Park Brake Mechanism

SliceOfLife · #1 (**permalink**) 07-23-09, 02:28 PM

While I've got the LR hub off, I thought I might address the park brake issue this car has had since I bought it 3 years ago. It has never worked. It was originally stuck down. When I was replacing the ignition switch last year I operated the little yellow lever to release it. It didn't spring back, as I was warned it would. So I figured it wasn't working somewhere else and left the pedal up.

Looking at the caliper now, I see the little coil spring is rather rusty, and I wonder how easy it should be to work it. I de-coupled the front part of the cable from the rear ala the FSM before I took the caliper off. The cable end at the caliper has about 6 inches of spring wrapped around it. Shouldn't I be able to pull on the caliper end of the cable, since it's disconnect at the coupler and get some amount of movement? It seems frozen in its sheath.

To get the caliper off I was supposed to be able to get a C-clamp on it but I couldn't see how. Luckily, it turned out not to be necessary to compress the piston to get the caliper up. But I wonder about the warning in the FSM to not compress the piston more than 1 mm, or else the park brake mechanism could be damaged.

Can anybody tell me what's up with this?

**Ranger** · #2 (**permalink**) 07-23-09, 05:51 PM

Quote:

It seems frozen in its sheath.

THAT is usually the problem. It's rusted in there and that is why it will not release. Not sure I am understanding about the piston as it must be turned in in order to replace the pads.

SliceOfLife · #3 (**permalink**) 07-23-09, 06:09 PM

Quote:

Originally Posted by Ranger

THAT is usually the problem. It's rusted in there and that is why it will not release. Not sure I am understanding about the piston as it must be turned in in order to replace the pads.

The cable sheath is plastic, so what would it rust to? Your piston comment confuses me, too. The piston goes in and out, right? I had to rotate the caliper upward after removing the bottom pin bolt because the top pin bolt is part of the caliper. Is that where you're thinking of "turning" going on? Are you saying the piston needs to turn within its cylinder? I'm just trying to get on the same page with ya, Ranger.

**Ranger** · #4 (**permalink**) 07-23-09, 10:07 PM

I think that plastic sheath might have a steel liner.

The piston has to extend, just like the front caliper, but unlike the front, you screw it in as opposed to compressing it with a C clamp.

SliceOfLife · #5 (**permalink**) 07-23-09, 11:07 PM

Quote:

Originally Posted by Ranger

I think that plastic sheath might have a steel liner.

Ok. That makes sense. I guess about all I can do is try to work it back and forth. Maybe it'll free up.

Quote:

Originally Posted by Ranger

The piston has to extend, just like the front caliper, but unlike the front, you screw it in as opposed to compressing it with a C clamp.

You gotta be pullin' my leg, Ranger! You're really throwing me for a loop here. FSM 5-102 says compress with a C-clamp; nothing about any screw action. Are you telling me the book is just whacked?! The piston is barely visible, let alone accessible. How could it be rotated in the cylinder by a service person? And during operation the friction of the lip of the piston against the back of the brake pad would be ridiculous, it seems.

Unless...it only works like a screw when it's mechanically operated in park brake mode. Then when the park brake is released it operates in normal hydraulic piston mode. So as long as that hefty little coil spring mounted on the caliper housing is un-sprung it should be in piston mode, if it's not been damaged? I'm still not so sure that makes much sense to me. I mean, why not just push on the piston mechanically in park brake mode? What's the point in rotating the piston? But I really hate the idea that the book is full of crap!

Can you help me out here, Ranger?

**Ranger** · #6 (**permalink**) 07-23-09, 11:20 PM

Did you see the NOTICE on 5-102 not to exceed 1mm of piston travel? I think that is just to free the clamping force and allow you to raise the caliper off of the rotor.
See page 5-97

SliceOfLife · #7 (**permalink**) 07-23-09, 11:41 PM

Quote:

Originally Posted by Ranger

Did you see the NOTICE on 5-102 not to exceed 1mm of piston travel? I think that is just to free the clamping force and allow you to raise the caliper off of the rotor.
See page 5-97

Yes, I asked specifically about that notice earlier in this thread. Thanks for 5-97. That's brake pad replacement, but it clarifies what you were talking about a little bit. But that page wasn't referenced in the rear hub replacement section, so it's probably not relevant to what I'm doing (the old pads look fine).

Thanks for hangin' in there with me. Sorry to be a pest.

**Ranger** · #8 (**permalink**) 07-23-09, 11:48 PM

These manuals are meant for factory trained mechanics. Not for guys like you and me so they do make some assumptions on the users knowledge. 5-97 is relevant only in our discussion about the piston. you are far from a pest. hope I was of some help.

SliceOfLife · #9 (**permalink**) 07-24-09, 12:26 AM

Quote:

Originally Posted by Ranger

These manuals are meant for factory trained mechanics. Not for guys like you and me so they do make some assumptions on the users knowledge. 5-97 is relevant only in our discussion about the piston. you are far from a pest. hope I was of some help.

You're always very helpful. Thank-you.

SliceOfLife · #10 (**permalink**) 07-27-09, 06:57 PM

Final update--I couldn't get the cable freed up. I did find a hole in the sheath just behind the caliper bracket that holds the cable. That's probably where the moisture got in. I left the cable end at the caliper disconnected. I need to replace the rear half of the park brake cable and the caliper, at some later date.

Thanks for your help.