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bigger brake master cylinder


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i have two questions...hopefully someone knows the answers



1) by any chance is there a bigger brake master cylinder that is a direct fit for the EP91 (has 2 holes to fit on to the servo)


the stock one is 13/16 (abs)



so looking for anything between 7/8, 15/16/, 1 inch



2) what size brake master cylinder does the twin pot levin or/and celica carry as standard?



any assistance would be appreciated


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i would appreciate that morgey



the size is usually imprinted/stamped somewhere on the cylinder itself (the shiny/aluminium piece with the brake lines going to it)....so when you need to buy a repair seal kit the owner knows the size



you should see something along the lines of 13/16,... 7/8....15/16...1....1 & 1/16....... indicating the exact size


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from what i can tell from investigations...seems the toyota corolla/levin is a possible match up



didnt some paseo come with 7/8 as well?



a lot of them seem to have the two lines run almost the same spots/angles as the ep82/91----but you still have to be careful not to go too big...i suspect 7/8 to 15/16 maybe ok, but 1' maybe pushing it as i see that size on bigger pick-ups/suvs


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what size Brake master cylinder did the EP82 (non abs and ABS) come with?



did all EP91 come with abs?



thanks to morgey...i found out the toyota levin ae111 that comes with twin pot calipers and ABS, carries a 7/8 brake master cylinder (BMC) as standard...from my past investigations, the twin pots from the Celica st202 are also the same (or very close) as the levin twin pots.


in the past, i've heard some persons say they experience a slightly softer brake pedal when upgrading to these bigger twin pot calipers over the stock units...and it seems logical in terms of pressure vs fluid movement



my ep91 came standard with abs and 13/16 BMC...i installed the twin pot calipers and astra discs recently and the pedal has more travel now---they are a great brake upgrade i must admit...however, i absolutely do not like the softer/longer brake pedal feel...and before anyone says, it may need bleeding, etc...i'm meticulous when it comes to this kind of stuff, so it was done properly...in fact it was bled more than once, as i even installed new brake master cylinder kit shortly afterwards (as i thought it may be failing, but got the same effect)



my aim is to try the 7/8 once i can find it locally...and see how it feels



while researching the last few days...a few 15/16 and 1' BMCs look like they may also fit our cars...as many share the top and side brake line connections and two bolt connection (these all looks to be in the same place or very close). however, i suspect 15/16 maybe possible, but 1" is maybe too big as i said above ---leading to a very hard brake pedal and less effective braking


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Have you worked out the difference in the piston surface areas?

i had it before,,,but will work it out now again...give me a few mins

ok..stock piston i believe is 51mm diameter...so 22/7 x 25.5 x 25.5 = 2044mm2 approximately

twin pots i see are 40.4mm diamater...so (22/7 x 20.2 x 20.2) x 2 = 2565mm2 approximately

that's an area difference of 521mm2 or 25.5% increase in piston area over stock

another variables to consider maybe the volume of fluid in the back of the caliper, piston length differences, BMC displacement for a given bore size/length, etc

in the theory and strictest sense of things, if we consider a 25% increase in BMC bore size, then we would end up at about 1'...however, i believe that is way too big as said before...so maybe its not so directly correlated between the two....plus the levin is a slightly bigger sedan car with ABS (a lot of additional brake piping and abs pump for fluid to flow through), so if 7/8 can work for that, then i see no problem with 7/8 for the ep82/91 if one is running the same brakes----just some simple logic. ...7/8 is about a 10% increase in bore size over stock 13/16.

as well, the paseo is also slightly bigger than the ep82/91...again this model with abs is using 7/8 BMC kit from what i gathered...so it points strongly to this size bore being decent for us (in theory...lol)

can any one confirm that a paseo with ABS has a 7/8 BMC??----i can only tell from internet research, which we all know how the internet can be for reliable information lol

if the paseo has a 7/8 kit...it may well be a direct fit to the ep82/91.........from the pics, the levin kit looks like a close fit too, but different reservoir(i'm not sure if the ep82/91 reservoir can bolt on to the levin cylinder, it maybe possible)

Edited by gorganl2000
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I have a 17/16 fronm an R34 GTR and know people using 15/16 from Navaras and also Impreza looks like to fit.



Pretty much everything with the correct bolt pattern (2 bolt or 4 bolt) would probably fit.


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A bigger servo would probably would make the pedal even lighter.



You need a bigger master cylinder... but don't overdo it, as the bigger the master cylinder, the bigger the force you need to apply to the the pedal.



I would say that the sweet spot for stock gt calipers is 15/16


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ok..i just checked my friend's 1992 gt ep82....it has on 7/8 BMC---confirmed (the part number according to toyodiy is 47201-16190)




i will try this 7/8 on my own car and see how it feels and report back ---maybe in the next week or two, if time permits



i'm kind of in agreement with mech5107 on not going too big....the 7/8 to 15/16 is probably good enough for the twin pot conversion




PS another part number 47201-16210...for the paseo BMC seems to be 7/8 in size as well--not confirmed


Edited by gorganl2000
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