# mk3 brake booster upgrade



## jstn (Jun 18, 2008)

hey guys,

i've got a 97 tdi and i've recently upgraded my front brakes to the girling 60s with the larger master.

the pedal is firm but in order to get the aggressive braking response you really need to stomp the pedal. 

is it possible to upgrade the brake booster? if so, which booster would fit my car? i was thinking a vr booster maybe?

thanks!

justin


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## GTijoejoe (Oct 6, 2001)

you just described the exact reaction from upgrading a MC....

Hard firm pedal and now you have to apply more pressure for the same brake torque.... larger MC's move more fluid, they do not apply more pressure, they actually apply less for the same input force. Go back to your smaller MC and you may solve your problem....

Moving to a larger booster diaphram or overall area (tandem) will increase your boost assist... but understand booster tuning is unique often to the vehicle and engine..... changing your entire booster sometimes can be a bad mistake and lead to brake drag. 

For instance, my Evo uses a 17mm MC... my GTi uses a 22... which car do you think has bigger brakes?


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## jstn (Jun 18, 2008)

GTijoejoe said:


> you just described the exact reaction from upgrading a MC....
> 
> Hard firm pedal and now you have to apply more pressure for the same brake torque.... larger MC's move more fluid, they do not apply more pressure, they actually apply less for the same input force. Go back to your smaller MC and you may solve your problem....
> 
> ...


but your evo must obviously use a larger booster.

does anyone know which booster would be an upgrade on a mk3? do the mk4 boosters fit?

justin


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## GTijoejoe (Oct 6, 2001)

jstn said:


> but your evo must obviously use a larger booster.
> 
> does anyone know which booster would be an upgrade on a mk3? do the mk4 boosters fit?
> 
> justin


Thats backwards thinking, smaller MC will give higher pressures, the larger MC will need increased booster ratio and/or diaphram diameters.... that is also considering close pedal ratio's.
Most likely if you look for a booster out of a heavier vehicle (overall GVWR) it should have higher boost ratio or diaphram's to compensate for the large MC to supply the larger calipers.:thumbup:


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