I use a GRP4Fabrications hydraulic clutch pedal box. Originally I set it up with the clutch master on the left, front brakes (0.75) in the middle and rear brakes (0.625) to the right. I was never very happy with the power of the big AP calipers I have up front and could never lock them up. The pedal was very hard with little travel. The balance bar was straightish at all times when using 50:50 bias. I knew something was wrong.
After a heap of research I developed a calculation spreadsheet to determine what size master cylinders I needs on the car and it turned out that I needed to replace the front 0.75 with a 0.625. This makes sense as a smaller bore means a longer throw but more pressure. Calculations below;
Now I have a pair of 0.625 M/C in there and set to 50:50 bias. I can lock the front brakes with a big pedal push and they feel much more powerful on the front. But, when applied the bias bar is cocked over at a big angle. Also, when bleeding the brakes I get plenty of fluid out of the front but little out the rears. Having used a pressure bleeder I am confident this is not an issue with air in the M/C (the M/C are angled such that the inlet is high so the air would bleed back into the reservoir anyway). I am confident there is no air in the hydraulic handbrake M/C also as the handbrakes feels breat (HB plumbed into the rear brake line). This picture shows what I am getting;
What I am seeing with the bias bar cocking over does not make sense. Both M/C rods are currently set to the same length (I realise this needs to be changed but until I get to the bottom of this I wont touch them). The front caliper pistons have an area 217% that of the rear. This tells me that the front M/C will need a bigger throw than the rears in order to reach pressure. The bias bar shows the complete opposite!!!! In order for the bias bar to cock towards the rear M/C, the rear M/C must be showing greater travel than the front!! I cannot comprehend this.....
Further, if the rear M/C has greater travel then I would expect it to be flowing fluid when bleeding the brakes. (The pressure bleeder pushes fluid out no worries so there is not a blockage.)
The easy answer is to run the bigger (0.75) M/C on the front again but the maths and physical evidence shows this not to be correct even though 99% of people automatically do this. I won't get full braking though.
Are there any brake engineers on here who know the answer to this conundrum????????
Out of interest these are the calculations using the 0.75 front M/C showing only 74% front braking effort;
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