car
3500# = Good street & track braking system
4000# = Track braking system with good tires
4500-5500# = Full race brake systems

Tip: Pay attention to the yellow highlighted areas.





Notes:
a. I didn't show any aftermarket brakes in the middle example, because any more front braking would just make the front to rear brake bias even more out of balance.
b. I am showing 150# of force at the foot pedal ... when I normally plug in 100# ... because you have a power booster.
c. I am showing the stock pedal at 5-1 ratio, but we need to confirm that.
d. The Dynapro 6 calipers suggested in the right hand example are just one of a few calipers that would work. These happen to be the least expensive. If you were running 1-2 hour & longer sessions, I'd recommend a caliper built for more abuse.
e. You will want to add an adjustable proportioning valve to the rear brake system for balancing purposes.

Did this make sense? I'm happy to discuss any thing to help you get better brakes.

[jtwoods4]

Ron Thank you so much for the detailed response! Sounds like I need to return my D 154 brakes! I'm on my mobile device so I will read your full post details when I get back to the house. Thanks again I really appreciate the help.

[jtwoods4]

Ron, should I scrap the D154 all together and look at something else? I chose the D154 because it was a floating caliper and would eliminate knock back when on the race track. The 120-11875-BK I have show 1.98 Piston area. This one fits the same size rotor and shows 2 pistons and 4.12 piston area. Still it doesn't seem like much improvement over the drum. Should I scrap the D154 all together?

http://www.wilwood.com/Calipers/Cali...o=120-11873-BK

[Ron Sutton]

JT,

From 744# of braking force to 1177# of braking force is a big jump & a MAJOR improvement over the drum brakes ... 58% in fact. If you increase your fronts by the same amount ... to keep the bias correct ... you would have 58% more braking. That's a lot ... too much actually ... for treaded tires. You'd need slicks to make that work.

Quick braking force primer:
Most cars like a 65/35 to 70/30 front-to-rear braking bias. Obviously, if you get too much braking force on one end of the car ... it will lock up the tires on that end of the car under hard braking on corner entry. Too much rear braking force makes the car loose under braking & too much front braking force makes the car push under braking. If you get too aggressive with total braking force ... for the tires you're running ... you simply lock up the brakes on corner entry.

The D154 is a good caliper. Maybe the best caliper for the money. The bonus it is floating, which just means it's will be less issues for you to deal with. It is difficult to get a front caliper & rotor combination with enough braking force to keep up with this rear caliper, without going super aggressive on the brake pad compound. I already had to spec all 3 options with stock oem rear pads & "B" compound front pads to get the fronts to work balanced with the rears.

I made an error earlier, when I listed the DynoPro 6 caliper with 13" rotors. You can probably get it that way, but in Wilwood's off-the-shelf kit, it comes with a 12.19" rotor. Another option is to have Wilwood put together a kit for you using the W6A caliper & 13" rotors. It offers a step more front braking force & will bump the price considerably.

The Dynapro 6 kit, even with the 12.19" rotors is a pretty good low cost 6 piston front brake system, available from Wilwood for around $1100 or $1200, depending if you go drilled rotors or not. You can see the kits here. Scroll down the page. You can get red or black calipers ... and drilled or solid rotors.

In the chart below, option #1 is the Dynpro 6 kit with 12.19" rotors. Option #2 is the Dynpro 6 kit with 13" rotors. Option #3 is the more expensive W6A calipers with 13" rotors. No idea on cost other than to say "more". With Option #1, by the time you reduce the rear braking enough to get the bias right, you'll probably end up around 3200-3300# total braking force.

[jtwoods4]

Since I am NOT running slicks and running the NITTO 555 performance street tires do I still need to increase the piston size on the D 154? Which option above would work best with the sticky street tires I am running?

[Ron Sutton]

The options I posted.

[jtwoods4]

Ron what an awesome post. thank you for all the help

[Ron Sutton]

No worries. Glad to help.

When you're running slicks, you can start getting the braking force up into the 4000#-5500# range. With high grip, low wear treaded tires around a 200TW rating, you want to be in the mid to high 3000's.

Best wishes & please post photos of your build.

[Skip Fix]

Wilwood's site is not acting good tonight for me to check out some of the stuff..Seems liek half the time their site doesn't work well for me.

I guess we need clarification which D154 calipers you have on the rear they make a single piston,larger dual piston as well as smaller dual pistons. Factory iron D154s use a 2.5" piston as did the 79-81 TA 4 wheel disc setup. I think if you have the smaller 1.12 dual piston caliper front selection will not be as tough to balance out. Heck even using their dual piston D52 caliper on a 12" 1LE/B body rotor would probably be close to the factory F body system for balance.

Ron plug the 2.5 rear single piston caliper in with a 11 3/16" rotor 1" for a factory F body rear disc setup as a comparison also besides the disc/drum.

Also most factory power brake systems disc/drum or the 79-81 disc/disc used a 1 1/8" MC, the '81 was quick take up aluminum.Manual systems did get a 1".

Ratio is probably around 5:1 I know moving the rod up for a manual gets right around 6:1. 79-81 TA 4WD used a ratio even lower than 5:1 as they used a more assist dual diaphragm booster. Booster selection makes big difference ion the system also.

[Ron Sutton]

Wilwood's site is not acting good tonight for me to check out some of the stuff..Seems liek half the time their site doesn't work well for me.

I guess we need clarification which D154 calipers you have on the rear they make a single piston,larger dual piston as well as smaller dual pistons. Factory iron D154s use a 2.5" piston as did the 79-81 TA 4 wheel disc setup. I think if you have the smaller 1.12 dual piston caliper front selection will not be as tough to balance out. Heck even using their dual piston D52 caliper on a 12" 1LE/B body rotor would probably be close to the factory F body system for balance.

Ron plug the 2.5 rear single piston caliper in with a 11 3/16" rotor 1" for a factory F body rear disc setup as a comparison also besides the disc/drum.

Also most factory power brake systems disc/drum or the 79-81 disc/disc used a 1 1/8" MC, the '81 was quick take up aluminum.Manual systems did get a 1".

Ratio is probably around 5:1 I know moving the rod up for a manual gets right around 6:1. 79-81 TA 4WD used a ratio even lower than 5:1 as they used a more assist dual diaphragm booster. Booster selection makes big difference ion the system also.

Hey Skip,

Thanks for chiming in. JT hasn't purchased a master cylinder yet, so he doesn't have a stock 1-1/8" version. I am recommending a 1" M/C to provide more overall braking force. Of course, when we compare different brake set-ups ... and we keep the M/C & pedal ratio size constant ... it shows us the true braking force differences in the caliper/rotor/pad combo ... and that difference percentage doesn't change with master cylinder size.

I worked up the examples you suggested. I put 1-1/8" M/C across the board. The first one is the 1970 set-up with drum brakes & 11" rotors. The second one is a 1980 TA with disc brake rears & the larger 11-7/8" front rotors.

The third one shows trying to use the small piston Wilwood rear calipers that JT currently has. You can look at the numbers & see they just don't produce enough braking force for a good hot rod, let alone a road course track car. The fourth set shows option #1 from the list above ... but with a 1-1/8" M/C.

[NOT A TA]

This thread caught my eye because I'm trying to figure out what master/booster combo to use on my 70 bird. I ran a stock disc/drum system with race pads & shoes from Porterfield using dedicated rotors/drums on track (20 min sessions) with Yokohama DOT R AO 32 tires 275/315 17's and I would crystalize rotors in a weekend at HPDE's. Now switching to the newer Yoko AO 48 Tires (40 TW) 285/295 18's with Baer 6 piston 14" all around. I'm considering the late 2nd gen dual diaphram booster & 1 1/8 master and already have a rear bias valve to use instead of a prop valve.

JT, you'll want more tire than a 255 street tire if you're going to try and run fast at Road Atlanta or you'll end up with greasy tires by mid session. I've run there several times and it's one of my favorite tracks. Without good brakes & tires you'll have to brake early for turns like 10A which costs lots of time.

[Ron Sutton]

This thread caught my eye because I'm trying to figure out what master/booster combo to use on my 70 bird. I ran a stock disc/drum system with race pads & shoes from Porterfield using dedicated rotors/drums on track (20 min sessions) with Yokohama DOT R AO 32 tires 275/315 17's and I would crystalize rotors in a weekend at HPDE's. Now switching to the newer Yoko AO 48 Tires (40 TW) 285/295 18's with Baer 6 piston 14" all around. I'm considering the late 2nd gen dual diaphram booster & 1 1/8 master and already have a rear bias valve to use instead of a prop valve.

JT, you'll want more tire than a 255 street tire if you're going to try and run fast at Road Atlanta or you'll end up with greasy tires by mid session. I've run there several times and it's one of my favorite tracks. Without good brakes & tires you'll have to brake early for turns like 10A which costs lots of time.

John, how did you like the Porterfield pads?

[jtwoods4]

I have been reviewing the charts above. The Dynopro 6 clamping force with a 13" rotor increases a lot when going from a 1.13 MC to a 1.0 MC!

So as I understand it I can run High Performance Street tires and Get the Larger 2 Piston D154 with 12.19" rotors and the Dynapro 6 with 13" rotors. This would give me a total force of 3605 and a front to rear ratio of 67% / 32%. I should use the 1 inch master cylinder and proportioning valve also. And this is a nice setup for the 1970 TA.

Just wanted to confirm this before I make the purchase.

[Ron Sutton]

I have been reviewing the charts above. The Dynopro 6 clamping force with a 13" rotor increases a lot when going from a 1.13 MC to a 1.0 MC!

So as I understand it I can run High Performance Street tires and Get the Larger 2 Piston D154 with 12.19" rotors and the Dynapro 6 with 13" rotors. This would give me a total force of 3605 and a front to rear ratio of 67% / 32%. I should use the 1 inch master cylinder and proportioning valve also. And this is a nice setup for the 1970 TA.

Just wanted to confirm this before I make the purchase.

Hi JT,

All I can offer is my advice, but yes, I believe you will be happy with that package for road course track days on treaded tires. What I laid out there is big step up in braking from what you had.

Yes ... Get the Larger 2 Piston D154 with 12.19" rotors and the Dynapro 6 with 13" rotors. This would give me a total force of 3605 and a front to rear ratio of 67% / 32% ... and the Wilwood 1 inch dual master cylinder and adjustable proportioning valve plumbed into the rear brake system ... plus you need BP-20 front brake pads.

I want to add to what John said about going with bigger tires & grippier tires than the Nitto 555 if you want to be secure & fast at Road Atlanta.

[jtwoods4]

Hey Ron, one last question. Wilwood also makes a Superlite 4 piston caliper. I could order this with a 13 inch rotor. Do you have any experience or advice on these?

[Ron Sutton]

Hey Ron, one last question. Wilwood also makes a Superlite 4 piston caliper. I could order this with a 13 inch rotor. Do you have any experience or advice on these?

Hi JT,

For your application ... the Superlite pistons are too small & don't offer enough clamping force with your pedal ratio & M/C size. We run these on 2900# cars but with super aggressive brake pads, more pedal ratio & much smaller M/C size.

Just for giggles, I attached two worksheets showing a wide range of different front brake calipers. The Superlites are model NSL6P ... which stand for Narrow Super Lite 6 Piston.

The TOP CHART shows all the calipers with the same brake pads, pedal ratio, master cylinder, input, etc, as I outlined for your car. Go look at the different braking force numbers.

The BOTTOM CHART shows the brake pads, pedal ratio, master cylinder, input, etc ... that we would run with the Superlite Caliper in Short Oval Track racing in a 2900# Late Model Stock Car. Now ... go look at those different braking force numbers.

You'll notice the Dynapro 6 I suggested ... has more braking force with a 13" rotor ... than the Superlite has with a 14" rotor.

Clamping force by itself doesn't mean a particular caliper is good or bad. Just realize, when you put a brake system together ... EVERY detail matters. I like the Superlite caliper for running 2900# short track stock cars. But you need to design the whole system to achieve the desired braking. My opinion is the pistons are on the small side for 3500# PT street cars ... requiring a aggressive race pads to achieve the optimum braking numbers. Aggressive race pads wear out quicker & cost more.





HEY GUYS following along with this thread ... Please do not just "Run with these Numbers" for your brake system.
I posted these for our discussion only. Getting a brake system designed correctly for your car is one of the most important things you need to do. If you have questions ... please ask. I'm happy to offer information, guidance & calcs to help you in your decision.

[Todd in Vancouver]

Who Ron, every time I read one of your posts I realize how much I really don't know. Rather than add my 2 cents when you post should I just send you everything about my car or would you like to come over and tell me what I should be changing. Sadly the old school of bigger is better type build is gone and I feel way out of touch on what the hell I'm doing. I've only been out of the loop a couple decades but man has a lot ever changed.

On a serious note, I really never realized that over building the braking system could lead to issues. I've started down a path with Wilwood so am I right to assume that if I contact them and go through what the hell I'm building they can make proper recommendations? Or, are you going to be in the Vancouver, BC anytime soon?