It must be an aggravation to have this small niggle.
I understand that the internal drillings of the rear calliper casting are not consistent & can lead to trapped air. A gentle tap with a plastic hammer on the caliper can assist with removing trapped air - allegedly.
What I do know is that after rear calliper overhaul or pad change the hand brake should not be adjusted or operated before initial bleeding. After the bleed settle the rear calliper pistons against the pads by depressing the brake pedal. Then adjust the handbrake, operate a few times then re bleed.
Don't forget to leave the hand brake off during all bleeding.
There will be more air & the pedal then firms up. This procedure seems to overcome any foibles with the rear calliper/handbrake combination but if the handbrake is disturbed before the bleed it will require the caliper pistons to be wound back to start over.
Geoff, I completely understand your exasperation! My experience with my last Caterham is exactly as you describe, Gunson Easybleed, a litre of brake fluid & hey presto! A solid pedal & the best brake feel I’ve ever experienced in a car.
I’ve bought a five litre bottle of dot 4, so when the garage gets a bit warmer I’ll carefully run it through the system whilst paying close attention to all the advice given in this thread.
Gravity bleeding has been mentioned by 7 Wonders & David Long & I’ll definitely give that a go. It’s not a method I’ve tried before. I have the car booked in for a flat floor session with DPR in the spring, so if all else fails, I’ll ask them to have a look at it.
Peter’s experience reflects mine, in that the pedal isn’t TERRIBLY bad & the car certainly does stop when you stand on the brakes, but there is sufficient movement & mush at the pedal to make heel & toe a bit hit & miss.
I used to heel & toe completely unconsciously in my previous Caterham. It wasn’t something I thought about at all, it was simply the way I drove the car, even when pootling to the shops. With the 420, the positioning of the pedals meant I couldn’t heel & toe at all when I first bought the car, but having spent some time fine tuning the position of the pedals relative to each other I’ve got to the point where heel and toe is possible, but it never feels completely natural. I always have to think about what I’m doing.
I think the reason for this is, when you have a firm pedal with minimal movement, your foot is in broadly the same position when you rock it across to the throttle pedal during a gear change, whether you’re braking hard or more gently, but when there’s more movement on the pedal, you find yourself having to ‘feel’ for the position of the throttle, relative to the brake & that means the process always requires conscious thought. It becomes a distraction. It sounds like a small thing, but it actually has quite a large impact on the way you find yourself driving the car.
Anyway, thanks again to everyone who has provided thoughts & advice. It’s all very much appreciated!