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Join Date: Nov 2003
Location: Menifee, CA
Posts: 240
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Brake bias help
The PO put in a brake biasing valve, but I am not sure how it works. I also don't want to jack with something and get it completely off. I took a picture of what I think is the biasing valve, could someone please enlighten me with any thought of how it works. It says one way "increases" and one way "decreases" but not what it increases or decreases. Also, any idea how much turning affects it by how much?
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Alan Jackson 77 911S 3.2 |
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12-11-2004, 02:42 PM
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Alan,
Do you track your car? If not, you probaby won't notice much change from playing with the adjustment. If you're continuously locking up either the fronts or rears on the street....well, you get the picture. I would assume that "Increase" refers to rear brake bias.
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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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12-11-2004, 03:01 PM
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At autocrosses, I have been locking up the rears so I think it does need some adjustment. There is another one next weekend, I think I will try to adjust it. Any idea what increments I should change it in?
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Alan Jackson 77 911S 3.2 |
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12-11-2004, 04:58 PM
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Join Date: Jul 2002
Location: SC - (Aiken in the 'other' SC)
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The fronts should lock sightly before the rears so yeah it is a problem.
Your car shouldn't have a proportioning valve. It sounds like the previous owner changed the calipers and ended up with way too much rear bias. A proportioning valve can help alleviate that problem (read as mistake) but a better solution is to have correctly matched calipers. Another possibility (low probability) is they really screwed up and put the proportioning valve into the front brake system. If so pitch it as far as you can throw it. Wayne
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- "Speed kills! How fast do you want to go?" - anon. - "If More is better then Too Much is just right!!!" - Mad Mac Durgeloh -- Wayne - 87 Carrera coupe -> The pooch. |
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12-12-2004, 01:13 AM
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The biasing valve generally goes to the rear brakes. "Increasing" will allow more brake fluid to flow to the rear calipers, adding rear braking. This is an extremely touchy situation if you are tracking your car or braking near the limits (lock up). It is alway better to error on the side of front prodominant braking and to gradually add rear brake. Too much rear brake and you will have the go kart braking phenomena of rear only braking which is very treacherous, especially in a rear heavy 911. Any high speed stop that is made when the car is not perfectly straight will cause the back end to come around incredibly fast.
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12-12-2004, 07:11 AM
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Quote:
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Alan Jackson 77 911S 3.2 |
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12-12-2004, 08:32 AM
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Pure guess here, but based on I've seen it before.
The m/c wasn't changed to the bigger 930 unit(I'll bet the rotors weren't changed either  ), rear brakes lock in very heavy braking, so the genius owner thinks "aha I need a p/v on the back to fix this problem"It didn't, frustration and disillusionment set in and the car is sold to an unsuspecting new owner w/ raves about how great the brakes are.  They're not, not w/o some additional parts any way
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Bill Verburg '76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone) | Pelican Home |Rennlist Wheels |Rennlist Brakes | |
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12-12-2004, 09:38 AM
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1976 Porsche Carrera 3.0
1995 Porsche 993 Carrera Coupe
