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      10-19-2008, 12:07 PM   #1
lucid
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Aaargh! Can't loosen the 18mm bolt connecting the front caliper to the suspension!

I went through a pair of Carbotech intermediate compound, XP8, front pads in a single day (they had about 70% left in the morning). I sure am not using that compound again. My real problem is to get the damn things out. I wrestled with the caliper assembly at the track in a semi-lit area, and as far as I could tell with limited light, it is not enough to unscrew the two 7mm caliper retaining bolts on the back of the caliper (#6 and #7 below). Releasing those simply disconnects the caliper, but the whole assembly seems to be restricted in place by another component (#2 below) that is bolted onto the suspension with 18mm nuts (#3 below). The only way to remove that restriction seems to be to undo those nuts as well. Again, I couldn't see very well, so I am hoping that I am not missing something here. Anyway, I tried to unscrew the 18mm nuts but they were torqued way too high for me to undo with a long wrench that would fit into the space available. I tried everything, including banging on the wrench with a hammer and so on, but the thing would not give. It seemed like the only way to get them out would be to put the car on a lift and use a very long lever arm from underneath to apply more torque. Since I was using a floor jack, I didn't have space for that kind of leverage. I am thinking I must be missing something here as it should not be this complicated to swap pads on this car. The rears don't have the same problem as they don't have that additional component, and look very similar to the E46 M3 front caliper assembly. Any suggestions?

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Last edited by lucid; 10-19-2008 at 12:26 PM.
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      10-19-2008, 01:38 PM   #2
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We need the full shop manual for the car!

I have not yet wrenched on my E92 brakes but from all the E36 work I did and from looking at the diagram they are fairly similar. The main way to replace pads involves removing the larger mounting bolts, 2 ea of #3. They will be torqued on very tight. Maximum torque for a class 12.9 M18 is 350 ft lb! So the likelihood of needing a significant breaker bar is quite high! The other bolts are guide pins and I suspect those are installed with locktite and are not designed to be removed. Although with some heat they certainly could be.

I'm sure you know this but your general progression here should be:

1. Beaker bar and high quality socket on the 18s

If you don't want to/can't get enough room try

2. Penetrating oil
3. Heat bolt with torch

Looking forward to learning about pads/compounds from your experiences!
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      10-19-2008, 02:09 PM   #3
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Quote:
Originally Posted by swamp2 View Post
We need the full shop manual for the car!

I have not yet wrenched on my E92 brakes but from all the E36 work I did and from looking at the diagram they are fairly similar. The main way to replace pads involves removing the larger mounting bolts, 2 ea of #3. They will be torqued on very tight. Maximum torque for a class 12.9 M18 is 350 ft lb! So the likelihood of needing a significant breaker bar is quite high! The other bolts are guide pins and I suspect those are installed with locktite and are not designed to be removed. Although with some heat they certainly could be.

I'm sure you know this but your general progression here should be:

1. Beaker bar and high quality socket on the 18s

If you don't want to/can't get enough room try

2. Penetrating oil
3. Heat bolt with torch

Looking forward to learning about pads/compounds from your experiences!
Thanks for the response Swamp. Yeah, my guess is that the #3 nuts have been torqued to well over 300 ftxlbs. I simply cannot get enough leverage from the side while the car is on a jack. The wrench had a solid grip, so not the issue. Torching is not an option at this point. I might try using some kind of fluid to loosen things up. Tho two pins (#6 and #7) actually seem to be load bearing, and seem like would keep one from pulling the pads out even if the #3 bolts were removed. When those are not tightened the caliper has some room for movement although #2 keeps me from pulling #1 and the pads out. But, boy, do I wish I had access to a lift right now. I sure am not jacking it any higher to be able to stick a breaker bar in there and getting under it.
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      10-19-2008, 05:49 PM   #4
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Finally managed to loosen those 18mm bolts. I cranked the jack even higher, and used steering lock to one side for the upper bolt, and to the other side for the lower bolt, but it wasn't pretty. I had to use a long bar for leverage. I highly recommend that you do this if you have some means of raising the car high and getting under it safely. #6 and #7 need to come out as well.

Oh, and you need a C-clamp to push the piston back. If you want to push the piston back while the caliper is on the car, then you'd better have a large C-clamp. Otherwise you can just use the worn out caliper blackplate to as a clamping surface after you remove the caliper.
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      10-19-2008, 11:14 PM   #5
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Quote:
Originally Posted by lucid View Post
as far as I could tell with limited light, it is not enough to unscrew the two 7mm caliper retaining bolts on the back of the caliper (#6 and #7 below). Releasing those simply disconnects the caliper, but the whole assembly seems to be restricted in place by another component (#2 below) that is bolted onto the suspension with 18mm nuts (#3 below).
I don't suppose you really want to hear this but I'll say it anyway...

You only need to pull the two caliper slide pins (#6 and #7) and the anti-rattle spring (#8) to remove the caliper.

There are only two reasons you couldn't get it off:

1. You didn't remove the anti-rattle spring (#8), or
2. The pads were tight to the rotor and needed to be eased out to release them. They get caught on the ridge that forms on the outer edge of the rotor.

1. is fairly straightforward - remove the spring.

To deal with 2., I put a long pry bar against the hub and gently but firmly pry the caliper body out from the car, freeing the pads and compressing the piston back into the caliper, saving you from doing it later.

Once the spring is off and the pads are free, the caliper assembly just lifts off.

The only reason to remove the two bolts you struggled with is to get the rotor off if it's worn out. Otherwise, leave them alone.
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      10-19-2008, 11:22 PM   #6
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Originally Posted by JAJ View Post
I don't suppose you really want to hear this but I'll say it anyway...

You only need to pull the two caliper slide pins (#6 and #7) and the anti-rattle spring (#8) to remove the caliper.

There are only two reasons you couldn't get it off:

1. You didn't remove the anti-rattle spring (#8), or
2. The pads were tight to the rotor and needed to be eased out to release them. They get caught on the ridge that forms on the outer edge of the rotor.

1. is fairly straightforward - remove the spring.

To deal with 2., I put a long pry bar against the hub and gently but firmly pry the caliper body out from the car, freeing the pads and compressing the piston back into the caliper, saving you from doing it later.

Once the spring is off and the pads are free, the caliper assembly just lifts off.

The only reason to remove the two bolts you struggled with is to get the rotor off if it's worn out. Otherwise, leave them alone.
All is good, so it's OK. And I know now how to get complete access to the rotors. I did remove the anti-rattle spring. First thing I did actually. I'll have to try 2 next time. Yes, the pads were indeed tight to the rotor. I tried to use the largest C-clamp I had to push the piston back and free the pads, but it wasn't wide enough. I'll try your pry bar suggestion. I think there is a BMW tool that is specifically designed to push the piston back while the caliper is mounted.

1. When you say "pry the caliper body out from the car" do you mean just pull the caliper body away from the car and compress the piston so that the pads have room to wiggle around and come out, or do you literally mean remove the caliper body? I don't see how the caliper body can be fully removed while #2 is still mounted to the suspension.

2. My track pads were worn to the degree that the pad wear sensors were activated. I didn't have time to investigate how they work. Do they simply wear out so that an open curcuit is generated? If that's the case, I am assuming the sensor needs to be replaced? Is that enough for the break light on the dash to go away, or does it have be reset electronically?

You went through this procedure on the E92 M3 yourself, right? I want to make sure you are not suggesting a method that worked for another M car. Thanks.
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      10-20-2008, 11:21 PM   #7
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All is good, so it's OK.

1. When you say "pry the caliper body out from the car" do you mean just pull the caliper body away from the car and compress the piston so that the pads have room to wiggle around and come out,

2. My track pads were worn to the degree that the pad wear sensors were activated. I didn't have time to investigate how they work. Do they simply wear out so that an open curcuit is generated?

If that's the case, I am assuming the sensor needs to be replaced? Is that enough for the break light on the dash to go away, or does it have be reset electronically?

You went through this procedure on the E92 M3 yourself, right?
1. To be clear - you are correct - the "pry" direction will be pulling the outer pad away from the rotor toward the outside of the car which will push the piston back into the caliper body. When the pads are "loose" and free to "wiggle" the caliper body (#1) will just lift away from the "carrier" (Item #2). The reason it's called a "floating" caliper is that the piston and pad assembly literally floats on the carrier and is held in alignment by the locating pins (#6 and #7).

2. The pad wear sensor is an insulated "pin" that is inserted into the pad body. When the insulation is worn off, the pin touches the rotor and completes a circuit that turns on the light on the dash. Changing pads with the used sensors will work, but the sensor may corrode and not function correctly the next time the pads are worn out. Replace them if they've been "set off" by wear. In earlier BMW's, there was no need to reset the Chassis Computer - in the E92 I don't know.

3. Yes - I've put new pads on my E92 M3 - they were Pagid Yellows (RS19) pads, and some time in the next two weeks I'll put the factory pads back on now that track season is over.

Front calipers and rear calipers are built the same by the way - the front pins (#7 and #6) are different lengths while the rear pins are not. Otherwise, no difference in the process, although the rear pads and calipers are smaller than the fronts.
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      10-21-2008, 10:43 AM   #8
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1. To be clear - you are correct - the "pry" direction will be pulling the outer pad away from the rotor toward the outside of the car which will push the piston back into the caliper body. When the pads are "loose" and free to "wiggle" the caliper body (#1) will just lift away from the "carrier" (Item #2). The reason it's called a "floating" caliper is that the piston and pad assembly literally floats on the carrier and is held in alignment by the locating pins (#6 and #7).

2. The pad wear sensor is an insulated "pin" that is inserted into the pad body. When the insulation is worn off, the pin touches the rotor and completes a circuit that turns on the light on the dash. Changing pads with the used sensors will work, but the sensor may corrode and not function correctly the next time the pads are worn out. Replace them if they've been "set off" by wear. In earlier BMW's, there was no need to reset the Chassis Computer - in the E92 I don't know.

3. Yes - I've put new pads on my E92 M3 - they were Pagid Yellows (RS19) pads, and some time in the next two weeks I'll put the factory pads back on now that track season is over.

Front calipers and rear calipers are built the same by the way - the front pins (#7 and #6) are different lengths while the rear pins are not. Otherwise, no difference in the process, although the rear pads and calipers are smaller than the fronts.
Thanks for the info. I examined the rear assembly illustration, and identified the carrier there. I just didn't look carefully at the actual assembly behind the wheel in the dark to notice it. I'll let you know if replacing the pads without replacing the wear sensors turns the warning light on the dash and the message on the computer off or not. I have a feeling it won't, and those will be electronically reset, but we'll see...

What has been your experience with the RS19s so far by the way? Do you see a need to go up to the RS29s (I don't think they are available yet though).
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