Dead Brake Feel

[UK Carrera]

Hi, I've done a search but not turned up anything particularly conclusive.

How can the 3.2 Carrera's dead brake feel be reduced?

My car has covered approx. 44000 miles and is just about due for front pads and discs (pads have about 5000 miles life in them).

Whilst reasonably effective (and better with some heat in them) the brakes have a solid pedal which I can only describe as 'dead' feeling. I'd really like to get more feedback.

Car is used on the street only.

Stainless braided hoses seem to get a cautious recommendation.

Front calipers were rebuilt just a few months ago, along with renewal of the flexible and solid brake lines (with OEM parts).

Any suggestions for mods that make a real difference to brake feel?

[Jdub]

Rebuild the master cylinder. You have already done what ought to be done with the calipers and brake lines -- that would have been the first thing I would have suggested.

New brake fluid of course...that might help?

John

[Doug Zielke]

Pads make a big difference in pedal feel.
John Walker recommended Metalmasters to me, and I liked the way they make the brakes feel and work.

[Superman]

Not sure what sort of "dead pedal" experience you're trying to avoid, but most folks want a solid pedal feel, with no sponginess. New pads help give this because their thickness displaces quite a bit of brake fluid. That is, there is less fluid in the system to compress.

[89911]

Dead feel. Interesting. I suppose many factors can be the cause. The biggest source, ruling out any problems with your present system is the pads. You may want to try a more aggressive pad for more feedback. Since the 911 brakes are not power assisted, they never seem to have the intial "bite" an assisted system has. This will make a casual observer possible feel they are lacking in stoping ability. The braking effect is very easily modulated with pedal pressure and after a short trial period can be easily varied to adjust lockup thresholds. I've since upgraded to 930 calipers and rotors and a turbo master cylinder. The pedal action is higher up now, but still takes the added effort to modulate between lockup and threshold stopping.

[masraum]

Actually the brakes in your car (UK Carrera & 89911, and mine for that matter) are power assisted. 3.2L Carrera's had power brakes. They just aren't overassisted like most American Barges.

[HarryD]

Hi,

I can't speak for the pad issues as I think mine are just fine with my plain vanilla Pagid Street Pads.

A long time ago I discussed the use of SS lines with a local expert. He told me that, in theory ss lines are better during very heavy braking since they will not swell like standard rubber lines. That said, he went on to say that unless you are an F1 driver, you will most likely never notice the difference. Add to that the fact that ss lines are more prone to sudden catastrophic failure (n race cars they inspect and/or replace these lines frequently), he felt 99% of the drivers would be better off with the OEM Porsche line that can last over 10 years.

On my car, 2 years ago, my wrench noticed that one of the lines looked like it was an orignal part (29 years old). We replaced it due to age but on inspection, noted no visual clues indicating an impending failure.

[UK Carrera]

Thanks for the replies.

The brake pedal is very solid, but the brakes lack initial bite and what I would call adequate feedback.

Since it will need pads and discs shortly, and these probably influence 'feel' more than any other, are there any suggestions as to what I should go with. I'm based in the UK, so may be limited on what I can readily get hold of.

I've seen Zimmerman drilled discs (rotors), but should I stick with OEM pads? Don't want to run the risk of noisy (squealing) brakes that some uprated pads seem to give.

[masraum]

stick with solid non-drilled rotors, they won't help. I went with the Axxis Metalmasters and they work great.

[89911]

Originally posted by masraum
Actually the brakes in your car (UK Carrera & 89911, and mine for that matter) are power assisted. 3.2L Carrera's had power brakes. They just aren't overassisted like most American Barges.

Are you sure about that? I've had my complete system redone and its pretty much a stand alone system, (no vacum hoses or items coming from the engine.) There also is no noticable braking advantage when the engine is off and coasting compared to when its running. Maybe your thinking of a 964?

[surflvr911sc]

You definitely have power brakes. I don’t remember when they went power but it was somewhere between ’74 & ’78.

There is one vacuum line that runs from the engine to the booster, which is behind the master cylinder. You can rebuild everything else and not touch the booster.

[masraum]

Positive, unless your car has been modified, and yes, it doesn't really feel like much when the car is running on my car either. I have often thought of pulling the hose to check, but the brakes work, so it isn't that big a deal.



uh, the arrow was part of the picture, the black round thing is what I am refering to.

[89911]

OK, I'll admit I'm wrong. Do they run a vacum line all the way from the engine through the tunnel? I was never able to trace the hose that was in the picture. But then again, I never really tried.

[masraum]

I believe there is a metal line with rubber at each end, but I have never tried to trace it myself. I have often wondered if mine was working as I don't generally feel a difference when I start the car as I would expect to, but as I said, the brakes work really well, and the car runs beautifully.

[surflvr911sc]

The metal line comes up in front of the pedals, toward the center of the car, and the rubber hose takes over and plugs into the other side of the fitting you see in the pic. If you remove the driverside floor board you should see it easily.

In the back, the hard line goes through the tunnel and comes out where the fuel lines, brake lines, shift rod, etc. come out just forward of the transmission. Then it's rubber line the rest of the way to the engine compartment.

That's how it is on my '81 anyway.

[ChrisBennet]

Without the booster, you would really need to stand on the brakes to stop. If you aren't used to it, you'd think earlier cars had no brakes.
-Chris

[bb]

I got done changing over from the 19mm to the 23mm master cylinder. I had to replace the front brake lines since they were all rusted. Here is my problem:
I have a great pedal now, but the car doesn't stop as well as it did before. If I stand on it I get a great pedal,(not spongy, or soft). But it doesn't want to stop that great.


Any suggestions?

Oscar
Akron, Ohio

[ChrisBennet]

Originally posted by bb
I got done changing over from the 19mm to the 23mm master cylinder. I had to replace the front brake lines since they were all rusted. Here is my problem:
I have a great pedal now, but the car doesn't stop as well as it did before. If I stand on it I get a great pedal,(not spongy, or soft). But it doesn't want to stop that great.


Any suggestions?

Oscar
Akron, Ohio

What year is the car?
-Chris

[dtfastbear]

Oscar,

You've changed the "hydraulic ratio" (is that the right term?) by going to a larger master cylinder, meaning that you should expect to have to exert a lot more force at the pedal to get the same force at the brake pads.

I don't have the exact formulas, but you are basically dividing the pressure at the brake pedal (times the mechanical advantage of the brake pedal lever) by the area of the cross section of the bore of the master cylinder (pi*radius squared). The difference between a 19mm master cylinder and a 23mm one will be an increase of about 30% in the force required at the pedal to get the same force at the brake pads.

The advantage of the 23mm cylinder is, of course, that the pedal doesn't need to travel as much to displace the same amount of fluid as the caliper pistons move, so the pedal feels harder. It is definitely a trade off.

Can anyone confirm that my theory/formulas/math is basically correct?

Dean

[widebody911]

Here's a trick I use when it doesn't seem my pads are getting a good 'bite', particularly after I swap pads front to rear. I take a DA with #36 or #40 paper, and rough up the rotors really well. Then go out and do a couple of hard stops. This will clean up any glazing on the pads and rotors, and give everything a fresh start.