Aussie RCR T70 capers

[Ron Earp]

Crappy production / design / choice , kinda sets your confidence level back a bit --until we find something that can handle the pace

I don't think the brakes or rotors are a bad choice for the car at all. I think they're plenty large enough and at least on our car the braking has been exceptional. I hate to hex anyone but I hope the rotor issues are isolated to your car or rotor batch, I don't want to fight a brake issue at the moment!

Which end of the car did the rotor crack on? What sort of airflow over the rotors do you have? What pads are you using?

We're using Carbotech XP10 pads, a compound that we're very familiar with from IT racing. Aggressive with a lot of initial torque when hot, but it can be modulated. We experienced no fade at all when testing over the last two weekends at VIR. We have two stops down from 135mph to about 50 mph, and around three stops from roughly 100mph to about 60 mph. Bias is set so that the front lock just before the rears. The front rotors have good airflow, the rears have essentially none save what gets over there via circulation. I think I will add some rear ducting.

 

[flatchat(Chris)]

Using a Hawk comp pad ? air flow - good, stoppers - good.

Its a front left that actually broke but they've all got failure cracks started.

Just can't afford a rotor failure at highspeed.

 

[flatchat(Chris)]

Whilst on the subject --the front wheel bearings (C4 or 5 Corvette) needed to be adjusted up a bit too

 

[Scott]

Flatchat,
I went through the wheel brng thing too. There is no adjustment. If there is play, they are shot! All of the corvette forums that I have been on indicate that the SKF replacements are the best. (that seems to be the opinion of the guys that do track and auto-cross) Fran has double-roller replacements at a good cost, but I could not tell you if you already have them or not. (my car was an early car and had chinese units that went bad)

I would give Fran a buzz/pm and see what he says. The new SKF units are like 300usd, and I think the ones he sells now are about half of that and american made. I bought a set to try, Scott

 

[Ron Earp]

Yep, what Scott said on wheel bearings. Check the Corvette forums and you'll find it is a well-covered topic. Cheaper bearings will fail. I had one fail and bought the high buck ones from RCR and the auto store, thus far no trouble.

 

[flatchat(Chris)]

Oookay back to brake rotors --swapped out the fronts with some cryo treated spares we had - for the interim.
The findings :- Had to actually cut the old rotors to get them off the hats and the replacements slipped on with ease.
The old ones had collapsed by 2mm (.080" thou) on diameter - which is a frickin' lot -- hence the breakage --incidently a press fit on something is usually a thou per inch on dia. ~= on 6.38" dia = .0064" (.163mm) this would have been tolerable.
So it seems that these type of rotors need to be floaters at least.
On to re-engineering this drama. jeeeeez ! P.O.S.

 

[Scott]

Flatchat,
Thanks for posting the results! Please keep posting the upgrades as you progress for the rest of us. (I will be tracking my car next year and would like to avoid any costly accidents) Sincerely, Scott

 

[Dalton Veitch]

Good motto: "Avoid costly accidents".

 

[Jac Mac]

Mounting the Brake Rotor like that on the OD of an alloy Hat or Hub is a flawed idea, since the alloy can/will expand more than the iron rotor it will tend to crack the rotor at some point in the operating heat/cooling cycles if you start to cook things up..

 

[Ron Earp]

Oookay back to brake rotors --swapped out the fronts with some cryo treated spares we had - for the interim.
The findings :- Had to actually cut the old rotors to get them off the hats and the replacements slipped on with ease.
The old ones had collapsed by 2mm (.080" thou) on diameter - which is a frickin' lot -- hence the breakage --incidently a press fit on something is usually a thou per inch on dia. ~= on 6.38" dia = .0064" (.163mm) this would have been tolerable.
So it seems that these type of rotors need to be floaters at least.
On to re-engineering this drama. jeeeeez ! P.O.S.

I'm going to call Wilwood and see what they suggest. As far as I can tell the rotors center themselves on the hat. I've put new rotors on the hats and they just slip on the hat with maybe 0.001" of wiggle room. Not much at all but I suspect that is the way they are designed to work.

Aluminum has a COE of 12.3e-6 in/in F, cast iron is around half that value at 6e-6 in/in F. For rough calculations assume that we're operating at 500F.

I think we can approximate the hat as a pipe and the pipe will grow thus:

d1 = d0 (dt * a)

where do is the diameter, dt is the change in temp, a is the COE.

d1 = 6.38 ((500 - 75) * 12.3e-6)

d1 = 6.385"

So the hat would grow around 0.005". And the rotor is also going to grow, but around half as much as the aluminum, but in the end there is going to be around 0.010" of interference. That would seem excessive and likely to generate substantial force.

 

[Scott]

All,
Would it be possible just to use a different type of fastener and modify the hats to make it full-floating? I replaced the rotors on the front of my f-car with two-piece girodiscs and I seem to remember they were not hard-mounted to the hats........ Scott

 

[colin artus]

Since it is a GT40 forum and it is pertinent to the subject, it is worth noting that the GT40 Gulf cars, with the Girling 18/4 calipers, used steel hats. I presume earlier incarnations were the same.

 

[flatchat(Chris)]

The hats run nice and true still --m/c'd the location diameter down a bit to allow for the extra contraction -refitted the studs so that the disc now floats --will test in a couple weeks . Still persueing a better solution --the WW GT series disc may be it

 

[flatchat(Chris)]

The way we were:smoking:-- turn up the sound and imagine its about a car:-:laugh4:
http://www.youtube.com/watch?v=Ixqbc7X2NQY

 

[flatchat(Chris)]

OMG what have we done ?
Leyburn Packed to the Brim | Australian Driver Magazine
Hope its not a dangerous precedent :worried:

 

[Fred W Ballinger]

We look forward to the race report/video :thumbsup:

Cheers

Fred W B

 

[flatchat(Chris)]

We had a Win in class -- but it was an expensive win and with what could have been in the top 3 outright -- the car was a bit of a crowd pleaser but decided to bury its nose into a hay bale barrier --the hay bale was bigger than the car , we make 'em big around these parts and as it had rained all day Saturday the said bale has fairly water logged and I don't think it moved much.
Results being:- shattered nose cone and a radiator wright off --note to self, do not do this event again

 

[Keith]

Hey Chris, rubbin' is racin' whatever is you rub mate..

Mustang
Skoda Rapide (replica Skoda body on an F2 chassis and engine - don't ask)
Pontiac
Cabbage patch
WWII fire truck
Armco
Haybale

(PS have personally 'rubbed' all of the above)

:laugh:

 

[Roy]

Chris,
Sorry about you’re off track excursion. The Lola was definitely a crowd favourite with its speed and wonderful noise. I hope you reconsider and return to Leyburn, I think you’d have a great chance at top three. This shot was taken on your last run.

 

[flatchat(Chris)]

Great pic there Roy, thanks
Keith, you got me worried about the vegetables or shouldn't we ask ?