mistergrumpy
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| posted on 5/3/09 at 03:59 PM |
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Brake Idea
Just had an idea that may or may not alredy be available and may be considred crap. Just after your thoughts.
Part of my SVA fail was the braked weren't effective enough. Now to me, they stopped the car and you can't push it if I've got my
foot on the brakes so I can't really gauge anything other than perhaps it's because of the new pads not being run in at all and I'll
have to borrow a car and hire a trailer to take it around the corner to drive around and bed them in and stuff.
My idea. Could I make something, perhaps a slave cylinder with a pressure gauge tee'd into it and then place that between the pads, in place of
the disc and then go and press the brake pedal and measure the efficiency of things that way. Therefore determining whether it's the pads or
calipers at fault and saving me messing about all over?
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nib1980
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| posted on 5/3/09 at 04:08 PM |
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in all honesty i'd go and run the pads in. what are you using? green stuuf or originals?
mine were green stuff and it was marginal as they were'nt run in.
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James
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| posted on 5/3/09 at 04:10 PM |
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I think I did 4 miles around the local roads plus driving 20 or some miles (back roads) to SVA.
Mine passed so it can't be that hard to bed them in.
Cheers,
James
------------------------------------------------------------------------------------------------------------
"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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Guinness
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| posted on 5/3/09 at 04:17 PM |
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Can you change the pivot / ratio on the pedal to make them more effective for a given "push"?
Might just be a case of drilling another hole, moving the pushrod up or down (I can never remember which).
Mike
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mistergrumpy
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| posted on 5/3/09 at 04:24 PM |
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Well my pads are from Brakes direct, can't remember the make, possibly Ferodo and they have done no miles on them. Like I say I'm unable
to run them in without hiring a trailer etc. and I can't really drive around unlicensed.
The pedal ratio isn't really an issue I don't think at this stage.
But what of the idea though? The fail was just a prompt to it. Is it a good one?
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JAG
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| posted on 5/3/09 at 04:27 PM |
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Your idea won't give you any idea of the effectiveness of the brakes because their ability to stop the car is decided by the torque output.
Which means you would have to measure the effective radius of the caliper, the tyre size and the pads coefficient of friction and do some calc's
to work out the effectiveness from your pressure measurement taken by;
quote:
a slave cylinder with a pressure gauge tee'd into it
Best guide is whether you can lock the wheels, front first 
If not then bed the pads a bit and try again.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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mad-butcher
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| posted on 5/3/09 at 04:32 PM |
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I think there is already a competition gauge availiable from demon.but why waste your money
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matt_gsxr
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| posted on 5/3/09 at 04:57 PM |
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front or back.
You can bed the back ones in by lifting the rear and running the engine etc.
matt
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mistergrumpy
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| posted on 5/3/09 at 05:13 PM |
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Yes I suppose you're right enough there Jag. I didn't think so much into it, I just thought that if I could measure an acceptable force
being created then I would could rule all that side of the system out.
Incidentally it's one front brake and the two back ones that aren't up to scratch. He said the handbrake performance was cack too but
I've put it on and tried to push the car and it won't budge.
Have to hire a trailer then before my retest I suppose.
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BenB
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| posted on 5/3/09 at 05:21 PM |
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On a Seven type car if you can't get your brakes to pass SVA criteria there's a serious problem.... 99% sure they just required bedding
in, it's the usual problem. My first SVA (trailer job) showed they were pants but the time I got to my second they were fine.... At least the
fact that the handbrake function was rubbish shows its the pads and not something else (like air in the line)...
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mistergrumpy
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| posted on 5/3/09 at 05:29 PM |
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I didn't actually think that new pads would have such a massive effect. I've changed them on tin tops in the past and they still stop
okay. Except for that first one at the end of the street when you very quickly remember that you've not pumped the pedal again
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britishtrident
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| posted on 5/3/09 at 09:22 PM |
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Not rocket sicience
(1) Your master cylinder came from a tintop that had a much longer brake pedal.
Llonger = more leverage. In a Seven type car you will be hard pushed to get a pedal leverage ratio of more than 4:1 or 4.5:1 Tin tops have a pedal
ratio of between 8.5:1 and 9.5:1
(2) Your mastercylinder also came from a car with a brake servo which provided 40 to 60% of the braking effort.
To put it simply with the system the way it is to get the same hydraulic pressure in the system you need to push the pedal 4 times as hard.
However because the car is lighter than the donor you only need half the hydraulic pressure.
Solution fit a smaller diameter master cylinder from a model not equiped with a servo.
Hint ---- Caterham and Westfield both use a 0.7" bore master cylinder -- your master cyilnder will be at least 0.81" bore
A 0.7" bore cylinder will reduce your pedal effort by at least 25% and improve your brake feel.
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mistergrumpy
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| posted on 6/3/09 at 04:20 PM |
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Cheers BT. That's helped a lot.It was something that I was thinking about in the back of my mind.
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