Squishy brake pedal after bleeding

[TheKangarooMan]

Hello there,

Looking for some possible hints/suggestions here...

My brake pedal has been pretty soft lately. Bled the brakes in the correct order (furthest wheel first down to closest) and absolutely no air came out of the system. No bubbles at all. Didn't make a difference. Any suggestions on what might be causing the lack in brake pressure?

Thanks

[Dave.]

Master cylinder seals?

Hold your foot on the brake pedal as though you were braking firmly (not emergency stop) with the engine running.

Does the pedal continue to move after its initial stopping point?

[TheKangarooMan]

Cant remember off the top of my head. I assume if it does, it'd indicate the master cylinder?

[grumpy52]

What car ?
What sort of brake set up , discs all round , rear drums etc .
Usually if everything else is good its a master cylinder on the way out .
Occasionally on older vehicles it could be brake adjustment failures giving long brake peddle.
Brakes have two problems either the hydraulic side has leaks or seal failures or its mechanical parts broken or out of adjustment .

[TheKangarooMan]

Daihatsu Sirion Rally 2. Front discs, rear drums.

[bolide]

It could be a seized inner piston on a rear brake caliper. You can usually spot this if the inside of the disc is scored & rusty and the outside is clean & shiny

Nick Froome

[GreenV8S]

I assume that when you bled the brakes you completely flushed them through with fresh new fluid. If not, do that first.

Has any work been done on the brakes around the time the problem started? Some brake systems have places where pockets of air can collect which resist bleeding, such as the top corner of a slave cylinder, or a bias valve. Don't know whether your car has anything like that but it wouldn't hurt to check.

If the car uses the common cheap single sided calipers and the sliders are sticking, this can cause soft brakes (and poor braking). With double sided calipers, one piston sticking can cause the same effect.

Pads don't always wear evenly, especially under heavy braking, and can end up tapered. This makes the brakes feel horrible under light braking.

A thorough brake service would find any of these problems and fix most of them.

[grumpy52]

TheKangarooMan said:

Daihatsu Sirion Rally 2. Front discs, rear drums.

Inspect the rear drums for adjustment , if they are out the brake pedal will feel soft .
Adjust them up and suddenly the pedal will be nice and firm and the brakes will work so much better .

[TooMany2cvs]

grumpy52 said:

Inspect the rear drums for adjustment , if they are out the brake pedal will feel soft .
Adjust them up and suddenly the pedal will be nice and firm and the brakes will work so much better .

<nods> Auto-adjuster, I presume? Stuck?

Try putting your foot on the brakes, handbrake on, release pedal. Pause, two, three, four. Foot back on the brakes. If the travel's gone, then you've found your cause.

[TheKangarooMan]

I actually adjusted the auto-adjuster 2 weeks ago, so they should be set correctly.

[TheKangarooMan]

TooMany2cvs said:

<nods> Auto-adjuster, I presume? Stuck?

Try putting your foot on the brakes, handbrake on, release pedal. Pause, two, three, four. Foot back on the brakes. If the travel's gone, then you've found your cause.

No difference. No change in firmness of the pedal after a few seconds and a couple of pumps.

[Dave Brand]

grumpy52 said:

Inspect the rear drums for adjustment , if they are out the brake pedal will feel soft .
Adjust them up and suddenly the pedal will be nice and firm and the brakes will work so much better .

If the rear brakes need adjusting the only effect will be increased pedal travel.

[Classy6]

Easiest way to diagnose this is to clamp off individual brake circuits until you get the pedal feel back. If they're all clamped and it's still soft you have a master cylinder problem.

Start on the front flexis one at a time, then move to the back - you may have some difficultly clamping the rear if it's all rigid piping but if you get to the stage where both front flexi's are clamped and the pedal's till spongy, then at least you know it's an issue with the back end / MC.

How long fluid did you get out of each corner when bleeding? Was the any requirement to bleed the brakes? Had the system been opened?

Strangest issue I've had with a soft pedal, was a corroded disc. Felt fine when at a standstill, soon as the car was moving and on the first initial push of the brake pedal it would sink, second push it would tighten up again.

[GreenV8S]

Classy6 said:

you may have some difficultly clamping the rear if it's all rigid piping

Given that the car has working suspension and outboard brakes, how could it be all rigid piping?

[TooMany2cvs]

GreenV8S said:

Classy6 said:

you may have some difficultly clamping the rear if it's all rigid piping

Given that the car has working suspension and outboard brakes, how could it be all rigid piping?

It's entirely possible, and has definitely been seen for real... Post-60s 2cvs have no flexis whatever, to front (OK, inboard, but still - engine movement) or rear. There's a coil of metal pipe inside the rear suspension cross tube, so the arm movement's taken over a bunch of coils.


But in this case, there'll definitely be flexis...

[Classy6]

GreenV8S said:

Given that the car has working suspension and outboard brakes, how could it be all rigid piping?

I meant more for ease of access, rather than the literal sense.

[gordmac]

If you can't find any mechanical reason and you think air is still present, jam the pedal down hard overnight.

[TheKangarooMan]

gordmac said:

If you can't find any mechanical reason and you think air is still present, jam the pedal down hard overnight.

what would that do?

[Dave.]

It will compress the air which is supposedly meant to make it rise up to the reservoir.