Wilwood stopping power

[65 drop top]

I have a 65 Chevelle with Wilwood 14" rotors with the forged narrow superlite caliper 6 pistons front and 13" 4 piston rears. 7/8" manual master and bp 10 pads. Car has upgraded bolt-on suspension and 235/255 mm Nitto extreme 555 tires. Normal stopping from stop light to stop light seems ok. But when I stomp on the brakes the car seems to stop ok, but nothing overly impressive. I also can't get them to lock up, front or rear. I feel like I should be getting more stopping power than it is. I'm thinking about trying bp 20's up front to see if that helps any. But I also don't want pads that'll dust up too much I have fully polished billet wheels.

[andrewb70]

No air in the system?

Andrew

[65 drop top]

No air in the system?

Andrew

I don't think so. I just had the master off for the Wilwood recall. I did a bench bleed and then went around the calipers multiple times and I was getting fluid only(after the initial few bubbles). The pedal has a very slight travel then becomes very solid. It doesn't feel overly mushy either considering its a 7/8". I can feel the extra travel, but it does feel firm.

[dontlifttoshift]

If it's not a race car I would put power on it. Stopping force comes from two things, pressure and friction, you need a lot of one if you don't have a lot of the other. A little of both does the job also.



The E pads are so much better but not what I would call "low dust" and they can be "not quiet" sometimes, too. If you look at the chart you will see that 20s will be a step backwards on a street car.

[65 drop top]

I don't want to put a power booster on it, even with the trade off of less braking power. Are there any other aftermarket pads that I could use other than Wilwood's? Something low dusting but more aggressive that the bp 10's?

[dontlifttoshift]

Nothing I can think of. I have had good luck with CarboTech or GLoc but they are definitely not low dust.....Maybe the Carbotech 1521s but I have no experience with them.

[rickpaw]

Is your brake pedal ratio correct? IIRC, there are two holes on the brake pedal. One for manual, one for power brake.

[kevmurray]

I have a 65 Chevelle with Wilwood 14" rotors with the forged narrow superlite caliper 6 pistons front and 13" 4 piston rears. 7/8" manual master and bp 10 pads. Car has upgraded bolt-on suspension and 235/255 mm Nitto extreme 555 tires. Normal stopping from stop light to stop light seems ok. But when I stomp on the brakes the car seems to stop ok, but nothing overly impressive. I also can't get them to lock up, front or rear. I feel like I should be getting more stopping power than it is. I'm thinking about trying bp 20's up front to see if that helps any. But I also don't want pads that'll dust up too much I have fully polished billet wheels.

• Which piston sizes for front and rear? They are available in many different sizes. If you can provide the part numbers that is fine.
• What are you using for a proportioning valve? How did you come to the current adjustment?
• What is the distance from master cylinder rod clevis to the pedal pivot point?
• What is the distance from the pedal foot pad to the pedal pivot point?
• 235/40/18?
• 255/45/18?
• Need to know exact sizes to look up wheel diameter.

[65 drop top]

• Which piston sizes for front and rear? They are available in many different sizes. If you can provide the part numbers that is fine.
• What are you using for a proportioning valve? How did you come to the current adjustment?
• What is the distance from master cylinder rod clevis to the pedal pivot point?
• What is the distance from the pedal foot pad to the pedal pivot point?
• 235/40/18?
• 255/45/18?
• Need to know exact sizes to look up wheel diameter.

4.04 front 1.98 rear piston areas
Baer proportioning valve in rear brake line, fully open
Pedal ratio is stock manual, which is about 6:1. I can't measure it right now, but recall it being normal ratio when I did.
235/35/19 front and 255/35/20 rear

[kevmurray]

These are what I understand your specs to be, correct me if I'm wrong on anything:

Pedal:
Manual position (top)
Ratio 6:1

Booster:
None

Master Cylinder:
Dual pot, 7/8" piston
Area = 0.6in²

Front:
Caliper: FNSL6 (1x 1.62, 2x 1.12 pistons ~4.04in²)
Rotor: 14"
Wheel Dia: 25.5"
Pads: BP10

Rear:
Caliper: FNSL4 (2x 1.12 pistons ~ 1.98in²
Rotor: 13"
Wheel Dia: 26.6"
Pads: BP10

Using a reference leg force of 100lbs this calculates out to 2500lbs total stopping force at the tire patch. According to Ron this equates to the average passenger car so with those upgraded tires I can see why you are unable to achieve lockup. I would never question Ron's wisdom, maybe something was changed from his design or he was given bad info? Those calipers have a very small piston area to go without a booster. The front bias is a nice 70% which should not need much proportioning to be ideal.

[65 drop top]

These are what I understand your specs to be, correct me if I'm wrong on anything:

Pedal:
Manual position (top)
Ratio 6:1

Booster:
None

Master Cylinder:
Dual pot, 7/8" piston
Area = 0.6in²

Front:
Caliper: FNSL6 (1x 1.62, 2x 1.12 pistons ~4.04in²)
Rotor: 14"
Wheel Dia: 25.5"
Pads: BP10

Rear:
Caliper: FNSL4 (2x 1.12 pistons ~ 1.98in²
Rotor: 13"
Wheel Dia: 26.6"
Pads: BP10

Using a reference leg force of 100lbs this calculates out to 2500lbs total stopping force at the tire patch. According to Ron this equates to the average passenger car so with those upgraded tires I can see why you are unable to achieve lockup. I would never question Ron's wisdom, maybe something was changed from his design or he was given bad info? Those calipers have a very small piston area to go without a booster. The front bias is a nice 70% which should not need much proportioning to be ideal.

Yes, I'd agree with them being equal to the average passenger car. They stop ok, not good but not too bad. I guess I was just expecting a little more out of them. At the time, this was the best kit a Wilwood offered for my car. It had the largest piston area too. Now I see Wilwood has an aero6 kit, but I'm not gonna redo the brakes.

What would happen if I went with a 15/16 master? I understand pedal effort would increase, but how much more braking force could I make? And would the 15/16 require too much leg effort to be comfortable on the street?

[kevmurray]

...What would happen if I went with a 15/16 master? I understand pedal effort would increase, but how much more braking force could I make? And would the 15/16 require too much leg effort to be comfortable on the street?

That's actually going the wrong way. It would increase the leg effort and lower the line pressure. Your current setup will provide 2485lbs of brake force at the tire patch. Going to a 15/16 master would put you at 2165lbs while reducing the pedal stroke. If you have the stroke available going to a 0.750" master would bring you up to 3382lbs. I don't think anyone offers a 13/16 but a free option would be to raise the clevis a half inch or so, but would require fabrication. Otherwise it's going to require a booster of some sort. Maybe you could try a dual 7" if space is an issue?

[badolds]

Your brakes are just a hydroboost away from being awesome, just sayin. HIGH DROW BOOST = STOP TIME REDUCED. haha

Dan

[a67]

Just need better pads and a smaller M/C, simple as that. I have the total braking force lower at 2434 pounds. And this is with the pad mu at .45, which the BP-10s don't reach until they are at 700° F. At 100° F the mu is .40 for 2166 pounds of total at the tire stopping power. Not going to stop that well with this set up.

If we change to the E compound, same braking at 100°F, but at 500°F the mu is about .475, into the lower end of the G range. Which provides 2572 pounds of brake force. Better but still not great.

So, keep the E pads and fit a 3/4" bore MC:

At 100°F, a total of 2944 pounds of braking force.

At 500°F, a total of 3496 pounds of braking force.

That will work.

Bob.

[kevmurray]

Just need better pads and a smaller M/C, simple as that. I have the total braking force lower at 2434 pounds. And this is with the pad mu at .45, which the BP-10s don't reach until they are at 700° F. At 100° F the mu is .40 for 2166 pounds of total at the tire stopping power. Not going to stop that well with this set up.

If we change to the E compound, same braking at 100°F, but at 500°F the mu is about .475, into the lower end of the G range. Which provides 2572 pounds of brake force. Better but still not great.

So, keep the E pads and fit a 3/4" bore MC:

At 100°F, a total of 2944 pounds of braking force.

At 500°F, a total of 3496 pounds of braking force.

That will work.

Bob.

Bob,
He doesn't want pads that dust because of his nice wheels. Just curious, what did you use for rolling wheel diameter and effective rotor diameter? I'm wondering where my calculations differed from yours.

[a67]

Bob,
He doesn't want pads that dust because of his nice wheels.

Then he should swap to drum brakes...

Just curious, what did you use for rolling wheel diameter and effective rotor diameter? I'm wondering where my calculations differed from yours.

For the tire diameters I used what is listed.

For the rotor diameter I subtracted 2 inches. This is approximately the center line of the pad (1 inch of radius). Not all of the pad is exerting force at the outer diameter of the rotor, there is more pad at the smaller diameter.

Bob.

[GoodysGotaCuda]

FWIW, I have a similar setup with my 'Cuda using 7/8" bore with 6piston/4piston Wilwoods. However, I have a -very- long stroke and am able to go completely around the Wilwood 1500psi caliper pressure gauge [~3000psi?]. The stroke required is unusable, however. I have it raised ~1" over stock and can nearly get it to the floor. I'm a scrawny 150lb desk-worker, by no means someone with significant leg strength.

I will likely go to a 15/16" or 1" master cylinder this Winter, I will take the higher force/in of pedal travel.

[H8rDave]

Save your money. Starting with the pedal ratio of 6.0 - 1, you stated that the pedal has "very slight travel, then becomes very firm". OK, so, that's hard to modulate, with less feel, and it doesn't stop. Changing the pedal ratio to 7-1 (a 17% total output increase, or even 7.5 - 1 (a 25% total output increase) may be a smarter solution. Remember that these aftermarket brake companies build RACING brakes, and are designed to use RACING pads, with Race Car Drivers pounding away at them. Then, we want docile, smooth, clean and quiet from them. Not going to happen. Yes, you will have more pedal travel, but this = more pedal feel, not such a bad thing. So, pull out your pedal, do the math, and drill a 3/8" hole. If you don't like it, move it back. No loss. BTW, an OE GM full size caliper with a 2 15/16" bore has 6.775 sqin of piston area. This caliper on a 12" rotor, in your same system, would build just over 4000 lbs brake force on the front. I know it's not as flashy, but it stops 5000 lb cop cars with no problem. H8 on.

[Ron Sutton]

These are what I understand your specs to be, correct me if I'm wrong on anything:

Pedal:
Manual position (top)
Ratio 6:1

Booster:
None

Master Cylinder:
Dual pot, 7/8" piston
Area = 0.6in²

Front:
Caliper: FNSL6 (1x 1.62, 2x 1.12 pistons ~4.04in²)
Rotor: 14"
Wheel Dia: 25.5"
Pads: BP10

Rear:
Caliper: FNSL4 (2x 1.12 pistons ~ 1.98in²
Rotor: 13"
Wheel Dia: 26.6"
Pads: BP10

Using a reference leg force of 100lbs this calculates out to 2500lbs total stopping force at the tire patch. According to Ron this equates to the average passenger car so with those upgraded tires I can see why you are unable to achieve lockup. I would never question Ron's wisdom, maybe something was changed from his design or he was given bad info? Those calipers have a very small piston area to go without a booster. The front bias is a nice 70% which should not need much proportioning to be ideal.

Hey Kevin !

I agree with you. This package has too small of piston area for a manual system. FYI ... I didn't design nor sell this system. What he needs is more piston area front & rear. The issue is the Superlite caliper isn't rigid enough to handle more clamping force. The calipers will simply flex. Frankly I don't sell Superlite caliper front brake systems anymore. The Wilwood Aerolite 6 calipers are much better, much more rigid calipers. For manual systems, we increase the piston area to 5.40" with the Aerolite 6. In the rear, we run Superlites with either 2.46" or 3.00" piston area & balance the system with proportioning valve or bias bar. *The Superlite caliper works well with smaller piston areas. It's when it get up around 5" is where we start to see clam shelling of the caliper & mushy pedal.

Now for this particular application, a Aerolite brake kit may not be available from Wilwood. In that case, each of his options comes with negatives:
* Higher CoF brake pads, like BP20s, Hawk HP+, etc will create more braking force, but cost more, wear out quicker, wear rotors quicker, squeal & dust the wheels
* Switching to a power booster will create more braking force, but the calipers will flex & pads will wear uneven.
* A smaller master cylinder will create additional hydraulic force & more braking force, but will make the calipers flex the same as if they had larger pistons.
* With a power booster, the driver probably won't feel the caliper flex & the pedal will feel firm. Not so with smaller master cylinders.

Just my 2¢.

[AMC Racer]

Hi Ron,

Sorry for the hijack, but does the extra thickness of the FLSI or FSL4R/FSL6R (... assume the FSL4R/6R have better stiffness than FSLI) give noticeably less deflection than the FNSL4R/FNSL6R (narrow Superlites are in most kits ... assume to more easily fit stock wheels)?

Also, how would you rate a GN6R vs. the narrow-body Aero calipers in most kits? Been considering a GN6R front / FSLI rear combo.

Thanks.