The curious case of the Atom 4 brakes

[plip1953]

There seems to be lot written about how wonderful the Alcons are on the 3.5. Can anyone tell me if the calipers are exactly the same same front and rear - in particular whether the piston sizing is the same. Also, is it correct that the MC sizing with the Alcons is 0.7" both front and rear or something other than that? I believe the pedalbox on the 3.5 and 4s is the same?

[reg]

Hi. They’re the same if you have the BB kit. Think they are 304 calipers, same size pistons (4).

[plip1953]

Hi. They’re the same if you have the BB kit. Think they are 304 calipers, same size pistons (4).

image.png (229.04 KiB) Viewed 1092 times

Are these the ones? There appear to be two different piston size options. Do we know which ones were chosen for the 3.5?

[reg]

Hmm, interesting. Guess we could ask either Alcon or Ariel what the code was. As far as I knew they were standard 130 radial calipers?

[Winmoz]

[mention]Winmoz[/mention] Can you take a picture of the caliper/hose assembly for me please ?
I didn't get any adapter between the hose connector (female) and caliper connection (female as well).

Will do


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[Monza]

[mention]Lew[/mention]
the AP guy says that the AP 7600 are now obsolet ... but they still offer it on the AP website :
https://apracing.com/performance-upgrad ... x24mm-disc

One of my Atom 4 customer is testing CL pads RC8 5038W45T16-RC8 on all corners (i had RC8R on all my different Atoms during years, i like agressive pads), the pedal is totaly different, as with the Alcon he has on his 3.5 350. Let see what will happen with the wear after some trackdays.
Only problem for which i have no clear answer yet :
this pads are 16 mm thick and the garage was obliged to put out about 1,5 mm on each pads to fit them. As the disc is 24 mm thick, and that the 7600D46 caliper is for 16 mm pads (and 24 mm disc) , i don't understand why they needed to calibrate them. Perhaps the RC6 in 14,5 mm thickness will fit better.

[plip1953]

Hmm, interesting. Guess we could ask either Alcon or Ariel what the code was. As far as I knew they were standard 130 radial calipers?

Yes, same mounting centre at the APs. The piston sizing is potentially quite important, although the main thing is to match against the relevant MC (as well as stuff like weight distribution etc).

[plip1953]

@Lew

Only problem for which i have no clear answer yet :
this pads are 16 mm thick and the garage was obliged to put out about 1,5 mm on each pads to fit them. As the disc is 24 mm thick, and that the 7600D46 caliper is for 16 mm pads (and 24 mm disc) , i don't understand why they needed to calibrate them. Perhaps the RC6 in 14,5 mm thickness will fit better.

We've had the same problem re pad thickness, so you will either need to grind down a 16mm pad or purchase one of the thinner options of which I believe there are quite a few.

What I am also not clear about is why the need for a thinner pad given that AP themselves quote 16mm as standard on a CP7600 caliper. However, might it be possible that the caliper body used on the Atom 4 is actually a bit narrower overall than a regular 7600 - I've come across something similar with a CP5555 caliper that has been made 4mm narrower to suit a smaller thickness rotor. Without that having been done, maybe caliper to wheel rim clearance was considered to be too tight?

[Monza]

As you had the same problem with other 16 mm pads, i think you are right : it's perhaps a narrower caliper than the normal 7600.
So solution is to use 14,5 mm thick pads like this CL RC6 : 5038W45T14.5-RC6

[Charlie]

Could it be the calipers are actually the ap7645 like these https://www.questmead.co.uk/Categories/ ... 7645-5S0BG they say suit 315mm disc but wondered if they would accept a smaller disc also they take a 14.5mm pad with 22mm thick discs.

[plip1953]

Could it be the calipers are actually the ap7645 like these https://www.questmead.co.uk/Categories/ ... 7645-5S0BG they say suit 315mm disc but wondered if they would accept a smaller disc also they take a 14.5mm pad with 22mm thick discs.

I think that must be right. I'm pretty sure I've seen somewhere that the Atom 4 calipers are designated CP7647.

[Monza]

The Atom 4 discs with AP are 24 mm thick.

[Charlie]

The Atom 4 discs with AP are 24 mm thick.

The Cp7645 calliper also accept a 16mm pad so perhaps with a thicker disc they need the thinner pad option

[Charlie]

The Atom 4 discs with AP are 24 mm thick.

Where did you get this information as according to this thread https://www.ariel.club/forum/viewtopic. ... bbd5523668 the discs on the atom are 22mm although that is for the Alcon setup?

[Monza]

i have mesured them and it's written on a set of replacement ones i have received, so 24 mm for the AP discs (and it was 22 mm for the Alcon).