D52s and pads

[Skip Fix]

Here are some pictures of the new D52s and the Wilwood BP-10 pads vs the Hawk D61 police pads.Mainly the outboard is larger almost 1.25" at the top(look at the locating holes as a reference) and maybe .3-.4 at the bottom. Inboard pad no that much different. They are a very stout caliper, and take a banjo hose like stock vs 1/8 NPT like most Wilwood calipers. 5lbs 6 oz. The Wilwood pads do look like they have more organic in them than my Dynalite or Metric GM BP-10 pads-lighter not as black or hard.

[BonzoHansen]

I need to call Frank and get me a set of those calipers. Is this the same impala part# you used?

[a67]

Note that the pad with more face material it is a D614 pad. The D61 fits an Austin Healy or some such British car.

Just to add a bit more info, the D614A pads have a thicker layer of friction material. Because of this they won't fit in a stock D52 caliper over a stock rotor such as found on a '69 GTO.

Bob

[ProdigyCustoms]

Glad you got them Skip. They are purdy for sure.

[BonzoHansen]

What ones did you get? I assume you got ones with 2" pistons, but did you get the wider ones?

Part#		Piston Area	Rotor Width	Piston Dia
120-10936-RD	6.28		1.28		2"
120-10937-RD	6.28		1.04		2"
120-10938-RD	2.46		1.28		1.25"
120-10939-RD	2.46		1.04		1.25"

I believe the stock caliper has one 2.94” piston, so I think that is a 6.78” piston area, and the WW calipers with 2” pistons has a 6.28” piston area. If my math is right then what impact does the reduced piston area have on braking? I don’t have enough practical experience, I don’t know if 2 vs 1 piston changes things.

[Skip Fix]

The pads together are only 0.050 thicker than the Wilwood pads.

Yes I got the Hawk number here, I think from you.

I've wondered the piston size difference even when talking to Baer about their system being better.

[critter]

I'm no expert but I seem to remember my experience being that the more piston area scenario resulted in a soft pedal and less being a high hard pedal. MC bore size plays into the total balance of the deal.

Frank, I want the black D52s but I'm still waiting on a check. Sigh. I'm sure they're all sold by now.

[Skip Fix]

Then there is the argument about two pistons giving more even pressure than one single. Kind of the same deal if you actually compare a stock caliper to a C5 caliper.

I'll have to weigh one of the cast iron calipers this weekend to get an idea of the weight savings.

[Apogee]

Multiple piston caliper designs generally provide better support for the pads, and can have staggered diameters to help address uneven wear/taper. If you've ever seen somone push the D52/614's past their limits on a heavy car, it's not that uncommon to see the pad backing plates permanently deformed into a "W" shape over the piston. One piston equates to essentially two line-contacts, two pistons double that to four line-contacts.

Multiple-piston calipers do not generally have more piston area than many of the single piston calipers they replace. Less piston area means less clamping force for any given pressure. As such, calipers with smaller piston areas are generally intended to be run at higher corresponding pressures. Higher pressures (within reason) typically provide better feedback and modulation so long as the mechanical (pedals) and hydraulic systems are modified appropriately to suit the calipers being used.

If maximizing brake torque was the do-all, end-all of brakes, everybody would be running massive single-piston calipers. The fact that no manufacturer, OE or aftermarket, is in fact trending that direction should be a good indication that size, in this particular case, may not matter as much as configuration and good system design and/or execution.

Just a side note regarding Bob's comment regarding the D614A pads, they were used on the 9C1 police applications where the caliper piston faces were cut down by about .09" IIRC. Without the shorter piston kit, they're won't fit over a standard thickness rotor.

Tobin
KORE3

[BonzoHansen]

Skip, which part# caliper did you get? The wider one?

[SLO_Z28]

Ive asked a couple places but never got an answer, does the 614 pad fit in the wilwood caliper?

[critter]

Torbin, as always, great information.

With my current WS6 rear disc and 1LE front brakes on my 1974 Trans Am I have very responsive brakes. Swapping on these calipers presents a smaller total piston area. Should I expect my brakes to become more "touchy" due to the swap?

[a67]

Torbin, as always, great information.

With my current WS6 rear disc and 1LE front brakes on my 1974 Trans Am I have very responsive brakes. Swapping on these calipers presents a smaller total piston area. Should I expect my brakes to become more "touchy" due to the swap?

1LE front brakes use a 2-piston aluminum PBR caliper. So not sure what you are changing for.

The D52 caliper does not necessarily have a larger pressure area then the Wilwood calipers. Simply because it is piston diameter not bore diameter that counts. The seal is fixed in the bore and does not contribute to the pressure.

And the piston diameter is smaller then the bore diameter. IIRC, when I did the math a while back the piston area between a stock D52 and Wilwoods dual 2" piston D52 was darn near the same. Not enough difference to even consider.

Now, when talking master cylinders, the seals are attached to the pistons. So in this case bore diameter is used for pressure calculations. As both the piston and the seal is used to move fluid and create pressure.

Bob

[ProdigyCustoms]

Yes the 614 pad fits

[critter]

When I say "1LE" I'm talking about a popular mod for us second generation F-body guys who would use a B-body spindle and the 1LE rotor with our stock D52 calipers. This would all fit inside a 15 inch wheels. Sorry. I should have explained that better.

I'm guessing a swap to the new Wilwood D52 calipers would not result in a major change in brake response. For me it would be strictly a cosmetic change with the added benefit of weight savings. So that leads to the next question for me. Do I spend the money on these calipers or yank all this off and spend more money to go to a 13 inch brake up front since I'm now running 18 inch wheels? The cost of investment is significant for the bigger setup and I don't put this car on track more than once a year. Decisions, decisions...

[Skip Fix]

Those pictures are of the 614 pad in the wilwood caliper. They are only slightly thicker than the Wilwood pads so I would expect they should fit. I'll toss them on a GM rotor this weekend too. I'm pretty sure there are different thickness 614 pads.

My calipers are for the 1.04 disc I believe. I'll look again tonight.

I guess the big question that Critter touched on- is this(or a Baer twin piston 12" rotor system) an actual improvement on brake performance over the big single piston caliper on a same sized rotor?? Especially if coupled with the single piston rear caliper like the WS6 TA calipers.

[critter]

Uh huh. That's exactly what I'm saying. But I do like the idea of being able to slap the 15 inch Rally II wheels and tires back on from time to time for the old school look.

[a67]

The aluminum Wilwood D52 calipers will provide at least two benefits over the stock iron D52's. The first is less un-sprung weight. Which will provide better handling along with a better ride.

The second, which Tobin touched on, is that the pressure against the pad during braking is more even across the backing plate. This provides a better feel to the brakes. Which in turn makes it easier to control the level of braking.

Bob.

[Skip Fix]

My guess would be subtle improvement not dramatic with either of those over the cast iron calipers. As long as the performance should be as good they'll go on the car. But again it has a decent size single piston rear caliper to match with.

Kind of like our discussion on hollow vs solid sway bars and an 8 lbs weight saving showing track improvement

I think most of us second gen F body and A body folks think of the "1LE swap" as 12"(roughly) rotor on a B body spindle and the single piston 2 15/16" cast iron caliper.

I still get 6.74 sq in single vs 6.28 for 2 2" when I do the math. I do agree with a single piston you only get two contact surfaces, and some are thinner than others depending on the piston.

One good thing the new calipers do have O ring supports on the outer area for the bolts to glide on unlike some of the other replacement GM Wilwood calipers.

[a67]

I still get 6.74 sq in single vs 6.28 for 2 2" when I do the math. I do agree with a single piston you only get two contact surfaces, and some are thinner than others depending on the piston.

As I posted, with calipers it is piston diameter, not bore diameter that matters. Yes, with a 2-15/16" bore it will have 6.77 sq/in of area.

But the piston is smaller. Lets use a 1/16" smaller diameter then the bore. Which gives .031" clearance between the bore and piston.

Now the piston area, which is what counts, is 6.16 sq/in of area.

Which is smaller then the Wilwood's.

So, where does this lead? Anyone have a stock GM D52 piston around that they could accurately measure? This is the only way to be sure of the true piston area.

Bob.