Brake upgrades for early 911 help please

[74USCarrera]

I am having trouble getting enough stopping power on my early 911 (1969). It is set up as a hotrod, so upgraded suspension etc. When I got the car, it had the early S brake setup, which I had rebuilt, as the car just did not have any stopping power (it only weighs 2000lbs!). After the rebuild, they were remounted and still no difference. So, I then had a set of later Carrera fronts put on and although it is better, I still lack the instant brake response and firm braking that I would like. This is especially evident on track days.

I am running 15 inch fuchs (7s and 8s), so I know my options are limited. But, are there any good solutions (porsche or aftermarket) that will help my little car stop better?

Thanks for any help/advice/suggestions.

Nathan

[911 Rod]

Did you try race pads?
Carrera brakes should work fine for that car as long as you don't overheat them.

[jpnovak]

What exactly is the issue here?

You mention no stopping power. You mention lack of instant response and firm braking.

What has been addressed in the braking system besides rebuilt or replacement calipers? What rotors? Are they pitted or glazed?
What pads? How old are they?
What is the condition of the master cylinder? Does it hold pressure? What MC is in there? Any chance a 17mm 914 MC is installed?

Your description of lack of power and soft pedal point to MC issues or bleeding issues.

The stock S front and M rear setup should be more than enough for a lightweight 69. They just need to be working correctly.

Pads make a big difference in initial bite feel and overall pad-rotor friction.

The only reason to go to the Carrera calipers are the more thick 24mm rotors for heat dissipation.

[wayner]

Are you standing on them in the track braking zones, or are you braking like you would on the street and building up lots of heat for far too long, thus affecting your braking into the next corner?

Unlike other more modern cars you've really got to stand on them (relatively speaking).

Brake a little to shift the weight, then immediately brake a LOT

Let sat least eliminate driving technique before throwing money at it.
(and, as the others have said, don't underestimate the value of the right pads and fluid)

[djdsc]

Hoses. If they haven't been replaced. They swell and deteriorate over time and no amount of pushing will overcome it.

[James Brown]

http://vehiclecraft.com/Brakes/930_upgrade.htm
these guys have all the answers that fit under 15" wheels. if turbo brakes don't help, nothing will

[Ayles]

Originally Posted by James Brown

930 Brake Upgrade 911 - Carrera - 914 - 914/6
these guys have all the answers that fit under 15" wheels. if turbo brakes don't help, nothing will

Wasn't really expecting to see the $6000 + price tag there!!

[James Brown]

Originally Posted by Ayles

Wasn't really expecting to see the $6000 + price tag there!!

not too many years ago they were around $4k so get them while there "cheap"!

[VFR750]

Do you have vacuum boosted brakes or non-assisted? Non-boosted master cylinders require significant foot pressure.

[Bill Verburg]

Originally Posted by VFR750

Do you have vacuum boosted brakes or non-assisted? Non-boosted master cylinders require significant foot pressure.

Some of the 2.7RS guys we are on track w/ use non boosted 23.8mm m/c, talk about foot pressure.....

[winders]

I use a non-boosted 930 MC for my race car with 930 rear brake calipers front and rear. There is no proportioning valve either. The brakes don't seem to require an inordinate amount of foot pressure.

[Bill Verburg]

Originally Posted by winders

I use a non-boosted 930 MC for my race car with 930 rear brake calipers front and rear. There is no proportioning valve either. The brakes don't seem to require an inordinate amount of foot pressure.

911 A or S front & M rear has 11774.69 sq mm of caliper area, 930 front & rear has 18145.84 sq mm of caliper piston area
if the ea use the same 23.8mm m/c???

You do the math smart guy...

[winders]

Originally Posted by winders

I use a non-boosted 930 MC for my race car with 930 rear brake calipers front and rear. There is no proportioning valve either. The brakes don't seem to require an inordinate amount of foot pressure.

Originally Posted by Bill Verburg

911 A or S front & M rear has 11774.69 sq mm of caliper area, 930 front & rear has 18145.84 sq mm of caliper piston area
if the ea use the same 23.8mm m/c???

You do the math smart guy...

No, smart guy, you do the math. I have 4 rear 930 calipers on my race car.

I'll do it for you: my piston area is 11,309.73 sq mm.

In case you hadn't noticed, that is less piston area than the 911 A or S front and M rear setup.

[Bill Verburg]

Originally Posted by winders

No, smart guy, you do the math. I have 4 rear 930 calipers on my race car.

I'll do it for you: my piston area is 11,309.73 sq mm.

In case you hadn't noticed, that is less piston area than the 911 A or S front and M rear setup.

The brakes don't seem to require an inordinate amount of foot

Superman has blessed us w/ his feelings!!!

most mere mortals will disagree w/ you on that point

the pedal ratio of a stock A or S & M w/ 19mm m/c is 20.656 w/ 23.8 it goes to 13.234 thats 56% more effort required to achieve the same line pressure.

[winders]

Maybe....but you are the one that thinks my race car should be undriveable with the the 1:1 brake bias ratio it has.

[Tidybuoy]

Guessing from your signature, you have a '74. I also have a '74 and when I first got the car the brakes were terrible. I rebuilt all 4 calipers and they still sucked.

At some point I decided to change my struts so that I could use "A" calipers from an SC (not Carrera). I found, thru this forum, PMB performance and the sell "A" calipers that they rebuild for a very decent price. They will also rebuild your calipers if you send them in. Buying rebuilt or sending yours in is about the same price and I think I paid $375 per axle. http://www.pmbperformance.com/brake-calipers.html

The difference was amazing. My first noticeable item was that I now had to keep my foot on the brake when sitting at a red light or the car would roll into the intersection - this indicated that my old brakes were dragging.

My non-boosted '74 does not have the pedal feel of a modern car and most people would think there is something wrong. But! If you stomp your foot on the pedal, you could very easily throw your passenger into the windshield. If you've not had an early '911 for long, it takes getting used to but eventually, you realize how great non-boosted can feel.

Here's my brakes after they came back from PMB:

[Bulldog9]

+1 on PMB. Eric Shea is a great guy who does great work.

I'm not familiar with what parts and upgrades you are describing, but in my experience early 911 Brakes require much more force than other cars.

My 912E uses A and M calipers with solid discs front and rear. I pulled the car out of the woods after sitting 15 years so needed to replace everything.... I upgraded to Vented rotors and calipers front and rear with Hawk performance street pads, new MC and all lines except the center tunnel line to the rear. Once the pads were seated rotors broken in, the brakes are outstanding but need real force applied. Wasn't prepared for this at first. These upgrades did not increase swept area, just vented rotors now and should perform better as far as disbursing heat. The pistons and pads are identical in size. I used standard zimmerman rotors front and rear. Cant compare to modern cars. The stock system is more than adequate. It may be your expectations.

If everything is working properly (MC/calipers), I would:
- Bleed the brakes
- Replace the flex/rubber lines if they are older than 10 years
- Swap out the pads for more aggressive

And off topic . . . . . . did some of you guys in this thread stumble over from the Bimmer forums?

[74USCarrera]

Thanks for all the wonderful feedback/ideas advice. I can't claim to know what a lot of it means, but the following has been done also:

Replaced master cylinder (that was what the problem was initially thought to be)
Rebuilt the S calipers (made no difference)
Bled brakes several times and used good fluid (no change)
Installed carrera brakes (changed the brake performance noticeably, but probably only 50% improvement)

I am not sure what pads were put into the car, but I said that I do my mostly street driving with a few track days each year.

I like the idea of changing pads, as it seems like a reasonably quick and easy way to figure out if that would give me what I am looking for.

Sooooooo, any advice on pads that would get me much better braking and also not be horrible to live with on the street (I have heard race brake pads can provide lots of squeeking and no bite until they warm up).

Any ideas on a good quality pad that will strike a middle ground?

Thanks guys

Nathan

[Bill Verburg]

Originally Posted by winders

Maybe....but you are the one that thinks my race car should be undriveable with the the 1:1 brake bias ratio it has.

You get away w/ it because your pedal ratio is so low that it makes line pressure generation so difficult that lock up is rarely if ever approached.

My response above was directed to VFR750, a track friend, some of the guys we run w/ are 2.7RS fanatics but run the stock S/M w/ 23.8mm m/c. Track guys like a high hard pedal and aren't locking the brakes much if at all. Some even have 3.2 Carrera brakes w/ no p/v and the 23.8. They, like you, like the high hard pedal and get around the bias issue because the pedal ratio is so low that it's very difficult to lock the brake. w/ your setup and w/ the 3.2 Carrera if the brakes lock the rears will lock before the fronts, this is not something most drivers will find to be desirable.

A common complaint of drivers new to the non boosted 911 is the amount of leg needed for the brakes.

To the op, for more cold bite you want to avoid track or even performance oriented metalllics. Textar, Ate, Bosch, Pagid all have good street oriented pads.

[bkreigsr]

Originally Posted by 911 Rod

...Did you try race pads?....

Not the best alternative. 'Race' pads have a much higher operating temperature and have very little bite outside of track conditions. Most manufacturers have a chart on their site listing the optimum operating temp range for the pads they offer. Check out the Pagid, Hawk and KFP sites to name a few.
Bill K