Manual master cylinder help

[blown69nova]

I've searched and did'nt find my answer!
I have a 69 nova, running factory d52 front brakes, and Explorer discs in the rear. I'm looking to buy a Wilwood tandem master, just not sure what size to buy. What do you guys think?
Thanks, Steve

[Ron Sutton]

We need more info to help guide you.

Power booster or manual?
If booster ... what kind ... hydraulic or vacuum?
If vacuum ... what size booster & is it single or double?
What is your pedal ratio?

* If you're not sure of your pedal ratio, get under the dash & measure it.
Distance from center of pedal pivot to center of foot pad = A
Distance from center of pedal pivot to center of M/C rod pivot = B
A ÷ B = Pedal Ratio
Example: A= 12", B= 2" ... so 12 ÷ 2 = 6 ... so a 6-1 ratio

:cheers:

[blown69nova]

Spent the weekend at the summer nationals, I'll get under there this week.
I know the rod is in the factory "manual" hole, on the pedal.

[blown69nova]

Oh yeah, no booster.

[blown69nova]

10" from pedal to pivot
2" from rod to pivot
5:1?
what size manual brake master cyl.?
Thanks, Steve

[Ron Sutton]

We didn't discuss pad compounds, so I ran a few versions ...

If you run a 7/8" Tandem Master Cylinder & OEM brake pads with their typical .35 CoF (Coefficient of Friction) ... you'll only have about 2100# of braking force. Not great by any means. If you step up to an aftermarket pad, with a higher CoF ... you can get your system to make some decent braking force. But to get your braking up in what I consider performance car range, you'll need to run good pads AND modify your pedal ratio to around 6-1.


With 5-1 Pedal Ratio

129451


Total Braking Force Guidelines:
2500# = Average passenger car
3000# = Performance production car
3500# = Good street & track braking system
4000# = Track braking system with Wide Stickies
4000-6000# = Full race brake systems


With 6-1 Pedal Ratio

129452

:cheers:

[blown69nova]

WOW, thats a lot of great info! Thank you.
This is for a street strip setup, and yes, I'm using stock pads with a dodge d150 m/c 1-1/8". It stops but, I could never lock them up.

[blown69nova]

So, to get it closer to 6 to 1, do I move the rod closer to the pivot? Can I simply drill a new hole?

[malibudave]

Divide the pedal length (10") by 6. This equals 1.67" down from center of the pivot point. This will give a 6 to 1 pedal ratio.

Usually moving the rod up on the brake pedal increases angle of the push rod. An increased angle will put more side loading on the master cylinder piston and wear the master cylinder out by causing leaks in your seals. Another thing that will happen if you move the push rod up on the brake pedal arm will be that the push rod will be pointing down to the master cylinder piston, as the brake pedal moves through its range of motion while braking, the push rod attachment point on the brake pedal will move up and away from the master cylinder piston decreasing the master cylinder piston travel to almost nothing for the last few inches of the brake pedal stroke.

At the end of the brake pedal stroke, you want the push rod to be inline with the master cylinder bore and the master cylinder piston to have move (in most applications) about 1.0". This is optimum for most applications.

If you are running the stock 69 Nova manual brake setup, I would keep it as is and reduce the bore size of your master cylinder. 1.0" bore will increase your braking performance. A 24mm or 15/16" bore master cylinder will be the smallest I would try, but my guess is that the 24mm or 15/16" bore master cylinders are at the volume limit of a stock D52 calipers plus the Explorer rear calipers. The stock D52 caliper piston is massive at 2.95" bore. I know a 7/8" bore master cylinder will not have the volume needed to fill a stock D52 calipers. A D52 caliper has about 30% more piston area than a smaller GM metric D154 caliper. A D154 metric caliper has a 2.5" piston and a 3.9 sq in piston area. A D52 caliper has a piston area of 6.97 sq in.

Things that help improve braking performance are new rubber brake lines front and rear or aftermarket stainless steel braided lines. Old rubber lines will deteriorate and, when pressure is applied, start to balloon reducing braking performance.

If you do decide to move the pivot point up, you will also need to move the master cylinder up on the firewall to correct the angle of the pushrod. Another option is to increase your pedal arm to 12" in length and keep the pivot point at 2". Either option will require some fabrication.

[blown69nova]

I'm going to replace the 1.125 bore chrysler master anyway. So, a 1" bore would be best, 15/16" smallest?
I already have braided lines on all 4 corners, and new 3/16" line, front to back. I also have a Wilwood adjustable prop valve/dist block. This is for a 1000+ hp, street/strip rig, so no auto crossing.
Thanks for the help guys.

[malibudave]

I would step down to 1.0” bore master cylinder to see how it feels with your front and rear brake setup. You should notice a brake performance improvement, but will it be satisfactory for you?

15/16” bore master cylinder may be too small with those front and rear calipers, but you may try after you look at your pad selection and what's best for your car and driving. Ron should help you best with that. For driving around town, I would run a pad with more “cold bite”. If doing track time, I would change them out with something that more aggressive that works better when they have some heat in the pad.

[Ron Sutton]

Hey Dave,

Thanks for chiming in. I checked out your website. Cool stuff.

I have several customers on the big GM front caliper with the single 2-15/16" piston or Wilwood's replacement caliper with the two 2.00" pistons (slightly less piston area). I've also ran this combo on my NASCAR Modifieds out West. We run 7/8" master cylinders on them & none have had an issue of lack of volume from the 7/8" M/C. The pedal travel is long, but most racers prefer this because it makes the brakes easier & more accurately modulated, versus a short travel on/off switch. But the average street driver that is used to the short travel of power brakes doesn't like it at first.

--------------------------------

Hey Steve,

I made an incorrect assumption. I "assumed" because you're on a Pro Touring website that you're running a Pro Touring type car and had at least 245-275 wide front tires on your car. The Blown Nova title should have been a clue, but I missed it. Since this is a drag car ... can I safely assume you have narrower front tires? Please chime in & let us know your front tire size.

If that's the case, you won't want 3000# of braking torque. That would lock up your front tires. Depending on tire size, you probably want to have 2000# to 2400# of braking force. That amount of braking is easy to achieve with your set-up. I'd leave the pedal at 5-1, run Wilwood E Pads (great response for cold rotors on a drag run) and either a 1" or 15/16" M/C. See the chart below to see the braking force you have with the 1-1/8" M/C & OEM pads ... and compare to the 2 versions with E Pads.

129537

:cheers:

[malibudave]

Ron,

Thanks for the kind words.

Are you talking about running a single,tandem master cylinder or dual master cylinders?

I haven't run dual master cylinders, but they seem better at putting more volume than a stock style, tandem master cylinder. I'm not exactly sure why they do, but it seem that two separate master cylinders are more efficient than one, stock style master cylinder.

I have run oversized 2.75" Wilwood metric calipers with rear drums, with a stock MOPAR type master cylinder with a 7/8" bore and was not able to produce any pressure without pumping the brakes. This is where my experience comes from, but these types of master cylinders can only do about 1.0" of master cylinder piston travel.

If I could easily add twin master cylinders to a stock pedal assembly, I would, but this type of setup is not on my list to try and fit to a g-body.

[blown69nova]

Yes, I do run a 26x7.5x15 front tire. I do have a hard pedal, and somewhat short travel.
Thanks, Steve

[Ron Sutton]

Ron,

Thanks for the kind words.
You got some cool stuff going.

Are you talking about running a single,tandem master cylinder or dual master cylinders?
On my NASCAR Modifieds, we used Wilwood pedals & dual M/C's. On the Protouring cars, my clients run the Wilwood tandem 7/8" M/C with a proportioning valve most often. I have a few clients that run a dual master cylinder assembly we sell from CNC Brakes. It bolts right into place where the factory tandem M/C was & connects to the factory pedal. They are little bit more spendy than the Wilwood & a lot more than a factory style M/C. If we need to stagger the M/C sizes, it works well. Plus it has a brake bias adjuster built in, versus a proportioning valve. So that's a plus. You can see one here on my website: http://shop.ronsuttonracetechnology.com/shopping/?ic=7250

I haven't run dual master cylinders, but they seem better at putting more volume than a stock style, tandem master cylinder. I'm not exactly sure why they do, but it seem that two separate master cylinders are more efficient than one, stock style master cylinder. Technically they shouldn't, but I find they do also. I do find the Wilwood tandems work very well. So we use them "most" of the time for production based cars.

I have run oversized 2.75" Wilwood metric calipers with rear drums, with a stock MOPAR type master cylinder with a 7/8" bore and was not able to produce any pressure without pumping the brakes. This is where my experience comes from, but these types of master cylinders can only do about 1.0" of master cylinder piston travel.
Interesting. I can't speak to this, because I haven't run the OEM style M/C's in a long time.

If I could easily add twin master cylinders to a stock pedal assembly, I would, but this type of setup is not on my list to try and fit to a g-body.

The CNC dual M/C kit will work if you ever find a need to do it. It's probably more money than some want to spend. But it is a good solution.

Take care !

[Ron Sutton]

Yes, I do run a 26x7.5x15 front tire. I do have a hard pedal, and somewhat short travel.
Thanks, Steve

I would suggest the 1" M/C & leave your pedal ratio at 5-1. This is the combination shown in the middle column of the last chart.

Best wishes.

[malibudave]

The CNC dual M/C kit will work if you ever find a need to do it. It's probably more money than some want to spend. But it is a good solution.

Take care !



Ron, Thanks for the link. I totally overlooked it. That is exactly some of the things I was looking for.

Do the dual master setups mount to the upper holes that the vacuum booster used?
What do you do about a pushrod from the stock pedal assembly to the rear of the dual master setup?

[Ron Sutton]

Ron, Thanks for the link. I totally overlooked it. That is exactly some of the things I was looking for.

Do the dual master setups mount to the upper holes that the vacuum booster used?
What do you do about a pushrod from the stock pedal assembly to the rear of the dual master setup?

The Dual CNC M/C's mount in the same location & same holes as a manual M/C would on the firewall ... and the pedal rod lines up in the same, correct location. So if the booster holes don't line up with the pushrod, holes would need to be drilled. Depending on firewall hole layout, that may require a reinforcement plate. If the car was power boosted, the push rod itself has to be changed to one with a saddle mount on the pedal end & a threaded coupler on the M/C end.

[Skip Fix]

Ron, Thanks for the link. I totally overlooked it. That is exactly some of the things I was looking for.

Do the dual master setups mount to the upper holes that the vacuum booster used?
What do you do about a pushrod from the stock pedal assembly to the rear of the dual master setup?

My 79 Camaro the upper pair of studs lined up the MC with the pedal hole better when I converted it to manual. Ron what piston sizes were the C2 Vette 4WD cars to compare here? They had 4 piston calipers front and back and the manual brake cars used a 1" MC that most the aftermarket folks copy for their kits.

[Ron Sutton]

My 79 Camaro the upper pair of studs lined up the MC with the pedal hole better when I converted it to manual. Ron what piston sizes were the C2 Vette 4WD cars to compare here? They had 4 piston calipers front and back and the manual brake cars used a 1" MC that most the aftermarket folks copy for their kits.

Skip I don't know what pistons sizes the C2's came with. Probably could be figured out with a little internet research, but I'm sure Tobin from Kore 3 knows.

[Skip Fix]

Ron from what I pull up C2,C3 systems used 1 7/8 four piston calipers in front and 1.37" four piston calipers in rear.

Almost every basic aftermarket replacement disc system uses the 1" MC copy.

[blown69nova]

So, can I use d614 pads in place of the d52's? Stock iron calipers and rotors.
Thanks, Steve

[Skip Fix]

Yes D614(Impala SS/Caprice cop car) pads will fit D52s and have more surface area. I've trial fit them on stock iron calipers as well as the Wilwood dual piston D52s. They are on the 81 TA and 1LE 12" rotors up front when it gets rolling again.

[blown69nova]

Thanks for the info.

[blown69nova]

Well, I got my 1" wilwood master installed and tested. They definately feel better, like you might expect a "factory" system to feel. It takes less effort to achieve better braking.
Thank you guys for all your advice.
Now I need help finding some good pads. The problem I'm finding, is matching them. The d52's are no problem, but the explorer rears (d667's) only seem to be available in hd suv style, except the EBC yellowstuff. How do you guys think those would work for a street strip car? The car is about 3,600lbs with my big butt in it.