swftiii

Thanks Steve - I'll give this a try and then I'll have some real facts and we don't have to continue to guess.

-Skip

Bill Verburg

964 4 piston front and rear calipers used the same basic caliper and pads but there are differences
fronts are wider and have 36/40 pistons
rears are narrower and have 28/30 pistons

as has been mentioned the pedal goes soft because at least 1 of the calipers is getting too hot, usually the fronts

you can use temp paint on the edge of the rotors too put a metric on how hot

964s w/ 2 piston rears use the same rotors as the ones w/ 4 piston rears, the size of the pistons however means that there is more rear bias w/ them than w/ the 4 pistons. This means that more heat will go into the rear than w/ the 4 piston version.

So if you change the 964 2 piston rears to 964 4 piston rears you want to change the p/v to one that allows more pressure to the back to counteract the bias change from the calipers. I would go further and suggest that the p/v be removed totally. Even w/ a 55 or 60bar p/v instead of the 45bar oe one there is more front bias than I like to see. Again here heat paint can help monitor actual conditions, the fronts will almost always run hotter than rear but you also do want the rears to take as much of the load as possible

other things that help are modern track pads w/ built in heat barriers, Pagid yellow, black and grey have this feature as do other pads that I am not as familiar w/.

chassis set up can also affect how much bias you run, lower/stiffer cars and cars w/ more effective lsd can take advantage of more rear bias than others.

Jimjacqmx5

Ah. Poor dude I can sympathise with you.
For the Aussie update.
I have 'totally' flushed the system and added stainless goodridge brake lines.
Off to a hillclimb this weekend which may or may not test the effectiveness of this.
I have also got a new master on the way at the suggestion of Mr Bagodonuts?!!
Hopefully this will help and if the issue is still there, it's heat paint and more investigation.
I currently have the zProject Mu pads installed but think I may go back to the Pagid blacks for the track as the issue seemed less noticeable with the Pagids.

Again, thanks for all the tips.

I should also follow up re the bias valve as I updated but just whacked the bigger rear calipers on with no other changes as this is what others here have done with no ill effects.

I've got some big cams on the way so I better sort these brakes!!

joey bagadonuts

I would tend to agree and have removed the p/v on my car equipped with 993TT fronts and standard 4-pot 964 rears. I didn't try this when I ran stock brakes and p/v but, based on the difference in pad wear rates (3:1 front vs rear), it would seem that a p/v change made sense.

Has anyone using stock 4-pots all around removed, bypassed or gutted their p/v? Any impressions?

Here's Garrett's write up on how to gut your stock p/v (this mod is reversible ).

joey bagadonuts

Bill Verburg

w/ a bbk in front the bias issue is far worse. w/ 993tt front(aka Big Red) you ought to have 993 rear calipers and no p/v

darth

Dear sergiDA

Maybe some background history would help determine the cause? Have you always had this issue under the same track conditions? And if so was anything changed just prior to the problem arising or before the the time it started occurring sooner? Have you considered the MC as being the cause? They can leak internally without any external signs of leakage.

Bill

joey bagadonuts

Yes, that's exactly what I have: 993 rears and no p/v. I misspoke. The calipers appear to be the same as stock 964 4-pots and use the same pads but, of course, they have larger pistons.

Jimjacqmx5

Am update from Oz. New master cylinder as suggested by Mr Bagadonuts and my god, I have brakes for the first time in two years!!

Oracle

I don't agree, the small pot don't overheat as they don't work as hard as the front ones.. In my opinion your problem could've been solved by flushing the system with new fluid when you installed the 4 pot.
I have never overheated those small ones, and I know they wear really fast. The only reason I bought the 4 pots is the pads, way more selection that can match the front. Those small pads are more expensive and there is only 2 kind and only for the street...

boxsey911

While they don't work as hard, the smaller surface area focusses the heat back to the fluid more when compared to a larger pad. I could stop them overheating by flushing the fluid and putting fresh pads in before the trackday. They would just about last the day but had to changed again before the next trackday (along with the fluid again). As you say the choice of pads for these is limited. Over here we only have one choice - Textar. Also as you say the 4 pots give a much greater choice of pads. The Pagid greys I now use on the rear will do six trackdays before they need to be changed out and end up being much more cost effective. I'm much more confident that the brakes are going to the last day with the 4 pot set up.

joey bagadonuts

Congrats and, thanks, for the follow up!

rarebear

btw what are the prices in the US for brake pads for the 2 potters and the 4 potters ?

J richard

Sergi,

like Ken said and steve was leading to, before you start on a whole raft of upgrades you should make sure you don't have a basic issue. You are describing a typical cooking the brakes and resultant fade/soft pedal. Good pads and fluid take care of 90% of issues.

The best system will act the same way if you have ANY air in the lines. How sure are you that it was completely bled? It tales almost a full can to fully bleed the system. If you still have a soft pedal I would bleed it now and see what you get.

Do you have a lot of track time or new to this? Do you brake hard to the point that you are constantly into the ABS? (pedal hammer?) driver style/skill can really affect brake heat. Constantly triggering the ABS should be avoided. It's pretty common to overbrake as you start out, or even on new tracks until you're comfortable carrying speed and staying off the binders...

sergiDA

hi J Richard:

I havr go track experience but not with the Porsche, i bought it 5 months ago. I have done go Karting, Renault Clio Cup series, Endurance Series With Seat Leon and some others, I think i know how to brake and all the others.

I have been at my mechanic this morning and they have recommened the following: Upgrade to 965 fronts and move the current fronts to the rear. keeping original size cross drilled rotors all round.

Is this change feasible and/ or recommendable?

My mechanic says i don't need to change anything else or adjust any brake bias...?


Going through the internet I have found the front calipers at a very good price. 500 €.. http://albert-motorsport.de/fahrzeug...mse/index.html


Thanks