Cold rotors want to lock rear brakes

[David Pozzi]

I drove my wife's 73 Camaro at an open track at Button Willow. The car has the Baer brake 13" "Track" kit on the front and street kit on the rear.

One problem showed up. The first hard application of the brakes caused huge rear lockup, I almost spun out! Once the brakes warmed up, the front brakes worked much better and I actually wound up increasing the rear pressure over what we started with to get it balanced.

So now, we have the brakes fairly balanced when hot but the first cold application will put you in the weeds!

We are using the Baer supplied pads. I plan on trying some Hawk pads next time out.
Anyone experience this problem?



I think the front rotors are so huge compared to the rear rotors, that it takes one or two applications to warm them up. The rears get hot right way and throw the cold brake balance off.

I can't figure out why no one has posted about this before.

[Rick Dorion]

I like Hawk pads but you might want to put Hawk's on the front and a hard(er) pad on the rear like Perf Friction. I mention that brand because I experienced a significant improvement going from PF to Hawk - the opposite of what you are looking for on the rears. Was this with the prop adjuster all the way down for the rears?

[rizzos442]

I know that I experienced the same thing when I did my front C4 conversion. I kept the rears a 12" LS1. All was fixed when I messed with my adjustable proportioning valve. I totally forgot that I had it and when I got home, I moved it all the way down and then backed it off @ 3/4 turn. All is good on my front now.
If you are using residual valves, it is still a good idea to install an adjustable proportioning valve to take control of situations, just as you described.

[chicane67]

The initial bite on the stock/supplied pads is a little unsettling. But your right, when they warm up...... you can screw the pressure to them and they like it.

I like Porterfields R4-S for the initial bite and cold use for street and light track use.... and might even lean into a Pagid RS-421 for the rear only..... but none of this is really necessary, because you get a lap or two to warm them before the beating begins...... right ??

[andrewb70]

Something else you guys may not know about is that Hawk has a few new compounds:

New Hawk pads

Andrew

[CarlC]

No issues here, even on the street when there's not much heat in the system.

The pads are Hawk HP Plus.

However, one concern that I have is that the even with the propotioning valve set for maximum pressure to the rear, the rears will not lock up. They are biting hard based on wear, but how much more braking power is still available?

I'm swapping the 1/4" rear hardline for 3/16" soon to see if that makes any difference. If not, the valve is coming out.

[chicane67]

Oh yeah....... 3/16" is going to make a big difference.

Inline Tube part number SCCB67M3, stainless one piece. Its about 86.00 shipped to your door but call the order in and request the 3/16" so there is no possibility for a mistake.

[CarlC]

Nah, that's too easy. Aircraft Spruce 3/16" SS line, custom bent with my trusty Imperial bender, and AN fittings throughout.

If anyone needs a 20' length of 1/4" stainless, I have an extra that's gathering dust.

[David Pozzi]

Carl,
Some master cyls have built in proportioning. I wonder if yours does?

I use the R4 in the Lola and they are pretty linear through the temp range.
Whatever Baer supplies is terrible the first time you hit the brakes.
Mary also faded the brakes due to fluid overheat. We have some higher temp fluid to try. We had the Valvoline synthetic in it the first time.

[CarlC]

That's why I wonder if the Wilwood proportioning valve works above 1500 psi. The valve is rated for 1500, but what happens above that? I don't think (since I don't know the way the valve operates) that it simply stops at 1500 psi. It's probably the highest recommended line pressure.

It's not far off. That's why I want to first try the smaller line, then remove the valve, then play with pads if necessary.

I've had pretty good luck with the Hawk HP Plus and the NAPA HD fluid. No fading so far, and the dust boots had melted away from a track day at Buttonwillow in May 2004. The pads are darn dusty though.

[David Pozzi]

How about the carbotech panther +?
It seems to hold in there more at higher temps. Laguna Seca generates a lot of heat compared to other tracks.

[David Pozzi]

Well,
Mary's car sat all winter, we looked at the pads, and the rears are shot! They are down to the metal on two rear pads!!!

[zbugger]

Hmmm.... That may have been part of the problem, David.

[David Pozzi]

We had the lockup problem the first day, I reset the prop valve that afternoon, we ran several sessions the second day, still had the problem, - it happened only on the first hard brake of a new session. I checked the rear pads the first day and they were OK but the way the pads wore, the outer pads were shot, the inner pads were not yet down to the noise making wear indicators.
New pads are on the way.

[Damn True]

Odd. How much wear did the fronts have?

Wonder if you got a bunk set of pads?

[Jagarang]

Did you season your system David, and how? I'll need to do this on Eternity before the Tour and have been wondering if any else does it or if it's just witchcraft? I know that Baer has the process outlined on their page, but nothing beats real world experience.

[Steve68]

A couple of hundred miles of easy stops, not try to lock them up right away,

[CarlC]

David,

I have, to the best of my failing memory, five track days on the current set. There's at least one, perhaps two more left. I have the rear wheels off the car if you need some pics.

Did the car have the as-supplied pads from Baer?

[David Pozzi]

We put about 400 miles on the street with easy stops, a fiew brake tests while setting up the balance and trying different master cyls. We finally went back to the vac booster.

On the track we started out easy too, later I turned up the rear bias to get a better f/r balance.
Carl, The fronts are less than half-worn. The rears appear to be very poor pads, they are what Baer supplied, we just got the HP plus and they are much more of a metallic pad.
I'm going to mic the pad thickness so we can monitor the wear. The outer pads in the rear wore more than the inner pads, the outers were gone, the inners had 1/8" or a bit more.

[CarlC]

I took a much closer look this morning at the rear pads. The inboard pad is worn more than the outboard. The trailing edge of the outboard appears more worn than the leading edge. I'll get them out and take some pics.

Buy some of the orange citrus cleaner from Home Depot. It works very well getting the brake dust off. The Hawk pads are very dusty.