PBR parking brakes

Just wanted to share a few observations from mucking around with my parking brakes.

My CAV has PBR parking brake calipers set on the front side of the rear discs. These calipers are floating calipers and come from (I believe) certain GM cars of the 90's (transam? corvette?). In any case, diagram is below and they're a decent design.

Essentially, they are self adjusting. There is a brake pressure port at the back side which pushes a piston against the back side of one of the pads when the brakes are applied, and a mechanical lock is applied via the parking brake cable. The cable attaches to a pivot arm which is connected to a metal ring wrapped around the shaft of the piston. When the cable is applied, the pivot arm extends one side of the ring which then binds/clamps/locks on the shaft and extends the shaft further providing a lock on the disc. It's not very intuitive when you look at it. You actually unscrew the adjuster screw to increase the throw.

That all works fine, except that part of the back side of these calipers had been machined off on my car. This meant there's no port for brake pressure (or a bleed port). I imagine this was done so that the p-brake caliper clears the shock/spring without interference. Because there's no port for brake pressure this means that these calipers are basically NOT self adjusting, and need to be adjusted with shims or new pads when the old pads wear. I'm not sure if all/many CAV came equipped this way, but mine did.

I a) made a shim to go behind the outboard pad, b) ordered some new pads from online, and c) adjusted the adjustment screw outwards (to increase the locking travel of the pivot arm).

These calipers are a bit of a compromise obviously. Does anybody know of a nice elegant/simple mechanical locking parking brake I might use instead?

Thanks.
 

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Peter Delaney

GT40s Supporter
Cliff, this all looks very much like my PBR rear brake setup which is from an '88 C4 Vette. I'm guessing that your setup is used for park brake only (given no brake pressure port), whereas I am using the whole assembly for both normal rear hydraulic disk brakes & for the park brake feature.

I would have to say that the park brake feature on these calipers is less than satisfactory (being kind). To pass the rego tests here, you have to have the park brake hold the car on a 17deg slope for 5 minutes, & the max brake lever pull is 35lbs. Mine just made it, with a huge pull of 34lbs ! The problem seems to be that so much force is required to get them to work ok, & that huge force causes some cable stretch.

This then gives you 2 problems :

- Its hard to find a handbrake lever which has enough leverage for the job, and enough cable travel (I'm still looking for one).

- Over time, the cable stretches permanently, so repeated adjustments are required.

From what I understand, these park brakes are not viewed very kindly by the Vette brigade either - I am told that the earlier '84 - '87 setup was better (these had a "mini drum brake" inside the "hat" of the rotor). I had an '89 Vette & was not impressed by the caliper park brakes at all.

Not sure that any of this helps, other than to warn you not to expect too much from this type of caliper setup, even if its working "correctly" !

Kind Regards,

Peter D.
 

Julian

Lifetime Supporter
Does anybody know of a nice elegant/simple mechanical locking parking brake I might use instead?

Hispec out of the UK make a mechanical spot caliper designed to meet the rigors of the UK SVA test. They also have mechanical-hydraulic combos if you want a single caliper to do both. Great quailty and reasonable prices.

HISPEC Spot

The cheaper (and IMO inferior) US alternative is a Wilwood spot caliper (Designed for Karts)

Spot calipers - SummitRacing

or a better alternative made for the Pantera/Viper guys from IPSCO

IPSCO Mechanical Parking Brake Calipers
 
They also have mechanical-hydraulic combos if you want a single caliper to do both. Great quailty and reasonable prices.

HISPEC Spot

A friend has the combined Hi-spec caliper on his Pantera. It uses cables to actuate one of the hydraulic pistons in each rear caliper to serve as a parking brake.

He let a friend drive the car on a rally; the clown parked the car on an incline, set the parking brake, but left it in neutral? The next morning, they awoke to find that the Pantera had rolled backwards through the parking lot, missing an Aston Martin DB4 by about an inch, jumped a curb and went sailing into a hedge! It required a tow truck to extricate it. :veryangry:

The problem with hydraulic parking brakes is that as the fluid cools, they relax, and no longer hold the car. They also have zero function in the event of a loss of hydraulic pressure, so they don't meet the requirement for an emergency brake.

Just something to keep in mind....
 

Tim Kay

Lifetime Supporter
Search Mr Parker by Revolution Brake. I've recently installed a set. If you need further info or pics let me know. They are common among Pantera guys too.

Tim
 
Thank you gents, I appreciate the suggestions. Looks like there's some good ones to choose from. No big deal if I need to make an adapter plate - have a lathe and mill and some clearance to git 'er done.

Thanks again.
 

Julian

Lifetime Supporter
A friend has the combined Hi-spec caliper on his Pantera. It uses cables to actuate one of the hydraulic pistons in each rear caliper to serve as a parking brake.

He let a friend drive the car on a rally; the clown parked the car on an incline, set the parking brake, but left it in neutral? The next morning, they awoke to find that the Pantera had rolled backwards through the parking lot, missing an Aston Martin DB4 by about an inch, jumped a curb and went sailing into a hedge! It required a tow truck to extricate it. :veryangry:

The problem with hydraulic parking brakes is that as the fluid cools, they relax, and no longer hold the car. They also have zero function in the event of a loss of hydraulic pressure, so they don't meet the requirement for an emergency brake.

Just something to keep in mind....

Mike,

I'm not sure what part # your friend has, but a hydraulic handbrake will not meet UK SVA requirements for the reasons you state; no true e-brake upon hydraulic fluid loss. The Hi-spec SVA calipers use a completely independent handbrake pad and mechanical (cable) actuator, within the same caliper.
 
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