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The content is pretty much contained in the title. When I went to replace the brake pads, one pad was completely gone and the other was almost like new.
Now that I have replaced the pads, the wheel heats up quickly when driving even short distances.
I did notice that one of the guide pins seemed stuck - it did not move at all. Could this be the cause of the heat, and if so, what do I need to replace? Just the pins, or the caliper bracket as well?
If your guide pins are stuck, the caliper won't be able to slide properly.
With a sliding caliper, when you apply the brake, the piston pushes one pad against the disc (rotor), and simultaneously pushes back against the caliper (Newton's equal and opposite reactions), causing the caliper to slide along the guide pins, and pull the other pad against the disc. If the caliper cannot slide, the second pad remains forced against the disc, and you're effectively driving with half the brakes on on that wheel, hence why it gets hot. You'll find that if you jack up the the car, that wheel is much harder to turn than the other side.
Remove the caliper, and both guide pins. Clean them up until they both slide freely, re-grease and reassemble, using new gaiters if the old ones are damaged (which is quite likely, as that's the usual reason for them siezing). Do the same on the other side so that you know both calipers are in the same condition.
When replacing break pads it is incorrect and bad practice to simply push the piston back in, this will force brake back up into the master cylinder and sometimes even cause it to overflow. Just about everyone disregards this but it is very possible to damage the Master Cylinder this way. The "correct" way to do it is to open the bleeder screw, push the piston in (use a rubber hose & bottle to avoid making a mess), then close the bleeder screw. This will allow you to easily reset the piston. Also, this will not require that you bleed the brakes since you did not let any air into the system.
Also, using a wirebrush all slides and pins should be cleaned and then lubed. If the slides / pins are readily available or are included with the brake pads then it's recommended to replace them. Seeing that you were able to install the pads I'm going to say it's safe to rule out an issue with the caliper. I would take both sides apart and clean the slides / guide pins and calipers with a wirebrush and some Brake Cleaner. Then using some anti-seize lube all contact points between the caliper, slides, guide pins, and brake pads. This will ensure that there is unrestricted movement in the entire assembly. If the symptoms continue after you've done this let me know and I can help you start to look deeper into the system.
You should not drive the vehicle while it is like this. It's not only unsafe but it will further damage the braking system. If you have no choice then you have no choice but, try to keep it to a minimum.
With the brake piston fully compressed the pads should have a little clearance, enabling minor "play." When replacing brake pads it is important to make sure that the caliper itself moves freely in the horizontal direction (i.e., perpendicularly to the disc.) If not, one pad will wear quickly due to the fact that it will maintain pressure against the rotating disc.
I'm not sure that stuck guide pins can yield a similar result, but your best bet - considering that your brakes are getting hot - is probably to remove the pads and make sure that all moving parts are ... moving.
I just read the paperwork that came with my Wagner Disc Pads, which explains: When, Where, & What Chemical Compounds to use During Disc Pad installation, for different types of pads. In General, caliper rails or abutments (where there is metal-to-metal contact with the disc pad plate) should be cleaned and lubricated with Moly Lube. Guide Pins should be lubed with Silicone Lubricant. Petroleum based lubes WILL adversely affect the rubber guide pin boots. Wagner's top of the line "ThermoQuiet" requires that NO chemical compounds be placed on the insulator area of the disc brake pads. I never had read the paperwork before, but I'm waiting on other parts. So, best to find out what the Mfg. recommends for your specific design. And BTW, if you plan on keeping your vehicle for a long time, pay extra for "Lifetime" pads & calipers... new stuff free next time!
Scott B is giving terrible advise and I seriously doubt he is an engineer for GM, as an engineer would realise that forcing contaminant-laden fluid back into the master cylinder is not a good thing. Master cylinders require clean fluid in order to provide the fluid pressure necessary for proper braking. I'm also doubting that a Valedictorian would call a "bleeder" a breeder, nor misspell the word, "Mechanic" (Mechainc). But, I digress. Clean, new brake fluid allows full hydraulic pressure to braking components and reduces brake fade. The more moisture brake fluid contains, the less effective it is. Contaminated brake fluid also causes wear to bores and seals; for my money, I'd rather force the dirty fluid out when compressing the pads. After the brake service is complete, it gets followed up by a brake fluid flush.
Ideally as standard routine, when replacing brake pads, check that the cylinder body with the guide pins slides freely back and forth. You could also sometimes tell by uneven wear on the brake pads you are replacing visually. If this is not the case then you should clean the guide pins and re-grease them using suitable grease that won't damage the rubber covers on the pins.
I'm surprised you mentioned the brake pad heat as opposed to hearing some sort of grinding/noise whilst driving/braking.
If you are able to and have the resources refer to your car workshop/manufacturer manual in regards to the full procedure for replacing your brake pads.
To those comments stating to open up the brake fluid bleed valve in order to push the piston back in for a brake pad change. I haven't seen that being recommended in the few manuals I have seen. Wikihow is hardly an extensive manual/guide. You are far more likely to introduce air into your system that way if not done properly. Majority of guides advise to 'remove the master cylinder reservoir cap in your engine bay' leaving it open whilst the piston is pushed back in. Any fluid in the system will be pushed back up. Generally a good indicator of low brake pads is low brake fluid (unless you have a leak). Therefore there would be no need to top it up/extract any fluid when the piston is pushed back in for each side as long as your brakes are pumped thereafter respectively. You also have a recommended service interval (mostly every 2 years) for bleeding the brake fluid in your system that is what it is there for. Don't be confused with the logic of "bad" fluid that is exposed to the most heat and wear, the whole system is full of the fluid being slushed around, it doesn't just stay in one area, it is being shoved around every time the brake is being pumped, only way to empty it is with a full bleed.
Dude there is no reason to break the breeders when changing your pads. Pop the top on the master cylinder reservoir. Most of the vehicles I have ran into didn't add brake fluid and it just brings the level back up. Sometimes you have to drain off some. Before you start. I hate so called mechanics that know or act like they know what there doing, and do it wrong. I was a Natural self taught Mechainc, until I went to school for it. Where I Graduated Valedictorian and was offered I full ride to GMI aka Kettering. I wrenched on cars in a Service garage until I finished school. Then started as an engineer working R&D For GM C.P.C. V-8 Engines.
