The curious case of the Atom 4 brakes

[Monza]

Concerning the Atom 4 pads i have contacted the factory and can confirm that the thickness needed is 14,5 mm
So AP disc 24 mm and pads 14.5 mm ;-)

[Charlie]

Perhaps not a very highly rated pad but EBC do pads for the 4 and they are 15mm thick https://ebcbrakesdirect.com/automotive/ ... -2019-/295


Also these pads cross reference with the AP brakes from a MG TF 160 which had 304mm Discs I believe

[Monza]

Are you sure they are for the AP ? and i don't think 15 mm will fit as 14.5 mm is needed.
to my opinion Friction 0,52 is low to try to reduce the brake pedal free travel. A real high friction pads (cold and hot) is needed so that the braking really begins when first contact between disc and pads even when pressure is still not high.
CL RC8 are working well (when new) but they are 16 mm and 0.60 friction (even cold).

[Charlie]

Are sure they are for the AP ? and i don't think 15 mm will fit as 14.5 mm is needed.
to my opinion Friction 0,52 is to low to try to reduce the brake pedal free travel. A real high friction pads (cold and hot) is needed so that the braking really begins when first contact between disc and pads even when pressure is still not high.
CL RC8 are working well (when new) but they are 16 mm and CL RC6 with 0.60 friction (even cold) in 14.5 mm should be good to.

Yes definitely for AP please see this link https://ebcbrakesdirect.com/automotive/ ... o/yft/2019

[Monza]

pads in 14,5 mm , no thickness calibration to do :
https://www.questmead.co.uk/Categories/ ... Thick-Pads
also :
PAGID E8076 RST1 14,4 mm RST1-8076 friction 0,54 (very good)
CARBONE LORRAINE / CL 5038W45T16 RC6 14,5 mm 5038W45T14.5-RC6 friction 0,50

[reg]

Perhaps not a very highly rated pad but EBC…

The more I see, the more I’m convinced that the caliper is just not right. How, with AP on board, with Ariel and some talented test drivers is a mystery, but it is what it is.

Going back to the beginning … a set of ‘crap’ 1144’s or ‘crap’ 2500’s was enough to lock my previous car at most speeds and scrub speed easily. Pads lasted 5 years and there was never any fade. Why suddenly are RS14’s needed….? They were the best brakes pretty much I’d used. In comparison the 4 is eating pads, despite having less braking power than the average Kia. I do have the new master cylinder, but am questioning the logic of rolling a turd in glitter, only then having to add some more glitter every other weekend. The Alcons worked, all weathers, and it was never even a topic of conversation on the forum, or amongst owners. As for air being magically created once bled, never happened, not once in six years on the 3.5.

I’ve started digging more for calipers, one contact has already said the supply is a pain, I guess we’ll see? If not, there’s a few other 130mm radials out there which are specifically designed for non servo applications.

[Yorkshire]

Hi Reg
Have you fitted the new cylinder and tried it yet. It transformed my brakes. I'm sure the new AP's aren't as good as the old Alcons but i have the same feel and enough stopping power. Only time will tell if its a permanent fix or a glitter one!
Cheers
Stuart

[plip1953]

The more I see, the more I’m convinced that the caliper is just not right. How, with AP on board, with Ariel and some talented test drivers is a mystery, but it is what it is.

Unquestionably there are better (and much more expensive) caliper offerings out there, whether made by AP or Alcon, but many others too. Fundamentally, however, the 7600s are perfectly adequate, and along with other suitably matched system components can work really well. And I'm not just saying that, but have the on-track data to back it up - as you know. Also, as you know, I don't buy in to the suggestion (even if that's what Ariel might be saying) that dust seals are causing the caliper pistons to retract after every pedal press. But what will be happening is that a small amount of retraction will occur purely due to the way the caliper seals work - when pressure is applied the seals deform slightly (ie rather than the pistons sliding through the seal) and then they "recover" back to their resting position. This is normal and generally desirable, but if the amount of retraction (measured in thousandths of an inch) is deemed to be excessive it always possible to add anti-knockback springs behind the pistons. The Alcon's on the 3.5 have them as standard (but only 2lbs/ft rated), but they are not routinely fitted to AP CP7600s. And they are not expensive, albeit a bit of a faff to fit.

Going back to the beginning … a set of ‘crap’ 1144’s or ‘crap’ 2500’s was enough to lock my previous car at most speeds and scrub speed easily. Pads lasted 5 years and there was never any fade. Why suddenly are RS14’s needed….? They were the best brakes pretty much I’d used. In comparison the 4 is eating pads, despite having less braking power than the average Kia. I do have the new master cylinder, but am questioning the logic of rolling a turd in glitter, only then having to add some more glitter every other weekend. The Alcons worked, all weathers, and it was never even a topic of conversation on the forum, or amongst owners. As for air being magically created once bled, never happened, not once in six years on the 3.5.

How are you finding the change in master cylinder sizing. Are you now at 0.7" front and 0.75" rear? Does the brake pedal now have noticeably less "dead" travel? And any improvement after fitting the pedalbox brace?

I agree that just about any pad should strong enough to enable the driver to force a lockup, including with 1144s and DS2500s. However, that's only part of the story because as you found out for yourself at Anglesey your pedal went even longer than ever, which was simply because your pads got past their comfortable working temperature (classic brake fade). But once everything had cooled down a bit the pedal returned to you?

I’ve started digging more for calipers, one contact has already said the supply is a pain, I guess we’ll see? If not, there’s a few other 130mm radials out there which are specifically designed for non servo applications.

As you say, there are other 130mm calipers out there, and some very nice ones at that, but you also need to be very careful to take into account offsets and all that stuff. My guess is that you'd most likely need to change brackets, and rotors/bells too. And then beware to ensure you still have clearance between caliper and wheel spokes/rims. Oh, and be mindful of caliper piston sizes too as this will determine the size of master cylinder!

[K20A2]

I am no Atom 4 owner, however I am following this conversation with interest.

With regards to plip1953 statement above you can find a picture in the following link, roughly showing how the retracting ring (Rechteckring, rectangular ring) is working and it is designed especially for that purpose, to retract the piston back into the caliper. This does not mean milimeters but tenths of them if at all, normally.

The images show one of your 4 pistons per caliper. On the left it is the resting position, on the right the brake pedal is pressed down.

https://www.at-rs.de/Bremskolben.html

So if this indeed is the reason for the long pedal way, will not the helper springs probably be the only reasonable solution to solve the problem in its origin?
Any change in pads or master cylinder may result in an improvement, but isnt it more a trial an error and the outcome may not be satisfying as the problem itself would still exist?

[Lew]

So, is anyone going to try those anti-knockback springs ?
https://apracing.com/race-car/brake-cal ... ck-springs

[reg]

So, is anyone going to try those anti-knockback springs ?
https://apracing.com/race-car/brake-cal ... ck-springs

It's a good shout. The Alcons have 2kg springs fitted and the pistons are approx. 20% smaller. After returning from Le Mans with a sick Griff maybe this weekend I'll ignore it and fit the brace and master cylinder, take a look at the pads to see if they can be rescued and see what the difference is. Have found a set of Alcons but sod paying nearly £2K, unless the factory want to buy them

[plip1953]

So, is anyone going to try those anti-knockback springs ?
https://apracing.com/race-car/brake-cal ... ck-springs

Yes.

And I should correct an earlier point I made about the anti-knockback springs in the Alcon CRH304 caliper be rated at 2lb/ft. They are in fact, as reg correctly points out, quoted as 2kg, although I'm really not sure what that means relative the way you would routinely quote the rate for a coilover spring. I have a feeling it might mean that the spring will fully compress when a weight (force) of 2ks bears down on the spring, but maybe someone with more knowledge of these things can help me here? Nevertheless I think the main point is that the a 2kg rating is the equivalent of around 4.5lbs and so I'd say that's pretty close to the regular AP offering (although AP also do 7, 9 and 12lb springs - as perhaps Alcon do too).

[plip1953]

So, is anyone going to try those anti-knockback springs ?
https://apracing.com/race-car/brake-cal ... ck-springs

It's a good shout. The Alcons have 2kg springs fitted and the pistons are approx. 20% smaller. After returning from Le Mans with a sick Griff maybe this weekend I'll ignore it and fit the brace and master cylinder, take a look at the pads to see if they can be rescued and see what the difference is. Have found a set of Alcons but sod paying nearly £2K, unless the factory want to buy them

The Alcon CRH304s come with two different caliper size configurations, namely 4 x 31.8mm and 2 x 38.1mm and 2 x 41.3. So if you do decide to go down the Alcon route be very careful to make sure you'd be getting the same version as fitted on the 3.5 (which I assume would be the intention?).

[speedmachine]

I’m still confused about the discussion out here, I thought there was an other topic in the restricted/members area where the factory would reply and this would be a benefit for members.
Am I wrong here or did they never post the solution, surely they know about the problem?
Or does this not affect all owners?

[reg]

I’m still confused about the discussion out here, I thought there was an other topic in the restricted/members area where the factory would reply and this would be a benefit for members.
Am I wrong here or did they never post the solution, surely they know about the problem?
Or does this not affect all owners?

I created this thread so that everyone would benefit from shared knowledge. The ‘factory fix’ is currently a case of pushing the pistons out to release the seals. This lasts ‘some’ road miles and ‘less’ track miles. It’s not a solution for the problem merely a short term fix for the result. Anyone moving from an earlier car would surely notice. Anybody on track I guarantee it.