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BobnJoz
 
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Rear Brakes for Race car - Help

Hi, I've upgraded my front brakes on the race car and now have way to much in front and feels like nothing out back. I went from stock, late 70's S brakes all around to Wilwood Ultra Lites, 4 piston calipers on front. I was told that Carrera rear calipers are a match but they seem very similar to what is there now. Would that be a good choice? Or what would be a better option? Car is about 2K lbs, all fiberglass and carbon fiber (if this is important).
Thanks for any suggestions.

Old 06-15-2010, 12:32 PM
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Originally Posted by bobswei View Post
Hi, I've upgraded my front brakes on the race car and now have way to much in front and feels like nothing out back. I went from stock, late 70's S brakes all around to Wilwood Ultra Lites, 4 piston calipers on front. I was told that Carrera rear calipers are a match but they seem very similar to what is there now. Would that be a good choice? Or what would be a better option? Car is about 2K lbs, all fiberglass and carbon fiber (if this is important).
Thanks for any suggestions.
It would help a lot if you provided the current rotor diameter f/r, the piston sizes f/r(or for stock calipers just name it, A, M, etc)

w/o knowing the above it's impossible to make any suggestions.

just a note if you have stock rear M from '69 -83 then the rotor is 290x20 w/ 2x38mm pistons, the wide M from '84-89 is 290x24 w/ 2x42mm pistons
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Old 06-15-2010, 12:45 PM
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BobnJoz
 
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Thanks Bill,
I do have stock rear M with the rotor size of 290x20 w/ 2x38mm pistons. Front are the stock rotors (69 - 83) with the Wilwood 4 pistons (don't know piston size). Original front brakes were the Aluminum "S" calipers. Does this help the equation?
Old 06-15-2010, 01:07 PM
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Originally Posted by bobswei View Post
Thanks Bill,
I do have stock rear M with the rotor size of 290x20 w/ 2x38mm pistons. Front are the stock rotors (69 - 83) with the Wilwood 4 pistons (don't know piston size). Original front brakes were the Aluminum "S" calipers. Does this help the equation?
Not much, you will certainly get more rear bias by using 3.2 Carrera rears. Impossible to say what the net result will be w/o knowing front piston sizes

I hate to say this but using any caliper on the stock front rotors doesn't necessarily improve braking.

The issue w/ brakes is almost always heat and heat management. to manage heat you need to keep the brakes cool, use ducting scoops etc but if that doesn't work then you need to use bigger rotors, bigger calipers on the same old rotors just makes heat management more difficult to accomplish.
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Old 06-15-2010, 01:57 PM
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BobnJoz
 
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I've done a little reasearch, trying to find out piston size with not to much luck. One site says 1.88 for piston #1 and 1.75 for piston #2. Hum? Not sure if they are the identical calipers to mine.
Heat has never been an issue. I have ducting to front brakes. Maybe I don't drive hard enough. Back with the stock brakes (front and rear), the car slowed pretty good and even front to rear. I installed the Wilwoods and left the rear stock and the fronts would lock up and felt like no rear brakes. Street cars could out brake me in the corners by a long ways. So, rear bias is what I need. Maybe a brake bias control?
Thanks......
Old 06-16-2010, 01:19 PM
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Originally Posted by bobswei View Post
I've done a little reasearch, trying to find out piston size with not to much luck. One site says 1.88 for piston #1 and 1.75 for piston #2. Hum? Not sure if they are the identical calipers to mine.
Heat has never been an issue. I have ducting to front brakes. Maybe I don't drive hard enough. Back with the stock brakes (front and rear), the car slowed pretty good and even front to rear. I installed the Wilwoods and left the rear stock and the fronts would lock up and felt like no rear brakes. Street cars could out brake me in the corners by a long ways. So, rear bias is what I need. Maybe a brake bias control?
Thanks......
If the brakes worked well, then why did you change them?

w/ the 1.75/2 sizes mentioned above it's no wonder that you have issues

some background first
every 911 ever made before 1984 has front /rear brake bias of 1.596 to 1.604, this includes 930s, would you agree that they all brake pretty well from the factory? If heat is an issue the 930s are used otherwise the 911 A/M or S/M are used.

if the info you provided is correct then you have 2.947, wildly front biased, if you throw some wide Ms on the back it goes to 2.413, still wildly front biased.

I know that you don't want to hear this but what you need to do is go back and start over.

if the stock brakes were good then in order of increasing track worthiness because of the ability to handle heat, choice 3 also greatly increases available brake torque(this is useful if you have the tires for it)
choice 1 - use stock A or S on stock 20x282 w/ the stock M rears on 20x290, bias 1.596

choice 2 - use 3.2 Carrera wide A on 24x282 w/ stock M rears on 20x290, bias 1.596

choice 3 - use 930s f/r on 304x32 f and 307x28 rear, bias 1.604

if you insist on using the Wilwoods you need to get some much bigger rotors in front and even then its' almost impossible to get something in back unless Wilwood has something for you. The biggest possible rear would be off a 993RS which used 30/36 on 322x28 in back, w/ the Wilwoods you have bias 1.938, still too much front.

if you insist on something w/ 4 pistons in front(you like the looks or something) use Boxster calipers on 3.2 Carrera 24x282 front w/ 3.2 Carrera rear Ms and rotors, bias 1.642 This gets you barely more than looks over choice 2 above

if you want to spend a lot of money you can use 993RS, 36/44 on 32x322 & 30/36 on 30x322, bias 1.472(the car needs to be set up specially for this to work)

or 996tt/GT3 36/44 on 34x330 & 28/30 on 28x330, bias 1.919(most think this is too much front and will use high friction rear pads to compensate)

these latter choices are much heavier and should only be contemplated if you really need them. They provide massive torque and heat handling capabilities, but are really meant for faster/heavier cars
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Old 06-16-2010, 02:01 PM
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The guy I sold my 2.8 MFI twin plug 72 to converted to SL's on Carrera Front rotors and Carrera rear's and loves it for 30 minute DE's and club races on a 2200 lb race car with 315 R1's on the rear. It dose have Carrera calipers and rotors on the rear. This guy is fast and often gets very close to TTOD with only 265hp.

As Bill says this dose not increase brake TQ or heat management much but he did not seems to need it. With the increased surface area you my not need to replace pads as often. It is also lighter than the iron calipers but I suspect you had the Alloy S calipers.

We do not know your front pistons are the same as his so I do not know if this would work for you.

Did you fit the SL to a stock 20mm S front rotor?

A rear Carrera rotor is 24mm. If you are intent on trying a Carrera in the back because of there bigger pistons you may need to change the rotors or play with the caliper offset (2mm spacer?) to try it with the S rotors. Not a great idea. Also a bias valve on the rear circuit should probably be fitted so you can dial down the rear if it is to aggressive.

Some have modified front calipers to fit the rear.

How about some Willwoods for the rear to? Should save you some unsprung weight and might simplify your brake pad purchases. Also, might over size the rear's a little and use a bias valve to reballance your system.

Then there is your master cylinder size?

You really need to verify the front piston sizes from part numbers or measuring them.
Old 06-17-2010, 04:08 PM
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BobnJoz
 
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OK, this is getting complicated. I've done a little more research. A rough measurement of front pistons shows approx 1.25" piston size. Smaller then first thought. MC size is 19 mm. I got these calipers in a trade with a friend. He wanted my Alloy S calipers and had some Wilwoods to trade, I thought this may be a simple upgrade since you can feel a little flex in the S calipers. I didn't really care what they look like since you can't really see them with Duralite wheels. Someone else mentioned Wilwoods for the rear also. Maybe that is a less expensive alternative since budget is critical.
I do have the SL's (Superlites?) to stock rotors. There are spacer plates that take up the slack. And I have heard that Carrera rears are the way to go (also Boxster rears with adapters) with these fronts. And I have started pricing Carrera calipers and "rotors" so I was figuring on replacing both.
Maybe with the added info, the answer will appear right before me.....
Thanks for all the information. I need to digest it a little.
Bob

Old 06-17-2010, 05:35 PM
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Quote:
Originally Posted by bobswei View Post
OK, this is getting complicated. I've done a little more research. A rough measurement of front pistons shows approx 1.25" piston size. Smaller then first thought. MC size is 19 mm. I got these calipers in a trade with a friend. He wanted my Alloy S calipers and had some Wilwoods to trade, I thought this may be a simple upgrade since you can feel a little flex in the S calipers. I didn't really care what they look like since you can't really see them with Duralite wheels. Someone else mentioned Wilwoods for the rear also. Maybe that is a less expensive alternative since budget is critical.
I do have the SL's (Superlites?) to stock rotors. There are spacer plates that take up the slack. And I have heard that Carrera rears are the way to go (also Boxster rears with adapters) with these fronts. And I have started pricing Carrera calipers and "rotors" so I was figuring on replacing both.
Maybe with the added info, the answer will appear right before me.....
Thanks for all the information. I need to digest it a little.
Bob

Your friend got the better of the deal. One indication of how bad that install is is the fact that pad spacers are used because the rotors are too small for the caliper.

For your own safety, start over
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Old 06-18-2010, 07:02 AM
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What Bill said.
Old 06-18-2010, 07:48 AM
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Vote #2 for Bill
For your own safety - start over.
Even start with a complete Carrera setup (larger rotors) if you can't afford to go with something like the 930 setup. At least you would get back a decent bias.
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Old 06-18-2010, 07:55 AM
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As I said on the other Forum, come on over to Sears Point next weekend and take a look at a few of the GT cars. I will be there starting Friday.

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Old 06-18-2010, 08:27 AM
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not sure if you are talking boxter calipers on the rear. Boxter calipers are the same front and rear, the bias comes in with different pad compounds. I switched my race car 82SC to the boxster calipers, the recommendation was to use Carerra 3.2 front rotors, stock rears. Car breaks much better than with stock brakes when i use porterfield brakes (as compared to Perf Friction, Hawk Blue, and EBC yellows on stock, which all seemed about the same to me). I did try EBC yellows on the boxster setup, and either I got a bad set of pads, or something else, the rear inside pads on both sides had material that just looked like it melted. Swapped back to the porterfields and had no problem. your mileage may vary of course. One other thing. On my setup, there are no spacers needed between the calipers and the pads. In fact, it’s a VERY tight fit all around when putting new pads in.
Old 06-18-2010, 10:53 AM
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not sure if you are talking boxter calipers on the rear. Boxter calipers are the same front and rear, the bias comes in with different pad compounds. I switched my race car 82SC to the boxster calipers, the recommendation was to use Carerra 3.2 front rotors, stock rears. Car breaks much better than with stock brakes when i use porterfield brakes (as compared to Perf Friction, Hawk Blue, and EBC yellows on stock, which all seemed about the same to me). I did try EBC yellows on the boxster setup, and either I got a bad set of pads, or something else, the rear inside pads on both sides had material that just looked like it melted. Swapped back to the porterfields and had no problem. your mileage may vary of course. One other thing. On my setup, there are no spacers needed between the calipers and the pads. In fact, itís a VERY tight fit all around when putting new pads in.
Old 06-18-2010, 10:55 AM
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Originally Posted by bullethole View Post
..... Boxter calipers are the same front and rear, the bias comes in with different pad compounds. ...
not true at all
Boxster front

monoblock cal ~7 lbs
pistons frt 36/40
pad 78x114mm
F Disks 298x24mm

Boxster rear
monoblock cal ~7 lbs
pistons rr 30/28
pad 74x112mm
R Disks 292x20mm
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Old 06-18-2010, 11:03 AM
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BobnJoz
 
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Mike, I wish I could get out there but still working weekends. I already "called in" for the Vintage races the other weekend.
I guess for now, I will work on a simple way to solve my brake issue. Trade front Calipers.
Thanks for the suggestions.
Bob
Old 06-19-2010, 04:46 PM
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If going to Carrera front rotors and calipers you might leave the rubber dust seals off or they will just burn up on the track.
Old 06-19-2010, 05:16 PM
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I run the Wilwood 1949 rotor on the rear with a Carrera caliper. Wilwood hat as well.

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Old 06-19-2010, 05:21 PM
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brakes

You might want to look into Boxster fronts and Carrera rears, but use a proportioning valve. I use this for my spec911 and the cars stops wonderfully, no fade at all and really stable under hard braking. I use the Hawk HT10 pads, great overall set up
2450 #'s with driver.
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Old 06-21-2010, 08:48 PM
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You can buy brand new Carrera calipers here for a great price:

Pelican Parts - Product Information: 911-351-425-03-M4

Pelican Parts - Product Information: 911-351-426-03-M4

By the time you buy used Carrera calipers and rebuild them you will probably not save that much.

Again, for a track only car I would pull the rubber seals off as they will just burn up.

Here is another option that some like: Porsche 911 Big Brake Kit.

Old 06-23-2010, 05:13 PM
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