bavareze

as I am starting the engine on my 88 carrera, the brake pedal goes down a little bit. which shows the booster is working. Then I check vacuum with a gauge and I see 25 inHg.

however, while driving the pedal feels much harder than most cars I ever drove.

furthermore, front wheel seem to lock too easy. Might be the tires, however I feel other vintage cars I have such as my 98 C320 brake much better, despite all magazines and reviewers of the era calling the 911 braking to be better than anything else on the planet...

any ideas?

thanks

theiceman

What pads are you using ?

bavareze

i can't recall that. i only remember i used new sebro rotors in the front - made in germany.

i did not touch yet the rear brakes since I purchased the vehicle, i will probably take care of that sometimes this spring

Drisump

I would say my 3.2 has excellent braking and the feedback/effort required is very nice as well. Like Icy says, many metalic pads give a hard pedal but you should also check the action of your brakes. If a caliper piston is seized, all the braking effort has to be made up with the working side. Functionally, the brakes stop the car but much of braking quality is lost. Cheers

r911

how old is the brake fluid?

if the answer is "I dunno" then change it all immediately

how old are the rubber brake hoses?

if the answer is "I dunno" then change them all immediately

bavareze

ok, i just did the front wheel bearings and brakes, together with the rubber hoses.

when I have more time I will do the same for the rear. I want to lower the car a bit at the same time, so I need to find even more time for this job.

and before that I have to do the same thing for my old beetle that has far more problems.

so thanks for the input, I'll probably update you in about 3 weeks or so!

Mark Salvetti

When I first got my 911 one of the front wheels locked up prematurely in the wet. Part of that was the old, crappy tires, but I think the corner balancing of the car was also way off. Once I got new tires and had the car aligned and corner balanced, the problem went away.

If you are going to lower, you'll probably need to realign, especially if you re-index the rear torsion bars. Make sure you use a shop that will corner balance as well.

Mark

Amber Gramps

Interesting info on the pedal drop at start up. I don't recall my brake pedal doing that. It may, but I don't remember it. I always thought the Carrera brakes we weak sauce so when the opportunity came to swap in 930 brakes, I jumped on it. Now the car has brakes....But maybe I have a bad booster and would really have brakes if it were working. Don't like to admit it, but dang it, you have peaked my interest....And maybe my booster is bad. Will have to look into this. Funny thing is that I have a known good booster in a box on the shelf that I owe to Ken S. LOLzzz

rusnak

Braking performance basically comes down to the initial clamping force or "bite" and then "fade" or resistance to that.

The stock brakes come with more than enough initial bite to lock all 4 wheels at virtually any speed. The 3.2 comes with front rotors that are the same thickness as Big Reds by Brembo. So there is a lot of fade resistance due to speed. The thickness of the rotor allows the rotor to absorb heat, which the friction force creates from kinetic energy.

You didn't mention if the pedal is stiff as in, hard to budge, or does it move easily but the pads seem like bricks and require a lot of leg effort? If the latter, then I think you should change the pads. Also check the rotors for a glaze coating or rust. If that's the case, then you might just need to drive the car and excersise the brakes, but do so carefully at lower speeds.

r911

and then there's this possibility...

Bill Verburg

yes there's clamping force which creates brake torque but it depends solely on how hard the driver pushes the middle pedal. Yes, different pads have different initial bite and release and temperature related friction curves, but the differences are subtle and not usually noticed by street drivers. How much of that brake torque can actually be used depends on multiple factors including the tires grip the normal force on a given tire which in turn depends on the cars dynamic and aero characteristics. At speed on a warm track w/hot tires with a lot of weight transfer and an lot of aero and little slip angle the fronts can use a lot of brake torque, hit a patch of oil and not so much. Similarly in back lowish speeds and little slip angles you can use a lot more rear brake torque than when turning w/ lots of slip angle present.

for a 3.2 @70 bar line pressure(that's a pretty hard stopping effort) there's 1444N-M of brake torque at the front axle and 639NM at the rear. The ratio. is 2.260. Below the knee for the 33bar p/v the ratio would be 1.220 That means that there is a lot of front brake bias above 33bar(medium stopping effort) and a lot of rear bias below 33bar line pressure. It's easy to lock fronts in a hard panic stop. It's less easy to lock the rears but it can be done.

There will be no fade in a single stop unless the driver modulates line pressure. There will generally be fade over time from multiple hard usage such as track usage.

3.2 rotors are 24x280mm in front and 24x290mm in back, there are several big reed setups used on 928,964 and 993, all have 32x322mm front rotors, 964t has 28x290mm rear and 993RS has 28x322mm rear. So no 3.2 rotors are nowhere near as robust as Big Reds.

Generally the pistons are exercised as part of the brake bleeding process, it's best to do this manually w/ a pad spreader.

To the OP, a 3.2 doesn't generally have a particularly high/hard pedal wrt to other Porsches but it will wrt to most other cars. Assuming all other aspects of the brake system are nominal. Pad choice is a big factor in feel. All pads have a friction curve that is temperature dependent, use a track pad on the street and it won't get hot enough to generate much friction, Even in the street pad category there is a lot of variation, many cars have been fitted w/ low dusting pads which generally don't bite well, Pads that do bite well tend to make a lot of dust.

the 3.2 left the factory w/ Textar pads which are a decent compromise but do dust a lot, Ceramics tend to have much less dust but also less initial bite.

rusnak

Bill, I appreciate your sarcasm.

But your tech discussion is a rather Captain Obvious re-statement and rather meandering mash of data which also assumes given values for the driver's level of Nm force applied via the middle pedal. But we can ignore that.

I think it's your posting style mainly that makes people feel that they have to put up with you in order to dig for nuggets of math mixed in with your turds of contempt. In other words, your discussions are pretty much uni-directional. I don't wonder why.

n8kruger

The brake pedal feel in the 911 is much harder than most normal cars. I replaced the front pads with the low dusting Street pads that pelican sells and the pedal feel significantly softer. So much so, that I had an expert shop bleed the brakes just to make sure I didn't screw it up.

Bill Verburg

Post BS expect response

Try picking a topic where you have some competence

Amber Gramps

Bill I think Russell was trying to help. I've read the OP a dozen times and still don't understand what he is saying. His pedal is hard??? that's better than soft, right??? ....and ya, you are the brake and wheel God, but Russell is there for me day in and day out. He's sent me a spare DME, AFM, ICV, and numerous VOA meters and even a pair of Recaro seats once upon a time all without expecting a dime in return. .... You may be offended that he isn't as knowledgeable as you on brakes, but look at what we have to work with here. Russel is at least trying.....unlike some folks that pop in a couple times a month when they see an opportunity to solicit business. Should we all just keep our mouths shut if we don't have a PHD in the topic at hand?....or should we at least try to work through it?