84 911 Brake Upgrade

[gab997]

Getting a set of 993 calipers for my track toy and have a question. I am planning to install the front's first then around month later the rears. I understand that the larger mc is needed to push more fluid on the new brake setup. My question is, will I have any issue running the existing mc with the 993 fronts and stock rear calipers until I can get the rears modified to accept the 930 rotors? I would then install the larger mc when I install the rears.

Thanks,

Greg

[JeremyD]

just longer brake pedal travel = it takes more fluid.

[ShakinJoe]

How much more fluid... a gallon?!

[JeremyD]

for you Joe - a gallon - for gab997 just a little more travel.

[175K911]

Besides the mc, don't forget that the brake bias will be significantly shifted to the front so you'll need to be aware of front end lockup.

[KTL]

I'd install the MC now as long as you're messing with the brakes anyway. Besides the longer pedal throw, the bias will be rather goofy with the 993 fronts, stock rears and the stock MC. This is not only on account of the bigger front caliper pistons operating with the stock MC and stock rear calipers, but also because you'll still have the pressure limiting valve in place on the rear brake circuit. So you'll be even MORE front biased than one would suspect when simply considering the difference in piston sizes between the front and rear calipers.

If you decide not to do the MC at this time, at least remove the PL valve in the rear circuit. This is located in the front trunk near the smugglers box and steering shaft cover.

[911st]

If it is the 993 normal front calipers, you might try the stock Carrer master cylinder first. I have heard that one racer runs this set up very well. Also, remove your Carrera Proportioning Valve. The 993 w Carrera rear is a supposed to be a well balanced system.

Most the brake experts here will remind you that you need bigger front rotors to get the best form such a conversion. There may be a new larger front rotor from the latest 911 Brembo Big Brake kit that bolts right up that might be a new way to go but someone needs to look into.

Not an expert, just what I believe so far.

[KTL]

993 fronts with Carrera rears is too front biased. 964 (smaller Brembo, also from 951, 968, 944S2) is a better bias. 1.6 hyd. bias ratio seems to be a good number for 911 cars

993 Front/993 Rear = 1.57 hyd. bias ratio
Carrera Front or SC Front (same piston sizes)/SC Rear = 1.60 hyd. bias ratio
964 Front/964 Rear = 1.72
Carrera Front/Carrera Rear = 1.19 hyd. bias ratio w/out pressure limiting valve installed = very rear biased
964 Front/Carrera Rear = 1.64 hyd. bias ratio
993 Front/Carrera Rear = 1.83 hyd. bias ratio = too much front bias

And without a doubt the 993 fronts need to have a larger rotor. The simplest way to go is a 309 x 32 Wilwood HD rotor with a simple flat hat and simple caliper adapter block. It works. Period.

[911st]

Thanks for the correction, I thought the 993 normals were the same as the C2

[gab997]

Originally Posted by ShakinJoe

How much more fluid... a gallon?!

Gallon of SRF ouch! Over 240.00 in fluid alone....

[gab997]

Originally Posted by KTL

I'd install the MC now as long as you're messing with the brakes anyway. Besides the longer pedal throw, the bias will be rather goofy with the 993 fronts, stock rears and the stock MC. This is not only on account of the bigger front caliper pistons operating with the stock MC and stock rear calipers, but also because you'll still have the pressure limiting valve in place on the rear brake circuit. So you'll be even MORE front biased than one would suspect when simply considering the difference in piston sizes between the front and rear calipers.

If you decide not to do the MC at this time, at least remove the PL valve in the rear circuit. This is located in the front trunk near the smugglers box and steering shaft
cover.

I have an event coming up at Sebring mid november and know that I am not going to have enough time to modify the rears and get them installed. I could push it and get the MC installed. I will have to look in at the manual and see where the valve is to take it out. When I install the 993 rears will I need to reinstall the valve?

[JeremyD]

you doing instructors weekend?

[KTL]

The completed 993 brake setup installed on your car requires that you remove the PL valve anyway, so might as well remove it now and avoid unneccessary bias.

However I really can't attest to how the system will operate (too much pedal travel?) with the stock 20.64 mm MC. I do know that a number of people have installed 951/964 front calipers (40/36 pistons) with larger 299x28mm front rotors (this is the front rotor used in VCI's C2 brake upgrade) and kept the stock MC and Carrera rear calipers with positive results. The Carrera rear calipers have fairly large 42mm pistons and thus the reason for the PL valve in stock system. So that's why you can get away with using the small front Brembos with the Carrera rear calipers and still have suitable F-R hyd. bias.

[gab997]

Originally Posted by JeremyD

you doing instructors weekend?

Yes, looking forward to it!

[gab997]

Originally Posted by KTL

The completed 993 brake setup installed on your car requires that you remove the PL valve anyway, so might as well remove it now and avoid unneccessary bias.

However I really can't attest to how the system will operate (too much pedal travel?) with the stock 20.64 mm MC. I do know that a number of people have installed 951/964 front calipers (40/36 pistons) with larger 299x28mm front rotors (this is the front rotor used in VCI's C2 brake upgrade) and kept the stock MC and Carrera rear calipers with positive results. The Carrera rear calipers have fairly large 42mm pistons and thus the reason for the PL valve in stock system. So that's why you can get away with using the small front Brembos with the Carrera rear calipers and still have suitable F-R hyd. bias.

I would assume that the proper mc would be the 930 mc p/n 930-355-011-03-M4.

Thanks everytone for the input!

[JeremyD]

you ought to hook up with me and shakinjoe - we are doing almost the exact same upgrade to his brakes next weekend. He's in St. Petersburg

[KTL]

Originally Posted by gab997

I would assume that the proper mc would be the 930 mc p/n 930-355-011-03-M4.

Thanks everytone for the input!

That's the right one. Wow, the prices have really gone up on these over the years! Mine cost me $125 in 2005.....

[KTL]

Originally Posted by JeremyD

you ought to hook up with me and shakinjoe - we are doing almost the exact same upgrade to his brakes next weekend.

No way. It's actually going to finally happen?

[JeremyD]

He was actually ordering stuff earlier in the week.

[gab997]

One other question. When changing over to the 993C2 brakes will the existing brake lines work or do they need changed out as well?