MoTeC Global Forum

Why would a pedal box do this? Any Ideas what could be wrong?
Single seater with push master cylinders

Is it repeatable?

Sure is. All of them not identical, but repeatable yes.

See the rise of the rear pressure first....if you give it only a little bit of pressure this happens....

What are the ratios from master cyl bore to caliper bore(s)?

The rears will usually have a lot less caliper bore.

Also you may be seeing a lot of caliper flex, especially when hot.

Scott@FP wrote:What are the ratios from master cyl bore to caliper bore(s)?

The rears will usually have a lot less caliper bore.

Also you may be seeing a lot of caliper flex, especially when hot.

I can find out what the ratio is, but its all fixed throughout the series.
All calipers are the same, front and rear identical, whole series the exact same.

Should I find out the ratios in any case?


Do you think that the caliper casing might have gotten damaged and is now flexing?
(Have tried swopping front to rear, same problem)
(put new seals in the masters as well)

Diameter of master cylinders are the same? Bigger one should be connected to the rear calipers.
If there is a single master cylinder then closer one to the push rod must be connected to the front calipers.

Mazi wrote:Diameter of master cylinders are the same? Bigger one should be connected to the rear calipers.
If there is a single master cylinder then closer one to the push rod must be connected to the front calipers.

Master cylinders are different in size, and yes the bigger diameter is to the rear.

The problem is that it was always okay, and something change but I cant tell what. Any suggestions what kind of failure could cause this?

Martin wrote:

Mazi wrote:Diameter of master cylinders are the same? Bigger one should be connected to the rear calipers.
If there is a single master cylinder then closer one to the push rod must be connected to the front calipers.

Master cylinders are different in size, and yes the bigger diameter is to the rear.

The problem is that it was always okay, and something changed but I cant tell what. Any suggestions what kind of failure could cause this?

Just some thoughts...
Something binding in the MC would likely cause the pressure to go up slower and come down slow relative to the front.
Especially at light pedal action.
I am thinking corrosion of the pistons or seal issue.

Some binding in the balance bar assembly might be more likely.
Have you taken it apart and checked that the joints freely articulate?

What about different pad material front to rear.

Pad/caliper issues could be isolated by fitting aluminium spacers in place of the pads.

Steve

When the brake pedal is pressed hard is the bias bar at 90 degrees to the pushrods in the cylinders? It should be, if not try adjusting the pushrod lengths to achieve this. Is there some free sideways movement in the bar when at rest, maybe 2 or so mm?

If you didn't have data logging you would probably not be worrying yourself about this, does it actually manifest itself in braking feel or performance?