Hi guys,

 

Did a lot of searching on the forum and I can't find any information as to whether a master cylinder change is required when doing the AE86 & rx7 4 pot brake upgrade. Obviously the rear axles would have to be changed as well to suit the new stud pattern at the front.

Which axle swaps (ke30,35,55) would be best to not require a master cylinder change Or would the front rx7 4 pot require a m/c change no matter what ? If so what combination have others used with the rx7 brakes up front and which rears and master cylinder size ?

 

Any help is greatly appreciate it.

 

cheers

Its not easy for a few reasons, theres single and twin masters, twins in disc/drum, disc/disc and drum/drum,

bore sizes, mounting flanges, residual pressure valves, proportioning valves or internal mechanism, pedal ratios,

combination valves, metering etc Its a bit of work to get it right but look up some of this stuff to work it out.

Ah thats right 2x's don't have a booster, so will need to get the right size master cylinder I know for ke70's and that they use pajero master cylinder with front brake upgrades but not sure about 2x's.

yeh i know its going to be a lot of trial and errors involved and was hoping someone has already done it in the past and would shed some light on the topic. I guess there hasn't been many who have upgraded their ke25's with 4 pot calipers and ke30/35/55 rear drums.

Well AE86 is 13/16 as is TE27, and I am sure KE25. Not sure what engine you are going with, but there is a bees dick clearance if using a boosted TE27 master and a carbed 2TG. There will be other MC options but in other words you should be able to stick with 13/16 I should think.

 

I suppose you need to find out the MC bore of whatever MC is fitted to the RX7 donor.

rx7 fc 7/8"

rx7 fd 15/16"

i know of a ke25 fitted with a ke55 master/booster set up witch is 3/4. i would do this conversion and fit a vn 1 inch master instead.

Well AE86 is 13/16 as is TE27, and I am sure KE25.

 

Thanks heaps guys. Really appreciate your input.

 

According to some of the old posts on this forum the ke25's have 11/16" master cylinders.

 

I'll be sticking with the 5k motor for now but would like to upgrade the brakes since I'm fiddling with the AE86 front suspension and for future motor upgrade.

 

Looks like the ke55 booster and 1" VN master is the way to go.

 

I've read some thing about the rear drums brakes requiring residual pressure to work properly. Could someone explain why this is ? And would the ke55 booster and 1" mc still operate the rear drums?

Residual pressure valve stops the spring pulling the shoes back in on drum brakes 10psi

Residual pressure valve for disc calipers (only if above master height) stops bleed back under gravity 2psi

Disc calipers below master height - no residual pressure valve needed.

 

Often it can be removed if internal mechanism or added as an external in line unit if needed but this is a

specialist brake modification as if done incorrectly the brake setup will not work properly.

Edited June 26, 201214 yr by styler

Thanks Styler. I'll keep this in mind.

So far it looks like a ke35 booster with a 15/16" mc will work without changing anything else.

Ive seen a few people go ke35 booster and Pajero master cylinder which apparently bolts straight on.