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  1. #1
    Join Date
    Sep 2010
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    Nova Scotia
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    810

    Front Brake Caliper Upgrade; Ponderings and Questions

    I’ve been investigating a minor front brake upgrade. 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 I don’t really know how much more braking I could get before wheel lock-up. Maybe I\m almost there now, but I doubt it.

    I am using non-assisted GM front brakes D52 single piston floating 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 and are on the same side of the caliper. The pressure advantage by bore size is only 5.8%, but there may be an additional 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; slightly further away from the axle center yielding a bit more mechanical advantage.

    I have no feel for these latter two effects, but I doubt the overall effect would be much over 6%. 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.

    1/ So, for this small improvement, do any of you think it is a worthwhile upgrade, or am I just wasting time and money for an insignificant improvement?

    2/ Will dual pistons on a floating caliper be more effective, and if so has it been quantified, or even a reasonable guess as to the percent improvement?

    3/ Would the fact that the two piston caliper has the pistons moved slightly further out from the axle 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. Onl;y the pistons would be further out. More force along the outer part of the pad might even contribute to uneven wear...

    Thoughts please?


    Sidenotes:

    1/ I had previously changed pads for ones with a higher fiction coefficient. Not all brake pad manufacturers list those numbers, but after a little research I find I can go one grade up before entering the very high friction/high temp pads that are not recommended for the street. So there’s another thing to try.

    2/ Changing the master cylinder is not really viable. I really don't want to change the master cylinder from 7/8 to 3/4 to get more pressure as it would then need a 26% increase in MC stroke. This might mess the geometry quite a lot at the balance bar and the whole front/rear ratio. I was looking at a caliper piston increase instead 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.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  2. #2
    Join Date
    May 2011
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    Flimwell
    Posts
    775
    Have you thought about fitting a remote servo?
    Colin
    Dax Standard Chassis. Ford 302, AOD auto, DB s/s sidepipes, 2017 T reg.

  3. #3
    Join Date
    Jan 2012
    Location
    Perth
    Age
    53
    Posts
    1,675
    Hi John,

    If they are GM would there be an upgraded OEM caliper/disc combo that would bolt straight on ie 'vette or Camaro?

    A lot of the Brit kits use Jag running gear (our case series I, II or III) which have an upgrade four pot caliper system.

    cheers
    Kiel and Duncan (dad and the lad errr young man now)

    AHP Crendon Chassis No 1
    Ford FE 434, dual quad, Toploader total old school all the way
    https://www.crendonreplicas.com/
    http://www.absolutehorsepower.co.uk/

  4. #4
    Join Date
    Jul 2012
    Location
    NW England
    Posts
    416
    I'd focus more on what sort of deceleration you are achieving rather than whether or not you can lock the wheels (although I under stand that they should be capable of this). On my Jag setup I was easily able to lock the front wheels but didn't feel my rate of deceleration was what it should be.
    To quantify this I put an accelerometer in the car and measured it (I also back to back tested with my regular car).
    It turned out the braking wasn't as bad as I thought (I think the reduced weight transfer made it feel less as there was not so much dive) but could be better.
    What this told me was the only way to improve my braking was to focus on the rears rather than the front. That is what I did.

  5. #5
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    810
    Colin: The thought crossed my mind for about 2 seconds. I doubt it could be done without major changes. My brake and clutch pedals sprout up from the floor with all the master cylinders directly under the floor. I have no idea how a change involving a servo could be accomplished without a massive re-design.... Maybe the Project Binky guys would tackle it, but not me.

    Kiel: I've only found two aftermarket calipers that will fit. SSBC seems to have gone out of business although Summit still lists a lot of their stuff as "clearance". One wonders about re-build kit availability..... Wilwood has been making the upgrade for years and I suspect will continue to do so. Although a lot of GM cars used the D52, the Corvette was completely different. Corvette calipers won't mount on my steering knuckles. Lots of limiting factors here that aren't easily remedied.

    GDCobra: Odd you should mention this as I was just thinking something similar last night. The fact is, I'm used to servo assisted brakes in almost everything I drive. The Cobra's manual brakes take a lot of leg effort. I'm sure part of the problem is that I don't seem to be slowing down enough compared to the leg effort I'm putting out.

    I do have a little device (the original G-Tech meter) that measures G forces in a car as well as Hp and 1/4 mile times. I've never used it in the Cobra as it's designed for a cigarette light that I don't have. As it's a simple matter to run some wires back through the firewall temporarily, I could try it out. Another solution would be to mark stopping distances on a road using chalk and compare the Cobra to my Toyota.

    Thank-you all for your comments.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  6. #6
    Join Date
    May 2011
    Location
    Flimwell
    Posts
    775
    “The thought crossed my mind for about 2 seconds. I doubt it could be done without major changes. My brake and clutch pedals sprout up from the floor with all the master cylinders directly under the floor. I have no idea how a change involving a servo could be accomplished without a massive re-design.... Maybe the Project Binky guys would tackle it, but not me.”
    The whole point of a remote servo is that you can mount it anywhere convenient and plumb it into the brake lines. Doesn’t have to go anywhere near the brake master cylinder. They usually give 2:1 increase.
    Colin
    Dax Standard Chassis. Ford 302, AOD auto, DB s/s sidepipes, 2017 T reg.

  7. #7
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    810
    Quote Originally Posted by 1dayiwill View Post
    The whole point of a remote servo is that you can mount it anywhere convenient and plumb it into the brake lines.
    Really? I was picturing one of those vacuum units that mounts on the firewall. Anyone have a link for an example?
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  8. #8
    Join Date
    May 2011
    Location
    Flimwell
    Posts
    775
    CBS do a single line one
    https://www.carbuilder.com/uk/remote...0aAiD6EALw_wcB
    If you have dual lines you’ll need 2 of them or you can get dual line remote servos but they’re a bit pricey. Probably north of £300.
    Colin
    Dax Standard Chassis. Ford 302, AOD auto, DB s/s sidepipes, 2017 T reg.

  9. #9
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    810
    Thanks Colin. I understand now. It's definitely a possibility although finding room may have to be a bit imaginative.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  10. #10
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    810
    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. 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.

    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, and that's going to 0.55 from 0.46. Not great as there would be increased rotor wear. Not normally a problem, it is a bit more so as I have pin-drive wheels and the rotor is modified slightly so it bolts on the back of the hub. Pins go through the hub and the threaded part extends out to go through the rotor. Easy mod, but I'll have to find the part number of the un-modified disc.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

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