need input: Brake changes made pedal squishy..

[Doris]

It was time to replace the rear brakes (drum) on the Ace, so I ordered in some shoes, they were slightly wrong, but the bench grinder solved that issue,

The real issue is with the cylinders. Stock replacements were damn near impossible to track down, with only one supplier out of four having a listing, and at $50+ each! Politely told them what they could do with those cylinders, and scored some off a Justy that matched the dimensions for much much cheaper.

After bleeding the brakes, my pedal guy (dad) said the pedal felt nice and firm. Awesome!

But the shiny facade fell apart when I went for a test drive, to reveal a turd of a braking system.

The pedal is spongy as hell and takes 3 inches of travel to start really stopping...

My theories:

>there\'s still air in the lines

>a cylinder is leaking (it looked sorta wet in there when looking through the adjustment hole)

>cylinder bore size is causing the problem.

The stock cylinders are 9/16, absolutely tiny and will probably grenade when I install the hydro-handbrake. The new Justy ones are 3/4 bore, much better. But I noticed my master cylinder is only 3/4 bore and I\'m thinking its just too small for those big cylinders, and can\'t pump enough fluid quickly.

I\'ve ordered a new pair of cylinders, and I\'m pulling the drums off in the morning to check for leaks, but some input from someone that knows a bit about hydraulic systems would be great, I\'m just a self-taught garage cowboy.

[rslegy]

Sounds like air in the system and is it topped up

[loner]

does the pedal harden up if you pump it? if so, just air in lines probably.

[DRFVDR]

could be air in the system BUT running such a larger size in the rear slave cylinders will make a difference as well, can you source a justy master cylinder

[Doris]

Gave the brakes a good bleed all round, still taking heaps of pedal travel to stop (hauls up fast though)

98% certain the master cylinder is just too damn small

[Doris]

Entertaining an off-beat string of thoought here:

Suppose I deleted the booster, utilized two 3/4 master cylinders connected with a balance bar..??

I.e front circuit and rear circuit are completely separate fluid-wise

[Doris]

Actually, screw the dual circuit idea, my WOF guy would poop kittens over that one.

Thinking a 1" master cylinder and a proportioning valve will be the way to go.

[boon]

 Doris said:

Actually, screw the dual circuit idea, my WOF guy would poop kittens over that one.

Thinking a 1" master cylinder and a proportioning valve will be the way to go.

I think no matter what you do, if the WoF guy knows what he\'s looking at, he\'ll require a cert.

[jost]

I had the same issue with my old ace, i just pulled the master cylinder off and went looking at bnt for a suitable larger replacement, fixed it perfectly, the standard cylinder just can\'t move enough fluid to supply the larger wheel cylinders. Can\'t remember what the one i got was off, i think it may have been a mazda one, had to bend one of the lines to get it to fit but worked otherwise.

[Doris]

My wof guy is really old-school, he knows what he\'s looking at and if a mod is safe or not. If it\'s safe and done properly, it\'ll pass..

If it wouldn\'t pass a cert, it won\'t pass him either.

Eg installed new BC gold coilovers into my 525 few years back, and he passed it with no comments. Put 6mm slip ons on my hilux to clear front balljoints, he told me to change the rims and bring it back for recheck..