Sorry about the rather long-winded post, but following on from my thread about pedal box adjustment & master cylinder pushrod thread, I’d really appreciate any advice people have on brake bleeding.
I’ve had my 420R since Easter 2019 & I’ve never felt very happy with the brake pedal feel. The pedal has always had a somewhat mushy feel, as if there’s air in the system. The brakes do work & the car stops well, but the mushy pedal doesn’t inspire confidence & doesn’t provide a stable platform for heel & toe. The car has the standard two pot AP front callipers with the Sierra type rear callipers & the uprated AP master cylinder.
I’ve bled the brakes three or four times, with newly purchased, decent quality fluid & while that has given me a firmer pedal, I still feel it could be improved.
I had a live axle 7 before I bought the 420 (standard Girling callipers at the front, Ital drums at the rear & the standard master cylinder) & with that car I always found brake bleeding at the start of the blatting season a very satisfying job, resulting is a firm, confidence inspiring pedal.
I’ve tried the traditional, two person method, pressure bleeding using a Gunson Easybleed, vacuum bleeding & (in desperation!) a combination of all three methods at the same time.
The Sierra rear callipers seem to have a reputation for being awkward to bleed properly, so I’ve paid particular attention to those. I was told an effective approach was to remove the brake pads, wind the piston in fully and then bleed them, as that helps to push the air out of them. I’ve also disconnected the handbrake cable from the callipers, wound back the pistons & pressed the brake pedal firmly, to ensure the callipers are correctly self adjusted, before re-connecting & adjusting the handbrake. I’ve also tapped the callipers with a rubber mallet to attempt to dislodge air bubbles & vigorously waggled the handbrake lever during bleeding.
Another favoured method seems to be holding the rear callipers up high & ensuring the bleed nipple is right at the top when bleeding. I have the standard solid brake lines at the rear, so it’s difficult to move the callipers much. I have bought a set of flexible braided hoses, that I plan to fit before my next attempt at bleeding, so hopefully that will improve matters.
It really does feel to me as though there’s air in the system somewhere, although I’ve pushed many litres of fluid through & I’ve got to the point where I can’t see even the tiniest air bubbles emerging. I can’t see any leaks anywhere, the fluid level doesn’t go down in the reservoir. If you press & maintain constant firm pressure on the pedal, it doesn’t sink any further, beyond the initial mush.
I have felt tempted to try the ‘high effort’ pedal, but I feel I’d rather have another try at optimising what I have before I go down that route.
Have I missed anything? Or is it simply a question of bleed & bleed again, until the air is driven out? Any tips would be much appreciated!