Rogthebandit
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| posted on 27/2/12 at 08:37 PM |
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Obp pedal box
Hi
I have been looking at many posts on here regarding dual brake systems. I see most people recommend 0.625 and 0.7 size cyl for the front and rear. I
was thinking about getting one of the obp sets of eBay. Has anyone else got one? Do you get a good feel on the brakes? I am running sierra discs on
the rear and probably be getting a set of wilwood (I think that's the name) for the front. I have a gsxr engine so I recon the car will be
evenly balanced.
Cheers
Rog
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Hugh_
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| posted on 27/2/12 at 09:12 PM |
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I have an OBP box 2 pedal with cable clutch floor mounted box which I bought about 3 years ago, now its all in I'm very happy with it, good feel
and certainly stops the car well. I did have some issues getting it in though, the bias bar and pivot wouldn't fit into the tube because of the
powder coating, nothing a file didn't sort. Some of the holes to secure it to the floor are (or were 3 years ago when I got mine) beneath the
pedal pivot bars which made fitting a nuisance. None of these issues were insummountable but having spent SO much money on it I didn't expect
to have to start modifying it.
edited to add: mine has Wilwood fronts, and 9" drums at the rear with the standard master cylinder sizes.
[Edited on 27/2/12 by Hugh_]
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karlak
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| posted on 27/2/12 at 10:01 PM |
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During the engine change I took the opportunity of replacing the Pedals (also went from Cable to Hydraulic clutch - which has been more trouble than
its worth I think ).
Anyway I bought the OBP "kitcar" set, which to be honest has taken a fair bit of fitting. I stupidly thought it would all fit nice, but
ofcourse that doesnt happen in kitcar world does it  . Pictures below show the pedal set I have and shows them mocked up in postion. I need to get
some updated photos of them fitted as well. This involved strengthening the install wih an extra bar welded across the footwell floor.
Pics,
MK Indy - 2litre Duratec - Omex 600 - Jenvey throttle bodies - ETB DigiDash2
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Rogthebandit
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| posted on 27/2/12 at 11:24 PM |
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Cheers for the feedback chaps. What cylinder sizes did you use? Also I wasn't sure about the clutch cable setup, does the kit come with a
standard fitting for a cable or is that also something you need to mod yourself?
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Hugh_
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| posted on 28/2/12 at 08:19 AM |
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Mine is standard masters cyl sizes (0.625/0.700). It doesn't come with any fittings and you'll even need to drill the pedal. I ended up
with an escort rs2000 clutch cable as being one of very few that had an eyelet on the end that could be bolted through.
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contaminated
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| posted on 28/2/12 at 10:44 AM |
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I looked into this in some detail a while back. I opted for the comp brake pedal box after I'd looked at the same offering from OBP. Very
similar actually, although comp brake was a bit cheaper and slightly neater for my installation. Thread on fitting it below. Sadly the photos on the
first page don't always load, but after that they are ok.
http://www.southernkitcars.com/forum/viewtopic.php?f=7&t=1253
[Edited on 28/2/12 by contaminated]
Tiger Super Six Independent
www.southernkitcars.com
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Rogthebandit
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| posted on 29/2/12 at 07:02 PM |
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Well I Have forked out £170 and got me sell a pedal box. It's only money. I have gone for the 0.7 and 0.625 cylinders. Should be a good starting
point.
Something I can't seem to get right in me head is having the set up with the 0.7 to the rear and 0.625 to the fronts? There will be great weight
on the front end, or slightly heavier than the back. So why would you use the greater size on the axle with less mass? Would this not make it lock up?
Can't seem to get me head round this, can anyone put this clear for me? 
Cheers
Rog
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karlak
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| posted on 29/2/12 at 07:11 PM |
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I was chatting to someone today about the cylinder sizes.
Got me thinking. These brake bias type pedals with the adjustable bar, why would you need to have a different size cylinder? Surely the
"bias" is dialled in using the adjustable bar on the brake pedal. So if you had identical cyclinders, just bias the bar towards the front
brakes etc ?
Not that I really know what I am talking about - lol 
MK Indy - 2litre Duratec - Omex 600 - Jenvey throttle bodies - ETB DigiDash2
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Rogthebandit
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| posted on 29/2/12 at 07:35 PM |
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Thats what I was thinking but I suppose the cylinder volumes must be suitable for the calipiers to provide enough fluid?
I am sure I will get it all to work? I hope
I believe you also need to wire the bias for the iva. Have to sure it's set up reef before that's done
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Cornishman
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| posted on 29/2/12 at 09:13 PM |
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Roger
I believe that the hydraulics work like this.........
Force (in Pounds force or Newtons) is applied to a certain AREA, i.e pounds per square inch.
So if you had 100 pounds of force on a 1 square inch cylinder it would give 100 psi line pressure.
If you had 100 pounds of force on a half inch square cylinder it would give 200 psi line pressure.
Therefore the smaller front cylinder will give greater line pressure for a given force applied.
The opposite is true at the slave end.
Regards
Steve
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Rogthebandit
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| posted on 29/2/12 at 09:52 PM |
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Steve
Ya I see it now, should have picked up on that my self really but sometime I have the blond moments.
Anyway that's grand and thanks for the explanation, very clear
If you look at if from the equation p=f/a and as you say if you reduce the effective area then you increase the pressure, ya penny has dropped
Cheers
Rog
[Edited on 29/2/12 by Rogthebandit]
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