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I am trying hard to unscrew these two bolts. I've tried to hit, to heat it with a torch and I put lot of WD40. Nothing moves.

What am I doing wrong?

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I think the issue the OP has is that he has limited tools, and may be trying to turn things which have a little rust, and possibly were over-torqued during assembly.

So it may be helpful to talk about ways to get fasteners loosened where the threads may be unwilling to smoothly turn apart. Stuck fasteners or guide pins, are often over torqued in the previous assembly. While caliper retainer bolts are usually torqued to moderate torque levels, like 40 to 60 foot-pounds, caliper pins often have lower torque specs, like 15 foot-pounds.

Second, rust tends to be an issue for most of us, and an undisturbed fastener or caliper pin may have enough rust in the thread area to make removal difficult.

Here are some suggestions:

  1. If possible, pre-soak the area a couple of days in advance, to help get the oil in as far as possible.
  2. Percussion (not 5# hammer in full swing) helps shatter oxide in the threads. If an Allen or Torx fastener, tap on the tool with it planted into the fastener.
  3. It helps to reapply penetrating oil after tapping. If things look bad, you might try several cycles of tapping and oil. Using an socket drive extension or a metal rod, may help you get the percussion delivered, without risking other things in the area.
  4. Percussion reduces the need for brute force, which helps minimize fastener breakage and tool breakage. While air / electric impact wrenches are very handy these situations, there are a few alternatives. Hand impact tools, where a hammer is used to hit a tool, which drives a cam inside the tool, rotating a socket or bit installed on the tool can be very helpful. Even on brake parts. These handheld impact tools are usually about $20 from Sears, HFT and other places.

Other higher priced solutions include air/electric impact tools and torches and welders.

If using a torch, the best is something like oxy-acetylene. High heat, applied just to the fastener, causes a slight expansion of the fastener, and corresponding pressure within the threads. This crushes the metal oxides. Normally penetrating oil is applied as the fastener cools, and a wrench is used to turn it. Using a propane torch does not work nearly as well, because it cannot deliver a high level of heat to a small area such as the head of a fastener. Also, heating the area around the fastener doesn't help because the temperature differential needs to be high, so that there is an expansion difference between the fastener and the material it is threaded into.

If you just have propane, and have heated the area around the fastener, you might take a birthday candle and melt it into the fastener area. The wax will flow like penetrating oil, and helps lube things, even after it has cooled.

If you use an oxy-acetylene or some other torch, and the fastener got a dull red or hotter, I would definitely replace that fastener.

There are lots of other methods, but I wanted to cover what an under-tooled DIY mechanic might likely have available. 90+% of the difficult fasteners I have dealt with respond to penetrant and tapping. I have torches, air impact and even access to an induction heating tool, but I prefer to use the least invasive method, and one that preserves the fastener.

My recommendation is to pick up one of the hammer driven hand impact tools to have on hand. Use tapping on the fastener or the Allen/Torx head with penetrating oil. And where ever possible, and where you anticipate difficult fasteners, pre-soak with penetrating oil, even multiple times, over several days.

One final point, using a 18" breaker bar with a long section of pipe applies lots of torque, but brute forcing rusted fasteners is an easy way to break them. Tapping with a hammer and using a hand held hammer driven impact tool will likely yield fewer broken fasteners, although it may take longer.

Sorry about the long answer, but I wanted to walk you through some of the options, and related considerations. Good luck.

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A 1/2" drive breaker bar will give you way more leverage and mass than the box wrench in the photo (1/2" x 24" long breaker bar $21 @ Home Depot). Try different physical positions in which you can pull or push efficiently, using your body weight to advantage (be sure the car is secured on jack stands, with wheels chocked according to the owner's manual--you don't want to get the bolt loose but be crushed under that Yaris). Can you turn the steering wheel so that the offending bolts are pointed out, toward the outside of the fenders? If so, you can stomp on the end of the breaker bar with your feet, like when you loosen the lug nuts on the wheels.

If this doesn't work, or if a bolt or nut is truly seized (like on a muffler hanger), try PB Blaster Penetrant (stinks to high heaven but considered superior to WD-40 for this application). Spray liberally on the mating surfaces, then rap the head of the bolt or nut hard a bunch of times with a hammer, doing your best not to smash exposed bolt threads or damage the flats of the nut. Repeat this process a few times over, say, 20 minutes. The hammer raps vibrate the steel parts, hopefully breaking the bond and drawing in some of the PB Blaster. Do not slip with the hammer and smash the calipers themselves or you may crack them. Also, do not add heat at this point or you may ignite the PB Blaster.

If you are able to exercise Zen-like patience and let the offending parts sit for a few hours or even overnight, repeated beatings/sprayings during this time period will help even more.

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I'd pull the caliper off first, take those rubber plugs out and it's a 7mm hex to remove the guide pins. Get a big hammer and hit the wrench with the part that's just under the hammer head where the handle meets the head. It's unlikely it's seized, you can try removing the pads and heating the caliper bracket where the bolt screws in with a oxy/map or acetylene setup to ease removal. or if you have air tools just gun the bolt out.

  • Hit the wrench with a hammer? Er no. You know how to treat your tools better than that. And no you can't borrow any of my tools ever. Never. Ever. Use the right tool for your own safety and for the protection of the parts involved. (If you miss the wrench and wack the brake line on the car are you going to replace the brake line? The person that's sloppy enough to use that hammer is sloppy enough to leave that brake line in place cause it's not leaking yet. ). Key word there is yet. – zipzit May 22 '17 at 0:38
  • Actually, hitting the socket head tool with a hammer is a good idea. You are not trying to whale on it, rather set up some vibrations. That will help the penetrating oil get into the crevices a little better. However, the greatest benefit of tapping the tool (don't use a 5# hammer, you only need to tap it with a 12 oz hammer) is that it helps break up rust interference in the threads. Oxides of metal are harder, but also more brittle, than the underlying metal. The tapping shatters the rust at a micro level, removing some of the interference, and hopefully enhancing removal. – mongo May 22 '17 at 5:27
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I got the bolts off my Fiesta, (those hopeless bolts with 'washers' built onto the hex head, so making a clean socket fit difficult), with a helical-grip 'removal' socket, a torque wrench, (just because it was long), and a length of pipe to extend the wrench. After a good soaking with Plusgas and a firing up with a blowlamp, the bolts screeched off.

  • Over torquing a torque wrench has a high risk of throwing off the calibration of the instrument. I suggest considering a breaker bar next time. – mongo May 22 '17 at 5:23
  • ^^^ good point! – Martin James May 27 '17 at 6:40
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Having struggled with bolts on a 1998 Corolla, I know where you're coming from and destroyed many a bolt until I found out what to do.

First thing is you should get hold of hex sockets, not the 12 point star spanners you're using. If you slip with the 12 point spanners, you'll round the bolt off, so you'll then be stuck and need to buy special bolt removal nuts. Try if you can to purchase black ones, because you can then hit these without fear of them shattering. I learn this the hard way.

Secondly I would invest in some stuff called PlusGas. It's far superior to WD40 in terms of budging stuck bolts like this. If PlusGas doesn't work, then mix up a 50/50 mix of ATF fluid and Acetone. Be careful to not get this on plastic as it'll melt it. I picked this method up from an agricultural forum when someone had a bolt they couldn't shift.

Finally, invest in the biggest breaker bar you can find. I have a 600mm one, and when a bolt won't come off with the normal sockets, I use the 600mm on a bolt after several sprays of PlusGas and it'll come of.

Leverage is your friend, followed by chemicals.

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