The curious case of the Atom 4 brakes

[plip1953]

When are you trying the car with the springs / new MC on track?

Wednesday of next week at Cadwell Park.

[reg]

When are you trying the car with the springs / new MC on track?

Wednesday of next week at Cadwell Park.

Would you have the part number for the seal kits... CP4525-JJ, CP4949-114?

[plip1953]

When are you trying the car with the springs / new MC on track?

Wednesday of next week at Cadwell Park.

Would you have the part number for the seal kits... CP4525-JJ, CP4949-114?

What in particular are you wanting? CP4525-JJ is this..

https://www.questmead.co.uk/Categories/ ... -CP4525-JJ

And CP4949-114 is for a single piston seal.

https://www.a-pp.com/Categories/Braking ... CP4949-114

[reg]

Just thinking might buy a few seals in case one picks up in the process?

[plip1953]

Just thinking might buy a few seals in case one picks up in the process?

We did the same, but thankfully didn't need to replace any.

This was the kit we bought.

https://www.ebay.co.uk/itm/143558349394

Dust seals can be bought singly, but not cheap!!

https://www.ebay.co.uk/itm/114900487598 ... xycmBS3aNc

We damaged one dust seal on Car 'A' and two on Car 'B'. On Car 'A' they were left off, but were retained on Car 'B' after the anti-knockback springs were fitted. If the pedal stays nice and firm on both cars until the end of tomorrow's trackday at Cadwell we mostly likely will reinstate them in Car 'A'.

[Yorkshire]

Have all cars been fitted with new master cylinder and knock back springs? My car just has the cylinder altered so i'm interested in whether the knock back springs make any difference Thanks Stuart

[reg]

Have all cars been fitted with new master cylinder and knock back springs? My car just has the cylinder altered so i'm interested in whether the knock back springs make any difference Thanks Stuart

Had a chat again with Steve today, always a good guy. He said some testing is happening, perhaps [mention]HenryJS[/mention] could expand on this? If the new procedure is to ‘reset’ the pads then it could be the springs are 70% the solution. This weekend planning to fit springs/RS14 and master cylinder. In for a penny….

[plip1953]

Have all cars been fitted with new master cylinder and knock back springs? My car just has the cylinder altered so i'm interested in whether the knock back springs make any difference Thanks Stuart

Had a chat again with Steve today, always a good guy. He said some testing is happening, perhaps @HenryJS could expand on this? If the new procedure is to ‘reset’ the pads then it could be the springs are 70% the solution. This weekend planning to fit springs/RS14 and master cylinder. In for a penny….

To reg :- I'm really not sure what you mean by "reset the pads"? Can you elaborate?

To Yorkshire :- Part of the idea of different master cylinder sizes was to reduce brake pedal travel. The downside is that a bit more leg effort is required. If the fitting of anti-knockback springs simply of itself gives a nice firm pedal (rather like has been described with earlier cars running Alcons) it might not be necessary to change master cylinder sizing. Hopefully we will have more answers very soon.

[reg]

They way it was explained to me was that the procedure involved pushing pads out past the point where the seals retract them. This gave the good short term solution.

[Yorkshire]

To plip1953: So have some cars or one car been fitted with just springs no cylinder change that would be really good to show just the effect of the knock back springs

[plip1953]

They way it was explained to me was that the procedure involved pushing pads out past the point where the seals retract them. This gave the good short term solution.

Ok, but my point all along is that the dust seals are entirely passive - at all times.

[plip1953]

To plip1953: So have some cars or one car been fitted with just springs no cylinder change that would be really good to show just the effect of the knock back springs

Both cars now have the master cylinder size changes and both have springs fitted, but one retains the dust seals and the other doesn't. Also, both have the Corten Miller pedalbox brace.

[reg]

They way it was explained to me was that the procedure involved pushing pads out past the point where the seals retract them. This gave the good short term solution.

Ok, but my point all along is that the dust seals are entirely passive - at all times.

I'm sure the dust seals...are just dust seals. But IMO the piston seal is primarily designed for a servo system, it's grabby, and now (confirm tomorrow) the springs will overcome.

[plip1953]

They way it was explained to me was that the procedure involved pushing pads out past the point where the seals retract them. This gave the good short term solution.

Ok, but my point all along is that the dust seals are entirely passive - at all times.

I'm sure the dust seals...are just dust seals. But IMO the piston seal is primarily designed for a servo system, it's grabby, and now (confirm tomorrow) the springs will overcome.

The seals are exactly the same for any of the AP caliper range with 38.1mm pistons. I believe there is also a higher temp variant, but only needed in very extreme applications.

[Lew]

I did a trackday with the AP calipers at the rear (alcons front) and I can say I got pads knockback (can be overcome by pushing the pads to contact just before the braking zone).

My feedback on my current setup is:
pedal is a bit lower than before, noticeable but still ok for heel and toe
dead travel zone at the beginning
feeling is a bit spongy but I got better confidence and I could feel more braking power compared to my old rear "sports" brakes
at the end of the day it was okay for me, longer travel may be easier to have a precise braking.

I ordered springs and the 0,75" master cylinder, I'll definitely put the springs in, not so sure about master cylinder, i'll give it a couple of trackdays to decide.
Waiting for [mention]plip1953[/mention] feedback regarding seals