Bleeding brakes - new rear calipers and new flexible hoses

[John Cousins]

Having issues bleeding the standard brakes on my 2005 s3 Roadsport. I replaced the rear discs and calipers and fitted flexible rear brakes hoses. Used an eezibleed kit. Pedal is not firm. A short test drive confirmed the brake pedal is too soft. A little research suggests I could try removing the calipers from the ears and lift higher than the reservoir (using a piece of wood between the pads). I also have a rubber mallet for some gentle tapping. Any other suggestions appreciated.

[Shortshift]

I think you're on the right lines - you need to ensure that the potential air trap/void and nipple are positioned as the highest point (not heard that you'd have to raise them above the master cylinder, though).

There's also a handbrake element to this, IIRC.  Something like adjust it at the two adjusters and then cycle the handbrake mechanism (using the handbrake lever) fairly robustly 4 or 5 times.  The readjust the handbrake at the adjusters, then final check for bleed/air.  That does all sound a bit flaky so maybe someone else will substantiate it in general terms - and hopefully correct any inaccuracies.

James

 

[Geoff Brown]

JB - As long as the caliper pistons have been bedded using the pedal before adjusting & working the hand brake........

[John Cousins]

Thanks. I did originally bleed the brakes, operate the brake pedal, adjust the handbrake and then operate the handbrake which is set at three clicks. I will try a few handbrake cycles and proceed from there....

[Shortshift]

Ah - thanks Geoff; bed the pads against the disc using the pedal (firmly) before yanking the handbrake on and off a few times. I was nearly there!

James

[SM25T]

Don't need to raise calipers above M/C.

[aerobod - near CYYC]

Just undoing the caliper slide bolt nearest to the bleed screw and rotating the bleed screw end of the caliper upwards is all that is needed, in my experience. Enough of the pads still contact the rotor to prevent the piston being pushed out, but the bleed screw is high enough to expel any air.

It is also worthwhile to give the caliper some taps with a nylon mallet while bleeding to dislodge any tiny air bubbles that may be clinging to the caliper walls.

[Nigel B]

I’d be interested to hear if you reach a conclusion on this John. It’s something I’ve been struggling with recently. 

I had a live axle 7 for years & traded it in for a 2017 420R last year. I wasn’t happy with the brake pedal feel on the 420 from the beginning. I was convinced there must be air in the system, after all I was going from the standard front callipers & master cylinder & 1970s British Leyland rear drums to a modern AP Racing set up, with discs at the rear (albeit, not the ‘big brakes’ uprated set up). 

But despite pumping numerous bottles of brake fluid through the system, the pedal still doesn’t feel as confidence inspiring as my previous car. The brakes do stop the car & it passed it’s MOT last month without any problems, but the pedal still feels a bit mushier than I feel it should. 

I’ve tried the traditional ‘two person’ method, a Gunson Easy Bleed & a vacuum bleeder. I’ve also tried bleeding the rear callipers with the pads removed & the pistons wound back, this method failed to produce any further air bubbles, so I can’t help but feel there isn’t any further air trapped in the rear callipers.

Admittedly the pedal feel has improved quite a bit, in comparison to how it originally felt, but I can’t help feel there’s still room for improvement. I haven’t tried the ‘handbrake wiggle’, so maybe I should give that a go? I did slacken off the handbrake adjuster nut whilst bleeding the rear callipers & then gave the brake pedal a few hard presses before re-adjusting the hand brake.

I hope you manage to sort yours out. Any more ideas would be appreciated!

Cheers!

Nigel.

 

[John Cousins]

Thanks for all the advice - I'll feedback on how I get on....

[John Cousins]

A couple of months later I can report that using a volunteer brake pedal operator to assist with bleeding the brakes was the method that resolved the issue. I didn't notice large air bubbles being expelled but a couple of rounds on the two rear calipers soon restored a familiar brake pedal feel.