Im wheely tired so i need a brake...

[Konakid]

Lame jokes pulled from circa '2000' Motor magazine aside, I have replaced everything in the corona's brake system bar the metal lines, booster and front rubber lines.

Have bled it and the pedal goes straight to the floor still, has absolutely nothing.

When i got the car 3 months ago it was fine, brakes worked but since it wasnt rego'd i took it to the shops twice and they got slightly spongier, then i swapped to RA60 calipers, rebuilt them, new rotors, pads, new rear wheel cylinders, machined drums, new drum shoes, then i bled them and they were barely working.

I get the car home, bleed them properly (starting with the furthest away wheel from the brake master) pedal has pretty much nothing again, pop the bonnet and there is brake fluid pissing out between the master and booster. Fuck. Completely rebuild the master, new stainless steel piston as the iold one was pitted, new gasket, $260 bucks later, bolt it up tonight, new fluid, bleed, absolutely nothing again.

I can pump the pedal up and it gets harder, i can visually see the master sucking in fluid as the pedal is depressed but then when released it forces the fluid back up the reservoir and bubbles like there is a clot in the lines and there is a lot of pressure behind it.

All vac lines are still connected to the booster and it seems to be working perfectly.

Anyone got any ideas?

[R&D Mechanical]

so fluid is coming out at all fours?

[Konakid]

Yep, no bubbles.

[superbmobile]

Could have a real small leak, the same thing happened with mine replaced the master the rear slaves and bled the system countless times. After a week or so i saw that a small amount of fluid had diappered from the resivoir, but hardly anything. so i sussed all the lines for leaks and couldnt find anything at all, then after a couple of weeks of driving the hole must of expanded from the fluid pressure and i noticed it was losing a fair bit more fluid, turned out i was a leak in one of the rear solid lines only found this out though when the sack got defected and was off the road ahh well.

[Konakid]

Yeah? Ill get under it tomoro and sus it all out but would have thought that the fronts would still work even if the rear line had a leak in it. fuck knows.

[superbmobile]

yeah the fronts should still work for sure, did you bench bleed the master? but even if you didnt it should bleed up alright, thats all i can think of.

[Konakid]

Nah just chucked it on and bled the brakes, it seems to be working fine tho, it must be if fluid is still coming out the bleed screws.

Im thinking the actual calipers are fucked or something, maybe i rebuilt them wrong, tho they werent that hard to do and everything seemed to fit ok.

[Matt-AE86]

Sometimes when you rebuild calipers you need to have them honed. Maybe chuck on some calipers you know are good if you can and try again ?

[stanzzza]

cailpers right way up?

[Konakid]

As in have the piston bores honed?

Calipers are the right way up im guessing, the bleed nipple is at the top.

[sonsta]

yeh are they the right way up? as in are the nipples at the top?

otherwise u get an air bubble at the top of the calipers and it will sit up the top no matter how much u bleed it, they call it gravity or sumthing

i had the same problem when i did my rx7 conversion


EDIT** u already said u had them the right way up...my bad

[resol]

when you say you bled them properly, what do you mean by this? because clearly they arent working.

was there a steady, clean flow of fluid comming from the bleed valve, no bubbles? same for each caliper?

unless theres fluid/air leak then sounds like they havnt bled properly.

-dan

[Konakid]

when you say you bled them properly, what do you mean by this? because clearly they arent working.

was there a steady, clean flow of fluid comming from the bleed valve, no bubbles? same for each caliper?

unless theres fluid/air leak then sounds like they havnt bled properly.

-dan

Yep, steady, no bubbles flow from each caliper and the rears.

[slide86]

is the handbrake tight and does it lock the rears at low speed?

[Konakid]

yeah thats how ive been driving it around the burbs.

[slide86]

hmmm this is a weird one....

rod adjustment between the pedal and the master cylinder. lawsons van doesn the same thing.

are you able to get under the dash area and see if the rod that comes of the brake pedal has a threaded section on it.
if it does, try winding it out, so it extends and shortens the travel needed to push on the back of the master cylinder.

[Javal]

I think this car needs to pay a visit to metros.

[Konakid]

Will have a look now.

Javal, knoted. Clutch is mint tho!

[Konakid]

Forgot to add, the pedal is completely soft on first push, goes straight to the bumpstop, can be pumped up tho.

[driftke70]

sounds like a unbled master, take it off and bench bleed it, and then put it back in, its probably skipping a line somewhere.

[Konakid]

how do you bleed a master?

[slide86]

yeah i was thinking bench bleeding it before fitting it to the car.

put the master in a vice, grip it where one of the bolts goes through

- fill the resivoir with fluid.
- grab a large philips head screw driver
- gently push the piston in all the way (watch out, fluid shoots out pretty quick)
- before allowing the piston to return, hold your fingers over the ports so that they are pretty much air tight.
- allow the piston to return, you will see the fluid go down and air bubble.
- repeat this several times

then fit the master back to the car and refit the lines.

complete another brake bleed, have some one sit in the car, open the bleed nipple, pump pedal 10 times, close nipple (ensure pedal is still pushed down when you close the nipple)
pump the pedal up hard, while the pedal is being pushed, open the bleed nipple once more, close nipple while pedal is pressed down

[driftke70]

couldnt have said it better

i like quick sharp pumps to get the initial pressure up, then long smooth ones towards the end.

[slide86]

are you talking bout bleeding this master cylinder or something else?

[driftke70]

the pedal when bleeding the brakes, basically quick sharp pumps then hold down and undo nipple, as soon as it touches the floor do nipple up, then quick sharp pumps again, once it has some meat behind it you slow the pumps down.

[slide86]

i was just being dirty, read it again! lol

[Konakid]

Lol!

Will bleed the master tomoro, cheers guys.

[driftke70]

hahah

[racsov]

if your lazy / if you havent tried it you can just bleed the master by cracking off the lines

so wait

when you bleed them you get good fluid flow, but shit pedal feel? sounds like internal valve/seal fault of the master, get a known ok condition one and put it in and see what happens

[Konakid]

So the saga continues (4 years later! since i bought it!) and after having my brakes bled properly at a brake joint which is well known they were slighlty out of adjustemnt at the rear drums and the hub freeplay. The pedal is still pretty shit.

F series Tarago Drum (25mm bigger than stock or so) RA65 vented front brakes (10mm bigger than stock) and now that i have been doing some reading i am thinking of upgrading the master cylinder.


My reasons for doing this from what i have researched are: (feel free to shoot me down if you know better!)

- Bigger master equals more fluid to the front and rear calipers (bias valves aside)
- Results in a pedal which will not be as soft in its travel and will firm up sooner due to increased speed at which the caliipers will be filled with fluid.


Now i have heard mixed reports about the pedal EFFORT required with a bigger master, most say more effort but some have said less, i guess this depends on how much bigger than stock the brake upgrade is and how much bite your pads have?

stock is 7/8 from what my sources say so the next size up is 15/16. What will fit RT142? Its a different bolt pattern to AE86/ke70 booster.



Now another issue i had a look at wat the adjustment of the shaft of the brake booster where it enters the master cylinder. On some cars this is adjustable with a nut and if its only 1mm out before touching the piston in the master this can have a massive effect on the brake pedal feel, making it spongy and soft like mine. Im yet to have a look and see if RT142 is adjustable but will pull the master off in the next week to have a look. Im so sick of these shit brakes especially now that the thing is turbo i want a hard, good pedal!

[Skylar]

I put big brakes (r34 4 pistons) on the silvia on the weekend. Left the singl piston on the rear. Started bleeding brakes and realised that I forgot to swap the master out for the new bm44. I couldn't be bothered and was interested to see how bigger calipers would affect pedal feel, essentially the same as reducing the master cylinder for the same caliper. What I found was that it feels a lot more like the corolla. I feel with the corolla, that braking force is proportional to pedal force but it travels a lot. When I hopped in the silvia(stock brakes), I felt that the brake force was more proportional to pedal travel than force. Putting big brakes on it made it feel like corolla again. It's a bit weary now that I've gotten used to how the silvia felt but I think I prefer how it is now for feel. I think I can control the car on the braking limit better.

Going up in brake master will give you the opposite of what I described.

[ill-minded]

You're on the right track. Pedal effort should be more a result of the ratio of the master cylinder cross sectional area and the caliper cross sectional area. For example, say that you increase the total cross sectional area of your brakes by 10% and increase the brake master cross sectional area by 10% as well, the pedal should feel exactly the same as standard. I'm not too sure about piston size comparisons between Corona brakes and Celica fronts/Tarago rears, but there's a fair chance that if the pistons are larger than the standard Corona ones, increasing the master cylinder size should improve pedal feel.

With the booster/master cylinder pushrod clearance, there should be a minimal gap, but it's probably advisable to make sure that there actually is a bit of a gap so there is no chance of the brakes lightly engaging when driving around.

Hope that all makes sense.