964 Front brakes with Carrera rear?

[Noel]

I've been searching and couldn't find the answer to this question. I mainly track drive my 1980 911SC, but didn't want the expense of a 993 brake setup. I have Carrera front calipers with 24mm rotors on the car now, and I occasionally still have heat problems despite using Motul 600 fluid, track pads and cooling. Moving up to a 964 fronts with the VCI modifications and adapters would let me use a 28mm rotor, but what can I use for the rear, if I didn't want to pay VCI another $500 to modify the rear 964 calipers?

What is the formula for figuring if the bias would be appropriate if I use a set of Carrera rear calipers with a 24mm rotor (Which I have sitting in my garage)?

I know that Bill V says the best setup for most is the 993 fronts with the 965 rears, but I was looking for a more cost efficient alternative, since I am cheap.

As always, thanks.

[htron435]

If you want to be cost effective, install a parachute to deploy for the braking zone. Works well in other forms of racing. Or a boat anchor.

[MotoSook]

I've got a set of 951 calipers in front with stock Carrera setup in rear of my Carrera. Without the proportining valve, the bias is acceptable, but on cold tires or on street tires I have to be careful as I can lock the fronts up pretty easily.

On the track, the setup is a big leap from the stock Carrera. I use to have to bleed my brakes every or every other session. I'm probably harder on brakes than I should be, but the bigger calipers and rotors up front solved my problem.

The one complaint I have about the VCI kit is that the rotors rub on the A-arms. So you have to grind a bit off the A-arms.

Have you tried cooling? I never did and I still don't have any cooling to the rotors. I was too lazy and spent the money for bigger rotors instead.

[Noel]

Thanks Souk. Jay, thanks for the parachute recommendation...very helpful.

Yes, I have the AJ-USA under a-arm cooling now. I drove HTRONs (Jay's) 81 SC at Mid-Ohio last weekend and really liked his 993/965 brake setup, but the expense of that setup is extreme and too much for this cheap skate. However, if it really is the best option, I'll do it, but, I already have a pair of rear Carrera rotors and calipers sitting on a shelf in my garage so I would love to use them.

Any idea how Bill V calculates the front/rear bias? I thought there was a formula based on the caliper cylinder size.

[Noel]

BTW, Souk, what size rotors do you have with your 951 calipers? 28mm wide?

[Bill Verburg]

Carrera rear w/ 964 front(calipers&rotors) will work out ok. Don't use a p/v

Bias is primarily a function of effective rotor diameter and hydraulic piston ratios and p/v(if any). Secondarily tire size and suspension setup. Tertiarily aero effects

[MotoSook]

Noel,

I'm using the 28mm 951 rotors, a lot more heat capacity than the stock rotors. The VCI kit uses a spacer behind the factory spacer, which put moves the hub out a bit to clear the A-arm, but the rotor still rubs on the A-arm. You almost have to grind all of the flanged portion off in a 120 or so degree around the arm. It was a good compromise prior to the wave of big brake options. It's still a very cost effective upgrade (doing just the front and running the stock rear).

Since you have an SC you won't have the proportioning valve (p/v) to remove. Just run the Carrera rear brakes and you should be fine. I am using the stock master cylinder and the peddle feel is fine.

I use to stomp on the brakes without worry of locking them up, but now I have to be careful. Even so, knowing that I won't lose my brakes during a session is confident inspiring, and allows me to concentrate on the braking point and line at corners. Much better for my lap times

Good luck with the upgrade.

[Noel]

Many thanks Souk, that was exactly the info I hoped to receive.