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Old 10-10-2019, 01:24 PM
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Brake Caliper Upgrade Question

I am using non-assisted GM front brakes. The brakes aren't bad, but they could be better. However I think I've gone as far as I can go; experimenting with different pads.

The calipers are GM D52 single pistons units with a 2.75" bore.

I was thinking of replacing them with a dual piston equivalent by Wilwood. Both pistons use a 2" bore. The pressure advantage by bore size is only 5.7% and there may be a small improvement as the force is spread further along the pads. There may also be a small improvement as the dual bores are slightly closer to the outside of the pads. But overall, it's probably not over a 6% improvement.

Currently, I can slow down pretty good, but I can't lock the wheels (yes, you shouldn't do that, but if you can, it tells you that there's adequate braking).

So, for a 6% improvement (to the front brakes only), do any of you think it is a worthwhile upgrade, or am I just wasting time and money for an insignificant improvement?

Thank-you.

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Old 10-10-2019, 02:02 PM
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What size master cylinder are you running. To get more pressure between pad and rotor you need a smaller master cylinder or bigger caliper/wheel cylinder.
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Old 10-10-2019, 03:42 PM
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Quote:
Originally Posted by Tim C View Post
What size master cylinder are you running. To get more pressure between pad and rotor you need a smaller master cylinder or bigger caliper/wheel cylinder.
7/8" for front brakes. Going smaller ought to increase pedal stroke a bit, which is fine where it is now. So am looking at a bigger bore caliper. Am just wondering of a 6% improvement will help me get from acceptable brakes to locking the tires. I have doubts, but I admit, it's a 50:50 thing.

Mind you.... to try it is expensive (only if it doesn't work) at about $500 Cdn for a new set of Wilwoods.
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Old 10-10-2019, 04:17 PM
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We went from the same GM caliper to a set of Wilwood double bore units on the front of our '75 Monza. This is a 2x3 tube frame car with an A-Arm front.


Disc size on the Wilwoods was slightly larger but the biggest advantage out of the package was the weight reduction. Stopping power is good but whether it is all that much better than the old setup is tough to say. I drive the car and I can only say that I think fade is less but the Wilwoods are drilled, thin type rotors and of course the stock stuff was not.



We use an adjustable pressure valve between the front and rear discs but have just left it 100% open so far. It's something that we need to experiment with in the future.
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Old 10-10-2019, 05:58 PM
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I re-checked your math and got 5.939 versus 6.283, for a 5.8% increase. Nope, not worth the worry in my opinion. I would want at least a 25% increase in braking if I were going to change calipers. at least 7.423 square inches of pad area.
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Old 10-10-2019, 09:41 PM
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Call Hawk or PPE for other pads options.
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Old 10-11-2019, 09:50 AM
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Or..
You could install dual calipers.


The amount of actual surface area that even a second set of cheap easy to replace anywhere in the country single sliding caliper pads will place on that rotor will get you over that 25% mark.

There is math, brackets, and more math involved. But look into it.
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Old 10-11-2019, 10:16 AM
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Quote:
Originally Posted by techinspector1 View Post
Nope, not worth the worry in my opinion. I would want at least a 25% increase in braking if I were going to change calipers.
Yes, I was thinking between a 10 and 20% improvement would be nice, although admittedly it's a difficult thing to quantify. More of a seat-in-the-pants feel at this point.

I guess bore size can be eliminated now and the questions are:

1/ Will dual pistons on a floating caliper be more effective, and if so has it been quantified?

2/ Would the fact that the two piston caliper has the pistons moved slightly further out contribute to any mechanical advantage? If so, can that be quantified? I would think so, but it's a bit unclear as it's the same pad located in the same place, so would more force along the outer part of the pad so anything other than to contribute to uneven wear...

Quote:
Originally Posted by johnsongrass1 View Post
Call Hawk or PPE for other pads options.
I went through this a bit a while back and am currently using Hawk HPS pads. They've been the best so far.

I can't find a co-efficient of friction spec for them, but I can for the Wilwoods. I think typical friction levels are in the 0.35 range. Many of Wilwoods are higher at approx. 0.46. Their highest street/race pad is 0.55 and their highest race/high temp pad is 0.68.

Supposedly I could get a huge improvement in braking by opting for one of the latter (assuming the Hawk pads are 0.46 or less, which of course I don't know)

I also don't know what trade-offs come with the higher friction co-efficient pads. Maybe they chew through the rotors really fast.....

Quote:
Originally Posted by cerial View Post
Or..
You could install dual calipers. The amount of actual surface area that even a second set of cheap easy to replace anywhere in the country single sliding caliper pads will place on that rotor will get you over that 25% mark.

There is math, brackets, and more math involved. But look into it.
If I am picturing this correctly, then I doubt it can be done (reasonably) as the steering knuckles won't allow it. Something complicated would have to be fabricated. Interesting idea though. Thank-you.
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Old 10-11-2019, 10:48 AM
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hmmm... maybe I did find something out on the Hawk pads. Apparently there's a code for friction material for all brake pads and can be found here:

https://www.autoserviceprofessional....hnology?Page=3

Although I need to check the edge of the pads for sure, there's an "F" in the P/N on the box which may well indicate 0.35 to 0.45 coefficient of friction.

I'll have to take a wheel off again to confirm.

Gives me a rough idea of where to start I suppose...
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Old 10-11-2019, 11:05 AM
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Youre over thinking this...

Your choices are....
Call a Pad supplier and ask for recommendations for what you wanting to do.
Go to a 3/4 MC for more pad pressure
Go to a caliper with a larger bore for more pad pressure
Go to a four piston caliper and related brackets.

That's pretty much it.

Wilwood and Hawk have already figured it out for you.
I understand what your getting at as far as being able to lock the brakes however it's best if that doesn't happen unless at max pedal pressure to maximize feel and not just for the sakes of warm fuzzies.
Smoothness, drivability and feel mean so much more.

Last edited by johnsongrass1; 10-11-2019 at 11:11 AM.
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Old 10-11-2019, 11:23 AM
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Quote:
Originally Posted by Argess View Post

7/8" for front brakes. Going smaller ought to increase pedal stroke a bit, which is fine where it is now. So am looking at a bigger bore caliper. Am just wondering of a 6% improvement will help me get from acceptable brakes to locking the tires. I have doubts, but I admit, it's a 50:50 thing.

Mind you.... to try it is expensive (only if it doesn't work) at about $500 Cdn for a new set of Wilwoods.
Increasing the caliper size will also change the stroke. The master will have to travel further to move the difference in fluid displaced by the larger caliper piston area just as it would have to travel further with a smaller master cylinder bore because it's not moving as much fluid. That's the trade-off with playing with the hydraulic circuit.

Basically to get more stopping power with similar leg effort is to do any of the following: better pedal ratio, or power assist, smaller master or larger slave cylinder, better friction material, more friction surface area, bigger diameter rotors (which increase the brake torque). Anything involving the hydraulic system or pedal ratio will affect the pedal stroke however.
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Old 10-11-2019, 01:42 PM
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Gee Tim... I was hoping no-one would notice that. I really don't want to change the master cylinder from 7/8 to 3/4 as it would then need a 26% increase in pedal stroke. This might mess things up quite a lot at the balance bar and the whole front/rear ratio. I was looking at a caliper increase as it might not be so drastic. Unfortunately all I found so far for an easy bolt-on replacement doesn't appear to change it enough.

However, maybe a combination of higher friction pads along with those calipers might prove to be the cure.

Johnson: I don't necessarily disagree with you, but I prefer over-thinking to under-thinking. Hoping to fix something by throwing time and money at it in ignorance isn't the way I like to do things.

I will be calling some pad manufacturers, however I like to know as much as I can before I call so I ask intelligent/knowledgeable questions and not waste the rep's time, or my own.

By the way, calling is the best way to go vs. e-mail. One of the reasons I recently went with RAM clutch components was due to the excellent help I got from their technical support. McLeod wouldn't even respond to my e-mails. I currently have a simple question I sent to Tilton and despite their website promise of answering all queries in a max. of two business days, it's now been a week and no answer. A phone call will be next for them.

Anyway, the advantage to this forum is the vast experience of the members. I am still hoping someone might respond who has switched over to dual piston GM D52 calipers.

Thanks to all who responded so far.
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Old 10-11-2019, 03:17 PM
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Pads can make a huge difference in the performance, but more stopping power will mean less rotor life.
My first race car used stock GM calipers like yours, and I just got pads from AutoZone and stuck on there, could not lock up 10 inch slicks no matter how hard I smashed the pedal, got some PFC and could lock them up easily
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Old 10-13-2019, 07:15 AM
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Thanks Imsport. I hadn't heard of PFC,, so I looked them up. A lot of very positive reviews too!

Anyway, back to overthinking this:

I've been trying to put some numbers together to quantify the advantage of the new calipers I am considering purchasing. Not a whole lot of luck, but here goes:

1/ Total piston area increase, therefore more clamping pressure is about 5.8%

2/ Mechanical advantage as the dual pistons are located a little further out on the disc, is about 4.5% (based on an engineering drawing of the proposed caliper)

3/ Efficiency improvement due to twin pistons distributing the clamping force more evenly over the pads. I did a leverage calculation and got a little over 17%, but it's a ridiculous calculation as it assumes a flexible brake pad as well as other likely erroneous assumptions. So I'll assume a WAG of 10% of that, which is 1.7% Probably optimistic, but I wanted to get a number some how.

This totals up to a 12% improvement, but to the front brakes only. Since a typical front/rear ratio is probably about 70/30, I can assume a total improvement of about 8.4% at the pedal.

Not a lot, but I may go with the calipers anyway, especially considering I mounted the existing single piston calipers back in 1995.

As previously mentioned, the only other "easy" improvement I could do was to go to a higher friction pad. There's lots to choose from, but most are a high temp track pad, not recommended for the street. This leaves me with one higher friction choice for the street, and that's going to 0.55 from 0.46. Not great as there would no doubt be increased rotor wear.
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Old 10-15-2019, 05:28 PM
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I stumbled across some more info. Turns out GM D52 calipers were made with quite a variety of piston diameters. For example, the ones used on a 1974 Malibu are 2,15/16" in diameter. Compared to my current 2,3/4" pistons, this should bring out a 14% increase in force on the pads with the same pedal pressure.

...over-thinking.... quite probably......
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