Anyone Installed a Brake Bias Valve?

[North Coast Cab]

As mentioned once before, my Carrera stock brakes have been totally rebuilt and yet the front lock-up very easily. If I get on the brakes fairly hard at 40-50 I can lock them up. I'm contemplating installing an aftermarket brake bias valve. What do you think?

JG

[89911]

Here is one installed on an 87 911. There isn't much to it other then removing the old bias regulator and rebending some lines. Haven't had a chance to actually adjust it yet until the car gets rolling.

[North Coast Cab]

Why do you have to remove the old bias? I was just going to put inline with the front line and adjust from there.

JG

[RoninLB]

Originally posted by North Coast Cab

I'm contemplating installing an aftermarket brake bias valve. What do you think?
JG

I think that stock brakes may be too hard for some street use.. JW recommended soft Axxis pads to me.. and I love them.. no more front lock-up...........Ron

[Wil Ferch]

Northcoast:
First try and see how it behaves at 80+ mph. Maybe heavy front bias for lower speeds is normal. Once you do this, and still think thee is too much front bias, you can go to another factory bias valve ( for the 85 Widebody) which dials in a bit more rear bias ( see recent post of mine where I mention part number...don't have it in front of me). If it *still * isn't enough, then remove the bias valve altogether...but be careful and test at various speeds.
--Wil Ferch

[expat]

I shall be watching keenly (if you keep posting what you are going to do) as I have the same problem with my 87 cab. I can lock up real easy and it gets embarrassing on club runs when I get fenders-full of tyre smoke.

I really hate my Carrera brakes. I'm going to have to get someone professional to look at them.

My beater Mitsubishi Galant brakes better then my 911.

Please keep us updated on the proportioning valve.

Cheers
Mark

[TyFenn]

Sure, blame it on the car

[North Coast Cab]

Wil,
At really high speeds it's ok, but once I slow down it's trouble. If I run hard through some turn or autocross they lock-up every time I hit them. I read your post. Do you think I'm better off changing to the '85 valve or removing and putting a fully adjustable one in? I'm thinking of going with the adjustable one so I can dial-in based on pads, conditions, etc.

JG

[RoninLB]

Originally posted by North Coast Cab

Do you think I'm better off changing to the '85 valve or removing and putting a fully adjustable one in?

Axxis brake pads

[Wil Ferch]

If RoninLB's pads don't work fot you and you till are contemplating a valve, then an adjustable one may be just the ticket. But just like so many other "adjustable" devices, it can get you really crossed up. If you do, test, test at various speeds and dry/wet conditions so you really know what you've got.
---Wil Ferch

[North Coast Cab]

I did some more road testing today and it appears it's only the left front which locks up. If you hit the brakes medium hard at any speed it locks up. I rebuilt the calipers over the winter and I wonder if something was misaligned when I re-installed. I've read a little about where the piston/pad should sit when installing but haven't totally come up with a plan to fix. Any advise?

JG

[Chuck Moreland]

Originally posted by North Coast Cab

At really high speeds it's ok, but once I slow down it's trouble. If I run hard through some turn or autocross they lock-up every time I hit them.

Carreras have really well balanced brakes from the factory. If yours is properly functioning, and no other mods have been made to the brakes, I would not be in hurry to re-engineer the system.

Honestly that sounds like a technique problem, not an equipment problem.

With autocross induced adreneline in your system it is easy to apply the brakes too quickly. Easy on / Easy off. It should take about 1 second to go from zero brakes to full threshold braking. Try and do it much faster and the car doesn't have time to load up the front tires -> you will lock up the front end because you haven't let the weight transfer.

Alternatively, it's easy to have the front end wash out if you try and brake heavily while turning in. Leave the trail braking for the experts.

The correct way for less experienced drivers to approach a turn is:

- Brake
- release
- downshift
- throttle (judicious)
- turn-in

When you get that down, slip in heel and toe.

When you get really really good, then think about trail braking.

[RoninLB]

Originally posted by North Coast Cab


haven't totally come up with a plan to fix. Any advise?

Yeah!!! Wil will walk you thru it.. I give up..............Ron

[Chuck Moreland]

Originally posted by North Coast Cab
I did some more road testing today and it appears it's only the left front which locks up. If you hit the brakes medium hard at any speed it locks up. I rebuilt the calipers over the winter and I wonder if something was misaligned when I re-installed. I've read a little about where the piston/pad should sit when installing but haven't totally come up with a plan to fix. Any advise?

JG

Check for air bubbles first.

Other things that could be a culprit -

- Stuck caliper
- Corner balance hosed up
- Worn shocks
- Worn bushings
- Out of balance, out of round, flat spotted tires

[North Coast Cab]

Hmmm.
Though I'm a novice autocrosser, I don't think it's the driver. If I hit the brakes in the driveway medium hard the left locks up.
Calipers have been rebuilt and have checked out ok.
Bled brakes numerous times.
Shocks are in good shape.
A-Arm bushings are brand new.
Now that I think about it, I had this problem before I rebuild the brakes, bushings etc.
What about the seating of the piston vs. brake? Is it possible the pressure is hitting the left front b4 the rest?

JG

[AES]

IMHO you have a mechanical defect somewhere in the brake system. My '86 brakes perfectly with no drama whatsoever.

[911pcars]

JG,
Read Chuck's list again, then check off as you verify.

Pressure in all parts of a hydraulic system (non-ABS) is the same. However, if you have a pinched line, volume (to move the caliper piston) may decrease. I suspect an individual brake caliper issue rather than 3 corners that are not working well.

Sherwood Lee
http://members.rennlist.org/911pcars

[don911]

I agree that its a problem with the system. If you've locked them up a lot, you may have a flat spotted tire. The tire may be returning to the flat spot and locking up. That's probably a long shot and the problem is more likely in the brake system.