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Budget track car brake fade issues

culberro said:
The R calipers shift the bias drastically to the front when using a stock MC, and you get a squishy pedal. They work, but it is not what I would want for a track day car.
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I don't know how many people have done this over the last 18 years, but I think a LOT. I've received a lot of emails about results. Not all are perfect and there are many variables with people trying different master cylinders, removing or not removing rear reduction valves, different vacuum boosters (yes, this makes a difference too), and some with new plumbing and some with a Wilwood proportioning valve. My result with a stock MC was a perfect, firm pedal. I don't know why you got a mushy one, but I don't think it was a related to the R calipers. The R calipers only have 11% more piston area that stock 240 calipers, so any thought of a "drastic" shift in bias is BS. The primary performance change (or bias change) is from the leverage of the larger rotor. This can be managed other ways as I show in my page.
 
Nickagriffin said:
Dave, I'm sure you've tried every brake setup under the sun. If only doing fronts, would you recommend R brakes or Willwood/brembo? I'd like to stick with 17" wheels
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The reason I went with Wilwoods on my 242 (with 12.2 inch rotors) was because I couldn't get the R calipers (13.2 inch rotors) to fit with my 17s and I didn't want to to buy 18s. With the Brembo kits that BNE offers now, that's the direction I would go if I was to do it now.
Dave
 
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dbarton said:
The R calipers only have 11% more piston area that stock 240 calipers, so any thought of a "drastic" shift in bias is BS. The primary performance change (or bias change) is from the leverage of the larger rotor. This can be managed other ways as I show in my page.
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The radius for clamping is ~1.3" more than a stock 240, and that's where the biggest change comes from. Both of these combined increase the front bias to ~45% higher than a stock 240.

While this might be okay for a street driven and spirited driven 240, this is not what you'd want in a track car... especially if the track was wet.

I've helped numerous t-brickers get their alternative brake systems sorted out due to the bias being shifted one way or the other too much. With regular driving, it's usually ok. But when someone is drag racing and hits the brakes at 150mph and locks them up.... that's an issue. When someone is road racing in the wet and has chronic front brake lock-up, that's an issue. These are all issues that didn't show up until the car was pushed way past normal driving.

R Calipers and Explorer rear axles with stock brakes offer 40-60% more braking than stock, If used together with a larger MC it's a decent setup. Using just one of them will shift the total bias a significant amount, and that's an issue.

While a brake proportioning valve can be used to help, they have a "knee" pressure point that limits max pressure. Before the "knee" they do not limit pressure. I think the wilwoods lowest limit is ~150psi. So you have to build more than the lowest knee or break-over pressure before it starts to limit outlet pressure, and after that point it's not flat... just a slower pressure rise vs the inlet pressure.
 
After installing the R fronts in my 245 I tracked it and found the fronts were easy to lock up prematurely if I wasn't precise. I removed the rear reduction valves and tracked it again and any bias limitation was no longer noticeable. I did not try a proportioning valve, but I think it could have tuned out any issues with the reduction valves removed if needed.

The 245 rear reduction valves are different from 244 valves, but I'm wondering if anyone knows or has more closely estimated the bias changes with or without them.

Greenbooks describe their operating pressures, but doesn't offer much more.
242/244 (1975): 3.0 MPa (435 psi)
242/244 (1976-): 3.4 MPa (480 psi)
245 (1975-76): 4.5 MPa (640 psi)
245 (1977-): 5.0 MPa (730 psi)

Dave
 
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dbarton said:
After installing the R fronts in my 245 I tracked it and found the fronts were easy to lock up prematurely if I wasn't precise. I removed the rear reduction valves and tracked it again and any bias limitation was no longer noticeable. I did not try a proportioning valve, but I think it could have tuned out any issues with the reduction valves removed if needed.

The 245 rear reduction valves are different from 244 valves, but I'm wondering if anyone knows or has more closely estimated the bias changes with or without them.

Greenbooks describe their operating pressures, but doesn't offer much more.
242/244 (1975): 3.0 MPa (435 psi)
242/244 (1976-): 3.4 MPa (480 psi)
245 (1975-76): 4.5 MPa (640 psi)
245 (1977-): 5.0 MPa (730 psi)

Dave
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That's good to know on the pressures, and that all seems to make sense as far as models and rear weight added.
I'm assuming those pressures are the break-over/knee points in pressure.
 
We raced our champ car for quite a while on stock brakes with Hawk Black pads and some duct work. We never had an issue with brakes and the only reason we upgraded was for cheaper and better aftermarket pad selection. Currently we go through rear pads about twice as fast as we do fronts.
-Sam
172669854.jpg
 
On my 244 race car I run S60R front brakes and stock rear. No ducting, just Porterfield R4 pads all around and ATE racing fluid. I run the factory MC and have eliminated the rear reduction valves.

It feels great in terms of never getting fade and I am always very hard on the brakes. As far as the balance, it’s a little easier to lock up the rears if you jump on em too fast but besides that they feel great.
 
Ahh brake stuff is always so complicated. I do like the idea of getting the stock stuff to work but I also want a safety tolerance for brakes. We all know brake fade can kill fast and unexpectedly.

Those running stock calipers on the track - are you guys NA or Turbo? Stopping a 114hp car is a lot easier than a 200hp car. I would guess I'm right around 200hp right now and 2700lbs.

I also have some concerns about big brakes in the front and stock in the rear. I know the fronts are far more important, but I wouldn't want brake fade in the rear either. That would seem to cause another set of brake imbalance problems that don't have anything to do with bias.
 
Nickagriffin said:
Ahh brake stuff is always so complicated. I do like the idea of getting the stock stuff to work but I also want a safety tolerance for brakes. We all know brake fade can kill fast and unexpectedly.

Those running stock calipers on the track - are you guys NA or Turbo? Stopping a 114hp car is a lot easier than a 200hp car. I would guess I'm right around 200hp right now and 2700lbs.

I also have some concerns about big brakes in the front and stock in the rear. I know the fronts are far more important, but I wouldn't want brake fade in the rear either. That would seem to cause another set of brake imbalance problems that don't have anything to do with bias.
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My 740 is turbo, last dyno was 199.76 RWHP. Saw up to 117 mph at Willow Springs last month. Sonoma we see just under 100 mph. Over a dozen races with three of them being full 24 hour races.
 
Getting some track-specific high temp pads and good fluid will do wonders for your car.

That + some cheap ducting and you should be ok to stop reliably.

Keeping everything small (stock) has its consequences though.

You will work your pads and rotors much harder at the stock small diameter and there's less ability to dissipate the heat quickly that you will be generating.

So you will either be stuck with not getting the maximum stopping performance (it can be consistent) or not great brake component life.

Going to a large diameter rotor and a larger caliper with a bigger pad profile, lets you dial back the aggressiveness of the compound and get the same frictional forces... or get more aggresive and increase performance (if your tires can support it)

On our enduro racer 850 we run a stoptech big brake kit, all that stuff is really expensive.... and we run really expensive pads ($330/pair) but poneying up the money up front for higher rated components, we can run all of our parts at a lower duty cycle and get really long service life out of them. We typically get 4-5 races out of a set of front pads and at least 10 races on a set of rotors, once you calculate out all the consumable costs it usually breaks down to 6-7 $ / hr of track time... which is quite low.

Dont be surprised if you need to replace your performance pad every 6-8 hrs of track time
 
blkaplan said:
Getting some track-specific high temp pads and good fluid will do wonders for your car.

That + some cheap ducting and you should be ok to stop reliably.

Keeping everything small (stock) has its consequences though.

Dont be surprised if you need to replace your performance pad every 6-8 hrs of track time
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This.

In 3-4 races the wilwood kit on the rally car paid for itself. In rally we were getting ~4hrs of racing out of a set of front pads (Hawk blue, blacks, or DTC-60s). Rotors with every pad change.

We are usually seeing around 15 (25-30 hrs) races between pad changes now
 
blkaplan said:
Going to a large diameter rotor and a larger caliper with a bigger pad profile, lets you dial back the aggressiveness of the compound and get the same frictional forces... or get more aggresive and increase performance (if your tires can support it)
Click to expand...

culberro said:
In 3-4 races the wilwood kit on the rally car paid for itself. In rally we were getting ~4hrs of racing out of a set of front pads (Hawk blue, blacks, or DTC-60s). Rotors with every pad change.

We are usually seeing around 15 (25-30 hrs) races between pad changes now
Click to expand...

If there were Wilwood adapters for a 740 I would buy them right now.
 
culberro said:
To the computer!!!!!

Uhhhh?. Does anyone have a 740 strut and hub I can use 🤣
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I have early and late model 700/900 struts in my garage. Getting them to you is the problem. Measuring them and sending you pictures is easy.

Sorry to threadjack Nickagriffin
 
culberro said:
The R calipers shift the bias drastically to the front when using a stock MC, and you get a squishy pedal. They work, but it is not what I would want for a track day car.
Click to expand...

Fronts, rears, and a Mustang MC have resulted in the best-feeling power brakes I have used this side of a Porsche 911.

I have noticed, however, that pad knockback is far more apparent with these brakes than it was with stockers and RX7 stuff.
 
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