The curious case of the Atom 4 brakes

[speedmachine]

Hold that thought. There’s much more to come

Much more anti climaxes? All the “good stuff” locked behind the members area?

Pretty pitty if you are in the market for a 4 and cant get the complete info.

[reg]

I’ll always post outside of the members area with any updates tbh. One part of this which hasn’t yet been raised is the flex in the pedal box. Compared to the older cars it’s quite significant. Reading the original Autocar article the brakes were criticised for a lack of feel, and locking when cold. Perhaps that’s the feedback which prompted the switch to the smaller master cylinder?

[IanG]

Update
So after spending the morning with [mention]Peter255[/mention] and playing with his 4's brakes
Pressure blead the brakes with a twin drain on the callipers
Air in the lines mostly from the front calliper's removed, brakes feel much better
So a good result all round.

[stupot]

Following this with much interest as my Nomad has AP brakes all round. I've not done many miles so they still require bedding but so far the pedal feel doesn't inspire confidence. Like others, I much preferred the reduced pedal travel and feel from Alcons. Will see whether they improve as I put more miles on it, as I should already have had the latest bleed process applied during build. If they don't improve then I'll see what Steve thinks at the first service.

[jpswift]

i picked mine up friday having had an annual service.

Brake fluid changed as part of the service and pedal bite is noticeably better now

[mynamesnotbob]

i picked mine up friday having had an annual service.

Brake fluid changed as part of the service and pedal bite is noticeably better now

Great to hear, I have the bigger master cylinder sitting here. But agreed with Steve I'd let them do a fluid change and their bleed to see where it sits, as he was pretty confident

He was pretty confident that master cylinder change wasn't needed.

I also adjusted pedals to be higher and that made a big difference too (still want access a bit higher)

[devonatom]

Just as an aside but on the topic of brakes, I was at the factory last week discussing some options for my car which is on order - Ben mentioned that they are also now offering carbon brakes for the Atom as an option at build - think they have had their first car go out recently with these fitted and would be curious to know feedback/performance of these vs the AP's...

[reg]

Service today at the factory. Bleeding has really transformed the feel, it's night and day for travel and bite. I may well fit Pagids anyway, but the brakes are now pretty good. It throws a few theories up in the air but let's see how it goes.

[mynamesnotbob]

Excellent news [mention]reg[/mention]. Did they share the procedure? I’ll get them to swap fluid next month but hope it’s not a secret, wouldn’t want to need to return to base for a brake bleed!!

[reg]

No idea exactly what they did, but, whatever it was it has worked. After 2-300 miles of driving the discs now have some actual evidence f work on the surface. The pads are also dusting all round, I had literally none in 1800 miles before. I haven't got to the bottom of it all yet, but I'll do my best to find out.

[Monza]

I don't know if i'm supposed to write here about the new bleeding process, but i'll do 
It appears that the main reason for long pedal travel with near no effect on braking is because the pistons in the calipers are going backward during driving between each braking, so the first travel of the brake pedal will only push back the pistons/pads closer to the discs and, only after, it'll begin to really brake.
The new bleeding process is here to correct the problem, with putting "more " fluid between the pedal in rest position and the pistons so that the pistons can't go back so much when pedal is up/rest. The consequence is that, after this special bleeding, the pressure on the discs is quick, there is no longer dead travel only to push the pistons/pads back in contact with discs.

Every one can make this test : after some driving press the pedal a first time, release it and push it again immediately : the pedal on the second pressure will be firm and braking near immediat (pistons didn't have time to go backwards).
Hope this helps 

[Peter255]

So the question still stands. We all need to know how to do the "special" bleeding process for our cars. Its not practical to only ever bleed the brakes at the factory.

Other than postive pressure from the reservoir or negative from the caliper end how else can you bleed the brakes?

Not sure why it appears to be a secret. Surely its important safety info for owners?

[mynamesnotbob]

So the question still stands. We all need to know how to do the "special" bleeding process for our cars. Its not practical to only ever bleed the brakes at the factory.

Other than postive pressure from the reservoir or negative from the caliper end how else can you bleed the brakes?

Not sure why it appears to be a secret. Surely its important safety info for owners?

Couldn’t agree more, I’m a bit confused why it’s not published. Hopefully it will be shared if directly asked. It could be there is a knack or trick. i.e certain 2 pot AP callipers needed to be removed, rotated and tapped with a mallet to release bubbles that get trapped

Like you say you either push it in or suck it out till the airs gone, so I presume there is an air trap somewhere if a simple bleed doesn’t work. Can’t see why it wouldn’t be shared for such a common thing most owners will do at home.

To be fair I’ve not directly asked them for the procedure, so I’m sure it’ll be forthcoming

[plip1953]

I don't know if i'm supposed to write here about the new bleeding process, but i'll do 
It appears that the main reason for long pedal travel with near no effect on braking is because the pistons in the calipers are going backward during driving between each braking, so the first travel of the brake pedal will only push back the pistons/pads closer to the discs and, only after, it'll begin to really brake.
The new bleeding process is here to correct the problem, with putting "more " fluid between the pedal in rest position and the pistons so that the pistons can't go back so much when pedal is up/rest. The consequence is that, after this special bleeding, the pressure on the discs is quick, there is no longer dead travel only to push the pistons/pads back in contact with discs.

Every one can make this test : after some driving press the pedal a first time, release it and push it again immediately : the pedal on the second pressure will be firm and braking near immediat (pistons didn't have time to go backwards).
Hope this helps 

The first part of what you describe above is pad knockback, which can occur if your rotors aren't true or where they might be flex between the rotor and caliper eg when cornering very hard of going over kerbs on race circuits or running over pot holes etc. That said, in extreme circumstances, is can also happen if there is a mis-match between master cylinder sizing and caliper piston sizing.

The APs on the 4 have anti-knockback springs as standard (4 lbs/ft is standard, but harder are available) and I'd be very surprised if the pads are retracting of their own accord sufficiently to need a double application.

This so-called new bleeding process cannot possibly put more fluid into the system unless it is to substitute for any air that might have been there. So any bleeding mechanism, howsoever performed, is purely designed to remove any air in the system.

It may be worth bearing in mind that the Tilton master cylinder have their own bleed valve (ie in addition to the pairs of bleed valves on the calipers). The object of these is to allow expulsion of air that might be in the MC due to the orientation of the MC relative to the ground. As far as I known the MCs in a 4 are positioned horizontally, but it would be worth checking if there is any angle on them such that air could be trapped at a high point.

[mynamesnotbob]

These are the bleed valves referred to by [mention]plip1953[/mention]. Seem level when on the ground, but on axle stands it might tip them the wrong way? Vacuum on the bleed valve would sort or just keep rear jacked for final bleed?