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Brake Bias - too much in rear?
Running stock calipers/rotors on Carrera with cooling kit on front and Hawk Blue pads at the track. Prior to the front cooling kit I had to bleed the front calipers after a few sessions. Now I'm bleeding the rears (a couple of air bubbles showing up). Took it out for a drive today and rear wheels had MUCH MORE brake dust that the fronts. BTW - all calipers are fresh and fully functional.
Running ATE Blue fluid - what would cause more dust one the rear even with street driving? I can't imagine the cooling kit on the fronts have that much impact on the street. Can a stock proportioning valve go bad and lose balance?
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Mike - PBG, FL '14 958 Cayenne GTS '05 997 C2 - SOLD '79 911 SC Widebody PCA, NASA, PBOC - SOLD 2004 NASA-SE GTS4 Champ, 2005 + 2007 NASA-SE GTS3 |
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05-10-2003, 02:36 PM
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Re: Brake Bias - too much in rear?
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Ronin LB '77 911s 2.7 PMO E 8.5 SSI Monty MSD JPI w x6 |
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05-10-2003, 02:46 PM
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Forget about the dust for a second. Does your rear brakes lock before the fronts? If not then don't be concerned about the dust. I think the engine kicks up a lot more dust back there anyway, at least on my car. The proportioning valve is a fixed valve and I have never heard of these going bad. When you rebleed your brakes, keep tapping on the caliper with a mallet to free up any trapped bubbles.
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05-10-2003, 02:52 PM
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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
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The brakes on the 3.2L cars are different. They have an abnormal balance until they get to a certain pressure then they limit the pressure to the rear to keep from having too much pressure in the rear under emergency braking. My '88 gets more on the rear than the front with a stock system.
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa  SOLD 2004 - gone but not forgotten
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05-10-2003, 02:57 PM
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Mike,
For the thousanth time....."you've got to stop driving with the parking brake on!" Actually, after the way you spanked me at Barber last weekend, I'd be heartbroken to learn you did it with a handicap!
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Mike 89 Carrera 3.6 V-ram #94 Livin' for Targa time! Want to make God laugh? Tell him your plans! |
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05-10-2003, 03:53 PM
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Right...don't worry about the relative amount of dust, rears seem to dust more anyway, as well the rear quarters.
Front ductwork might act to "clean off" the dust that would normally accummulate there, too. ---Wil Ferch
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Wil Ferch 85 Carrera ( gone, but not forgotten ) |
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05-10-2003, 05:39 PM
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Dammit - left the hand brake on! Seriously though - no lockup in the rear - car is very balanced when braking - must be the front cooling system blowing off the dust and keeping the temps down more that the rears on the track.
Now . . . maybe time for the fiberglass rear bumper - get me down in the 2600 lb scene!
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Mike - PBG, FL '14 958 Cayenne GTS '05 997 C2 - SOLD '79 911 SC Widebody PCA, NASA, PBOC - SOLD 2004 NASA-SE GTS4 Champ, 2005 + 2007 NASA-SE GTS3 |
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05-10-2003, 10:00 PM
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I've got the opposite. Fronts lock-up under hard braking. What can I do? Car has new rotors, pads and rebuilt calipers.
JG
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05-11-2003, 05:11 AM
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Quote:
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Ronin LB '77 911s 2.7 PMO E 8.5 SSI Monty MSD JPI w x6 |
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05-11-2003, 07:26 PM
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My '86 Carrera rears dust up more than the front also. I believe that it is normal because under normal braking the bias is too much rear. Only under heavy braking does the p/v kick in moving bias forward.
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05-12-2003, 03:19 AM
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For 84, you likely have a 5/33 model brake proportioning valve ( located under the cardboard cover next to the smuggler's box). Meaning...model 5, set at a 33 bar brake line pressure before the nearly 1/2 brake proportioning takes place ( about half the brake force goes to the rears after you reach 33 bar)...making the fronts do most of the work.
Two options..go with a 5/50 ( or is that 55?) model used on the 85 Widebodies. Or, if you have the cojones...remove the brake proportioning valve altogether. Progressively , that would put more of the brake bias toward the rear. Personally, I think removing the valve would be too extreme, and I disclaim any legal responsibility for such actions ( just be aware that that *is * a technical option open to you). Another way would be to put in an adjustable brake proportioning valve, but then we'd be apt to play with it more and not know where you are most of the time. --Wil Ferch
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Wil Ferch 85 Carrera ( gone, but not forgotten ) |
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05-12-2003, 06:12 AM
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Huh?
If there is already too much rear bias, how would using a p/v that kicks in later help? Or even worse removing it all together? |
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05-12-2003, 06:17 AM
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If...as stated... the "fronts lock up"....then there's too much front bias...no?
trying to answer North coast Cab's problem...sorry if I wasn't clear. ---Wil Ferch
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Wil Ferch 85 Carrera ( gone, but not forgotten ) |
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05-12-2003, 06:38 AM
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911 Widebody NASA GTS3 / PCA E
Mostly Street
1984 Porsche 911 3.2
