547 replies to this topic

[Robert]

What's the word ?

Keen to see how it looks with the new wheels

[cowie165]

Jim those Arctic Blue Narvas look good. I used LEDs in mine and must've blown something because those lights no longer work! Swapped for other LED, original bulbs...nope.

 

Hey are you selling your 4pots?? Don't rate them?

[Jimbo]

Yeah I wasn't happy with the feel. Probably due to shit Bendix Ultimate pads and maybe still a bit of air in the lines or something. Pedal feel is solid, not spongy, but takes quite some force to brake moderately. 

It feels like the pads are just skimming the rotors with normal pedal force but the real "grab" point takes alot of pedal travel. It's pretty odd, air in the lines would make it feel soft and mushy but it doesn't feel that way.

I had 4pots on the Gen2 GTB and it never felt this way at all. Might be something Gen3 specific, no idea. I have a set of OEM 2pots now anyway so I'll make the swap when  I have time.


 

[cowie165]

Jim I remember reading somewhere (here?) about the Gen3 brake application and feel. It was designed for exactly the feel you're experiencing. Less race car and more gentleman's wagon, so the brake application is not linear. I've rebuilt all my (stock 2-pot) calipers, new DBA rotors, new QFM pads and I barely noticed a change to the "normal" braking, but an ABS stop will just about knock your teeth out.

 

It may all be broscience/BS from the internet, but thought I'd share anyway.

 

If/when you swap and decide to offload the 4-pots, please keep me in mind. I'm looking for a set.

[duncanm]

You probably remember reading this autospeed article.
 

[zahmad]

Interesting to see the B4 setup is different to the RX/Heritage...

[cowie165]

You probably remember reading this autospeed article.

 

 

duncan that is some impressive search-fu. Nailed it, and thanks for the pic!

 

I wonder if difference in braking force is due to different calipers or different MCs? Bang for buck, would it be worth swapping an STI MC onto your BE/BH instead of the calipers?

 

 

PS. Graph explains the point, but it's also worth noting the WRX STI has a 20% greater deceleration over the standard B4 system. That's quite a big difference.

[Jimbo]

This is what mine feels like..




When I was chatting to Dave about it (original owner in Japan) he had a Subaru engineer explain something similar to him. He told him that it was a "progressive" feel, so that you can adjust your speed with light application but when you need more braking performance, the bite is still there further in the travel.

It's similar to how mine feels. I think I might have a crack at re-bleeding the system and maybe trying different pads before giving up on the 4pots. The BH/BE Legacy S-Edition was fitted with 4pots up the front as standard but highly doubt they would have changed the M/C size?

In saying all this though, there's a big thread on Nasioc that claimed there wasn't a great deal of difference between the turbo 2 pot's and the 4 pots. Obvious advantage of the 4 pots being a bit lighter and better for heat dispersion. The pad surface area is nearly the same but the 4 pots win out with slightly more braking torque. 

I find how mine feel now is okay for spirited driving but day to day I just don't feel as confident as I should be.

[patttyfox]

Brembos..


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[Matt]

STi master and booster would make a good difference

I have an sti master you can have to try?

[CRUISN]

Factory option was 4 pot fronts. No change in MC. I found 4 pots to feel identical to the 2 pots both running Bendix GCT.

Im going back to 4 pots, have a set enroute because factory option spec.

[duncanm]

The pad surface area is nearly the same but the 4 pots win out with slightly more braking torque.

There's a couple of interesting things going on 4 vs 2-pot.

2-pots are 42.8mm piston diameter. 4-pots are 40.4mm (I think).

For initial bite, the pedal movement will be proportional to the pad/rotor distance (run-out) times the total piston area for the 4-pots - but double that area for 2-pots (as we have to move the caliper the same distance). So initial pedal run-out will be slightly more (~12%) for 2-pots because of the bigger pistons.

However, when you look at clamping force, only two pistons count - 4-pot or 2-pot. So the 2-pots will have ~12% more clamping force.

then - what's the rotor diameter difference 2-pot to 4-pot.

There's a nice spreadsheet here which calculates braking torque.

It says 2-pot to STI 4-pot is an 8% drop in braking torque.

[cowie165]

For initial bite, the pedal movement will be proportional to the pad/rotor distance (run-out) times the total piston area for the 4-pots - but double that area for 2-pots (as we have to move the caliper the same distance). So initial pedal run-out will be slightly more (~12%) for 2-pots because of the bigger pistons.

However, when you look at clamping force, only two pistons count - 4-pot or 2-pot. So the 2-pots will have ~12% more clamping force.
 

 

 

I want to understand the physics but I'm hitting a speedbump. Why do only two pistons count for clamping force? Isn't force being applied on both sides of the rotor by the 4-pot, whereas the 2-pots only apply force on one side?

[Jimbo]

2 pots only have pistons on one side but the clamping resistance from the piston side brings the inside pad to clamp the rotor. Hard to explain without seeing it.

Youtube how a sliding caliper works. I thought only one side clamped the rotor aswell until i saw a video!

[duncanm]

I want to understand the physics but I'm hitting a speedbump. Why do only two pistons count for clamping force? Isn't force being applied on both sides of the rotor by the 4-pot, whereas the 2-pots only apply force on one side?

it is a bit tricky to get your head around.

The other way to think about it is that all pistons work from both ends - they push both the pad against the rotor, and the caliper outwards.

For 4-pots, the outwards forces from either side just try to bend the caliper open - no useful effort there; but for 2-pots, the outwards force is used to clamp the other pad on the rotor via the sliding caliper.

[Jimbo]

When the piston is pushed into the rotor, the outward and opposite force pulls the outside part of the caliper towards the rotor.

Newtons law pretty much "For every action, there is an equal and opposite reaction."

[Jimbo]

Also just an update on me noble steed.

I fixed the climate control! Turns out, last time I pulled it apart, when I put it back together I shamefully crushed the cabin temp sensor into itself unknowingly. It would have given a dodgy signal and conked it out.

I discovered this while installing the de-greenification screen mod. Looks much better. Still have to fix one LED which has worked itself loose. 

While I was up in there, I installed the S401 hazard switch, which looks tits. I had no idea that the hazard switches were illuminated. Pulled apart the OEM one to find, indeed, they are (globe blown long ago).

I might chuck a LED into my old one and see how it looks. If it looks good I'll do a how-to



Some will also remember I had a problem with the Purge Control Solenoid fittings snapping off .... fixed it for $2.50. Result? No more vaccum leak and better fuel economy.

[CRUISN]

Looks identical to my centre console with the surround, white AC and S401 hazard.

[Adictions]

Looks good. got to love fixing a problem so cheaply to.

Never new about the hazard switch lighting up haha, are the cruise and fog light switches supposed to light up aswell. mine dont but i thought i saw 2 light fittings in one before. I hate them at night.