master cyl/brake booster advice needed - St185

[Classique71]

Hi guys - some of you might know ive upgraded my brakes of late to the bigger st205 units - i ahvent driven the car yet - so im just covering bases " just incase "

For those who have done the conversion or something similar - was there a need for a larger master cyl/booster combo to get pedal feel back or was the stock st185 unit up to the task ..

I know i have to move more fluid with the larger calipers - but i have a feeling this may have a negative effect with a spongier pedal ..

justen - yours is about the closest o know of with a large brake setup - iof you read this .. are you stil using the st185 booster/cyl combo or is there a larger unit i can swap for ?

Reboring the cyl is an option also i havent looked at - not all that sure what to do

[PlacentaJuan]

i was wondering the same questions; altohugh i have now finished my brake upgrade (r33gtst calipers into a mx83 cressida) and while it took alot of bleeding to get all the air out (let the MC run dry once ) its is perfect now, escpecially with greenstuff pads in there.

i dont know how much different the size will be to your conversion but the stock mx83 calipers is only one piston and i upgraded to a 4 piston caliper and pedal feels the same as before.

having said that, when i change my brake booster (for engine conversion) i would like to know if it would make a difference to bore out the MC a bit, even thought everything is fine now, would it improve anything at all?

[wilbo666]

i was wondering the same questions; altohugh i have now finished my brake upgrade (r33gtst calipers into a mx83 cressida) and while it took alot of bleeding to get all the air out (let the MC run dry once ) its is perfect now, escpecially with greenstuff pads in there.

i dont know how much different the size will be to your conversion but the stock mx83 calipers is only one piston and i upgraded to a 4 piston caliper and pedal feels the same as before.

That is because the piston area is pretty well exactly identical between the MX83 and R33 calipers. As such you don’t need a different/larger master cyl to mode enough fluid.

In regards to understanding master cylinder sizing (and in general braking systems) a bit better I think this pdf is quite good.

Cheers
Wilbo

[Toobs]

The ST205 master cylinder is 15/16th bore and so is the ST185 isn't it... why did you bother changing?
If anything I would have swapped the 185 bias valve for the 205 bias valve considering you have a complete ST205 brake setup now.

The UZS131 has a 1" master cylinder if you're looking for something bigger than the 15/16th one from the 185/205's

[Classique71]

havent changed them toobs - just asking questions atm ..

i get the car back from the engineer next week at this stage ..

Ill see if you can still get the bias valve from toyota though - as the bits i have didnt come with that