Help with brake pedal/Bias

[ecko]

So heres the story
St141 corona
front brake standard single piston caliper solid rotor (new pads)
rear drum brakes standard wheel cylinders and shoes (new)
standard booster and master cylinder


now i have replaced

Front calipers with ma61 and ma61 rotors which are vented caliper bore seems to be different
ma61 master cylinder and booster
all parts fitted using standard lines and hoses

rear brakes are the same standard corona ATM

Ok problem is brake pedal is very low and only really works and the bottom of the stroke
fluid has been bled 3 times but still no good

So my plan of attack is either

Fit Brake bias valve? although i dont think the bias is out more the pressure?

or im thinking of replacing rear diff with an avante diff which has disc brake rear end,

questions i have,

any ideas on what else may be causing the issue?
im thinking ill clamp off the rears and see if there is any change in pedal feel?

would a bias valve change anything?

does anyone have any data on corona and ma61 front caliper piston bore/volumes?


any help thanks in advance

[TRD-12A]

check your rear brake adjustment sounds like its out

[tojo]

+ possibly master stroke.

Sort out low pedal issue before worrying about bias

[lexsmaz]

As has been mentioned i would check & adjust the pedal clearance, sounds like there is too much free play ..

Also as has come up with some other people on this site in the past do you have the front callipers fitted correctly with the bleeder nipples at the top ...

Also you will have issues if the M/cyl is for a disc rear end & yours is a drum rear end, there is a fair chance the Drum rear end M/cyl would have a restricter in the line to keep the wheel cylinder cups against their pistons .. As you mentioned if everything else looks ok pedal clearance wise & calliper position, lock off the rear lines & see how it feels then, if it feels ok then its possibly the lack of a restricter in the M/cyl is the fault ..

[ecko]

rear brake adjustment? as in the shoes?

master cyl stroke? as in the adjustment at the pedal?

thanks guys

[CrUZida]

Bleed the master cyl before trying anything else.

The RT142 shares the same brakes as the MA61, not sure abut the ST though.

MA61 bore is 57.xx mm

[ecko]

yeah all bore sizes are the same
Master cyl is bleed already peewee but will give it ago again

[CrUZida]

If the caliper bores are the same, and all you changed is the calipers (and discs), then there is either air somewhere in the system, a leak somewhere in the system, or the MC has failed.

[ecko]

sorrry master cylinger bores are the same,
unsure about calipers

[tojo]

rear brake adjustment? as in the shoes?

master cyl stroke? as in the adjustment at the pedal?

thanks guys

Yes. but also check that the two different master cylinders have the same "operating stroke"

Pedalbox setupp from the two cars may
have different pivot distances ..