Brake pedal is not firm.

[notnilc20]

I've bled the brakes but the pedal still travels all the way to the floor and also the front brakes work decent but the rear brakes are weak.....if i jack up the rear and have someone press the brake pedal i can turn the rear wheels by hand.....what gives? If you haven't been following my build i did a chevy 7.625 rear end conversion with disk brakes. Please help....

[davew7]

I've had real good luck using a vacuum pump to bleed the brakes. You might also try jacking up the rear if there is a high loop in the rear brake line. After the conversion is the bleed valve the highest point of the caliper? Dave W

[notnilc20]

Yeah....the bleeder valve is the highest point of the caliper. I might try that vacuum pump. Thanks for the advice.

[jinx]

sounds like u runnin chevy rear calipers.
Dunno if u can get the small import master + prop valve to "play nice" together
My buddy tried that mix-match n never got 'decent brakes'. Good luck

[notnilc20]

sounds like u runnin chevy rear calipers.
Dunno if u can get the small import master + prop valve to "play nice" together
My buddy tried that mix-match n never got 'decent brakes'. Good luck

What about if i got an adjustable prop valve?

[jinx]

if the corolla master cyl fluid volume can't fill the rear chevy caliper, rears won't ever hold tight
an aftermarket prop valve won't fix or help that
I believe I mentioned in your rearend thread, about sticking with similar size/type import car rear calipers

[notnilc20]

if the corolla master cyl fluid volume can't fill the rear chevy caliper, rears won't ever hold tight
an aftermarket prop valve won't fix or help that
I believe I mentioned in your rearend thread, about sticking with similar size/type import car rear calipers

Hmmm....well. maybe a larger master cylinder? Wondwr if i went with smaller calipers what would fit?

What do the guys that go with the ford 8.8 do? Those calipers are even bigger than what i'm running.

What did your friend end up doing? Just drive it and live with it? Thanks.

[jinx]

gotta b careful modifying brakes. Systems have soooo many variables
a simple difference in pedal lever ratio can make a world of difference, via stroke
Our rollas split the brakes fr - rr. More modern pair the front left with the right rear on one circuit

i just stuck to eclipse rr calipers on one car, and miata? on another (both handbrake in caliper)
try making sure chevy rr calip full, by bleeding... to see if the rear can hold tight

lotsa ways to tackle bias; vary pad compound, mod caliper bracket + bigger rotor, etc
A ton of info on 'brakes'

some adjustable prop valve considerations; http://www.oocities.org/motorcity/2398/ ... tml?201618


my buddy wound up replacing ALL components with new.... still no luv
last conversation he was gonna milk the entire brake system from a donor. Frustrated

[oldeskewltoy]

Before you condemn the current rear calipers.........

AE86 M/C can be damaged by foot bleeding **IF** the pedal is pushed all the way to the floor.


Idea: Bleed brakes again (DO NOT START CAR), once you have bled the brakes try your same test - can you move rear wheel?

If you still have a problem (remember the car has NOT been started since you bled the brakes), then you likely have a rear caliper issue... BUT if the rear wheel now is held by brake pressure... you likely have a bad M/C.

[notnilc20]

Before you condemn the current rear calipers.........

AE86 M/C can be damaged by foot bleeding **IF** the pedal is pushed all the way to the floor.


Idea: Bleed brakes again (DO NOT START CAR), once you have bled the brakes try your same test - can you move rear wheel?

If you still have a problem (remember the car has NOT been started since you bled the brakes), then you likely have a rear caliper issue... BUT if the rear wheel now is held by brake pressure... you likely have a bad M/C.

Yeah....before i got this vacuum pump i was bleeding the brakes via pedal and pushing all the way to the floor. I'm gonna try again on all 4 corners with this vacuum pump. Sequence pass.rear, dr.rear, pass front, dr. front. Then see what results i get.

Also could i be having trouble with my brake booster? It was pretty rusty when i bought the car and i just cleaned it up and painted it but have no idea what's going on inside.

Thanks for everyone's help.

[notnilc20]

Update.....well i bled the brakes again and now the rear brakes are working! Yay! However the pedal is still not as firm as i'd like....still feeels spongy.....maybe it's just normal?

[SgtRauksauff]

When you increase the size of the caliper pistons area without anything else, you've increased the brake torque on the rear wheels. Depending on how the prop valve works you can then get a spongy pedal...

you push the pedal down the same distance as before, but since there's possibly higher line pressure than the rear caliper is designed for (smaller MC than chevy) and greater piston area than the toyota MC normally sees, the rears are getting to their "maximum squeeze" before the fronts are, which gives you a squishy pedal.

[notnilc20]

When you increase the size of the caliper pistons area without anything else, you've increased the brake torque on the rear wheels. Depending on how the prop valve works you can then get a spongy pedal...

you push the pedal down the same distance as before, but since there's possibly higher line pressure than the rear caliper is designed for (smaller MC than chevy) and greater piston area than the toyota MC normally sees, the rears are getting to their "maximum squeeze" before the fronts are, which gives you a squishy pedal.

Thanks for the info...so would an adjustable prop valve help at all?