I have a brake question
Discussion
what is a split braking circuit? and can it be related to brake bias. am i right in thinking that in order to adjust the brake bias on a race car two master cylinders are needed one for the front and one for the back?? can anyone tell me how brake bias works? so many questions yet i have so few answers!
many thanks
many thanks
A split braking circuit is basically 2 seperate circuits. If one circuit fails, then you still have the other circuit to break with, instead of just crashing into a tree and dying. Usually (on modern cars) one is to the front-left wheel and the rear-right wheel, and the other is front-right and the rear-left wheel, to keep better balance if one circuit fails. Older cars were split front and rear, but if the front circuit failed then the rear wheels locked up too easily under braking, which was just as dangerous as having no brakes. This is what uses 2 master cylinders that you mentioned (well, 2 in 1, called a tandem master cylinder).
As far as I know the split circuit isn't related to brake bias, it's purely for safety, though I may be wrong.
As far as I know the split circuit isn't related to brake bias, it's purely for safety, though I may be wrong.
Brake bias is simply the distribution of braking force between the front and rear of a car. This is controlled by the split of hydraulic pressure between the front and rear brake systems. Typically on a competition car you would have two physically separate master cylinders connected by a bias bar. The brake pedal pushes on a pivot between the two master cylinders, and the pivot can be moved toward one or other of the master cylinders to provide more force (and therefore more pressure) to that circuit. Like this
It's also possible to change bias simply by limiting pressure to the rear brakes, using a bias valve (essentially a pressure regulator). This gives you less flexibility since you can only reduce rear pressure pressure with respect to the fronts. This system is typically used on road cars, either with a fixed split or with some kind of load dependant split where the bias valve is connected to the rear suspension.
A split system on a modern road car connects diagonally opposite brakes together, and is simply for redundancy. If one system fails you have a front and rear wheel left that will allow you to slow down without too much instability.
It's also possible to change bias simply by limiting pressure to the rear brakes, using a bias valve (essentially a pressure regulator). This gives you less flexibility since you can only reduce rear pressure pressure with respect to the fronts. This system is typically used on road cars, either with a fixed split or with some kind of load dependant split where the bias valve is connected to the rear suspension.
A split system on a modern road car connects diagonally opposite brakes together, and is simply for redundancy. If one system fails you have a front and rear wheel left that will allow you to slow down without too much instability.
Yuxi said:
flemke said:
By changing position (L to R) of the threaded rod connecting the 2 MC pistons, you change the % of total pedal force going into each.
Apart form the wires hanging down in front of the clutch, the car is obviously being worked on at the time the photo was taken)
Busa_Rush said:
What's wrong with it ?
As a hint, can you see anything that is actually locating the bias bar and stopping it moving side to side (apart from the poorly installed adjuster cable)?The two main clevises are supposed to be adjusted close to the ends of the tube in the brake pedal. This properly locates the bias bar so the spherical bearing inside the tube remains where it's set, and also limits the angular movement of the bar so in the event of one circuit failing you can still operate the other circuit, albeit with more pedal travel. It's a dangerous lash up as it stands.
Edited by Mr2Mike on Sunday 27th February 17:15
Mr2Mike said:
Busa_Rush said:
What's wrong with it ?
As a hint, can you see anything that is actually locating the bias bar and stopping it moving side to side (apart from the poorly installed adjuster cable)?The two main clevises are supposed to be adjusted close to the ends of the tube in the brake pedal. This properly locates the bias bar so the spherical bearing inside the tube remains where it's set, and also limits the angular movement of the bar so in the event of one circuit failing you can still operate the other circuit, albeit with more pedal travel. It's a dangerous lash up as it stands.
Edited by Mr2Mike on Sunday 27th February 17:15
Busa_Rush said:
The car is obviously being worked on so to criticise the current adjustment is a bit mean. For example there's clearly holes for rolled pins which would be spot welded in the ends to stop the adjuster rod winding right out but it's clear the car is in a state of rebuild - just look at the debris on the floor.
You shouldn't actually need roll pins to prevent the adjuster winding out if it's installed properly (though certainly a good idea to fit them), one side will reach the end of it's thread before the other side falls off.The thing is I have seen much worse than this being used on the road and track; setting up bias bars appears to be a mystery to many people. My own car arrived with numerous scrutineers stickers on it from when the previous owner used to sprint it, but after taking the cover off the pedal box I found he'd made his own "bias bar" from a bit of M6 stud, which was unsurprisingly banana shaped. Walk around the paddock at a hillclimb and you are almost guaranteed to see a bias bar installed like the one in the above pic.
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