Bias Adjustable Pedal Boxes

[fetuhoe]

We have been making LHD and RHD Bias Adjustable Pedal Boxes for a few years.

The development process took a little time but we have had a stable design for several years now.

The manufacturing methods employed have involved the 'fitting' and adjustment of some parts and we felt it was time to refine this part of the process.

We have finally found time to fully model both boxes in 3-D CAD form and develop assembly jigs which will help us to make these parts more efficiently.

They are modelled after the SCRS type unit with cylinders inside the passenger compartment and have all of the features that would be expected on a well developed unit.



The brake pedals retain the same thickness as the standard pedals used by Porsche and the pedal faces are in the same position as the standard unit, not moved further away from the accelerator as is commonplace.

A Brake Pedal Stop is also used rather than using the pistons in the cylinders to stop the brake pedal which is often the case.

Over-travel stops are also fitted into the Bias Bar Mechanism which prevents the cylinders from bottoming out in the event of a hose failure on one of the braking circuits.

The base unit also fits directly into the floor pan of the car so fitting is reactively straightforward.

They are sold on an exchange basis and all of the hardware needed is refurbished and bronze bushes fitted throughout.

[604carsten]

Price would be nice..

[sladey]

Also are these limited to certain years? Mines an 87 G50 car and I know my pedal box is different to the earlier cars

[fetuhoe]

Price will vary a little depending on Master Cylinder Type.

Basic unit £750.00 exchange with fill lines, AP Racing Reservoirs and fitting kit.

[fetuhoe]

Also are these limited to certain years? Mines an 87 G50 car and I know my pedal box is different to the earlier cars

I think that the hydraulic clutch cylinder would be an issue with this basic design but I think I can find a basic pedal box and see what can be done.

[Darren65]

.....AP Racing Reservoirs.....

I'm doing the same to mine and was asked recently if I'd like AP or Girling master cylinders......I'm told that Girling have a more period look, is there any advantage going with AP?

Cheers,

[fetuhoe]

The AP Cylinders are significantly more expensive but are very good quality. The one thing I don't like about them is that the cut off is individually set so they can't really be rebuilt easily if there is a problem.

The RSR and SCRS always used Girling which are certainly less expensive and seem to work just fine.

We have Girling on Bias Pedal boxes since the Eighties and never had an issue.

[Darren65]

Thanks for the reply.....I'm told the AP cylinders have a better feel.

Cheers,

[fetuhoe]

Thanks for the reply.....I'm told the AP cylinders have a better feel.

Cheers,

???? - I would have thought caliper seals, brake fluid and pads would be much more significant and I have never really noticed any difference.

[Darren65]

Thanks for the reply.....I'm told the AP cylinders have a better feel.

Cheers,

???? - I would have thought caliper seals, brake fluid and pads would be much more significant and I have never really noticed any difference.

....interesting...the feel comment came from Tuthills I believe and was along the lines of Girling having a harder, more race type feel....

...information is second hand though and I could be wrong.....I often am!

Thanks for your comments

[fetuhoe]

Darren,

pedal feel/compliance is a matter of preference. The larger the master cylinders the shorter the pedal travel and the harder you need to push.

This is really an issue between the 'Pedal Ratio' and the hydraulic advantage.

A typical Tuthill pedal box seems to be supplied with 2 x 0.75" Master Cylinders which means for a given stopping force using standard calipers you would need double the pedal force. This assumes that the balance bar is set in a null position.

The standard cylinder diameter on an early non-servo car is 19mm diameter and as the Bias Bar is a simple Class 1 lever it is easy to see why the pedal force doubles. A Tandem cylinder acts in series so the force needed does not multiply when you change from a simple single acting cylinder.

2 x 0.75" cylinders will give a very short travel and a very hard pedal.

If you reduce the area of each cylinder the travel will increase and the pedal effort will reduce.

I have always found it beneficial to have some pedal travel when attempting, often unsuccessfully , to cadence brake so we generally tend to fit a smaller pair of cylinders.

As the Appendix K does not permit the 'pedal pivots' to be altered there is not much that can be achieved by changing the pedal ratio.

We have tired to achieve a braking effort/decal of around 65kg pedal force for 0.5g decal and have made measurement using a load cell and a Taplow and we are very close to our targets.

I have to say that I fail to understand how two cylinders of the same size give very different amounts of feel unless there is a huge difference in seal stiction and this seems a bit of a stretch.

As the mounting for Girling and AP Cylinders is identical we can and do supply AP when requested but all in all most of our customers have been happy with Girling but we have only delivered around 30 units.