supercat
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| posted on 21/9/07 at 01:42 PM |
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Setting up floor mounted brake pedal
Hi chaps,
Does anyone have any advise for setting up floor mounted pedals with twin m/c? I've put mine together with everything centered but the braking
is not very good (can't lock the wheels when moving).
Any ideas?
Cheers, James
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nitram38
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| posted on 21/9/07 at 02:05 PM |
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If your bias is set ok (bias towards the fronts), it could be your master cylinder is too straight.
Because the pedal follows an arc, if you start with the MC rod straight, then as you put pressure on, it too moves downwards so that you do not get
full pressure.
Try moving your master cylinder rod pick up point on your pedal up so that it starts off about 5mm on a slant.
This means it will level off under pressure.
Hope that makes sense.
I had the same problem at sva so I moved it up 5mm and the brakes are spot on.
[Edited on 21/9/2007 by nitram38]
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RazMan
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| posted on 21/9/07 at 02:26 PM |
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What is your pedal ratio and m/c bore size, caliper piston size etc? These are all factors which will affect your braking efficiency and pedal force.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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supercat
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| posted on 21/9/07 at 03:05 PM |
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Not sure of the pedal ratio - its an OBP pedal box - and so I cant easily change the pivot point.
The calipers on the front are Wilwood powerlites with a 0.65 m/c and rears are standard sierra rears with a 0.7 m/c
Cheers,
James
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jkarran
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| posted on 21/9/07 at 03:13 PM |
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I have a similar setup, same calipers, 0.65" MC front and rear, home-made pedal box. My brakes feel a bit wooden and uninspiring especially when
cold (most of the time), it pulls up fast enough but you do need to give it a good prod with the right foot!
jk
[Edited on 21/9/07 by jkarran]
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lsdweb
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| posted on 21/9/07 at 03:27 PM |
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James
There’s some great advice on the AP Racing site - link
An old friend taught me a method of setting up balance bars a few years ago - here goes:
Get the car off the ground on stands. Make sure the brakes are bled properly and that the bias bar is roughly where you think it should be (got to
start somewhere!).
Find an adjustable means of pressing the brake pedal – I use a length of threaded bar with a nut through the pedal (easy on the single seater) and the
other end against a chassis member. This means I can adjust the amount of pedal pressure very accurately.
Then I adjust the pressure on the pedal (using the nut on the threaded bar) so that the front wheels won’t turn. I then check the back wheels which
should be getting tight but will still turn. If this isn’t the case, I loosen the threaded bar, adjust the bias rod a little and then try again. This
takes a little bit of time but is pretty accurate and relatively easy to do. For greater accuracy, I can then use a torque wrench on the wheels
(centre nut) to accurately measure how much torque is required to get the wheel to turn against the brakes.
Sorry if this sounds complicated – I’d take a picture but the car is away at the moment.
Wyn
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RazMan
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| posted on 21/9/07 at 04:15 PM |
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Wyn, That method would only work if both front and rear systems are identical. If you have different m/c bores or caliper pistons, then the starting
points for front and rear can be way off.
Setting the bias bar is best done at your local friendly MOT station. He will have a pressure sensor that is placed between foot and pedal -
referencing this with the readout from the rollers. It will probably only cost you a drink and is totally accurate 
James, Do the brakes get better when hot? Pad compound is another factor and on a light car such as yours you want bog standard pads for max cold
performance unless you are hooning round a track.
[Edited on 21-9-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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lsdweb
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| posted on 21/9/07 at 05:03 PM |
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Hi Raz
It definitely does work! And it's totally independent of what the system is. All it does is measure how much effort it takes to turn the wheels
when the brakes are partially applied - much the same as an MOT.
I probably didn't explain it very well though!
Also, there aren't many MOT stations that will / can take a single seater :-)
The MOT station would be my choice as well!
Wyn
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jollygreengiant
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| posted on 21/9/07 at 06:32 PM |
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quote:
Originally posted by RazMan
He will have a pressure sensor that is placed between foot and pedal - referencing this with the readout from the rollers.
[Edited on 21-9-07 by RazMan]
I spent quite a few years Doing MOT test and I NEVER came across a pressure sensor pad in any MOT station.
Specialist sports car testing station might have one but not an every-day run of the mill testing station. They are only interested in pushing
MOT's through.
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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rusty nuts
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| posted on 21/9/07 at 06:41 PM |
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The only pedal pressure devices I have seen in 40 years in the motor trade was at the technical college I attended and the one at the SVA test center
when my car was tested.
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RazMan
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| posted on 21/9/07 at 09:06 PM |
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Ah, it could be just my MOT guy then - he tends to be a bit nerdy about his gadgets 
Mr SVA will certainly have one though, but he might not be too happy about adjusting the bias bar during the test (mine was ok though)
In any case the brake tester machine thingy is the best way to set up a bias bar, even without a pressure guage on the pedal - you can judge the
pressure applied fairly well and tweak accordingly.
[Edited on 21-9-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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