Brakes (again) and pad choice.

[henry21p]

Current Setup

 

Caterham 21 with

Big front brakes

Standard rear brakes

Big master cylinder

Assorted (god knows what) pads

Dot5.1 fluid

 

No air in the system, had brand new fluid flushed through. No air trapped around the handbrake.

 

10-12 very spirited laps at Llandow and my brake pedal completely faded. Suspect boiling the fluid. Went instantly from hard as a rock to no pedal at all, though it would pump up (Mav had to use the OHSH1T lane)

 

All pads are getting a little low, so don't mind changing them. Caterham suggest uprated rear pads and PAGID RS14's for the fronts, but only if I'm using a brake valve to shift the bias to the rear slightly as I will be over-braked at the front. I don't have one and it's a pain in the 'arris to fit.

 

This is probably opening a big can of worms, but would anyone care to venture any alternative ideas?

 

Bear in mind that the 21 is 640kg, that the front wheels aren't in airflow like your skinny little cars are, neither are the rears and yes, someone has already suggested a bit of ducting to them to keep everything a little cooler.

 

There is a lot in the archives, but I'm sure technology moves on a bit as does opinion.

 

[Irrelevant]

A brake proportioning valve is easy to fit if you don't run it back into the car. . . . Stick one on the front circuit so you can limit the front to balance the rear out. I don't think you want a bias valve . . . Look at the difference in how they work compared to a proportioning valve to see why. Of course you could just fit some manly rear brakes and be done with it . . . Though you may have to live with a carp hand brake . . . .

[Shaun_E]

If you run RS14s front then you could try RS4-2s at the rear - thats the combination that I am using as suggested by John at Performance Braking. The thing I don't like about the Pagids is that they glaze over if used lightly i.e. on road. I used to run an RS15/RS14 f/r combination but that is only really suitable for track use as they glaze over very rapidly on road. Also they do need some (only a little) heat in them before they work so the first stop is always a bit interesting.

 

Yellow SL #32 - member of Drowned Rat Racing

[Powderpuff]

Have a word with Dave Kimberley at Demon Tweeks.

 

I've swapped from Pagids to EBC yellow stuff in the 7....seem to be very good so far

[henry21p]

i'll drop dave a line. glazing them is a concern as the 21 is quite often also used for road driving...

[Nigel Fox]

I tried some RS14s this year and had exactly the problem you described, the fronts locking. I took the advice of Richard Price in a recent thread and fitted Mintex 1144s which find much easier to modulate the braking, have only used them at speed events so far though so don't have the full story.

 

Full time class 4 Zetec

[mav]

I run 1142 compound in the front and 1144 in the rears (same spec calipers as yours).

 

Halfords sell a 'race spec' brake fluid, it may be worth experimenting with srf or similar although not cheap, may provide adequate results before going to the difficulkty in adding ducting etc due to your space limitations...

[Richard Price]

Dave,

If you're getting a soft pedal, its not the pads!

It's most likely to be fluid boil in the rear calipers. When you last replaced the fluid, did you wind the pistons back first? If not, then you may still largely have the old fluid in the calipers (even if you did wind back the pistons, you'll still have only diluted the old with new)

 

SRF may well be expensive, but not as expensive as Pagid pads! I'd give SRF a go before trying all sorts of pads.

 

 

 

[k.russell]

I had the very same experience at cadwell yesterday, going to wind the pads back and bleed with new fluid as i dont think i did this when i replaced with the better fluid earlier in the year. think it is difinately heat related on my car as the car was fine on the short mallory track with lesser braking and a wet rockingham where it was more difficult to get the car moving than stopping 😬. i have been using castrol response but may try the Halford s stuff. my car is also a heavy Vx circa 580-600lbs i guess even more with me and passenger 😳

 

Kevin R

 

black(but sometimes orange)-ali HPC

here

[henry21p]

Richard - the thinking behind the pads being wrong was really to do more with over heating either front or rear as they're doing more work than they should be - i.e. the balance of the braking in the car.

 

I didn't wind the pads back, no.

 

Regardless, the pads i have on there are pretty thin now, so could probably do with replacing them sometime soon anyway. I wasn't getting braking problems at Rockingham, though I have at the last 2 Llandow days. After bleeding them, they were better and lasting longer, but by the end of the day they overheated/went soft again after 2 fast sessions back to back with passengers on board then on solo run to round off the day.

[Richard Price]

Dave,

Llandow is very hard on brakes, with the two very heavy braking points, and so little time between them.

With big brakes on the front, and standard rears, its the rears that are the weak link, and struggle to deal with the heat.

You could use pads with a lower coefficient of friction in the back, but then you'd end up with the brakes biased to much to the front, and have less overall stopping power.

Don't under estimate how much stopping power the rear brakes add.

 

Ideally, you need the rears to work quite hard, and you should be able to lock the fronts, and then with just a little more pedal pressure, lock the rears. I have dual master cylinders, and an adjustable bias bar, so I'm able to experiment with balance.

 

If you're currently happy with the balance then stick with your current pad types, and deal with the heat. Yes, ducting may help, but SRF will cure your problem.

 

 

 

 

 

[henry21p]

ducting to the fronts won't be a problem as I'm already making some discreet modifications to the bonnet "fake" air intakes to help reduce underbonnet temperatures.

 

At the rear, as the aframe is underskinned, I was looking at a pair of holes in that and some donkey dick to near the discs/calipers to provide some airflow to the rears.

 

Ideally, I need to get one of those remote temp jobbies from Maplin and look at the temps when I get back in

[Archie Procter]

I thought you'd retired from BC?!

 

Boiling the fluid - esp older fluid in the callipers - is easily done with big brakes. In fact I have done it. Go for AP600/SRF and some new pads. Am curious as to why you haven't gone for big rears with the AP fronts and M/C - I would, then balance the wheel locking on the pads definitely not a valve of whichever sort. As you probably know, most of us have removed ours from the racecars. Could see how it would be helpful with the road/track combined use though.

 

And as for

I've swapped from Pagids to EBC yellow stuff in the 7....seem to be very good so far

or any of the advice to move to 1144s - forget it for any kind of track usage. Pagids (I use 15s) are simply the best track pads there are for the fronts on a 7 and there is no reason to think it would be any different on a 21. Maybe the answer to your glazing worry is to have a different setup for road and track - changing the fronts is only a 5-min job after all.

[henry21p]

Fair point about swapping pads for different usage.

 

I didn't go for larger rears as the handbrake was an issue. Researched it extensively after the last time at Croix when i boiled the fluid (it has similarly hard stompy braking zones), but all in all it came out as a pain in the arse.

 

i think at this stage will be pads and fluid and see if I can't get some ducting to the brakes.

 

Edited by - Dave21P on 16 Sep 2010 08:09:43