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  1. #1
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    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
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    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
    Falmouth
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    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
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    582
    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
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    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
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    Location
    NW England
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    Quote Originally Posted by Eggbert View Post
    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.
    Now there's a coincidence, when I did the testing on min, the car I used as a "control" was also a Toyota!
    Most mobile/cell phones (the so called smart ones) have accelerometers and gyros in them and there are apps available to measure performance, why not use that instead of wiring?


    IIRC I got 0.96G for the Toyota (ABS just kicking in) and 0.74G for the cobra (fronts locling up). I improved the rears by swapping my inboard discs to outboard and fitting some Wildwood four pots. I later fitted similar calipers to the front (slightly larger pistons) so I could use same pads all round, but it was the change to the rear system which upped my deceleration figure.

    One problem you may have is that any changes you do to the mechanical or hydraulic leverage ratios to give you higher pressure at the pad will require longer pedal travel which may not be practical in a cobra footwear. Other options are higher friction pads, which it sounds like you already did, or larger diameter discs. What diameter are your discs now?
    Another possibility is grooved discs which are supposed to stop the pads glazing. Probably give more dust though.

  7. #7
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    Thank-you for your reply. It was starting to get lonely in this thread... LOL.

    Quote Originally Posted by GDCobra View Post
    Now there's a coincidence, when I did the testing on min, the car I used as a "control" was also a Toyota!
    Most mobile/cell phones (the so called smart ones) have accelerometers and gyros in them and there are apps available to measure performance, why not use that instead of wiring?
    That's a very good idea. I've never owned a cellphone, much less an iphone, but my son has one and I'm sure he'd be glad to help. He's always adding Apps, so that should be easy for him.

    Quote Originally Posted by GDCobra View Post
    IIRC I got 0.96G for the Toyota (ABS just kicking in) and 0.74G for the cobra (fronts locking up). I improved the rears by swapping my inboard discs to outboard and fitting some Wildwood four pots. I later fitted similar calipers to the front (slightly larger pistons) so I could use same pads all round, but it was the change to the rear system which upped my deceleration figure.
    I've been researching that too. Basically I have a narrowed XJ6 rear suspension mounted in a cage that bolts to the chassis. I'm not prepared to make the changes to outboard discs although the factory offers a new set-up with outboard brakes and larger front brakes. Very expensive, and since I feel close to success here... and am self-proclaimed as "frugal", it's a no go for now.

    However I am researching rear brake pads with a higher friction rating. I started doing that in order to help maintain the front/rear brake bias when I switch to larger calipers. At this point EBC Yellowstuff pads seem to be the best choice, but needs further confirmation. Brake pad manufactures don't often list the coefficient of friction for their pads, and even if they do, it changes with pad temperature. Goes higher as things heat up... to a point, and then drops off. One needs a graph.

    I'm currently using Hawk HPS front pads which did give a significant improvement, but they don't make pads for the Jag rear. Wilwood offers a really good pad and with data too, however once again, no go for Jag pads.

    It's a difficult thing to sort out as most of it is advertising hype about things like "great cold bite", "easy on the rotors", "low dust" etc., but without numbers these sort of things are fairly useless. So I take my best guess and try them.

    Quote Originally Posted by GDCobra View Post
    One problem you may have is that any changes you do to the mechanical or hydraulic leverage ratios to give you higher pressure at the pad will require longer pedal travel which may not be practical in a cobra footwear. Other options are higher friction pads, which it sounds like you already did, or larger diameter discs. What diameter are your discs now?
    Another possibility is grooved discs which are supposed to stop the pads glazing. Probably give more dust though.
    The difference in the front calipers and my current ones will only require about a 14% throw increase at the front master cylinder. Due to the balance bar feeding both front and rear cylinders I can expect only a 7% increase in pedal throw. This works out to be about 0.1 inches for my current 1.5" of throw. But your point is well taken. Too large a front change will require a lot of other changes.

    Current front discs are 11". I have room to 11.5" easily enough... maybe 12, but I don't have any idea of what caliper will work with my steering knuckle if I go to a larger disc. I think the rear discs are 10", but should probably confirm this.

    So... in a nutshell, if I go to the larger piston front calipers AND install pads with a co-efficient of friction around 0.55, I should be able to reduce my threshold braking pedal pressure from 128 lbs to 98 lbs. I know theory doesn't always work out in practise, but it's a good place to start.

    I'm almost ready to order all the parts, but am still investigating at my choices for high friction street pads that won't chew up my rotors (the front ones being precision re-drilled for mounting on my pin-drive hubs).
    John

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

  8. #8
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    “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.

  9. #9
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    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.”

  10. #10
    Join Date
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    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.

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