OBP Pedal Box Fitting Tech Session
OBP Pedal Box Fitting Tech Session
A good quality bias pedal box is an absolute must for any serious track day car or race car. Most car brakes systems, even when fitted with ABS, use a vacuum servo to increase the pedal force and help with braking, however in a track or race use this system is often not up to the job and you get an inconsistent brake pedal due to heat build up and general wear and tear.
Also on most ‘standard’ brake system the master cylinder is typically only one unit that splits the braking effort to each brake within only one cylinder, this means that break bias is effectively set and although an in line adjuster valve can be fitted to change the bias.
This is not ideal or as ultimately effective as a bias / balance pedal box setup. Most saloon cars now use a dual line brake system so this means just fitting bias lever is not possible.
Link To: Obp Pedal Boxes
What is a Bias Pedal Box?
A bias pedal box system firstly removes the vacuum servo that can give the inconsistent brake pedal and the pedal force from brake pedal is connected directly to the brake cylinders. This means there is no longer a reliance on a vacuum from the engine to help with the braking force.
This means the pressure you hit the brake pedal with is exactly the pressure the brakes work with giving you more feel for what the brakes are doing. The other and most important part of the pedal box system in that it uses two brake cylinders as opposed to only one.
This means you have one cylinder for the front brakes and one cylinder for the rear brakes, the two cylinders are connected by the adjustable ‘bias / balance’ bar, giving you control over adjusting the braking efforts between the front and rear brakes helping you to fine tune your brake to suit both your driving style and the weather conditions, typically in the dry you would want the front brakes doing most of the braking and in the wet or damper conditions you would adjust the braking effort more towards the rear.
The bias setup procedure will be explained later. Also a ‘full’ pedal box system will typically replace both the accelerator and clutch pedals/systems.
Will A Bias Pedal Box Work With My Cars ABS system?
In a word with a standard manufacture ABS system NO…… however expensive ‘Motorsport’ ABS systems are available but these are very rarely used.
The main problem with a using a bias pedal box with a ‘standard’ manufacture’s system is that one of the main reasons for fitting a bias pedal box is to give you more control over your car’s front to rear brake balance and a cars ABS system works to prevent your cars wheels locking up under braking…… therefore a ‘standard’ car’s ABS isn’t programmed to allow both the adjustment front to rear of the brake balance because as it sense’s wheel ‘lockup’ it would then try moving the brake pressure to the other wheels to prevent the wheel locking and therefore acting against your chosen brake balance.
Choosing the Pedal Box for Your Application.
The main options when choosing a pedal box are whether you go for the standard ‘over the top’ type system or a ‘floor mounted’ system, the main criteria for this is basically the available space to fit it.
You need to take into consideration whether your car has a cable or hydraulic clutch system also bare in mind that whilst you are changing the pedal box it may be worth also converting the clutch system to a hydraulic system if it is not already.
Something that is more important in later cars you need to check how your throttle is controlled, a great deal of newer cars use a ‘fly by’ wire system to control the throttle rather than a mechanical cable.
Finally OBP Ltd do make a number of ‘custom’ pedal boxes which are normally floor mounted systems that bolt straight to the floor pan. If in any doubt contact us for advice.
Fitting Your OBP Pedal Box.
Firstly if fitting a pedal box to a ‘road’/saloon type car you will need to remove all your standard pedal box system and its ancillaries such as the servo and ABS systems etc… However, before you do this either measure or take photos of the positions of the standard brake pedal so that you know you fit your new pedal box in the right place. These photos are helpful because you may need to refit some items as some cars use the pedal box to support the bottom of the steering column.
When bolting the pedal box in make sure you use high tensile bolts and large washers to spread the load when the brake is applied, never use riv-nuts or similar fixings to mount a pedal box!!!
If you are fitting a universal pedal box more care is need when deciding where and how to mount the pedal box. Firstly the pedal box needs to be mounted to a strong and secure surface. Secondly again make sure you use high quality fixes to secure the pedal box.
Also when fitting the bias adjuster firstly check your race regulations allow brake balance whilst the car is ‘in use’. Mount the adjuster in accordance with the regulations.
Fitting Master Cylinders, Plumbing In and Bleeding Brakes.
When fitting the cylinders first it will be easier to build the pedal box assembly up out of the car and the fit the whole unit in to your car in one piece only leaving the plumbing up of the brakes, clutch and the fitting of the throttle cable.
The normal sizes for the master cylinders are:
- 0.750″ Clutch
- 0.750″ or .700” Rear Brakes
- 0.625″ Front Brakes
When plumbing the brakes in this will be one of the most time consuming part of the job. At this point you will require a rethink of the plumbing of the system and it will most probably work easier to fully re-plumb the whole system as standards car system can be complicated with dual line systems etc.
- Front brakes – Single line up to a 4 way t-piece and the split into two lines of equal lengths to each front calliper. In this t piece you will install an in line BRAKE LIGHT pressure switch this will save lots of hassle and time mounting the standard switch.
- Rear brakes – Single line through a hydraulic hand brake (if fitted) to a t-piece and the split into two lines of equal lengths to each rear caliper.
- Clutch – simply a single line to the slave cylinder in/or on the gearbox.
The pressure lines you use (either hard line or flexible) are again down to personal preference, although where any flexible lines are used they need to be done in high quality Motorsport spec braided lines.
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