93 replies to this topic

[JohnTurbo]

Tee hee hee.

 

There is many ways to skin a cat you know.

 

I was something of a worst case in my VXT as I had plenty of power, pretty high weight, but low cornering speeds so the brakes got abused and i repeatedly had issues with plain disks/mid range track pads and good fluid. No braking at all boiled fluid!

 

Some fact and some opinion here but:-

- The first thing is to make sure your rears are doing their share of the stopping! On a standard setup use the same rear pad as fronts.

- I don't like the 2 pot calipers, the pad is tiny and MANY compounds can't cope with this sort of pressure and break down with heavy use. Sintered and full on race pads are an exception, but they all seem to wear unevenly which for me ended in the pistons sticking due to the moment generated.

- Other than this, yes the disks are the main heat-sink in the system. (Aluminium IS a better heat sink than steel by the way, by a margin!) so one way or another you need to address this in order to solve the heat issue.

I used the (cheap) 4 pots from the TF and bigger (cheap!) 308mm disks and then 50quid pads and cheap fluid was suddenly more than good enough which made for super cheap running costs. Unsprung mass - slightly worse than stock.

On the civic i've stuck with the stock 1 pots all round and these work fine (as they have a decent size pad!!) but bought new castings to allow the use of bigger disks, and I bought BETTER disks with proper vents. I have a picture somewhere. A proper disk should have more vent than metal imho!

 

On a VX i'm sure good disks/pads/fluid will do the job fine, but this is a lot of money at ~150quid a set of pads ~400quid a set of disks and still you are left with the stupid wedge shaped pads from calipers which look to ME to have been designed for use as rears on something.

[Scuffers]

an't say as I have not looked/used a AP 308...
 
if I remember, I'll take a gander at one tomorrow

this is the AP 308 EP stock...
 

 

 

 it's not one of the horrible ones.

[Exmantaa]

This one will fit in nicely here:

 

On the German Speedster forum, they are currently developing new (special type of steel) pistons for the 2-pot callipers. They say that all calculations show that the stock system should be more then enough for the light Speedster/VX in all cases, but still various people experience braking issues.

What I quickly read there is that the stock pistons are aluminium and it's said that these therefore will conduct the pad heat rapidly into the fluid, causing the brake/boiling problems. Also due to the heat and material they can expand quite some, which in extreme cases can lead to sticking pistons in the (cooler) caliper housing...

 

Thoughts?

Will be interesting to follow the results of this, as when this works it sounds like a cheap and easy brake upgrade. 

 

Edit; Googling around I found that such pistons are already available in the US => http://www.boefabric...caliper-pistons

Edited by Exmantaa, 09 May 2014 - 08:37 AM.

[Scuffers]

sound theory, issues will be:

 

1) steel rusts, so they will need to be plated with something very robust and heat proof.

2) steel expands less than ali, so the pistons will get looser the hotter they get (relative to the ali housing)

3) Titanium is a better material to use (and hence why it is with some makes)

 

aside all that, only ever seen fluid boil once, and that was with Mr. left foot braking with questionable quality/age fluid.

 

Pad material has more of an impact in heat transfer to the piston, and you can also get ceramic backplate shim's to insulate them too (although as I said, never needed to)

 

 

[Steffen]

@Scuffers

 

You have tested this pistons?

So how you can decide that they are wrong?

 

 

The discs from AP on all Lotus which participating to the Challenge in Italy are going broken after 2 days on track!

Now they are running mostly with 2piece Opel discs.

 

 

 

I prefer to test befor I say what works and what not!

[Exmantaa]

They are using a Stainless Steel type for these and initial tests showed to solve the braking issues a customer experienced...  

 

Some quick info I found from AP:

Racing calipers use piston materials designed to reduce heat transfer and this does not include aluminum. The CP 8350 has stainless steel pistons which reduce heat transfer to the brake fluid.

Benefits:

Heat management is the primary goal of a big brake kit and stainless steel has a much lower thermal conductivity than aluminum. Titanium and ceramics are also a great option for piston material but they are MUCH more expensive. Stainless steel offers a great balance of heat reduction, weight, and price.

 

http://www.knsbrakes.com/c/ap-caliper

[Exmantaa]

 

 

The discs from AP on all Lotus which participating to the Challenge in Italy are going broken after 2 days on track!

Now they are running mostly with 2 piece Opel discs.

 

 

 

I prefer to test befor I say what works and what not!

 

2 piece Opel discs??

[Steffen]

Yes....not really orignal opel, but the base is from Opel!

 

[Scuffers]

@Scuffers

 

You have tested this pistons?

So how you can decide that they are wrong?

 

Sorry?

 

Never said they were wrong, just not convinced they are needed?

 

I have used stainless pistons, and they are ok, but not a fit and forget item, they did need to be serviced/cleaned a lot more offten.

[JohnTurbo]

They use titanium shims in the states for the 2 pots as an insulator.

- Or at least these are available over there.

 

 

[Exmantaa]

Hmm, that is even easier to fit...

http://www.tibrake.c....html?mode=grid

 

Only not sure if the thin layer of Ti between pad<>piston will prevent enough heat transfer. Best is to do both.

[Exmantaa]

Thinking about this; a stainless steel shim plate will have only slightly higher heat transfer coefficient than TI, but for a fraction of the cost.. (SS-304)

For sure these must be available somewhere?

[Scuffers]

OK, let's get down to it...

 

exactly who on here has ever experienced brake fluid boil on a VX with 2 Pot's?

 

(no, I don't mean brake fade, I mean pedal to the floor - NOTHING cause the fluids boiled).

 

What I am getting at here is why are we trying to solve a problem I am 99.99% confident does not exist 

[smiley]

exactly who on here has ever experienced brake fluid boil on a VX with 2 Pot's?

 

Me, but I am horrible at breaking so do it incorrectly.

Going for high temp fluid, and Cl6 this season to better match my poor way of braking.

[Steffen]

Me too

[Scuffers]

 

exactly who on here has ever experienced brake fluid boil on a VX with 2 Pot's?

 

Me, but I am horrible at breaking so do it incorrectly.

Going for high temp fluid, and Cl6 this season to better match my poor way of braking.

 

 

 

Me too

so, you both lost all brakes then?

 

I assume you left the cct (as in un-intentionally?)

 

Look, being blunt, I want to see some real evidence of this happening, because being frank, I don't believe it. 

 

I can see you getting chronic brake fade and slack pedal feel cause the disks/pads are overheated, but to actually boil the fluid is another thing entirely, if this did happen, I would expect to find you in a gravel trap or tyre wall.

[Steve.i.am]

I think I boiled my fluid at Blyton.

 

After about 10 laps or so the pedal went nearly to the floor approaching the corner at the end of the back straight. I just had enough braking to make the corner. I obviously immediately eased off & tried the brakes - pedal to floor and no stopping. I nursed it off the track using the handbrake - then nursed it back into paddock. Pedal just went to the floor.

 

About 30 minutes later I tried it again in the paddock and brake pedal had returned.

 

I assumed I had indeed boiled it.

 

I have standard 2 pot calipers and discs, CL RC5+ pads. The fluid was halfords DOT 5.1 which had been replaced about 8 months previous (but it had been in it over winter and the car lived outside). I put it down to moisture in the fluid and changed it.

 

 

[smiley]

 but to actually boil the fluid is another thing entirely, if this did happen, I would expect to find you in a gravel trap or tyre wall.

 

 

It was pretty close, and I had to go home after this happened, as it was just unsafe.

The only thing that saved me from a crash was my pussy driving, making me (try to) brake at some safe stupid corner where I noticed pedal to the floor.

I had to handbrake myself back into the pitlane.

Edited by smiley, 09 May 2014 - 03:18 PM.

[Graeme Lambert]

OK, let's get down to it...   exactly who on here has ever experienced brake fluid boil on a VX with 2 Pot's?   (no, I don't mean brake fade, I mean pedal to the floor - NOTHING cause the fluids boiled).   What I am getting at here is why are we trying to solve a problem I am 99.99% confident does not exist 

I think Me. Not brake fade like I've experienced in other cars anyway, pedal to floor with no real braking effort produced. Pembrey national last year, I even have it on video. But I'm aware that my discs and pads were limiting factor. Standard discs and Mintex pads ( either 1144 or 55 can't remember), OEM bridgestones (sub 2 yrs old) and 240bhp stg2 vxt.

Edited by Graeme Lambert, 09 May 2014 - 03:28 PM.

[techieboy]

I had exactly the same as Steve on my very first VX trackday at Bedford, what feels like decades ago. Definitely boiled but the whole braking system was generally shagged. The fluid looked like tar and pretty sure it had never been changed in the 6 years since it had rolled off the production line, it had Green Stuff pads in, shitty old dimpled EBC disks and what turned out to be a slightly sticky OSR caliper. Could manage three or four laps at a time before the brakes just gave up. Would leave it for 30 mins or so and they'd come back again.

 

Also had pad "fade" with Yellow Stuff pads. Shockingly crap, brakes did barely anything to slow the car except turn the front disks blue and when I removed them, they were just falling apart. Went straight in the bin with less than 100 miles use.