Brake Bias set up using twin M/C

[oldbutnotslow]

I am currently helping to sort out a new build BIRKIN

 

Never seen one before this week other than in pictures never mind worked on one.The owner has imported the chassis suspension and running gear from Birkin in South

Africa see here

 

Lots of very nice features (IRS for one) and some that I am not that keen on. The quality looks good in the majority of instances but I digress.

 

The brakes have twin master cylinders and the pedal assembly has a brake bias bar fitted.

 

Now I understand the principle of the bias bar and its operation but what I was hoping was that a trip to my local MOT station and a session on the brake rollers would enable me to calculate and adjust the bias to the factory specification of 60% front and 40% rear.

 

The problem is that there is an imbalance on the front brakes of about 30% so there is something amiss that need sorting before I go any further.

 

I was hoping that I could use the KG force reading on each brake to calculate and adjust the bias. ie 125kg front Right 126kg front left total 251kg. Rear Left 111kg rear right 110 kg Total 221kg or 53% front 47 % rear. Then with a combination of the balance bar and M/C rod length adjustments achieve the desired 60/40 split

 

However I very quickly realised that the in effective front wheel required greater force before it locked which cocked my simple Excel sheet calculations. (I wasn't expecting there to be such an imbalance)

 

Any ideas or advice from someone who has worked on this type of arrangement before would be much appreciated.

 

 

[jonboylaw]

Quick question, were the brakes bedded in? if not then any measurement is irrelevant at this time.

 

 

[7 wonders of the world]

Is the car LHD by any chance? if so only having the driver on board increases the load on that side hence your able to generate more braking effort prior to locking up.

 

The 'porkier' the driver the higher the reading.........