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?

https://static1.pt-content.com/images/pt/2010/03/1LE_HawkPads-1.jpg

[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.

[BonzoHansen]

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

[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

[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?

[ProdigyCustoms]

Yes the 614 pad fits

[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

[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.

[Skip Fix]

Bob I have one in my storage space I'll drag out this weekend. Want to weigh it also to compare weight.

Also got a rear caliper with the piston out to measure.

[critter]

If Skip doesn't. I might have one in the attic but I really don't want to go up there on these 100 degree days.

[Skip Fix]

I might have one in the attic but I really don't want to go up there on these 100 degree days

Amen!

I'm assembling a motor in the garage and keep dripping sweat in it making the deck get rust spots!

[67 455 Bird ragtop]

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.

I have several in my garage that are easy to access. What exactly do you guys want measured?? Some are even still disassembled. So shouldn't be to hard to get the measurments you want.

And just to be clear. We are talking about the large stock single piston front calipers. Right ???

[critter]

Correct. The OD measurement of the piston is what's needed if I'm understanding all this correctly.

Skip, suspension work in my garage so it's a little less critical. I'm just sweating on the greasy parts coming off right now. :)

[67 455 Bird ragtop]

Correct. The OD measurement of the piston is what's needed if I'm understanding all this correctly.

Skip, suspension work in my garage so it's a little less critical. I'm just sweating on the greasy parts coming off right now. :)

OK I took a measurement of one of my pistons then double checked it by going online to Rock Auto. So, I'll use Rock Auto's measurements which is 2.934" diameter. So basic calculations yields 6.761 sq/in.

Hope this helps.

[a67]

OK I took a measurement of one of my pistons then double checked it by going online to Rock Auto. So, I'll use Rock Auto's measurements which is 2.934" diameter. So basic calculations yields 6.761 sq/in.

Hope this helps.

Can you post the piston diameter? Rock Auto lists the bore diameter. Which we don't care about.

To measure the piston OD will need to use a set of dial calipers (no pun intended). Or a fancy digital set. A steel rule most likely won't cut the mustard.

Thanks.

Bob

[67 455 Bird ragtop]

Can you post the piston diameter? Rock Auto lists the bore diameter. Which we don't care about.

To measure the piston OD will need to use a set of dial calipers (no pun intended). Or a fancy digital set. A steel rule most likely won't cut the mustard.

Thanks.

Bob


Actually they list this as the piston diameter not bore diameter.

RAYBESTOS Part # DPS85010 https://static1.pt-content.com/images/pt/2010/07/MoreInfo2-1.png Professional Grade; 1.95" Overall Length / 2.934" Piston Diameter / Steel
Front; Steel

[a67]

Actually they list this as the piston diameter not bore diameter.

RAYBESTOS Part # DPS85010 https://static1.pt-content.com/images/pt/2010/07/MoreInfo2-1.png Professional Grade; 1.95" Overall Length / 2.934" Piston Diameter / Steel
Front; Steel

And these are listed under the '70 Camaro and the same size as bore diameter:

RAYBESTOS Part # FRC4059 More Information About this Part Professional Grade; Friction Ready - Pads Not Included, Remanufactured; Bore Size=2.94"

Which is rounded up from 2.9375. Which when combined with the other value, a piston to bore clearance of 0.001,75". Which is real tight, too tight.

This is why it is important to get measurements from actual parts.

Bob

[67 455 Bird ragtop]

I'll look and see if I have a front caliper I can take apart. All I could find in the garage were rears which are different piston sizes. But the bore is 2 15/16 which is 2.9375. Subtract the piston size of 2.934 and you get a gap of .0035. Not all that tight if you've ever rebuilt these things. They are a snug fit.

Ok I went out and pulled down one of my front calipers and popped the piston. I had been contemplating stripping and repainting them so this gives me an excuse. I used a digital caliper on the piston and it indeed measured 2.934". And these are stock original pistons. They just don't have much use on them since I haven't driven my car since 1990 and I did the switch over in 1982 using a junked 1970 Chevelle disk brake setup.

[critter]

So it appears that our original assessment on how the brakes will react to the change in caliper is the same. While there will be a slight increase in brake performance with the swap one shouldn't expect earth shattering differences in the feel or reaction of the braking system.

[67 455 Bird ragtop]

Bob I have one in my storage space I'll drag out this weekend. Want to weigh it also to compare weight.

Also got a rear caliper with the piston out to measure.

I weighed one of mine when I pulled it out to measure the piston diameter. I used our digital bathroom scales and did the old weigh myself holding it and not holding it. The caliper weighed right at 10lbs without pads.

Also, you'll find the rear caliper piston bore will be a little smaller than the fronts based on my experience with the rears. Closer to 2 1/8" bore and they use 154 pads I believe. At least the Caddy rears with parking brake calipers I'm using are setup this way.

[a67]

I'll look and see if I have a front caliper I can take apart. All I could find in the garage were rears which are different piston sizes. But the bore is 2 15/16 which is 2.9375. Subtract the piston size of 2.934 and you get a gap of .0035. Not all that tight if you've ever rebuilt these things. They are a snug fit.

Ok I went out and pulled down one of my front calipers and popped the piston. I had been contemplating stripping and repainting them so this gives me an excuse. I used a digital caliper on the piston and it indeed measured 2.934". And these are stock original pistons. They just don't have much use on them since I haven't driven my car since 1990 and I did the switch over in 1982 using a junked 1970 Chevelle disk brake setup.

Thank you for measuring the pistons. As for the "get a gap of .0035", you need to divide it by 2 for the clearance. As there is clearance on each side of the piston (hopefully equal).

Using this information lets then go back and compare the Wilwood D52's to the stock D52's:

Wilwood: dual 2" pistons, 6.28 SqIn
GM D52: single 2.934", 6.76 SqIn

Now, what kind of difference is this: 6.28 / 6.76 = 7.1%

This is a 7.1% difference in brake pedal pressure for the same clamping force. Which is 107 pounds on the stop pedal vs. 100 pounds on the stop pedal.

Is that enough to worry about. And, since you are serious about braking, do not the higher friction pads make up for this. And, does the better braking feel mean anything.

I know the answers to this for one of my cars. Because in the front brake swap I gave up more then that in clamping force. And have absolutely no qualms about it. It was/is a very good trade off.

Bob

[Skip Fix]

You saved me a trip to the storage place-well I got to drop a check by today anyway. At least not digging in there with 95 and 100% humidity-rained last night supposed to again today.

I'll measure one of my WS6 rear caliper pistons. Wilwood is supposed to be coming out with a dual piston metric caliper that would fit the rears, just no E brake.

Here is a picture of the caliper the Hawk pads on a GM 1LE rotor. Slides right on.

[Skip Fix]

Cast Iron on a dgitial is 8lbs 15 oz(8.94)

Also the rear WS6 caliper piston is 2.492" where it rides on the O ring. Smaller on the outer portion that has the pad clip groove. Not sure how that compares to the Caddy rera calieprs or the Explorer calipers with the integral E brake.

[critter]

A little under 3.5 pounds per side in weight savings then. That's unsprung weight as well. That alone is a big help.