? on manual brakes

[JIM1]

It is a cast iron disc/drum unit.

Tobin
KORE3

Thanks Tobin, are the resorvoirs reversed on that unit? I had heard that somewhere. Here is what I have....
I used to have a power booster setup, but now it is a manual setup. Low vacuum forced this plus I have a lot more room to work in there with no booster.
I have the Wilwood Dynalite Pro front dics kit on my Chevelle. (kit #140-2285). Rear is stock drums. Braking was marginal before with my stock discs, now it is terrible. Hard pedal. From what I can see, the total square inch surface area of these Wilwood 4-piston calipers is 4.80 sq-in. My old calipers (stock GM) were 6.5 sq-in surface area. GM used a large diameter piston compared to the 4 small pistons that Wilwood uses. What Master Cylinder are you guys using with your Wilwood kit? It would seem that I would need to use a smaller bore MC to make up for the smaller bore calipers, but Wilwood says not to do that. Stock was 1-1/8" when i had the power brake booster. Tried that with no booster and the pedal was rock hard and I had to stand on it to barely slow the car down. I have a 1" bore now and while a bit better, it still sucks. I saw a Wilwood 7/8" MC, but the tech at Wilwood said it would give me way too much pedal pressure. Kind of sounds like what I needed. So I tried it and it gave too much pedal travel to stop the car and the pedal felt mushy. So I removed it and went back to the 1" bore. What are you guys using with this kit/setup that I have?
Wilwood Dynalite pro up front
Manual brake setup with rod in top hole of the brake pedal
1" bore MC for disc/drum
Stock style combo valve on frame from CPP (their PV2 valve assy)
All new lines front to rear
stock drums in the rear
Power bled everything with a Motive power bleeder
Hard pedal, not much travel and I have to press real hard to stop the car.

[Apogee]

First, unless I'm missing something, you are not you're running KORE3 kits, so I'm not sure what you mean when asking about "your Wilwood kit", as it is Wilwood's kit, not ours. The Wilwood kit that you're running is what I would consider to be a step up from factory drum brakes but comparable or even a step down from the OE A-body disc brakes...Wilwood #140-2285 uses a 10.75" diameter rotor verus 11" for the OE, and it measures only .81" thick versus 1" for the OE, making it both smaller and with less thermal mass. This would be a great kit for a pro-street drag car as it is light and has minimal inertia, but is not what I would choose for either street or track (road course, auto-x, ect) performance on a 3000# car, let alone something that probably weighs in closer to 3700#. While the Wilwood kit does have more pistons providing good, even pad support, you still have less piston area at 4.80 sq-in versus 6.7 sq-in as you noted. Ignoring the minimal change in rotor diameters, you'll need approximately 30% more pressure at the calipers to achieve similar brake torques due to the differenc in calipers alone assuming comparable pad compounds.

That said, in an application where we're running C5/C6 discs up front (4.0 sq-in piston area) and factory drums in the rear, we're usually running a 7/8" to 15/16" bore master cylinder in manual applications. I would probably lean towards the 15/16" for your application given the slightly larger piston area relative to the C5/C6 calipers and the fact that you still have drums in the rear. This would make the 76-77 Malibu unit a good choice IMHO. The reservoirs on this particular MC are "reversed" assuming you mean front to rear outlet port and rear to front outlet port, basically the large reservoir is for the disc brakes, true for any disc/drum master cylinder regardless of configuration.

I'm guessing that whoever told you not to reduce your master cylinder bore size when moving from OE to aftermarket discs with less piston area was mistaken or didn't understand the hydraulics of the situation fully, as that is exactly what sizing a master cylinder is about. You need to take your pedal ratio, rotor diameter, caliper piston area and pad compounds into consideration and one change to any of them can then require a change to one or both of the others.

Tobin
KORE3

[JIM1]

Tobin,
My apology for the confusion. When I said "what are you guys using with your Wilwood kits" I was referring to basically anyone that was reading the thread that was using Wilwood front disc setup. I didn't mean you in particular. Sorry.
Admittedly, when I purchased the Wilwood kit, I was more interested in weight reduction and did not calculate the piston size. Bad decision on my part. That was a hard lesson to learn. I am kind of stuck with the configuration now as it would be too costly to redo the front braking systemagain. So perhaps that 15/16" MC that you speak of may help my issue. At least that would be an inexpensive test/route to go. Thanks again for the detailed information and explanation.
BTW, Tobin...does your company offer a 15/16" MC with standard port configuration so that it would be a plug/play without me having to re-route my brake lines at the MC?

[Apogee]

Sorry, but we do not, and there really aren't that many aftermarket options in that size. The three most popular 15/16" [24mm] bore master cylinders at the moment based on our customer base would probably be the 76-77 Malibu disc/drum unit (reverse port configuration), the CPP 15/16" C3 Corvette knock-off disc/disc unit (standard port configuration) and the 24mm bore DSE unit that looks a lot like either a G-body or GMF3 quick take-up aluminum unit (reverse port configuration). We do stock the Wilwood tandem master cylinders in 7/8" and tend to use those as our default with manual C5/C6 brake setups.

You haven't mentioned what you're running for pads, however they can make a huge difference in your stopping power and brake feel. A 1/16" reduction in bore size from a 1" to a 15/16" is going to net you about 12% more pressure and pedal travel. Moving to a 7/8" would be double that. A change from a .3 coefficient of friction pad to a .4 would be a 33% increase in brake torque...you do the math as to which gets you where you want to be quicker.

Tobin
KORE3

[JIM1]

...You haven't mentioned what you're running for pads, however they can make a huge difference in your stopping power and brake feel.

Tobin
KORE3

Pads are #150-8850K (came with the kit).
#120-6816 Forged Dynalite caliper.
I will do some math and see what combo of MC and pads would equate to at least the front clamping force I would have with the larger GM caliper and a power disc setup. I tried the Wilwood 7/8", but never liked the feel of it. Also was a bitch to bench bleed. Maybe I got a bad one?? Thanks again for the info.

[a67]

Pads are #150-8850K (came with the kit).

It's the pads, they are the BP-10 compound. There is another thread here where someone else had the same problem, couldn't stop the car. Switched to the BP-20 compound (IIRC) and it was night & day difference.



Bob.

[Skip Fix]

The Dynalites also use a smaller pad than many OEM GM calipers.

[Skip Fix]

So on the topic of pad coefficients how do you find that out Tobin? Manufacturers like Wilwood have it listed?

I know alot of strictly autocross guys who used soft pads since they rarely warmed up like the semi metallics took. Figure drag cars also a softer pad since fade is not as big a deal.

[Apogee]

So on the topic of pad coefficients how do you find that out Tobin? Manufacturers like Wilwood have it listed?

I know alot of strictly autocross guys who used soft pads since they rarely warmed up like the semi metallics took. Figure drag cars also a softer pad since fade is not as big a deal.

Wilwood publishes the coefficient of friction curves for all of their friction compounds, and kudos to them for doing so, as not all friction suppliers are so generous with technical data.

http://www.wilwood.com/BrakePads/BrakePadsApp.aspx

Some may argue that it isn't fair or particularly informative to compare friction compounds by their CoF due to the somewhat non-standardized testing procedures used to determine them, however I find it useful information to at least compare friction compounds and performance within a specific manufactures range of compounds. Plus, the CoF versus temperature curve lends itself to how linearly the pad behaves throughout it's temperature range, something some pads do much better than others. Brake dynos are somewhat similar to engine dynos as the absolute numbers can vary from dyno to dyno, so absolute comparisons from brand to brand may not be as fair or accurate as comparisons within one mafufacturers range of compounds, but they're still fairly indicative in my experience.

If you have some sort of generic pad of unknown origins, the best you're probably going to get is the alpha-code in the manufacturing stamp for the hot and cold CoF range, typically "EE", "FF" or "GG" for most of things we play with. Each letter represents a range for the CoF with E=.25 to .34, F=.35 to .44 and G=.45 to .55. Most will be the same, however some compounds skirt the line and will have a "EF" or "FG" type rating.

Tobin
KORE3

[JIM1]

It's the pads, they are the BP-10 compound. There is another thread here where someone else had the same problem, couldn't stop the car. Switched to the BP-20 compound (IIRC) and it was night & day difference.

Bob.

How do I know mine are BP-10? I put the p/n into the Wilwood website and it comes up with a list of all friction CoF available for that p/n. There are like 10 different ones.
Then the first page says BP-20 is Street Performance/Racing pads. So I click on it and there is a caution that says race only, not for street! A street pad that is not for street???

[Bryce]

FYI,

EBC has CoF on their website.

[Apogee]

...Then the first page says BP-20 is Street Performance/Racing pads. So I click on it and there is a caution that says race only, not for street! A street pad that is not for street???

That's CYA-speak for "dusty, noisy" pads. Lots of people run them on the street, just don't whine about the dust or noise, simlar to the Hawk HP Plus and EBC Yellowstuff's.

Tobin
KORE3

[a67]

How do I know mine are BP-10? I put the p/n into the Wilwood website and it comes up with a list of all friction CoF available for that p/n. There are like 10 different ones.
Then the first page says BP-20 is Street Performance/Racing pads. So I click on it and there is a caution that says race only, not for street! A street pad that is not for street???

This link:

http://www.wilwood.com/BrakePads/Bra...emno=150-8850K

Right at the top, lists the pad plate footprint and the compound. Scroll down a bit and there is a graph that shows the different compounds CoF versus temperature. BP-20 is much better as the pads warm up over the BP-10.

Bob.

[JIM1]

That's CYA-speak for "dusty, noisy" pads. Lots of people run them on the street, just don't whine about the dust or noise, simlar to the Hawk HP Plus and EBC Yellowstuff's.

Tobin
KORE3

Gotcha, thanks again!

This link:

http://www.wilwood.com/BrakePads/Bra...emno=150-8850K

Right at the top, lists the pad plate footprint and the compound. Scroll down a bit and there is a graph that shows the different compounds CoF versus temperature. BP-20 is much better as the pads warm up over the BP-10.

Bob.

Yep, I see it now. I just ordered a set through Summit. I figure that is a real quick/easy test. Thanks for the info.

[Skip Fix]

Thanks for the info on pad coef. Comments on drag or autocross car pads vs track day needs?

I can tell you back in the day my semi metallic pads and shoes(yep there were a few companies that had semi metallic shoes for drums) sure didn't work good that first stop of the morning, then they were OK.

[Apogee]

Thanks for the info on pad coef. Comments on drag or autocross car pads vs track day needs?...

I'm probably going to catch flak for this, but drag brakes? Who cares? Drag brakes tend to be engineered so specifically for low-weight, low-inertia, rear biased applications that they're not really in even the realm of practical street brakes any more because they don't need to be, they just need to stop a car once from a high rate of speed over what would be considered a very long distance by street or road course standards. You get over certain speeds, and you have a parachute backup, so you can have even less brake. The brakes are more a function of roll control at the line than they are for slowing the car.

Good performance street and auto-x brake setups are actually quite similar. You want something that works well cold with a reasonably high initial bite...the stickier the tire, the higher the CoF pad you can tolerate, but your temperature range doesn't really need to be anything exceptional since most auto-x events are over a minute or two after they begin. Actual CoF can and will depend on the application, manual versus power, etc, but most tend to run FF or GG pads.

Road racing is in a class by itself. You can run street pads on a road course with respectable results (at least until they fade around 750 F), especially if you're running street tires. The faster you go, the stickier the tires, the harder the track is on brakes, the more you're going to want a track pad suited specifically to the course and car you're running. Driving style counts for a lot as well. If there was any single compound that served as the silver bullet, it would be simple and everybody would be running it. There are lots of opinions on what works best where, but it ultimately comes down to what you like.

Tobin
KORE3

[Yoda4561]

For weekend fun only drag racing regular old street pads work fine. 1960's 4 wheel drum factory brakes in good repair will reliably stop a car from 120 MPH (not repeatedly but that's not a big deal with drag racing).

[Skip Fix]

"they just need to stop a car once from a high rate of speed over what would be considered a very long distance by street or road course standards."

Depends on the track how long before the turnouts are! Chutes not needed until you start getting over 140 in the 1/4, which is a pretty darn fast car. OK street/strip car needs Bigger rear tires also affects the braking needs and design also I assume.

I agree driving style has alot of impact on braking needs. Some of us go into a turn a little too hot and need more brake