Parking brake drag (Page 1/2)
1985 Fiero GT AUG 16, 08:15 PM
Ok, this is a weird problem I discovered with my dad's Fiero. It has always had a very loose parking brake lever, always able to go up to 90° easily.

Today I was bleeding the brakes, and had it on 4 wheel jackstands and realised that even though the parking brake was applied, and both of the levers on the caliper were being pulled by the cable, the right rear wheel wasn't locked up, at all.

So i tighten the lever 1/6 turn (remove lever, turn nut that connects to lever 1/6 turn so lever can be reinstalled in original position), now the parking brake actuates perfectly, evenly, and about the right amount, and both levers rest on the stop when parking brake is not applied.

Here comes the puzzling part, while the car is in motion that wheels brakes squeal a little bit, not enough to slow the car, just enough to rub the pad(s), and when jacked up that wheels brakes is applied just a tiny tiny bit,

I have verified everything else, and there seems to be no logical reason why that brake is dragging, but it is, so the two options that I have right now are either have the parking brake only work on one wheel or work normally but have that wheels brakes drag a tiny amount.

There must be some reason why this is happening, unless the mechanism inside the caliper is partially broken.

Thanks.
Patrick AUG 16, 08:49 PM

quote
Originally posted by 1985 Fiero GT:

Here comes the puzzling part, while the car is in motion that wheels brakes squeal a little bit, not enough to slow the car, just enough to rub the pad(s), and when jacked up that wheels brakes is applied just a tiny tiny bit.



There's a slight bit of drag on all disc brakes.

On one of my Fieros, the parking brake when released dragged a bit more on one side than the other. I installed a spacer to compress the return spring a little extra on the "tighter" side, and I can now sleep better.

Make sure all three(?) parking brake cables slide freely.

[This message has been edited by Patrick (edited 08-16-2023).]

1985 Fiero GT AUG 16, 09:11 PM
Yeah, I know all disc brakes rub, but this one is a little more then what I would consider normal, on a 4 km drive, that wheels brakes starts very quietly squealing (starts about 0.5km into drive), inaudible above about 70km/h (due to wind noise), and by the end of drive that wheel is hotter to the touch then the others, and that wheels rotor and caliper remain hot longer then the others. That leads me to believe it is dragging more then it should. The cables are also functioning perfectly normally, with the lever resting firmly on the stop whenever the parking brake isn't engaged
Patrick AUG 16, 09:39 PM

quote
Originally posted by 1985 Fiero GT:

...by the end of drive that wheel is hotter to the touch then the others, and that wheels rotor and caliper remain hot longer then the others. That leads me to believe it is dragging more then it should.



Now you're talking about a different kettle of fish. I suspect that one caliper is not gliding freely on its slider pins. Probably time to check all calipers and service them accordingly.
1985 Fiero GT AUG 16, 09:44 PM
No, it isn't that either, the caliper moves freely on the sliders, but the pads don't seperate enough, due to the parking brake being just a tiny bit to tight, the problem goes away when I rotate the nut the parking brake lever attaches to, but then for whatever reason the parking brake is entirely non functional on that wheel, so out of everything that one nut is what decides what problem the car has, either no parking brake action at all on that one wheel, or a parking brake that never fully releases
Patrick AUG 16, 09:52 PM

Okay, I suggest you disconnect the parking brake entirely and tie the car to a tree when not in use.

Maybe The Ogre will come along and offer some advice.
1985 Fiero GT AUG 16, 09:54 PM
Haha, good idea, yeah I have just left it to tight for now, as the car is rarely driven, so hopefully we can figure it out before anyone drives it next
Vintage-Nut AUG 16, 10:07 PM
Rear Brake Calipers: Piston Actuator (a.k.a. Parking Mechanism)

The mechanism has two pistons - outer piston which you can see and the inner piston which you can't see AND they must turn separately.

IF the outer and inner pistons aren't free or 'sticks', send the calipers out for service (a.k.a. rebuild)

Isn't a DIY job....
1985 Fiero GT AUG 16, 10:13 PM
Yeah, they are turning separately, as the outer piston is connected to the brake pad, and isn't turning, and the parking brake mechanism does rotate, which indicates that that isn't the issue either, somehow it isn't able to disengage fully, causing the pads to rub.
Vintage-Nut AUG 16, 10:27 PM
Piston Actuator

The inner bearings and thrust washers maybe sticking..

From The Ogre's Fiero Cave



Edit: This image is not exactly the same as an actual Fiero caliper.


quote
The Ogre's Fiero Cave - Hand Brake Operation
It is important to remember something about the piston guts... The ONLY parts that are used when the Hand Brake is applied are:

The Activator Lever on the back of the caliper rotates the Activator Screw.
The Activator Sleeve translates the Screw rotation into pressure on the inner and outer pistons.
None of the other parts in the piston are used during Hand Brake application. The other parts might be affected but are not actually part of Hand Brake the process.

So why doesn't it work?
The biggest problem seems to be that the two pistons bind up and the spring cannot overcome the increased friction. You can't see it well in the pictures above but the space between the pistons had some rust dirt and wear particles in there. In the caliper used for this article, the pistons were so stuck I put over 200 pounds (My full weight) on the screwdriver I inserted in the piston hole to get the inner piston out.

Another factor is the bearing. The bearing consists of three 1mm (Approximate) balls that corrode and go bad. It was a known point of failure and upgraded in the post recall, solid faced, pistons used on manual transmission cars. However I expect that the post recall pistons still don't work much better than the original one seen here. The larger issue is still the binding pistons, not a weak bearing.

[This message has been edited by Vintage-Nut (edited 08-16-2023).]