High Brake Pedal Pressure

[MCRacer]

I put new Porterfield shoes on for this year and did what I believe was a proper bedding procedure. On track it seems I need an inordinate amout of pedal prerssure. The stopping power is OK but even "standing on" the pedal I never locked a wheel (and I don't think I'm that good!) I was hoping for a decrease in pedal pressure over the previous shoes but there is little if any change. So should I be looking at brake lines (have flex only in front, flex from MC to hard lines rear), master cylinders (using Girling 5/8 front and rear) or a leg press machine?

Thanks
Mike
Caracal D

[tiagosantos]

Were the drums brand new, or did you have them turned before bedding in with the new shoes? Also, have you checked that the shoes are making contact with the drum all around? I hear that there are different sizes for shoes to match new or oversized drums, so maybe your shoes are only touching either at the tips or in the center..

[brian]

Tiago has made some great points but could you tell us what type of shoes you were using before?

[MCRacer]

Previous shoes were Carbotech. The drums are old but I had them turned and measured. Porterfield radiused the new shoes and they matched the drums fairly well but not perfect - just barely off on the ends. Perhaps that's the issue.

[Bob Posner]

When I had a Caracal with the stock VW pedal cluster I had to change the pedal fulcrum point to decrease the required pressure. Couldn't lock a wheel and it became like power brakes with the change. Added an inch or so to the pedal stroke.

[MCRacer]

Bob, Did you move the bias bar tube downward?

Mike

[hardingfv32-1]

I have found that the Porterfield shoes do not have the same grip level, but they do wear better.

Brian

[Bob Posner]

As I recall the result was to lower the pushrod that also leveled the stroke from what had been misaligned originally. Tiago has this car and maybe could send you a pic.

[tiagosantos]

My brakes are sort of taken apart at the moment, but I can try to take a picture tonight. I'm not sure if they're still the same as when Bob had them - The previous owner relocated the whole pedal assembly, so I don't know if he might have affected what Bob was mentioning..

[sharplikestump]

Several good points here, and while I realize this thread is from some time ago, it is also a very common problem...........so:
Lowering and aligning the rod as Bob stated can make a big difference. Good alignment is obvious, and lowering the attachment point on the pedal increases your leverage. What I will add is that it is critical that at full force, the pedal be just slightly back of vertical when testing. The reason I like it slightly back is for two reasons: First, there is always going to be some wear during the race or weekend. Also, the pedal always travels slightly further when the wheels are rotating. Whenever the pedal is allowed to travel past vertical, your braking forces plummet.
Mike P.

[MarkP-2]

Mike,

I have the opposite problem! Both my son and I continue to lock up the front right at Nelson Ledges turn 12
and Beaverun's turn 10, to the point that were almost cording the tires. I've tried the following since obtaining
the car (the previous owner had a similiar problem) ....

1.) Had the drums turned
2.) Replaced the brake wheel cylinders on both front wheels.
3.) Changed the brake drums with other used turned brake drums.
4.) Flex lines from the master cyl. to drums.

** The brake pads are carbotech and the brake pedal is at the 2 o'clock position when stationary (leaning towards the driver).

**Any thoughts on switching to a different size master cylinder or other brake lines etc??

Thanks!

Mark

[brian]

Let me start from the beginning of what I'd do. If I sound redundant, I apologize.

1. Make sure the shoes and drums are free of grease. I use break clean everytime I handle shoes.

2. If, and it's not likely, you have mastercylinders under 5/8" they may be too sensitive. If the master is too large, it will reduce the foot feel on the pedal and keep you from being able to modulate the brakes. Most vees are somewhere between 5/8 and 3/4. Make sure you have front wheel cylinders on, the front wheels. They should be 22mm id. The rears come in two sizes, 17 and 19 mm.

3. Check the backing plates to make sure the shoes are straight, relative to the drums. A cocked shoe will tend to grab. Place the shoe in the drum and confirm that the radius of the shoe is close to the radius of the drum.

4. Confirm that your rears are working. I use a ratchet lock tie down on the pedal to crank down until the fronts won't turn and check to see if the rear drums are dragging. If the rears are free, you may have to adjust your bias on the pedal. Make sure the bias beam assy is free and there is clearance between the tube and clevises.

5. You could change the position of the pedal and move the starting point up to 1 oclock.

[sharplikestump]

Using a ratchet-lock tiedown to induce pressure for setup....never thought of that...What a great idea! Thanks Brian.

Mark, assuming that you have the proper adjustor screws all around, W/O pulling a nose, (or several) I would be guessing, so maybe others can chime in and help here, but that will make a difference.
Also, is the locking problem consistant, or is is more prevelant when you first hit the track? With the Carbo's, I have seen that the fronts heating up to operating temps before the rears would cause them locking up prior to the rears coming in. If that is the case, try working the brakes harder on the pace lap. Might shorten the life of the front shoes/drums a bit, but it made a difference for me, especially during the first lap.
Mike P.