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nagging brakes still


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i'm still trying to analyze what is causing my 99 C4 to exhibit inadequate braking at speeds above 60mph. i have flushed the system twice with a powerbleeder, the pads and rotors are fine. the tires are good. is there a component in the braking system that i have to check? at speed the brake pedal firms up but does not stop the car proportionately to the pressure i apply. im hesitant to replace the seals of the calipers as they look intact. suggestions pls on what to do next. TIA

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Seals don't need replacing unless they are letting fluid leak and will do nothing to help your problem. Unsure but may be a proportioning valve that is malfunctioning or a problem ABS related. Have you tried braking really hard over 60 in a safe area? What happens? Is your stopping distance much greater than it should be?

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i'm still trying to analyze what is causing my 99 C4 to exhibit inadequate braking at speeds above 60mph. i have flushed the system twice with a powerbleeder, the pads and rotors are fine. the tires are good. is there a component in the braking system that i have to check? at speed the brake pedal firms up but does not stop the car proportionately to the pressure i apply. im hesitant to replace the seals of the calipers as they look intact. suggestions pls on what to do next. TIA

man, i'm dealilng with the same thing ('99 boxster). for me, it happens at slower speeds, too. i have to push the pedal really hard to get it to stop well. if i do a few panic stops, everything gets really good for awhile. then, back to crappy stopping power. i've power bled w/ Super Blue, replaced pads w/ multiple brands, replaced rotors, replaced master cylinder, replaced rubber lines w/ SS. what kind of brake fluid do you use? i'm starting to wonder if the higher viscosity of ATE Super Blue can somehow cause problems....

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i'm still trying to analyze what is causing my 99 C4 to exhibit inadequate braking at speeds above 60mph. i have flushed the system twice with a powerbleeder, the pads and rotors are fine. the tires are good. is there a component in the braking system that i have to check? at speed the brake pedal firms up but does not stop the car proportionately to the pressure i apply. im hesitant to replace the seals of the calipers as they look intact. suggestions pls on what to do next. TIA

A little more context would probably help us to advise you. Have you been driving Porsches for years or is the '99 C4 new to you? My experience is that Porsche brakes are not heavily boosted and do require a lot more pedal pressure than many other cars. I think this is a good thing. It allows you to modulate the braking more precisely and makes heel-toe down shifting easier than a car with a lot of brake boost. If the pedal feels stiff and you can activate ABS with a firm application of the pedal, I would say everything is fine. If it is almost impossible to activate ABS and feel the pulsing of the brake pedal, then you may have a problem with the brake booster or other components.

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A little more context would probably help us to advise you. Have you been driving Porsches for years or is the '99 C4 new to you? My experience is that Porsche brakes are not heavily boosted and do require a lot more pedal pressure than many other cars. I think this is a good thing. It allows you to modulate the braking more precisely and makes heel-toe down shifting easier than a car with a lot of brake boost. If the pedal feels stiff and you can activate ABS with a firm application of the pedal, I would say everything is fine. If it is almost impossible to activate ABS and feel the pulsing of the brake pedal, then you may have a problem with the brake booster or other components.

yes this is my first porsche and yes i am firm believer that great brakes should exibit good feel, etc. i have yet to notice if i have triggered abs in my runs. my brakes are stock pads, rotors, ate brake fluid. what i do have is at speed (60mph and up) is a firm pedal that doesnt slow down the car proprotionately to the pressure i apply to it. im pretty sure that the car brakes longer than it should from 60mph and up. once my brother was driving he was able to lock up the brakes and we stopped short of 8 feet from the car ahead that stopped (abs faulty?) can i check with my durametric if my brake booster, proportioning valve or whatever brake component is fuctioning normally? no lights appear on my cluster nor any malfunctions when i hook up my scan tool. :help: again ur help is most appreciated. thanks to all who responded.

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I am going to dealer soon for something similar. Here are my 2 cents, relative to my 1999, the 2003 C2 stops like crap sometimes. At low speeds, no issues. But at high speeds, as you said, I am concerned since I have to bury the pedal. Doesn't feel good, and I can compare back to back both cars braking on the same roads, same fluids, same pads.

Not sure what it is, all I can tell you is that one car stops amazingly fast at all speeds, the other doesn't. Also makes for less than perfect track days, as I am leery to brake as late with the '03 as I was with the '99. I am not sure if there is any logic to decrease braking power at high speed or not. Our local dealer is pretty good, so will let you know what they say and get back to you.

But I have seen the difference

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I am going to dealer soon for something similar. Here are my 2 cents, relative to my 1999, the 2003 C2 stops like crap sometimes. At low speeds, no issues. But at high speeds, as you said, I am concerned since I have to bury the pedal. Doesn't feel good, and I can compare back to back both cars braking on the same roads, same fluids, same pads.

Not sure what it is, all I can tell you is that one car stops amazingly fast at all speeds, the other doesn't. Also makes for less than perfect track days, as I am leery to brake as late with the '03 as I was with the '99. I am not sure if there is any logic to decrease braking power at high speed or not. Our local dealer is pretty good, so will let you know what they say and get back to you.

But I have seen the difference

i look forward to hearing from you soon. thanks

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Check out link below. It's packed with information on braking. They don't recommend using power bleeders. They claim that power bleeders force air into the brake fluid. I just changed my rotors and bleed my brakes (with a power bleeder) and they work great.

Improper bedding in of either the pads or rotors can affect braking performance.

http://www.stoptech.com/tech_info/tech_white_papers.shtml

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Check out link below. It's packed with information on braking. They don't recommend using power bleeders. They claim that power bleeders force air into the brake fluid. I just changed my rotors and bleed my brakes (with a power bleeder) and they work great.

Improper bedding in of either the pads or rotors can affect braking performance.

http://www.stoptech.com/tech_info/tech_white_papers.shtml

man, that's a lot of GREAT info. thanks for the link.

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  • 2 months later...

Boxstermao,

I finally got around to the dealer, as the brakes where fading worse on track. They tried a full flush thinking it was air on the system (using the PIWI), and it did not work. Next they recommended my front calipers are toast, and I need new ones. The pistons where not moving as they should and the seals shot.

I got the new ones Friday, ordered the Boxster S red calipers and installed them, got them centered on the calipers, and did another flush. Now it does seem to stop perfectly, have not done track time yet but going on the 6/18.

Now the old calipers I just cleaned up and removed the pistons. The boots where pretty shot, so I can see the issue. I will order new dust boots and take them to the dealer, see if they see anything else wrong. Otherwise, will either keep them as spares or sell them on Ebay, recoup the costs of the new ones. Sunset has them (red or black) for $365 plus shipping, my local gave me the same deal plus tax, so went with them. They are my track buddies anyway, and I owe them for their advise.

Hope this helps you, as a minimun try to clean them up and new dust boots. If you have the tools to remove them and a compressor to remove the pistons, it doesn't seem to be a big job.

Izzy

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you can get the inner seals from HRP world. they're $13 each. usually it's those that go; they overheat. they're only designed to take 400 - 500F of heat at the seal. there's a thermal barrier coating on the pistons that helps prevent this, but on the track it can still happen. once the seal has been overheated, it won't retract the pistons properly. the result is that the pads drag slightly and overheat the pads / calipers, causing fade. replace the inner seals in your old calipers and they'll be fine.

if you haven't moved to a full race pad yet, do so. you will be suprised at the difference. it's more economical to keep a street set and a race set if you go to the track a lot. i like hawk HT-10, pagid orange, and carbotech.

Edited by insite
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Insite,

Having a hard time determining which seal I need from HRPWorld. Do you remember for front 996 which one it is?

I am partial to Pagid Oranges for track days, have had great luck with them. Also, going to Road Atlanta in August, try out the new surface. You drive it with PCA or NASA?

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Insite,

Having a hard time determining which seal I need from HRPWorld. Do you remember for front 996 which one it is?

I am partial to Pagid Oranges for track days, have had great luck with them. Also, going to Road Atlanta in August, try out the new surface. You drive it with PCA or NASA?

you want to do both front calipers. you will need four 40mm seals and four 36mm seals. if you do the rears also, you'll need 4 x 30mm and 4 x 28mm seals. they're on this page: http://www.hrpworld.com/index.cfm?form_pro...;action=product

use 99% rubbing alcohol to clean out the calipers (it dissolves brake fluid & doesn't leave moisture or residue). soak the seals in brake fluid for 30min before installing. use high temp moly assembly lube on the pistons when you reassemble. put the outer dust boots on the pistons BEFORE you put the pistons in the calipers.

the new surface at RA is great. i primarily do PCA and private events; no W2W stuff until i have a larger budget.

Edited by insite
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Awesome, thank you. I was waitlisted for the last PCA. NASA HPD3 is not W2W, if you are ever inclined to try it. HPDE4 is combined with Time Trials so it gets hairy on turns 10A-B and 12. Can't wait to do the new asphalt. Thanks again

Izzy

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Awesome, thank you. I was waitlisted for the last PCA. NASA HPD3 is not W2W, if you are ever inclined to try it. HPDE4 is combined with Time Trials so it gets hairy on turns 10A-B and 12. Can't wait to do the new asphalt. Thanks again

Izzy

yeah, PCA DE is tough to get into at RA. there is a DE coming up in September at Roebling Road that's a lot easier to get into. i'll be going. I may also do RA in october. i've never done a NASA event. probably next year. i'm getting to the point where i want to / am able to do a lot more driving...

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Long finger nails! Or a pair of tweezers. But to get to the seals, you have to remove the calipers and the plug off the break line going to the caliper so you don't leak the fluid.

Then you have to remove the pistons, a compressor set at a low pressure is needed, and a block of wood to prevent the pistons from hitting the metal or each other. This is not a simple task as the caliper has pistons on each side, and you have to balance them out as they are pushed by the compressed air and keep your fingers out of the way. Once the pistons are out, the rings are set in a groove inside the caliper, easy to see and remove.

If you have never done it, not a bad idea to do a google search for "caliper rebuild" and read through a series of instructions on how to do it before you tackle it.

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what tools do i need to replace the seals of my calipers? does anyone have a diy on this? would appreciate it.

1. remove calipers from your car. don't push pistons back in.

2. open bleed screws and pour out excess fluid

3. use two screwdrivers to pry each piston out of its cylinder.

4. remove inner seals w/ plastic covered paperclip to avoid scratching cylinders.

5. clean all parts w/ 99% rubbing alcohol. this will dissolve the brake fluid.

6. powder coat calipers at this point if desired.

7. soak new inner seals in brake fluid for 30 min.

8. install new inner seals into calipers.

9. coat inner ring of each outer seal with silicone grease.

10. slide an outer seal onto each piston.

11. lubricate each brake cylinder with a light coat of brake fluid.

12. begin pressing the piston into its cylinder by hand until you hit the seal.

13. twist the piston slightly as it passes the seal

14. once past the seal, seat the outer dust boot in its groove

15. press cylinder all the way in. use a long piece of wood if you need some leverage.

16. repeat for all pistons.

17. install calipers and bleed system.

to do this job you will need inner seals AND outer dust boots. the outer dust boots are about $10 a pair from Sunset Imports. the inner seals are about $13 each from HRP World. don't do this unless you're sure you need to. you likely have no problem with your calipers unless you track the car.

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thanks for all ur replies

After reading this series of messages, I started wondering if my brakes were okay. They always seem to be fine, but you alway wonder after reading this kind of thing. Today with my wife and 3 year old in the the car with me at about 55 MPH, a car made a right hand turn right in front of me (about 20 ft). I can't imagine how they didn't see me! Anyways foot to the floor and I managed not to hit them. I was truly impressed with the braking. Car never wanted to veer of course and antilocks worked like a charm. The funny thing was as soon as I hit the brakes and felt the rapid deceleration I knew we were fine (wife on the other hand was not so sure). If we had been in our Expedition, we would have been toast!

Will

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