Brake master cylinder question 2

[Ferrarist]

Have standard tandem brake master cylinder and i plan to convert my braking system to non-ABS.
My question is which port(pipe) provides more volume(pressure) to brake calipers - rear(closest to servo) or front.

 

[BrianPetersen]

They are hydraulically balanced. Both ports will deliver the same pressure - PROVIDED that the master cylinder does not contain any integral proportioning valves. (most ABS don't have proportioning valves, the ABS hardware serves the same function and more)

As for which one could deliver more volume ... this depends entirely on how much reserve travel is available for the piston inside the master cylinder. It's possible - but unlikely - that this will be different for the circuits that are intended to be for front or rear.

Just maintain the existing layout. Whichever port is connected to front brakes, keep it to front brakes, and whichever is connected to rear brakes, keep it to rear brakes.

You haven't told us what car this is for. Be aware of the possibility that non-ABS versions of your car had additional proportioning valves and the like, in order to get proper front to rear brake balance, which would have been eliminated on ABS-equipped versions. Some have load-sensing proportioning valves on the rear axle in order to get better brake force distribution when carrying a load. Some have diagonally-connected brakes, not front to rear. Some (Volvo) have multiple cylinders in each front brake caliper with some on one circuit and some on the other so that in the event of a hydraulic failure, you still have some braking on both wheels instead of all on one side and none on the other.

 

[Ferrarist]

Car in question is Alfa 156 mid-engined RWD 3.0V6 using brake servo and MC from Alfa 166(2001year) - 25mm piston size.
AFAIK our ABS use one pipe for FR and RL wheels while other is for RR and FL - but not 100% sure. And that's my concern - if ABS distributes pressure to FR-RL(main pipe) and RR-FL(second pipe) will it make any difference connecting wrongly??

 

[BrianPetersen]

So they're diagonally connected. The center piston inside the master cylinder is hydraulically balanced so that both circuits get the same pressure, and on a master cylinder for a diagonally-connected system, they will certainly be designed for the same delivery volume of brake fluid. (It HAS to be that way. If it were otherwise, the car would want to veer left or right when braking. With the two circuits balanced, the only way there is any asymmetry is if one circuit fails, and in that situation, one is not concerned about a little effect on the steering, only that somehow in some fashion the car gets stopped ...)

 

[GregLocock]

If theh circuits are pressure balanced then if you have a leak in one circuit you lose all the brakes. Perhaps its a terminology thing.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

They are pressure balanced during normal operation. If one circuit loses its fluid and can't develop any pressure, the central piston hits a travel limit stop allowing the other circuit to keep pressure. Dual-circuit master cylinders have been like this since the beginning.