master cylinder upgrade ?

[filh]

Yes I did measure the the piston depth from Navara , which was a bit deeper in BMC than the Ae86 .

Rallye is achieved , but i'm not very convinced with the upgrade .
Pedal is hard (sometime like a piece of wood.....) but wheels(front and rear ) can't be blocked !

So it's braking , but there must be something working wrong .

My brake booster was ok before I removed the Ae86 bmc.
I'm very sorry about that , as It was an easy bolt-on upgrade

I'll have to check further . But i had another engine problem on my last race (see my new post)

[Ivan141]

Maybe the capacity increase is too big. There is a reason they keep the master cylinders small, namely pedal effort. The extra volume of your master cylinder should closely match the added volume of your new calipers.

[filh]

stock is 13/16 , and the one I fixed is 15/16.But I can't measure the increase
volume of caliper .
But I guess there's a problem between booster and BMC.
phil

[Ivan141]

13/16 to 15/16" amounts to a 33% increase in capacity.
Effective pressure from the master cylinder is force divided by piston area.
So you need 33% more force to get the same pressure you did before.
Force exerted on the caliper is this pressure multiplied with the surface area of one side of the caliper. Multiply that by 2 to get the effective clamping force for any caliper type.

Anyways.. enough theory. The stock rx7 master cylinder is 15/16, so besides the fact that you might need more pedaleffort to achieve the same pressure, the size is not as far off target as I thought earlier.
Maybe bigger brake systems compensate for this by using stronger booster assistance?

[filh]

Maybe , but I don't know how the Booster power is calculated .
I also have to check with both adjustment : the rods that goes into bmc is adjustable , and the rod between pedal and booster too.
Phil