Rear Brake Pad replacement

[mac 108]

I have a 92 AWD without ABS. I started to replace my rear brake pads, but I can't get the piston to turn like the Haynes manual describes. What can I do?

 

[1GawdJunkie]

You should simply be able to insert a pair of needle nose into the caliper piston, the two recessed triangle and turn clock wise. with the cap off the brake reservoir this should be fairly easy. I had a problem with my passenger side locking up, the pads on the locked side were twice as thick as the working side.

 

[Steve_P]

for ~$10 you can buy a generic tool at most auto parts stores like they show in the manual to screw the piston in. They are pretty hard to turn w/o the proper tool IMO.

 

[steve]

I don't think the generic brake cubes work in our calipers because the edges of the cube hit.
Here's how I did mine. I bought the tool at Sears about 20 years ago.

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Steve

 

[Dream On]

Or go to Autozone, rent the tool, then take it back and get your money back. We had this same problem on my friends 94 AWD.

 

[mac 108]

i took the one off of my eclipse GST, it took no effort to turn it, so I bought a new caliper

I had even taken the brake line off of the AWD caliper, and it wouldn't turn.

 

[justin0469]

I have a 92 AWD without ABS. I started to replace my rear brake pads, but I can't get the piston to turn like the Haynes manual describes. What can I do?

Unless something is different with older pistons, if you just need to press the piston back in to make it fit over the new pads, you can buy a tool specifically for that at autozone for like $7

From reading other responses though, it seems like the piston needs to be screwed in, I dont want to jack the thread but why do they need to be screwed in vs pressing in like modern caliper pistons?

 

[VelocitàPaola]

These types of pistons utilize a different mechanism altogether than the ones found on 2g's. Rather than having hydraulic pressure/cable actuation (the e-brake) simply expand the piston axially, these still expand axially while braking, but via radial movement along a series of threads (i.e. similar to a screw) while the e-brake is in place. In order to get it to return to the original point, the piston needs to be screwed back in, which usually requires a special tool, although I've been able to ghetto-rig the tool when in a pinch.

Despite the fact that these are found on 1g's, neither style is particularly "newer;" I've seen both styles of rear disc brakes on many cars.


I found that cracking the bleeder valve often helps when screwing the pistons back in.

EDIT: Sorry about that; I was a little unclear. It's fixed now though.

 

[carwizard1]

Is your e-brake on?

 

[mac 108]

no, even if I hadnt completely disconnected the cable, it would be impossible to get access to the piston with the cable in place

 

[DevilSperm]

I ended up going to a mechanic and asking him to use his tool because my e-brake mechanism was stuck for apparently a REALLY long time. The passenger side one went in just fine with some large vise grips and a thick rag I dont recommend doing that though. Try to find the tool that steve posted.

 

[justin0469]

These types of pistons utilize a different mechanism altogether than the ones found on 2g's. Rather than having hydraulic pressure simply expand the piston axially, these expand axially via radial movement along a series of threads (i.e. similar to a screw). In order to get it to return to the original point, the piston needs to be screwed back in, which usually requires a special tool, although I've been able to ghetto-rig the tool when in a pinch.

Despite the fact that these are found on 1g's, neither style is particularly "newer;" I've seen both styles of rear disc brakes on many cars.

So since hydralic pressure cannot provide a rotating motion obviously, like you said, how does the motion of pressing the pedal change into rotating motion, and releasing rotate the other direction? The only thing I can think of is some type of fan or gear shaped part that rotates with the pressure? Doesn't seem right...

 

[steve]

The piston doesn't turn in normal operation. The threaded rod is the actuator for the parking brake. It's self adjusting. When you apply the service brake the piston moves out under the pressure of the brake fluid and internally it freewheels on the rod. When you pull the parking brake it rotates a cam that pushed the adjuster rod out compressing the piston, pad, and rotor.

Here's the various parts. I had to strip them down because water got in the Parking Brake and rusted the needle bearing the cam sits in. You can just see the open bore for the cam behind the piston bore on the caliper.

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Looking down the piston bore the adjuster is held in place by a c-clip in the bottom. The piston then threads down the adjuster.

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Steve

 

[justin0469]

So unless the parking brake is engaged, it is not threaded out, it is just under hydralic pressure? What I got from what you said is that only the parking brake extends and retracts the piston via threading.

 

[steve]

I'm not sure how to explain.

As the pads wear the piston extends. They don't retract all the way back in but just back off a little.

The threaded rod is the self adjuster for the parking brake actuator. When you use the parking brake it doesn't cause the piston to thread. It turns a cam that pushes the rod straight out the small amount needed to clamp the rotor.

The piston threads on the rod during normal braking. The part inside the piston that threads on the rod is what turns. The only time the piston turns is when you thread it back in. The pads usually have little nubs that fit into the spots on the piston so it can't rotate

These are called integrated parking brakes. The 2Gs use a drum in disk parking brake that actually has more parts than this.

Steve

 

[justin0469]

I'm not sure how to explain.

As the pads wear the piston extends. They don't retract all the way back in but just back off a little.

The threaded rod is the self adjuster for the parking brake actuator. When you use the parking brake it doesn't cause the piston to thread. It turns a cam that pushes the rod straight out the small amount needed to clamp the rotor.

The piston threads on the rod during normal braking. The part inside the piston that threads on the rod is what turns. The only time the piston turns is when you thread it back in. The pads usually have little nubs that fit into the spots on the piston so it can't rotate

These are called integrated parking brakes. The 2Gs use a drum in disk parking brake that actually has more parts than this.

I think I got it. Still just not understanding how pressing the brake rotates the rod to push out the piston. If the brake system still requires fluid, some part of it has to be hydralic.

These are called integrated parking brakes. The 2Gs use a drum in disk parking brake that actually has more parts than this.

I noticed that my GST has braided lines for the parking brake, like what you would see on a bicycle or something but when I look at the caliper, I see only the hydralic line.


I suppose it doesnt matter all that much since I've never messed with a car that didn't have disc brakes that worked completely off of hydralic pressure. Just for my own knowledge. Thanks for takin the time.

 

[VelocitàPaola]

I think I got it. Still just not understanding how pressing the brake rotates the rod to push out the piston. If the brake system still requires fluid, some part of it has to be hydralic.

Pressing the brake [pedal] does not rotate the rod; Pascal's law simply takes effect to squeeze the piston up against the rotor via hydraulics.

The only time the rod rotates is when the e-brake is pulled (which is based off of a cable actuation system); when this happens, the whole piston assembly permanantly (until you change the pads again) moves closer to the surface of the rotor.

Brake pads and rotors require a very small gap between them. If it is too large, you would have to pump the brake pedal to get any braking power.

By pulling the e-brake cable, and subsequently moving the whole piston closer to the rotor as the pads wear down (just as Steve said), you keep a consistent gap between the pads and the rotor. I've actually seen it recommended in owner's manuals to set the parking brake once or twice a month, if you don't normally, just to keep your rear brakes working as efficienty as possible.

All brakes require hydraulics to operate normally, but it is required that a secondary braking mechanism be present too; hence the cable actuated e-brake.

 

[justin0469]

OK, between all that I think I have a good enough idea whats goin on. Thanks!

 

[steve]

Pressing the brake [pedal] does not rotate the rod; Pascal's law simply takes effect to squeeze the piston up against the rotor via hydraulics.

The only time the rod rotates is when the e-brake is pulled (which is based off of a cable actuation system); when this happens, the whole piston assembly permanantly (until you change the pads again) moves closer to the surface of the rotor.

I don't think this is correct.

When you pull the parking brake the cable pulls a lever attached to the cam. The cam in turn pushes a short link rod, the other end of which, rides in a cup at the base of the threaded self adjuster rod. The piston is threaded on the self adjuster rod as we've discussed. This is what converts the pulling of the lever to the in and out of the piston.

There is little to no rotation of the self adjuster rod in this movement.

When you use the normal brakes the piston moves in and out as described. In doing so it moves up and down the self adjuster rod.

The part of the piston that threads on the self adjuster rod isn't fixed inside the piston so it spins as the piston moves. It's a somewhat one way ratchet that allows the piston to move up but not down without the piston turning.
It has to allow a little reverse travel to the piston can back off the pad during braking but not allow the piston to move down the self adjuster rod when the parking brake is actuated.

In the picture of the parts. the self adjuster rod and related parts are in the upper left starting with the rod link next to the caliper, then the self adjuster rod, a retaining plate, spring and spring holder, and last the c-clip that lock the plate and spring down.
You can imagine that the plate holds the self adjuster rod from turning but allows it to move up and down against the spring. I don't have any good pictures of how the piston threads on the self adjuster rod.

Below that is the piston and under it the cam and lever that attaches to the parking brake cable. in the upper end of the cam you can see the "cup" the link rod sits in. As the cam turns the link rod moves up and down.

If you look at a 2G rear brake what you'll find is two brakes. The caliper, pads, and rotor for stopping (service brake) and a mechanical drum brake with shoes that fits inside the hat of the rotor (Parking brake).

I think we pretty much covered this.

Steve

 

[VelocitàPaola]

I don't think this is correct.

When you pull the parking brake the cable pylls a lever atached to the cam. The cam in turn pushes a short link rod the other end of which rides in a cup at the base of the threaded self adjuster rod. The piston is threaded on the self adjuster rod as we've discussed. This is what converts the pulling of the lever to the in and out of the piston.
There is little to no rotation of the self adjuster rod in this movement.

You're right. I didn't mean that the rod rotated; I don't know why I said that it does...