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Thread: Brake Cooling

  1. #1
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    Default Brake Cooling

    Got the Ocelot on the track for the first time in probably 15 years only to have it cut short by severe braking vibration. The body has 3" holes for brake cooling ducts. but did not have any ducting when I bought the car. We found the rotors warped so have fixed that and will try again this week. The front upright set is rather standard Spitfire type an the flat plate rotors are both drilled and slotted. So the questions are, first, where would I fasten a bracket to hold the brake cooling duct, the only logical place to me is either the top or bottom of the steering arm? Second, Since it has to be disconnected every time the front body half is removed is there some sort of quick disconnect system? Last, how do modern cars cool the brakes, SRF cars don;t appear to have any ventilation openings?

    Hopefully my pictures get attached. Body photo is from when purchased, cleaned up a bit now.

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    Senior Member 924RACR's Avatar
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    SRF's don't go fast enough to need brake cooling?

    Kidding - I'm fairly sure they do have ducts for the front brakes, I've seen them hanging from ripped-off noses enough...

    3" seems overly generous; could probably neck that down to 2" without suffering.

    As for how to attach at the upright end... you are correct, that won't be easy with those uprights. Seems like the only thing you could do, short of adding new holes (which would definitely be a concern for strength) would be to use the brake caliper mounting bolts, piggyback off of those with a shroud mounting.

    That said - you might find you could get adequate cooling by just pointing the hose end at the caliper/rotor... you could support this by clipping a hose to a bracket clamped onto one of the suspension arms. Something like a P clip around the lower a-arm, with something to attach the hose to bolted to that. Perhaps a short length of aluminum tube, which the hose can be clamped to for retention.

    As for how to connect to the front duct openings without a quick disconnect... well, without a splitter you're going to struggle IMO, as that's the easy way to create that quick disconnect. You'd want the hose connected to a tube/duct on the splitter, which then interfaces with a tube/duct on the nose... if you consider those two parts as a single tube, with a diagonal flange facing upward, then when you drop the body down on the splitter then connection is made automatically. And since it's a brake duct, it doesn't necessarily need to be an airtight seal - just so long as most of the air goes where you want it. Think about Porsche and all the brake cooling they achieve just with deflector shields and blades on the suspension...
    Vaughan Scott
    #77 ITB/HP Porsche 924
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  5. #3
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    I don't have any other ideas that vaughn hasn't suggested. We used round fabricated brackets that mount to a brake caliper bolt and 2" hose.

    And congratulations on getting the car back on track. Good to see the older cars out there again!

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    Classifieds Super License stonebridge20's Avatar
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    What brand rotors are you using?
    Stonebridge Sports & Classics ltd
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    Global Moderator Mike B's Avatar
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    On Brian Lindstrand's P2 with HRP bodywork we developed a rigid duct that is bonded to the backside of the nose and directs air to the caliper/hub vicinity. It stays with the nose and is not attached to anything else so no disconnection needed when removing the nose. Testing has been good so far.
    I also would reconsider using drilled rotors, especially on a full-bodied car.

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    Mike Beauchamp
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    Senior Member 924RACR's Avatar
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    I like the idea of the fixed ducts you show above.

    I don't agree with the suggestion of drilled rotors. Mass reduction, so can make heat management worse, and turns the rotor into a cheese grater on the pads, causing a reduction in their service life... me, I run solid floating rotors.
    Vaughan Scott
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    Senior Member kea's Avatar
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    Default Brake Cooling

    I'm with Vaughan, solid rotors.
    Also, if air gets in, it must have a way out.
    I can't we your wheels, but if they had solid centers (old Centerline design comes to mind), there is a limited way for the heat to escape.
    Keith
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    Global Moderator Mike B's Avatar
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    Quote Originally Posted by 924RACR View Post

    I don't agree with the suggestion of drilled rotors. Mass reduction, so can make heat management worse, and turns the rotor into a cheese grater on the pads, causing a reduction in their service life... me, I run solid floating rotors.
    The OP is using drilled rotors so I said reconsider using them, as in DON'T use them. We see warping on drilled rotors on open wheel cars, let alone a full-bodied car.
    Mike Beauchamp
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    Quote Originally Posted by Mike B View Post
    The OP is using drilled rotors so I said reconsider using them, as in DON'T use them. We see warping on drilled rotors on open wheel cars, let alone a full-bodied car.
    They also crack more!

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    A few answers, The wheels are old Revolution 4 spoke with long sleeved lug nuts that even go into the spacer plates The rotors are a complete unknown, they after machining as it had to be mounted to the hub(and the hub trued) are about .375 thick. This is a case of send one to Coleman(?) and say make a pair similar to this. There are not a lot of holes in the disc, but I'll keep that in mind. I like the fixed duct idea also as the existing body duct is about 8" inboard of the rotor and 11" in front of the coil over A flex duct would have to anchor to the front lower control arm and below the steering tie rod and have several bends in it. I'll take some more pictures, unfortunately I don't believe I'll be able to get the car high enough to take pictures with the body on. The point about not using the brakes is well taken as I'm an older vintage driver so getting up to speed will be an issue.

    The last owner who did anything to the car was a John Alpers in Tuscon probably in the mid '90's, he also probably put the Kawasaki KZ motor in replacing the Suzuki 750 water buffalo. They next two owners barely used it. So, much of what I'm dealing with is ancient technology and well out of date, with little to no historic information available.

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    Contributing Member scorp997's Avatar
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    Something else to check, this actually happened to me.

    what is the clearance from the OD edge of the rotor to the inside face of the caliper bridge? I had an issue where this clearance was so small that heavy braking would cause the rotor to expand slightly from heat and rub on the caliper. Had just enough clearance when cold so we didn’t spot it right away. Check the outer edge for witness marks of rubbing.
    -John Allen
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    (‘72 Royale RP16 stolen in 2022)

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    Didn't you say they were Fiat rotors? Probably 128/X19 as those were fairly popular on the A-Mac and Cheetah of those days. They should be available if not I may have some but they're probably machined down to .250 to fit our calipers.

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    If FIAT, they are VERY inexpensive new. Try and find the Brembo brand discs. I had never turned one down when I ran my Lancia Scorpion, it cost more to turn them than to buy new. FWIW, nearly all of the FIATs of that era used the same disc (124,x1/9,128,Scorpion,850). Only the ‘85 124 and the Lancia Beta ran different parts.
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    Not sure how the Fiat subject came up. These rotors ar a flat plate, 9-9/8" OD x .375 thick with a center hole of 2-1/2"mol and a bolt circle of 4" which had 10-24 cap screws and we converted to 1/4-20 as the hub is aluminum. I've contacted Colman for approximate delivery time. The calipers are currently Wilwood Dynapro with 2 1.75" pistons, I believe maximum rotor width for these is .375". I have an old upright which had different mounting lugs welded to it with a non US typical bolt spacing, So who know what the original caliper was. The brake pads are tiny little things, but then the car is about 830lbs. For info, the rear is a single rotor with an AP/Lockheed Escort GP(I believe) Caliper. Car is chain drive with no differential.

    Looking at Pegasus it appears that a .280 thickness is fairly common, I might want to convert to this width when I get new ones. I would need to stay with the same base thickness to keep the caliper to rotor alignment, or redesign the caliper mounting which is marginal and would be a good idea anyway.

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    We used LD19 calipers which wanted approximately .25 thick rotors. We would get them from junk yards and put them on a brake lathe to narrow them down. We liked using used rotors as they were already heat cycled and if they were going to warp they would already have done so, and the brake lathe trued them up. I can't remember that we ever had problems with warped rotors.

    You may think that stopping a 830 pound car isn't a big deal but it certainly can be. If you feel you need the brake cooling that should tell you that the components are being pushed to capacity.

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    Default Update

    Took the car to Pueblo on Friday. What a kick to drive! The reworked brakes worked very well. Of course the next multiple problems showed up. The motor is air cooled which in my mind says that the oil does most of the cooling. There are 4 large cooling fans for the Kawasaki KZ motor, which shows me that some one didn't really understand it and did not do much more refinement. The oil temp pegged at 250F and I wasn't pushing it. The oil cooler is a tube and fin about 9"x10" stuck horizontally in the driver side pod. with a cooling fan blowing up. I had improved the airflow from below by reworking the standoff brackets and increasing the lines from -6 to -8(the outlets from the motor are the restriction point). So I'm starting out by installing a NACA duct and 2 3" hoses to get some air in there and reversing the air flow direction. Compounding the situation, this is a roller bearing crank motor so the oil pressure is only about 3 psi with supposedly a lot of flow. I can't find any information comparing tube and fin versus plate and frame coolers for pressure drop vs cooling so in a hard spot on that one. Hopefully I can remount the cooler at angle or vertical to improve that situation. Logic tells me the tube and fin would have a lower pressure drop, but??

    I'm also going to get some ducting toward the brakes, I have long radius rods(correct term?) instead of the more modern A-arm and will tie the ducting to them for now and just get some air in the general direction. Depending on how it works and the convenience of hooking it up I may try to go to fixed duct later, gut the radius rod movement will always be a problem.

    But the real kicker is I started getting a lot of steering vibration on acceleration. Thinking it was maybe the old Spitfire wheel bearing and seal system or wheel balance, but no the wheels do not have any play. The Spitfire gurus say to torque the bearing nut to 60 in-lb and put in the cotter and it feels may a touch too tight, but works. I'll get the fronts balance checked this week, but it is probably the 50 year old rack and pinion. I've had them apart before and cleanup seems to be the biggest general problem if the outer bushing are still good. We'll see.

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    The tie rod ends appear to have a cap screw, holding them onto the rack, but neither inch or Metric sizes fit so I can't take the rack apart. There is a lot of play in the cross bar/rubber cross connection from the steer column to the rack. The rack comes with grease fittings but supposedly racks would prefer 140wt oil than grease. The rack has no markings as to where it came from but the pinon is offset rather than centered for a formula car. I'll get some pics.

    The tie rod which is for a 1/2" bold is held on with a 3/8" hex cap screw, (1/2" thd?). The input plate was a bit loose as held on with aq/4-20 cap screw wit a broken tie wire and the input pinon appears to have a worn bushing. There are no identifying marks for the manufacturer for the assembly
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    Default Brake Pad Temperatures

    Many years ago several of my customers were having issues with front tire ware and braking performance.

    The problem turned out to be an issue with brake pad temperatures.

    The problem was that under hard braking, as the driver released the brakes, the front tires would slip just a bit. It was not enough that the drivers realized that the brakes had locked up but that was the problem. What was noticeable was that the front tires wore much more than the rear tires.

    As the driver released the brake pedal, but before the pads retracted completely from the rotors, the pad temperatures increased due to in increase in the friction between the pads and the rotors. This raised the pads temperatures up and simultaneously, the coefficient of friction increased causing the pads to grip harder even with less clamping pressure.

    Bottom line, we had to keep the pad temperatures withing a certain range for the brakes to function correctly. Over time the pad materials improved and the problem went away.

    I bring this up as a warning that brake and rotor temperatures are very important and can be hard to figure out what is optimal.

  23. #19
    Senior Member 924RACR's Avatar
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    Tough to comment on the cooling topic other than to say it seems like you should be heading in the right direction... I've been extremely happy with the plate style coolers in my racecars, very durable too... but can't speak to relative efficiency.

    On the steering wheel shudder... interesting to note that it's confined to acceleration. For sure, ironing out any play in the front end is wise and relevant, but one would expect that to be more of an issue on braking when that end's respectively more heavily loaded. As this is the opposite, have you performed a similar investigation on the rear?
    Vaughan Scott
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