Brake Bias Valve confusion

[charlie_pank]

I'm sure that the race-setup makes a difference to your car. But I've never found it to be super-hard work to lock up the wheels in mine.

[andy bell]

Right so created custom scene and did a test to see if its car or me being weedy. Its all uploaded here(I edited to only 26 seconds) but here is what I saw/felt on circuit tools.

 

Normal - Accelerated to 61mph then did what I would 'usually' break as - it showed I applied about 37% brake and stopped in about 90m (ouch that's shocking) and long G was about 0.4.

 

Pretending I have strong legs - Went at about 55mph and I tried to hold it as hard as possible. Applied about 55% brake, stopped in roughly 50m and long G was about 0.56. Better but I wouldnt say it was easy to try to maintain brake effort - takes concetration and too much effort.

 

Tried same again and managed stopping distance down to 40m ish - still shocking. Best brake effort I managed was 61.184% - still means I was wasting 40% of braking effort of car.

 

I then sat in car and summoned all my tiny strength when car was stationary and the preview monitor was plugged in and managed 100% - but it would not be realistic to hit this. Thats me shifting weight and all force on brake pedal.

 

As can be seen I never once manage to lock up brakes. I do not see how under normal driving you could ever get 100% brake or even close and I guess to my mind thats a bit dangerous - lets not mention stopping distances...

 

So solution I guess is to do away with the high effort brake pedal and replace with normal one? Or can you adjust how much 'force' is required to apply 'high effort' pedal.

[Roger Ford]

The standard brake pedal is pretty cheap so I'd go for that to start with. I'd strongly recommend the standard master cylinder as well, but that's a lot more expensive. Try a post in "wanted", I'd say there's a pretty good chance someone will have one that they've upgraded from.

[andy bell]

I think I may be in luck as I have all the parts. I have a spare brake pedal and appears to be slightly longer than the one in it. Here is it next to measuring tape and here its aligned actually in the car - can see its a bit longer.

 

I guess as its longer you have to put less pressure on to get same effort therefore I should be able to reach 100% far easier?

 

TIme to try swapping the brake pedal and repeating test and then decide how I want to proceed.

 

Again thanks for all the help and anything to watch out for in swapping brake pedal *looking* at it quickly seems easy enough

 

Edited by - andy bell on 12 Jul 2013 19:08:30

 

Edited by - andy bell on 12 Jul 2013 20:00:09

[Roger Ford]

Yup, as someone once said "Give me a lever long enough and I will stop a Caterham" (or something like that). Put 'em on, bleed the brakes, see what it's like then. Then maybe think about changing pads if it's still not great.

[Birkin S3 ZA.]

Keep at it Andy your on the right track, and your getting some good advice to follow.

One thing you could try is to check your brake line pressure, 1000 to 1200 psi should be possible with a good hard push like your doing a emergency stop.

less than this the pads won't work at there best and could start to glaze and loose there efficiency.

I went through the same problems as you and ended up fitting smaller master cylinders which made a huge improvement, then changed the front pads to a lower temp race pad.

Now it stops like it should I will attempt to out brake other sevens in a race and manage it without locking wheels, lots of feel and it will lockup with a good push if I had to.

Big improvement in the wet as the extra feel helps not to lockup the wheels.

Good luck

Chris.

[Z3MCJez]

Roger's advice is good but I'd be tempted to change the front pads first as there is evidence on this thread of your current pads glazing and I'm not sure how the 100% effort has been set up. Does that mean the hardest you could ever push, in which case 50% should be plenty to induce a lock up.

 

Jez

 

 

[Z3MCJez]

And changing the front pads is really quick and easy.

 

Jez

[andy bell]

So I managed to swap back to the original (longer) brake pedal after staring at it for 15 minutes and figuring out about the small pin that needed removed and then big screw that holds clutch/brake in place.

 

Was quite happy after changing that and did a stationary test - was (with my normal braking) hitting 60%/70% and 100% seemed to be a easy with a little effort. Decided best to see how it broke under same conditions out on road now. For my total lack of skills mechanical wise every little thing seems like an achievement.

 

Started her up and well she didn't start... When I switch ignition on the temperature gauge goes to max and sits there which I don't remember before. And when I start engine I just get it not catching as it were http://www.youtube.com/watch?v=qG4NxBqHJ-M

 

Given my tampering was limited to the brake/clutch/accelerator housing bit bemused and off to try to figure out what I may have poked/prodded incorrectly.

 

Edited by - andy bell on 13 Jul 2013 16:23:39

[Roger Ford]

Don't know much about Sigma wiring (it is a Sigma, right?) but the only wiring anywhere near where you've been working ought to be the brake light switch, and any datalogging sensors which may or may not be connected to the brakes. Presumably whatever you're using to measure your 60/70/100% must have some wiring to it.

 

I'd suggest going through all the fuses one by one and seeing if you've blown any of them Look out for extra / secondary fuse boxes as well as the main one.

[andy bell]

Yeh I think I must have definitely fat fingered something in my poking aboot. Yes it is a sigma and im measuring the brake effort with the vbox preview monitor that you can plug into the aux port. Strangely even more its not detecting throttle (although both go into micro input module) and it should at stationary from memory.

 

The brake light is working ok but yeh time to start a checkin!

 

Just visually checked all the fuses and they are all fine so (unfortunately) methinks it could be garage time never touch car again!!!

 

Edited by - andy bell on 13 Jul 2013 20:47:05

[Roger Ford]

You might want to start a separate thread for your starting issue.

 

Shame that your first attempts to change anything have caused problems - fiddling with stuff should be an integral part of the Caterham experience.

 

Do you have AA Home Start or the like? If so, call them out and get them to take a look. Some of the guys are very knowledgeable and it will make a change for them from sorting out Fiestas that have run out of fuel.

[Paul Deslandes]

If you're going to change the pads, particularly to a different material, you should clean the disks with abrasive paper to remove traces of the previous pad material from the surface. Garnet paper is recommended but I've never managed to find any so use decorators sand paper. Don't use emery paper or cloth as it leaves an abrasive residue on the disk which is hard to get off.

 

About 15 minutes a disk side suffices. One way is to take off the wheel and, holding the abrasive against the disk, rotate the disk by hand. If the disks are a bit 'iffy' and you have standard rather than large APs, buy some new ones for not much more than about a tenner each. The 'big brake' disks are too expensive to trash unless they're really knackered but you can get them refaced by a local engineering firm for a lot less than the price of a new set.

 

If you don't do this, plus any bedding-in recommended by the pad manufacturers, you might find it takes quite a while for the effect of the new pads to become apparent, if ever.

 

Edited to add:

 

If you want some real stoppers on the front, try herePerformance Friction 01 compound. They work from almost stone cold but do make the wheels black. Otherwise the 1144s are a good road choice.

 

 

 

Edited by - Paul Deslandes on 14 Jul 2013 17:50:52

[andy bell]

thanks for all the help brake wise as ever if I meet you in person pester me for a drink.

 

As for non-starting car apparently putting in 5l of fuel is sometimes not enough to get car started ☹️ ☹️ ☹️ ☹️ ☹️ ☹️ From reading threads people were saying 'it does not start with anything less than 5l'

 

I put another 10l in and funnily enough it starts.

 

Its funny how in my line of work I know so much and in this something simple can kick me in the butt. Lesson here is after every use put more fuel in

 

Edited by - andy bell on 15 Jul 2013 14:52:02

[Z3MCJez]

Is it parked somewhere flat? Because I've heard this rumour before, but run my race car down to <4l at the end of a race. I guess that the fuel does get moved around a lot during the race whereas if you're parked on a sideways slope, then I guess you could starve it quite quickly. Anyway, glad to hear you're up and running again.

 

Jez

[andy bell]

so again funny you say that. My garage floor is flat but I had jacked the car up so obviously the angle of jacking would have put it on a very steep incline - if only temporary.

 

Then to get better access to the car I had to move it away from back wall and its sitting on a slight incline at the moment. Also had charged battery and topped up fluid as was low

 

I guess if I had a cutaway of the fuel tank it could make sense but for now I will just hide ;)

 

Edited by - andy bell on 15 Jul 2013 16:27:59

[andy bell]

So just went out for a test and the swap from the high effort brake pedal to the normal brake pedal has made a massive amount of difference. As a cleverer man than me said - high effort brake pedal + uprated master cylinder without bigger brakes = need a leg like the terminator.

 

I still have the standard master cylinder in the spares I got so may decide to go back once I do track day on Saturday. Or else sell the standard and all the other misc bits I have

 

Edited by - andy bell on 18 Jul 2013 19:11:23

[charlie_pank]

That's great news - just imagine how much faster you'll be on track now that you can stop properly!

[andy bell]

So had it out on Trackday and the brakes were like night and day. Was looking forward to really getting to know car but alas the starting issues returned after I had done 7 laps and went to go back out again.

 

never mind :)

[A_redstone]

Appreciate this is a really old thread !

BUT I was looking for advice on same subject.

my bias valve I am told should be left in the vertical position and not messed with !

thats quite different to fully forward 

i refer to just normal road use

 

Thanks 

 

andy 

[Richard Price]

Andy,

If I were you, I'm try adjusting it and braking hard where there is plenty of space around you!

In my experience, I'd say that much more stopping power comes from the rear brakes than most folks appreciate, however, too much rear bias will make the rears lock first potentially resulting in the back end coming around.

With standard brakes, running the same pad material front and rear often results in too much rear bias, which is why some cars are fitted with an adjustable valve of some sort.

[Keith_T]

My ex-Academy car has a Brake Bias valve but the lever (which I was told to leave forward) is very floppy ie can be moved forward or back without any resistance.

Need to investigate further (car not in use at the moment) but intend to keep for authenticity. 

[A_redstone]

Hi this was put on my car for previous track days, it does have the big brakes option fitted already !