Brake bias on a completed car.

[FarmerDave1321]

Did some searching and couldn't really find an answer to my question (I could have also just missed it).

I need to adjust the brake bias on my roadster, it's waaaaay too rear heavy. The rears lock up before the front so it's clearly not biased correctly. There are no other issues, brakes aren't dragging, fluid is clean and no air, etc.

So, my question is - what's the best way to get to the bias adjustment on a completed car? While I'm in there, I'd like to install the bias adjuster as well.

[edwardb]

Need more information. If you have the Wilwood pedal box it can be adjusted via the balance bar. https://www.youtube.com/watch?v=ZYK4VEOae6w&t=6s. Sounds like maybe you do if you're talking about a bias adjuster, which I assume is the cable attached to the balance bar and allows for external adjustment via a knob. Should be able to get it corrected.

If you have a Mustang pedal box with a single master cylinder, then a brake proportioning valve might be what's needed.

But before going too deep, is this a new condition? All four corners working properly? Pad condition?

[FarmerDave1321]

Yep, all four corners work excellent. Pad wear is even, rotors are smooth. When you brake, it's really easy to feel that the balance is heavy on the rear and not much braking is coming from the front. While the car stops moderately fine, it is far from ideal.

I have the wilwood pedal box with the balance bar adjustment between the two reservoirs. That's why I was thinking about getting the bias adjuster setup while I'm in there fixing the bias itself. That would give me better access to fine tune it while driving without having to tear back into the car.

The challenge I have is that I'm not sure I see a really good way to get access to install the bias adjuster now that the car is fully assembled and painted. I will be pulling the dash off in a few weeks to fix a gauge/electrical issue, so I'm thinking that would help me with access to it. Is there anything else I need to consider?

Backstory - I didn't build the car, my father did. I helped on a few bits here and there, but I'm mostly in learning mode at the moment.

[Jphoenix]

The access panel on the right side of the attached photo allows access to the top of the balance bar - if you have the same setup as my car, if you have a MKIV, then it should be the same.

207424

Get the bias bar set up per the instructions in the manual. There is a screw on top of the inboard clevis, locked by a 7/16 nut (maybe 1/2"?). Release the lock nut, and loosen the screw with a flat blade screwdriver, loosen the adjuster bar locknut with a wrench (the nut with the torque-stripe on it in the photo, just inboard of the screw you loosened) - then you can turn the bias adjuster bar with your fingers.

After getting it set initially - by adjusting the pedal input rods and bar per the manual, those can be turned with a 1/4" open end wrench - I then set my initial brake bias setting same as how I do it on the race cars:

Bleed brakes really good - which means do it twice, then wait a week, do it again until the pedal is firm.

I use an adjustable clamp to put just enough pressure on the pedal to lock the front brake so I can't turn it with my 4' steel bar/strap wrench around the front tires. You can use a large breaker bar attached to the wheel somehow. I can also check that both front brakes are close to being the same lockup. It is important to use a clamp, or maybe one of those load securing adjustable bars so you can apply just enough pressure to brake pedal to lock the front brakes and keep that pressure steady. A helper pushing on the brake pedal doesn't work because it has to be a steady pressure.

Then I go to the rear wheels and see if I can turn them with the bar, typically I can if I've set the bias up properly initially.

I want the front brakes to lock up just before the rear brakes lock up.

To adjust the front/rear bias - release the pressure on the pedal, turn the bias adjuster until you can get the rear brakes to lock up just after the fronts. Takes a few iterations and a couple hours to get it how I like it, also sometimes gotta bleed the brakes again because left side locks before the right side, always going to be some difference, but it's a good way to see if I still have air in the system somewhere.

That's the initial setup, final setup is on the skidpad, parking lot, whatever, even better if the road is wet, you find out real fast if the rear locks up first as you enjoy that merry-go-round ride. This being solely a street car, I'll adjust the bias to the front and leave it. On the race car I adjust often with the knob, dial in a bit more rear when it's raining, but not so much that I lock up the rears and spin - I can easily spin in the rain with poor downshifting technique, don't need help from too much rear brake bias!

This is a lot easier with the body off - except for the road testing. Also, once you get the bias adjusted properly - or how you like it - you do not need an external adjuster knob unless you want to adjust the bias routinely, as you would when tracking or auto crossing/racing the car. I don't have an external adjuster on my Cobra, but will on the Coupe-R because I'll be racing it.

[FarmerDave1321]

Hugely informational response, thank you Jim!

Looks like I'm going to have to create an access panel. My brother is a pretty solid machinist so I'll enlist some help as to not screw it up and make it look nice.

[MaxVmo]

If it’s a MKIV the access panel is already there, isn’t it? It may have been riveted in place instead of a threaded assembly. Just thinking out loud. Excellent post as I’ll be doing the same thing soon.

[F500guy]

Jim has it nailed, but make sure you Know what you have as far as master cylinder size and front and rear brake calipers, that is a huge concern. I did some brake calcs with the wilwood standard set up (3/4 master cylinder both front and rear) and it is heavily front biased with equal balance bar set up.

[Avalanche325]

Early MKIVs didn't have an access panel.

[Nigel Allen]

Hi Dave,

It is worth adding some details into your signature, about your car and its history (which is a lovely story). This will get you more help as other forum users will be able to see what configuration of powertrain etc you have and also 'where you are at' ie, have inherited a nicely built mk4 that just needs some maintenance / finessing etc.

It's a great car and I look forward to following along.

Cheers,

Nigel

[CraigS]

One thing to ad; the MC on the side w/ the most visible thread on balance bar will have the most bias.
207429

[CraigS]

One thing to ad; the MC on the side w/ the most visible thread on end of the balance bar will have the most bias.
207429
Ckick to enlarge. See the green arrows. If there is a jam nut, include the threads inside of it when comparing length.

[Blitzboy54]

Adjusting them manually is not that hard. You have the access you need with the panel removed. The bias adjuster cable is thick and not very flexible. My recommendation is to also purchase the Tilton 90 degree adapter. I did not on my last build and brought he cable out of the side of the footbox into the engine bay. This was just ok. The 90 deg allows you to attach it in a front to back arrangement. You can then put the adjuster anywhere you want.

Also FYI, I was back and forth on the adjuster. I recently decided to do it. Speedway motors makes the same adjuster. It’s almost half the cost, it’s the exact same but the knob is billet aluminum instead of plastic. I needed another item on a recent order to get free shipping so I threw it in. I was really pleased when it arrived.

[FarmerDave1321]

Hi Dave,

It is worth adding some details into your signature, about your car and its history (which is a lovely story). This will get you more help as other forum users will be able to see what configuration of powertrain etc you have and also 'where you are at' ie, have inherited a nicely built mk4 that just needs some maintenance / finessing etc.

It's a great car and I look forward to following along.

Cheers,

Nigel

Yeah, planning to update the signature as soon as I have the post count to do it.