parking brake 'worn'

How many miles on the car? Have you replaced rear brake shoes yet? It may be as simple as adjusting the adjusters in the rear drums a little tighter. I just changed my rear shoes after 180k miles and after adjusting them, I have a perfect parking brake again. It was barely working before.

dave

 

Apparently you neglected the rear brakes and never had them adjusted, thus the lack of engagement now.

You want the rear brakes throughly inspected and cleaned. This should involve removing the rear wheels & brake drum. Inspection of rear drum (replace if below minimum diameter/thickness, stamped on the drum itself, or out of round, or may be possible to machine). Inspect rear brake shoes for minimum thickness (replace if below the factory specs) or if the wear is very uneven, which may be your case. Inspect rear brake cylinder for leaks.

If the rear brake shoes need to be replaced, they will likely have to bleed the rear wheel brake cylinder b/c the brake shoe piston will likley get moved unintentionally; this is fine and not an issue as long as the rear brake lines are bleed to remove the air that was just introduced, and the various ABS codes cleared. All will be well and the brakes will feel normal at the brake pedal.

Maybe $50-$75 for a through inspection and adjustment. Make sure the wheel and drum are removed.
If the rear brakes need to be replaced, maybe $300?

You really need to call and ask. Each shop/dewler and zip code has differnt labor rates: some charge a lot, some charge average, some charge low.

Working rear brakes are good to have in case of complete brake system failure. Low probability, but Murphy exists for a reason.

 

Second gen Prius has rear drum brakes. When you apply the "parking brake" all that's happening is a cable is tensioned, mechanically engaging the rear brakes. The rear's have auto-adjustment, keeps the shoes just clear of the drum. I'd suspect the subtle effect is just the parking brake cable having a bit more play/flex.

Do periodically have both the front and rear brakes inspected and lubed though. For DIY of the rear drum brakes, you would pull off the brake drums*, blow the dust out, check the shoe thickness, drum inside condition, and lube the (3) contact points between the shoes and the backing plate. That's about it.

* That can be a fight. Typically there's a pair of threaded holes on the drum face. They're there so you can screw in a pair of M8x1.25 bolts. You just keep turning them in, one then the other, and eventually the drum will pop free.

 

I should mention that the rear brakes are self-adjusting by design, so as long as they are working as designed, you shouldn't ever find them out of adjustment, or need to adjust them manually, until such time as the linings are worn out.

But one key point is: the self-adjustment depends on you using the parking brake regularly. The adjust mechanism has a kind of ONE-TWO action, where ONE happens every time you put the parking brake on, and TWO happens the first time you step on the foot brake after letting the parking brake off. Each ONE-TWO reduces the lining clearance by some tiny amount, like 0.03 mm but don't quote me here.

If you aren't in the habit of using the parking brake every time you park, it is possible this just hasn't happened often enough to keep up with brake wear. Assuming the adjusters aren't stuck, you can catch up without even taking anything apart, just by repeating (apply parking brake, release parking brake, apply foot brake, release foot brake) a bunch of times, though bystanders will wonder what you're doing.

If you listen closely enough, you can hear one faint click on each one of those cycles, until you stop hearing it when the proper adjustment has been reached.

But yes, if they've not been checked for a while, or have been acting out of adjustment for a while, it is worth opening them up for a look. Driving with the parking brake on can leave a hard, smooth, glassy surface on the shoe and drum surfaces, reducing braking effectiveness. If it's not too severe, a few minutes of elbow grease with 150 grit sandpaper can bring back the dull smooth surface you want.

-Chap

 

While the Gen 2 had rear drums in North America, I think it had discs in some markets and the OP has no info about where he is. (It always hurts our ability to help, to not tell us where you are)

 

Coyote's are from the States?

 

I have doubts about the shop OP goes to.
1) If the car was truly being serviced and critical items checked, the OP would not be here reporting the parking brake does not engage.
2) Aggresisve driving is subjective. What is not subjective is the regenerative braking system doing the bulk of the braking, which is why many people get welll over 100K miles on the original brakes. Given the current lack of rear parking brakes, this implies lack of inspection to me. I would not be surprised if the front caliper pins have not been lubricated either, which would explain the need to replace the front pads so early: one of the pads on a sticking caliper has worn down unevenly and prematurely. What is the current amount of front pad material left? A new pad will have 10mm of brake material. Factory specs is to replace when it hits 1mm. So this "excellent" shop measured the pads and indicated it is close to 1mm, say they measured it to be 2.5mm? If it was 2.5mm, you could still go further, if you wanted to, but nothing wrong to change now.

Why are you not getting your car serviced by Art's Automotive (Berkeley) or Luscious Garage (San Fran)? I sincerely doubt regular service by these shops would have allowed the rear parking brake issue to manifest.

 

Yeah if I see 2.5 mm remaining I would replace, it's like near-bald tires. The remaining material starts to flake off, and the wear can be uneven, ie: even thinner in places.

 

Forgot to clarify. The reported braking material thickness should always be reported as the thinnest spot.

Never experienced flaking. But then never ran pads/shoes that low.

 

It is your car and money. Spend how and where you deem fit.

My only concern, which is based on very little information and making assumptions, is that if the shop was servicing your car regularly, the brakes (front and rear) should have been a check item, with the rear shoes getting adjusted, as needed. Essentially regular service should have caught the excessive slack in the parking brake pedal travel and inability of the parking brakes to hold the car when in D/B or R, w/ no or very little gas pressure,

Regen does the bulk of braking. Pads supplement regen, as required, say in a panic stop. If "normal" driving and "normal" pressure applied to the brake pedal, likely only regen is used. Speeds at 7MPH and under, regen ends and hydraulic brakes take over. This is why brakes last a ridiculously long time with the Prius and likely all of Toyota's Hybrids.

I hope you were using B mode when going down hill, vs D and hitting the brakes a lot. Perhaps this may have contributed to your brake pads having a short service life.

 

There is a limit to how much power the battery wants to accept, so at high speeds you can also use friction braking. You have more energy to burn off than the battery can accept.

Below about 7 MPH the motors are spinning too slowly to regen effectively so you use friction braking.

This is rare for most of us, but if the battery ever 'fills' to the point it does not take more charge, regen stops and the friction brakes may be aided by engine braking. (you can force this with B, if you know the hill is so long you will 'fill' the battery)

Panic stops are friction braking, so it uses all 4 wheels. Regen is just the fronts.

 

That's not typically the way self-adjusters work. Normally self-adjusters operate when the car is in Reverse and then stopped from about 3 - 5 MPH. This action forces the brake shoes to hit the stops backwards which operates a small screw-like device to expand thus pushing the shoes closer to the drums. The click you hear is a locking mechanism engaging as the screw advances. Several stops in Reverse might be required to let the self-adjusters fully engage; as you said, each click is only a small adjustment and each stop advances only 1 click.

 

You are unlikely to get a long enough down hill except the Sierras and the Rockies,

 

It is how the Prius rear drum brake self-adjusters work, though. Toyota has used drum brake adjusters of both types in different vehicles and years. In the Toyota training literature (available under the Library tab on techinfo), the kind you are describing are called "reverse-travel adjusters", and the kind in the Prius are called "parking-brake adjusters".

The mechanisms look similar, except for the location of the strut and adjusting screw. In the reverse-travel type, the strut and screw are low, acting on the bottom ends of the shoes. In the parking-brake type used on the Prius, they are high, acting on the tops of the shoes, just below the hydraulic cylinder.

You can easily pop the drum off and see which type the Prius has. You can also easily watch how it works ... as it doesn't require the car to be moving, and only depends on alternate motion of the parking strut and the hydraulic cylinder, it's pretty easy to see it do its stuff.

-Chap