Adjusting the brake bias

[Mike Garrett]

I need to adjust my brake bias on my completed Mark 4. It has the wilwood pedal assembly. Can it be done though the the panel on top of the driver side foot box? Are both master cylinders the same diameter? Thanks

[BradCraig]

Both of mine are same size, 3/4 if I recall. I have been adjusting mine via the panel on top, only way to do it as far as I can tell.

[Blitzboy54]

Yes, you have to use the panel in the top unless you have a remote bias knob installed. Two things, as I understand it the MC used to be different sizes so double check they are the same. Also, make sure you confirm what MC is plumed to what set of brakes. I wouldn't assume the one closest to the engine bay is the rear. It doesn't have to be.

[Mike Garrett]

Both of mine are same size, 3/4 if I recall. I have been adjusting mine via the panel on top, only way to do it as far as I can tell.

Thanks, that’s what I thought.

[Mike Garrett]

Yes, you have to use the panel in the top unless you have a remote bias knob installed. Two things, as I understand it the MC used to be different sizes so double check they are the same. Also, make sure you confirm what MC is plumed to what set of brakes. I wouldn't assume the one closest to the engine bay is the rear. It doesn't have to be.
Thanks.

[GWL]

I think, the early Mk IV's were the same size, then they changed to different sizes, then they changed back to the same size in the later, today's, Mk IV's.

I've modified my car (the first Mk IV) to be different sizes.

Someone correct me if I'm wrong.

George

[Rdone585]

I don't know if the bias control you have is compatible but I installed a remote control knob connected via cable to the bias control. This was a Wilwood setup in a non-cobra. I think this is one I installed - Wilwood 340-4990 Remote Brake Bias Adjuster Cable. With this you can change the bias "on-the-fly".

[CraigS]

I haven't made any effort to track MC sizes but do seem to remember comments when they started supplying both in the same size. MC sizes are determined mostly by caliper sizes. Piston area of MC vs piston area of caliper needs to be a certain ratio to get the hydraulic system pressure needed w/ a reasonable pedal effort. I think I also remember seeing comments that the rear calipers that FFR supplies have changed so not a surprise they had to change MCs. Some info on adjusting front to rear balance.
-I like to do my testing at about 40 mph because it can get pretty exciting when the rears lock first. 40 is a nice balance between going fast enough that the car doesn't just stop in 20 ft vs not going so fast that you end up sideways.
-I only do 3-4 stops/adjustments and then I drive using the brakes as little as possible maybe 2 miles to let them cool off.
-At the beginning you can adjust a full turn at a time. After you get the rears to lock first then back off 1/2 to 1/4 turn at a time.
-As soon as you get the fronts locking first stop there. The nice thing is that setting them up in good conditions automatically works when traction is less like gravel or rain. As traction drops, braking drops, which means there will be less weight transfer to the front brakes. So the fronts will start locking first. This is what you want in lesser conditions since fronts locking first keeps the car stable vs a spin.
- Look at the ends of the adjuster shaft indicated by the green arrows.
https://live.staticflickr.com/65535/49749270886_f614edbdbe_z.jpg (https://flic.kr/p/2iNb1ZL)Wilwood balance 3 (https://flic.kr/p/2iNb1ZL) by craig stuard (https://www.flickr.com/photos/152454123@N04/), on Flickr
The end w/ the most threads visible will actuate that MC more strongly. Note; in this pic there is a jam nut on the right side. Include that thickness in your thread length.

[J R Jones]

Craig, Another advantage to "bias front" is that the front tire skid recovers faster than the rear.
In my experience I do the brake bias test with the clutch disengaged to factor out engine drag influence. More significant in lower gears.
jim

[CraigS]

Agreed.

[Mike Garrett]

Yes, you have to use the panel in the top unless you have a remote bias knob installed. Two things, as I understand it the MC used to be different sizes so double check they are the same. Also, make sure you confirm what MC is plumed to what set of brakes. I wouldn't assume the one closest to the engine bay is the rear. It doesn't have to be.
Thanks again. One more question- how to you attach the panel to make it easier to remove it.

[phileas_fogg]

Most of us use nut-serts into the foot box top. The picture below doesn't focus on the opening & cover, but you get the idea.


John

https://live.staticflickr.com/1869/29703019117_586957afc4_4k.jpg (https://flic.kr/p/MfKJKg)IMG_4895 (https://flic.kr/p/MfKJKg) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr