19mm Master Cylinder Options

[e30mclow]

For those that have deleted their brake booster/servo, what master cylinder are you running?

The preferred setup appears to be a 19/19mm master cylinder with the brake proportioning valve removed.
I have a 19/20mm one from an early 316 (drum rears), but would prefer to start with a 19/19mm as people have reported success.

VW Beetle 19mm? - Bolt pattern looks OK, but is a 4 port.

Tilton 19mm - mounting point are in the 6 & 12 location rather than 3 & 9.

Before anyone asks: My engine swap doesn't allow adequate room for a relocated/smaller servo (intake plenum & 3" IC piping are in the way).

[e30mclow]

Pasting this old thread here in case someone else's search brought them here.

https://www.r3vlimited.com/board/showthread.php?t=386495

Looks like old VW is the way to go. I'll post part numbers once I have the plan in place.

[varg]

This might help https://www.bimmerforums.com/forum/s...r-Delete/page3

[e30mclow]

This might help https://www.bimmerforums.com/forum/s...r-Delete/page3

Thanks, a lot of great info there!

[TobyB]

The slightly bigger rear m/c piston is nice, because then you
can run a limiting valve and actually use the rear brakes.
A 1:1 master puts more than 70% forward, and there's then
no way to bias it to the back.

t

[vpilarrt]

A 1:1 master puts more than 70% forward, and there's then
no way to bias it to the back.

Couldn't you install the limiter on the single front brake line out of the master before it splits at the tee?

[TobyB]

Yes.
But it will limit front pressure and let rear rise
right when you want rear pressures NOT to rise-
when weight's transferring off the rears and onto the fronts.

It's a recipe for rear- end lockup under heavy braking

t

[Massive Lee]

A 1:1 master puts more than 70% forward, and there's then
no way to bias it to the back.

t

The original MC has a differential piston sizing. Larger in the front and smaller in the rear. Smaller means that for the same effort, it puts out more hydraulic pressure. Therefore, a stock MC shoots more pressure at the rear and the valve limits it to avoid locking rear brakes.

When using a same size bores MC, my recommendation is to ditch the valve, or otherwise you will end up with not enough rear braking and will be unbalancing the car's braking distribution.

Allow me to post the same graphic I have made 15 years ago showing how the OEM valve limits the rear pressure vs the front.

In red is the linear progression without a valve. You can see a knee, and how the rear brake pressure evolves with the valve.

[jsta1109]

The original MC has a differential piston sizing. Larger in the front and smaller in the rear. Smaller means that for the same effort, it puts out more hydraulic pressure. Therefore, a stock MC shoots more pressure at the rear and the valve limits it to avoid locking rear brakes.

When using a same size bores MC, my recommendation is to ditch the valve, or otherwise you will end up with not enough rear braking and will be unbalancing the car's braking distribution.

Allow me to post the same graphic I have made 15 years ago showing how the OEM valve limits the rear pressure vs the front.

In red is the linear progression without a valve. You can see a knee, and how the rear brake pressure evolves with the valve.

Just to clarify on this point, if you were locking rear brakes with a factory master (318is, 22/19 master) there is a possibility that the valve is no longer functioning correctly? Currently facing this with my setup on track, fronts seem to not function much at all, rears locking quite easily. (my lines are not back to front)

[Massive Lee]

Just to clarify on this point, if you were locking rear brakes with a factory master (318is, 22/19 master) there is a possibility that the valve is no longer functioning correctly? Currently facing this with my setup on track, fronts seem to not function much at all, rears locking quite easily. (my lines are not back to front)

It is indeed possible.

[TobyB]

The original MC on the later ABS cars has a differential piston sizing.

Fixed that for ya. The earlier m20 cars w/o ABS had a 22/22, and then
strangely, early ABS cars seem to have 22/22 as well, switching to
the 17/22 roughly around the time of plastic bumpers.

I've seen several valve iterations, too, for the different systems.
And I've had them fail, too.

t