Help with Brake Upgrade, Rear Vented rotors Options

[brant]

what pads?
you can buy pads to run in different temp ranges

when you bleed the fluid, is there obvious air?
try upgrading the temp range of your rear pads
go with cool carbon and select the next temp range up
cool carbons, now called KFP's work great on sub 2000lb vehicles.
Pagids are better on 2500lb+ cars, but not as great as the KFP's on the light weight vehicles.

I go through rear pads at a 2 to 1 ratio compaired to my fronts.

have you ever added cooling to your rears?
It would be easy to do as a temporary test

I finally modified my S calipers, by removing the knock-back pins to eliminate a little of the spongey feeling. are you running aluminum calipers up front or steel ones?

b

[Racing916]

what pads?
you can buy pads to run in different temp ranges

when you bleed the fluid, is there obvious air?
try upgrading the temp range of your rear pads
go with cool carbon and select the next temp range up
cool carbons, now called KFP's work great on sub 2000lb vehicles.
Pagids are better on 2500lb+ cars, but not as great as the KFP's on the light weight vehicles.

I go through rear pads at a 2 to 1 ratio compaired to my fronts.

have you ever added cooling to your rears?
It would be easy to do as a temporary test

I finally modified my S calipers, by removing the knock-back pins to eliminate a little of the spongey feeling. are you running aluminum calipers up front or steel ones?

b

Not really obvious air. maybe a bubble or two when bleeding after a weekend back to back sessions with my dad sharing the car. I have been running KFP's on the back and like you said they last 2 to 3 times longer than the front while running Hawks on the front calipers. I have run KFP front and back with not much gain. (IMG:style_emoticons/default/wacko.gif)

[brant]

no.. my front KFP's last 2times longer than my rears
I can get a whole season out of a set of fronts... only 3-4 weekends from a set of rears. and our car is a double driver too.. with my dad.

what compounds (what color) are your front/rear pads
try KPF gold color on the back or go up one step from there if you need to

which calipers do you use front/rear?

[brant]

absolute waste of time

Agree... that said, there's only about 4.2lbs. difference.

Vented = 13.6lbs each
Solid = 11.5lbs each

really?
my memory was a lot more
of course I don't have them sitting with me currently as you no doubt do
still we weighed them at the time and it was more in my head...
b

[Racing916]

no.. my front KFP's last 2times longer than my rears
I can get a whole season out of a set of fronts... only 3-4 weekends from a set of rears. and our car is a double driver too.. with my dad.

what compounds (what color) are your front/rear pads
try KPF gold color on the back or go up one step from there if you need to

which calipers do you use front/rear?

I was running M caliper fronts and stock 914-4 calipers in back both with KFP gold compound and found the fronts still wear 2X as fast as the rear.

I than upgraded to Wide A calipers on the front and still had 914-4 stock on the rear. I decided to try the Hawk HP on the front because they are much cheaper and people at the track really liked them. The rears were still KFP golds, as Hawk did not make HP pads for the rear. I did notice better braking with the upgraded front calipers, but the wear remains the same with the fronts wearing 2X faster than the rears.

[Van914]

Racing916,
I bought my vented rotors here: http://www.aircooledracing.com/
Van914

[914Sixer]

There is a correct rotor for the 914-6 racing application from the Competition Parts Book. Part number 901.352.041.12(rear vent rotor). Last time I checked there were 46 rotors left in Germany. Special order item about $150 EACH.

[Racing916]

Brake Update Pictures of the front and rears, thanks for all your advice. Wide A calipers in the front, M calipers in the rear (38mm), with T installed and adjustable proportioning valve.

steve

[Racing916]

front

[Racing916]

rear

[Eric_Shea]

(IMG:style_emoticons/default/smilie_pokal.gif)

[Racing916]

(IMG:style_emoticons/default/smilie_pokal.gif)

Thanks for all your input Eric!

[charliew]

I always thought that if you need to pump the brakes more than once the wheel bearings were too loose and the pistons were getting knocked back from disk wobble. Also I would think that the venting clearance would be a factor in the temps the rear disks and pads see on the 914. Don't race on a track so I probably shouldn't even be here. I have two sets of the 48mm brembos from the alfa and am going to put 38mm sleeves in the rears or whatever the smart guys think it needs after I get the front and rear weights stabilized with the suby motor and tranny and boxter wheels and tires. My fieros use solid rear disks and a caliper very much like the stock 914 and they are a heavier faster car than the stock 914. The 88gt I have has a 3.4 v6 with bigger ss valves and chevys hottest cam, the ecu has been reprogrammed. I probably has 180-190hp. The stock brakes with good pads works good on the street and doesn't fade with hard street use. I can mash the brakes hard from 120-130 and bring it to a stop with no problems. Of course thats nothing like the track stuff. I know the brakes smell hot but the fluid seems to hold up ok. I use the dot 5 and most people say it's junk but I don't have any water problems and most of my stuff sets a lot between uses. The dot 5 is a little spongier than 4.

[Krieger]

So is it worth it, and is it possible to get the rear m calipers & remove the spacers and make them "non vented" and use 914/6 solid rotors? Minimizing weight and keeping correct bias with front A calipers.

[Eric_Shea]

So is it worth it

Andy, in Steve's situation... maybe. In most, no.

I agree with your 914-6 rear rotor assesment. And yes, you can take the spacers out and have them fit on a 914. Very nice set-up for a track car that doesn't need a handbrake or, a street car with a different handbrake solution.

You get:

38mm pistons - Same as the 911, 911RS, 930 (early), 914-6 and 914-6/GT. These bias well with any 48mm front pistons (M-Calipers, A-Calipers, S-Calipers, Brembo 3")

Large #31 pad size - Same as the 911, 911RS, 930 (early), 914-6 and 914-6/GT. Again, these balance well with any of the following fronts - M-Calipers, A-Calipers, S-Calipers, Brembo 3"

Slightly less rotating mass with the solid rotor in the back (as you mentioned).

Biases well with the A-Calipers (as you mentioned).

I have a set of those exact calipers sitting on the bench right now.

[Krieger]

So what "m" rears are they: 84-89? for my front A's. Yes mine will be a lightened track car. I may have a line on a set of used ones near me. Do you have rebuild kits for those? What about o-rings for splitting the rears? How much for your pretty rebuilt ones. What bias vavle do I use? Stock 914/4,none, aftermarket? Thanks!

[Eric_Shea]

1969 through 1983. The 84-89 have larger pistons and I would not recommend them.

Rebuild kits are in stock. I've got the caliper 1/2 o-rings as well.

Oooooooooooops, forgot: I can't stress this enough; The stock "biasing valve" is NOT. It is a saftey shut-off valve that comes into the system at 535ftlbs. In a panic stop this shuts the rears down and slowly brings them back into the system preventing them from locking and causing a catastrophic spin.

Until the point where the panic stop is noticed, this valve ACTS LIKE A "T". It does not bias anything. The pistons and pads in a 914 are properly biased from the factory. This is just one of the many reasons I recommend staying with factory biasing options like:

43/33 -or- 48/38

This is also why I never recommend removing this valve (anymore... there was a time when we were all spouting the virtues of a "T")

[914Sixer]

Rear 914-6 GT vented rotors(901.352.041.12)were still available from Porsche about a year ago. Around $150 each and have to come from Germany . Said they were about 70 in stock.