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Obp pedal box
Rogthebandit - 27/2/12 at 08:37 PM


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.


Hugh_ - 27/2/12 at 09:12 PM

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_]

karlak - 27/2/12 at 10:01 PM

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.


Rogthebandit - 27/2/12 at 11:24 PM

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?

Hugh_ - 28/2/12 at 08:19 AM

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.

contaminated - 28/2/12 at 10:44 AM

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.

[Edited on 28/2/12 by contaminated]

Rogthebandit - 29/2/12 at 07:02 PM

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?


karlak - 29/2/12 at 07:11 PM

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

Rogthebandit - 29/2/12 at 07:35 PM

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

Cornishman - 29/2/12 at 09:13 PM


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.



Rogthebandit - 29/2/12 at 09:52 PM


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


[Edited on 29/2/12 by Rogthebandit]