Front Brake Pad Replacement Query

[slanej]

Hey all:

So I'm going to try doing some brake work for the first time on my 2000 Bonneville. I've looked at the online Chilton's guides from Carnegie Library, and I've watched a few YouTube videos on the subject.

Seems pretty straightforward. No special tools needed, and the parts are relatively cheap.

One thing I just can't get into this thick noggin of mine is using a C-clamp to compress the pads and/or cylinder prior to removing the caliper.

From what I've seen, you attach the clamp in such a way as to push the outboard pad inward. Doing so (so they say) should compress the brake cylinder in order to give me enough leeway to allow the caliper to be unbolted and slid upward, downward, or off completely, easily enough to replace the pads/retaining clips.

I suppose I'm just stupid enough not to understand this point; How does pushing the outboard pad into the rotor create the gap needed to remove the caliper? Is the inboard pad applied first and the outboard pad is a kind of backstop? Or am I completely off base?

Keep in mind that none of this is stopping me from actually DOING the replacement. But I'd like to know HOW the mechanics of the thing work before I start hogging up my brake system by squeezing the [expletive] out of 'em with a giant C-clamp.

Any lessons would be appreciated. Thanks in advance.

[CMNTMXR57]

The calipers on these cars (and most cars nowadays that don't use a "Fixed mount" caliper like Brembo's, Wilwood's, etc...) is a "floating" design. The caliper itself mounts to a caliper bracket with guide pins/bolts, which allow it to "float." Meaning it can move inward/outward based on brake pedal movement. So when you push on the brakes, the piston pushes on the inside pad against the disc, and for every action there is an equal and opposite reaction. In this case, the caliper, which glides (or "floats") on those guide pins, retracts inward more or less, causing the outside pad to also clamp on the rotor.

So when you use the c-clamp to push the outboard pad in, it's kinda doing the inverse, in effect forcing the caliper outward, and pushing the piston on the inboard side, IN it's recess a little.

Personally, I've only done this on a handful of cars when the brakes were REALLY bad. Like when there is zero material on the pads and it's metal backing plates grinding on the disc... in which case the piston was out of it's recess most of the way, causing very little play to work it loose. Otherwise, in most cases, it's usually more that rust/road grime is holding things together than anything else.

[MattStrike]

My preferred method - with these floating design calipers, is before even pulling or unbolting anything, is use a prybar to pull the outside of the caliper away from the rotor (first prying against the vents in the middle of the rotor and then as the gap opens up the wasted pad) - therefore compressing the piston back into the caliper fully first then pulling the parts. This works better with the dual piston calipers on the GXP, in my case the F-body calipers I have on everything...

[dougtoth]

One thing I found helpful when changing the pads is to remove the cap off the master cylinder.
That way the piston moves in easier.

[dougtoth]

One thing I found helpful when changing the pads is to remove the cap off the master cylinder.
That way the piston moves in easier.

[CMNTMXR57]

I do what Matt does. You should always remove the cap on the resevoir because when you push the piston back as you prep for the new pads, that pressure (it's a hydraulic system after all), could damage the cap.

[rustyroger]

Another school of thought is to loosen the caliper bleed nipple as you move the piston(s) back. then top up the reservoir as you pump out the new pads. The idea is to avoid sending dirty fluid back through the system.
When you pump out the new pads I suggest you only push the brake pedal around half way down, I have seen master cylinder seals fail after pushing the pedal through all its travel, maybe not such a big deal in the USA, but in the UK it means a wait for new parts, they have to be ordered from specialist suppliers or somewhere like Rock Auto.

Roger.

[96 SSEi]

One thing I found helpful when changing the pads is to remove the cap off the master cylinder.
That way the piston moves in easier.

since my 92 GTP, I remove 1/4 of fluid in master - makes it faster and no mess.

make 100% sure, the turkey baster is clean and dry - thats what I use to remove...lol