Jason F

The "big red" twin turbo brakes on my 1977 911 tend to lockup the front tires when threshold braking, and generally don't seem very dialed in because of this. I have the front and rear twin turbo brakes, not just the front.

I would like my front/rear brake bias to be adjustable, so I can dial it in at the track without swapping pads.

What is the recommended product for this, and how much should I expect to pay including installation.

Input is greatly appreciated.

Jason
1977 911s 3.2

Steve Weiner-Rennsport Systems

Hi Jason:

What you have noticed about the brake bias setup of the Big Red TT brakes is normal.

You have 2 choices (aside from installing different rear calipers):

1) Install a Tilton lever-style adjustable brake bias valve in the front circuit.

or

2) Install different brake pads front-to-rear to alter the bias.

We do all three things but I'd suggest the latter 2 as less expensive alternatives that work very nicely.

If I knew what pads you are using, I'd be happy to make some suggestions.

Bill Verburg

Assuming that you put the 322mm rotors and Big Reds on the front. What's on the back? What m/c is installed?

Jason F

Bill & Steve,

I believe I have the 930 Turbo Master Cylinder.

The brakes are new all around, and I don't know the specific size of the rear brakes, but the disks and calipers are definately HUGE like the front. I got the kit through Racers Group.

Right now, I have on some street compound pads of forgotten brand, which seem to work good at the track except for the brake bias issue, which was slightly less evident with the Pagids.

I also have Pagid Black, and Dark blue that I have tried, but I could not bear the screeeeeeeeeccccccccchhhhhh.

The Tilton adjustable lever appeals to me. Do you sell this, Steve, and how intricate is the installation. (how many hours can I expect to pay someone to install it)

Thanks,

Jason F
1977 911s 3.2

Bill Verburg

First you need to know what you have on the car.

Right now we are pi**ing into the wind.

If you have Big Red front on 322 and the matching 993tt 28/28 on 322 rear then yes, the bias will be way too front, but no, a p/v on the rear circuit will not help(it will in fact make it worse)

I use and have always advised 3034 or tyhe 993RS 30/36 rear calipers to balance the Big fronts. W/O any p/v!

Th 930 m/c is the correct one, be sure that is what you have.

Jason F

A p/v will help if put on the front circuit as mentioned by Steve, correct? I assume this will add a bit to pedal pressue. As it is, it doesn't take much pedal input to lock them up.

Bill, here's what I know.

930 master cylinder (ty shop where the brakes were installed told me thats what I have)
993 Twin Turbo front brakes on the front, 993tt rear brakes on the rear.
Fronts lock up too soon, and I want it more balanced, and don't want to fuss with pads & calipers.

The tilton adjustable brake proportioning valve seems like what I am after. I will discuss this with my local shop for install cost, and take it from there.

Thanks for the input, it is all valued.

Jason F
1977 911s 3.2

Bill Verburg

With all due respect to Steve, do you really want to introduce a non linear device to your front(main) brake circuit. A device that the harder you wish to stop cuts an increasing % of your braking power?

Jason F

Interesting l...

Is it not safe to put a p/v on the front brakes? This is a pretty big consideration!

Jason F
1977 911s 3.2

911pcars

Since you have spent the big bucks on big reds and rotors and such already, it's just a relatively incremental amount more to go with a twin master cylinder pedal assembly. That way, you can use the pedal assembly's balance bar to trim the front-to-rear brake force (also features dash-mount, on-the-fly adjuster). Not sure how serious you are, but this is the next step for a serious track car.

However, as Bill suggests, find out what you have first, then go from there.

Sherwood

Bill Gregory

I haven't looked at one for awhile, but don't the MC have the size on the casting? If so, you could check to see if it says, roughly 24mm for the turbo or 20mm for stock.

I agree with Bill that putting a bias valve on the front wouldn't be my first choice. Sherwood recommended a good option, or, Bill also mentioned what I would probably do first, which is install the rear calipers which have the largest pistons. This given you don't want to approach this with different brake pad compounds.

smb51315

You need to alter the crack point on the M/C. I've done mine. Balance is now 50/50.

911pcars

Please explain "crack point". I'm not familiar with it.

Thanks
Sherwood

smb51315

This is all from memory and i'm sitting at my office desk and not in my workshop but from what i can remember....The master cylinder has a dual piston that moves over the front and rear brake outlets. When you press the brake pedal the two springs on either side of the pistons compress at different rates. The crack point is the moment when the second spring starts to compress after the first (both springs are different lengths and rates.) What you need to do is take off the m/c, remove the circlip and pull out the piston. You then need to change or shorten (only by a few mm) the front spring. This makes it stiffer so applies a higher rate sooner to the second spring. Now if you replace the piston and springs and push the piston by hand you will see, when you look down through the brake fluid outlets the two pistons moving over the outlet holes at different times. What you need to achieve is for the front piston to move over first hole and the the second piston to quickly follow, rather than lagging is it does now. On my sc I use a turbo m/c I think it's 23mm with 930 front calipers and 944 turbo's on the rear. My front brakes still come on first but then the rears activate almost immediately, the front and rear pressures then move in tandem giving a about 50/50 brake split through the rest of the brake pedal travel. When I lock up now both front and rears lock at the same time. ps. If you end up with too much rear brake you can install a pressure reducer in the rear circuit.

Hope this is clear enough.

Steve.