Help for brake

87 clubsport · 05-21-2007, 10:03 AM

Hi I have installed monoblock boxster brake caliper with TRE adapter front and rear, with pagid black pads new rotors Motul 5.1 brake fluid , steel lines, and brake duct cooling. initial bite was excellent . But after 5 laps in lapping day, the brake getting fade and the pedal feels abit spongy, Did I miss something such as master cylinder its 20 years old, or switch to turbo one or higher temp fluid such as Motul 600? or even try pagid orange? thanks for your input.
Cheers Steve

Dave Nordhoff · 05-21-2007, 10:51 AM

Steve,
Your fluid and pads should be fine. I would bleed again with the foot on the pedal method. It may take several times and also tap on the calipers with a soft hammer to help release air bubbles.
Dave

87 clubsport · 05-21-2007, 08:16 PM

thanks should I change the fluid to higher boiling points such as motul 600?

911pcars · 05-21-2007, 09:10 PM

Spongy brakes = fluid is boiling. In the area of brake cooling, brake fluid is cheap. Even expensive brake fluid is a cheap upgrade. I'd begin with Motul RBF 600. You can go all the way up to Castrol SRF until you find the fluid that does the job.

http://members.rennlist.org/911pcars/brakefluid.htm

Does the air flow have the most direct path to the rotor? Do you have room to install an inline blower motor?

The master cylinder size shouldn't make a difference as long as you can lock the brakes and don't run out of pedal.

If Bill Verberg decides to chime in, he might suggest going to a larger, wider rotor, one with increased heat sink properties. The next larger size rotors used in 911 upgrades are 951 rotors (28mm), then 993 or Turbo rotors (32mm). There are compatible calipers for each of the above rotors.

If your rotors are currently drilled, replace with undrilled rotors.

Sherwood

Jeff Alton · 05-21-2007, 10:05 PM

The boxster caliper is designed for a 24m rotor, so a 28 is out of the question..... The TRE kit Steve has is designed to use factory Carrera rotors.

I would try the RBF600, it is great fluid. I have seen it make a big differenece on several cars with carrera rotors. It may be all you need to keep a firm pedal.

Steve, bring your car by, and we can bleed the brakes here with my pressure bleeder. I have plenty of RBF600 on hand and the beer is on me if you stop by that same chinese deli on your way here

The last stuff you brought was fantastic!

We can make a night of it on a wed/thurs/fri night and maybe even invite the local PCA crowd over to learn how to bleed brakes.

Cheers

87 clubsport · 05-21-2007, 10:24 PM

Thanks I will arrange it.

DinFtown · 05-22-2007, 05:50 PM

You will find the Boxster mono block upgrade is infact no upgrade at all.... you are using the same rotors you had been using but now you have more pad surface area.... this equalls more initail bite along with more heat then your stock brakes..... only advatage is less weight, but in no way should the boxster brakes be considered a trackable upgrade.... sorry...

Bill Verburg · Bill Verburg's Garage

w/ Boxster brakes front and rear you definitely want a 930 23.8mm m/c

But the issue, as always, is rotor temperature, you have to keep it under control.

cooling/pads/fluid all help, but rotors big enough to absorb the thermal load and then dump it while keeping max temp down are key.

I wish I had a dollar for every time i've pointed this out.

an '87 clubsport is still a heavy, fairly quick car, Carrera size rotors (stock or used w/ Boxster calipers) are going to have a very tough time dealing w/ the KE absorbed during track sessions.

I would suggest a minimum of 964 size or even better 930 size rotors for that car, unless you are racing(class rules prevail, when everyone is in the same boat it's easier to deal w/)

JeremyD · JeremyD's Garage

The turbo master cylinder will effect the brake pedal feel, but little else. As others have stated - you really did not upgrade your brakes as you did not increase the size of your rotors.

I think you'll find that Motul RBF 600 is better, The castrol SRF is the next step. Without increasing the thermal capacity of the rotors though , you will still be going through pads and rotors quickly. BTDT

87 clubsport · 05-23-2007, 07:55 PM

Thanks everybody because I like to run 15 inch fuchs wheel in track and 16 on the road thats why I still keep this set up.I will try every thing to improve it first. but any way any idea to improve the brake system I can run 15 or 16 inch fuchs wheels. Thanks

barney911rs · barney911rs's Garage

Steve,

For the 15" wheels about the only option is the 930 brakes ($$$). I use your same setup on my car with a BMW rear caliper on the stock early rear rotor, but my car is probably a lot lighter then yours. Last corner balance 2221lbs with 200lbs driver ballast.

I was looking to change the mechanical leverage more then overall braking. I feel the larger swept area of the bigger pad accomplished that. Bill you have any comments on that?? I've been very happy with this setup on my race car.

Jeff thanks for the rotor info, I was wondering if I could put in a wider rotor with that caliper.

JeremyD · JeremyD's Garage

I have one of Dave's first 993 brake products - I think he has something now for 15" wheels

http://www.probraking.com/index.html

Bill Verburg · Bill Verburg's Garage

Quote:

Originally posted by barney911rs
Steve,

For the 15" wheels about the only option is the 930 brakes ($$$). I use your same setup on my car with a BMW rear caliper on the stock early rear rotor, but my car is probably a lot lighter then yours. Last corner balance 2221lbs with 200lbs driver ballast.

I was looking to change the mechanical leverage more then overall braking. I feel the larger swept area of the bigger pad accomplished that. Bill you have any comments on that?? I've been very happy with this setup on my race car.

Jeff thanks for the rotor info, I was wondering if I could put in a wider rotor with that caliper.

I agree that '78 up 930 would be ideal for that car and still fit in 15's(sortta easily)

Yes, you can change the pivot point to gain more or less mech. adv. just make sure the whole mech. linkage and mounts are stiff enough. Flex in the mounts or firewall can really mess up brake feel. The larger swept area mostly influences the life span of the brake pads and rotors, it has very little to do w/ feel.

At < 2300# all up you don't need much more than stock S&M, so most any caliper on Carrera rotors would do as long as the hydraulic balance worked out ok.

barney911rs · barney911rs's Garage

Bill,

Maybe I'm missing something. To my thinking, using a larger pad and 4 pistons as opposed to 2 would allow you to get the same braking effort with less clamping force on the rotor by enlarging the swept area? This is the mechanical leverage I was referring to, not the pedal. I guess an example of that would be to stop a wheel from turning with your finger tip, you would have to press down harder then you would if you used your whole hand.

I was having intermitent lockup issues under very hard braking when I had the stock carrera calipers. After I changed to the Boxster caliper, this went away unless I really stomped down on it. I am still able to get the car to brake as hard as it did before, but only using firm pedal pressure. Some of this may have also been caused by other changes.

I removed the stock brake pedal and master and replaced them with an overhung Tilton with dual masters. I found this gave me a much firmer pedal overall and would highly recommend for any race car that is allowed to make this change. I also found a BMW caliper that bolted right up to the rear that is about the size of a stock Carerra front. I've been pretty happy with the balance and have done very little to adjust anything since I installed it all.

Bill Verburg · Bill Verburg's Garage

Quote:

Originally posted by barney911rs
Bill,

Maybe I'm missing something. To my thinking, using a larger pad and 4 pistons as opposed to 2 would allow you to get the same braking effort with less clamping force on the rotor by enlarging the swept area? This is the mechanical leverage I was referring to, not the pedal. I guess an example of that would be to stop a wheel from turning with your finger tip, you would have to press down harder then you would if you used your whole hand.

I was having intermitent lockup issues under very hard braking when I had the stock carrera calipers. After I changed to the Boxster caliper, this went away unless I really stomped down on it. I am still able to get the car to brake as hard as it did before, but only using firm pedal pressure. Some of this may have also been caused by other changes.

I removed the stock brake pedal and master and replaced them with an overhung Tilton with dual masters. I found this gave me a much firmer pedal overall and would highly recommend for any race car that is allowed to make this change. I also found a BMW caliper that bolted right up to the rear that is about the size of a stock Carerra front. I've been pretty happy with the balance and have done very little to adjust anything since I installed it all.

Swept area is a sort of archaic metric that used to be commonly used. Swept area =~( rotor radius - pad width ), to increase swept area you need a larger rotor diameter and a wider pad, so the current practice is to specify those items.

Believe it or not the swept area of a Boxster caliper is ~ the same as an A, an S or a Carrera wide A becuse they all use the same rotor and the pad width is ~ the same

2 pistons, 4 pistons, 6 pistons are irrelevent wrt brake torque, total piston area and line pressure and effective rotor diameter and pad coefficient are the critical factors influencing brake torque. The advantage of the multiple piston calipers is the ability to apply clamping force in a graduated manner along the length of the pad. This is imporatant because the leading edge has a thicker plasma boundry layer than a trailing edge and so needs greater clamping force. In the 2 piston calipers the only way to achieve that was by rocking the pad on a machined in fulcrum.

pedal firmness and height are a function of master/slave ratio, a nice high firm pedal has a master/slave ratio of ~16:1, most street cars are closer to ~20:1 it varys w/ manufacturer, mechanical setup of the pedal linkages and boost.

barney911rs · barney911rs's Garage

Great info Bill, thanks.

87 clubsport · 05-25-2007, 12:35 AM

Bill, is 930 m/c will help? I will try it with Motul 600 fluid, thanks.

Bill Verburg · Bill Verburg's Garage

The larger 23.8mm boosted m/c used on 930 from '78 on will help w/ initial pedal feel, but will not cure over heated rotors from track use.

w/ Boxster f/r you definitely want the 930 m/c

As far as track heat goes you may want to improve the cooling to the greatest possible extent and try a less aggressive pad than a Black(assuming we are talking RS14Black). The more aggressive pad puts heat into the rotor more quickly. Something like an RS 19Yellow is far gentler but still track appropriate.

87 clubsport · 05-25-2007, 08:57 AM

Thanks, If this time still wont work is that any one try 964 brake set up? thanks for your input.
Cheers

Bill Verburg · Bill Verburg's Garage

The next step is indeed 964 28x298 front rotors. For comparison Carrera are 24x282.5

after that it is the '78 up 32x304 930 size rotors which are the most popular because they are almost always more than adequate for most people most of the time.