I have my Bias pedal box up and working, but had some real grief bleeding the brakes with the 0.625" on the front and the 0.70" on the rear. put the larger cylinder on the front and it was better. I realise this goes against the grain, but lets not forget that my brake system is hardly conventional.

So, looking at it as 2 separate systems, I have standard RST drums on the rear and FRS Brembo 4-pots on the front. Currently, I have the 0.70" cylinder supplying the front and the 0.625" on the rear.

Given the improvement of replacing the front 0.625" cylinder with a 0.70", we're thinking that the front cylinder needs to be larger. What do you think?? Is there a guide somewhere of what size cylinder is needed for each type of caliper? e.g. What cylinder would be used for AP 4-pots etc.

 

the smaller bore cylinder should apply more pressure,
and as the front brakes should be more efficient than the rears,then 6.25 on the front,and 7.0 on the rears
isnt 7.5 normally used for hydraulic clutch.?
if it stops ok then dont worry about it lol,last thing you want is the rears locking up first.

 

as said because you have poor brakes on the back and good on the front you might not want as much pressure to the front and give a bit more to the back,

give it ago and see what you think, start with the "abnormal" setup and see what you think play with the bias ect then try it the other way round, as you do have bias pedal box if you find it works better the normal way round then you can always adjust it with the bias so you cant lose

 

i plumbed my bias box 0.7 to front & 0.625 to rear the pedal was hard as fook but the brakes were absolutely crap last year .swopped them around this year to the correct way around pedal felt softer but brakes are a huge improvement better so id say swop now imo

 

What was the problem bleeding them ? Thats the first issue to get over, there is nothing really abnormal about your set up Christian. Going larger up front will push more fluid but under less pressure and would be a step backwards as the backs will have more pressure until it is dialled out.

Give us another call tomorrow, missed the one tonight sorry.

AP 4 pots with something like 38/42 pistons would normally run .625 front on 5/5 or 5.5 or even greater ratio pedal box.

 

your legs will need to be massive to stop a car on front four pots with a large front cylinder, there will also be no feel whatsoever to the brakes.

what position is the bleed nipples on the calipers ? and have you tried a vaccuum bleeder?

 

When we were bleeding them, we just couldn't get the fronts to move any fluid. Less than an inch of fluid movement in the pipe for each pedal press.

Swapping the cylinders and re-bleeding sorted it, but maybe it was just coincidence?

It's early days, but I'm happy with how the brakes actually feel, with the cylinders how they are, despite it not being actually 'right'.

 

have you driven it at any speed down the road yet ?

 

Did you wind the balance bar over to the fronts to bleed the front lines, then over to the rear to bleed the back ones ?

Or are you trying to do it all with the bar in situ in the same place ?

 

Can i just ask why you are still using drums at the back of your car Christian. With that much power and the speeds you are stopping from would it not be better to get a disc setup at the back?