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Project for bleeding brakes: Fabricating simple wooden blocks for brake calipers


NoHeat

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Here's a description of how to make wooden caliper blocks for bleeding ABS 3 brakes (this is intended for R1150 oilheads -- it might work for R1200 or other BMWs but I'm not sure if the dimensions are the same.)

 

The design for the wooden calipers is based on the wisdom page at advrider, written by Dana E. Hagar and Charles B. Gilman in 2004.

 

In that advwisdom page, the dimensions of the wooden blocks (based on the dimensions of a BMW special tool) are:

 

front brake caliper:

3.00" X 1.25" X 0.86" rectangular block, quantity 2

 

rear brake caliper:

2.75" X 1.125" X 0.43" block with scallop shape, quantity 2

 

Tolerances are not given in that advwisdom page, but based on my experience in fitting the blocks into my calipers I'd say the tolerances are about:

+/- 1/32" for the thickness, and more for the other two dimensions. In particular, for the other two dimensions, +/- 1/8" is okay for the rear calipers, and even looser tolerances are okay for the front. The thickness is the most important dimension.

 

In the advwisdom page, power woodworking tools are used to achieve the desired thickness of 0.86" or 0.43".

 

In this project I show how to make these blocks without power woodworking tools, using supplies that cost about $3 from a home improvement store.

 

The fabrication of the front-brake caliper blocks is shown here:

 

950008-front-entire-project.JPG

 

I used two packages of Shims/Wedges, size 1-3/8" X 4", 14 pieces per package. These are a home-improvement store item intended for shimming cabinets, doors and windows. For a wood product they are remarkably consistent in their dimensions. Cost: about $1.50 per package.

 

950008-raw-shimstock2.JPG

 

What makes these work so well for my purpose is their wedge shape. Stacking these wedges alternately, you can achieve any desired thickness by displacing the wedges slightly. I then glue them together with white glue, using C-clamps overnight.

 

For the front caliper I stacked four wedges alternately and displaced them to achieve a thickness of 0.86". For the rear caliper, I used only two wedges, stacked alternately, and displaced to achieve a thickness of 0.43". After gluing, I sawed them to the desired length using a bandsaw, but you could just as easily use any small hand-operated saw like a jigsaw or a miter saw. I then sanded the surfaces a little. For the front caliper, that's all that was required, and here's the result: 3.00" X 1 3/8" X 0.86" rectangular block. You need two, one for each of the two front calipers.

 

950008-front-finished-shim.JPG

 

For the rear brake, I also trimmed it a little more to get 2.75" X 1.125". To fit into the rear caliper where the brake pads go, I used a coarse file to give them a scalloped shape, like this:

 

950008-reartopview2.JPG

 

Thickness for the rear brake is 0.43"

 

You'll need two of these blocks, one to replace each of the two pads in the rear brake caliper.

 

950008-rearedgeviewflash2.JPG

 

 

Tools required for this project:

a pair of C-clamps (first photo)

saw

sandpaper

calipers or micrometer

half-round file (see below)

 

950008-tools.JPG

 

materials required are:

wood shims/wedges

glue

 

The dimensions for the thickness of the blocks are based on the BMW special tool. Using the wedges, it's possible to match this thickness within a hundredth of an inch or so, which is better than necessary.

 

When I used my wooden blocks to bleed my brakes, I found that when I pushed the brake piston in all the way (which is a good thing to do, in order to expel as much of the old fluid as possible when bleeding), these wooden blocks weren't quite thick enough to hold the piston there, so I used my wooden blocks plus an additional loose single wedge (left over from the package shown in the second photo), and that worked perfectly.

 

I'm sure it's not necessary to try to copy the advwisdom design as closely as I did, and you might have good success shimming your calipers with whatever junk you find around your garage, but for those who do want to copy the advwisdom design, this project allows you to do it for only a few dollars with minimal tools.

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ShovelStrokeEd

All real nice, however, you still now have to pry the caliper pistons apart before inserting the tool. A pair of flat outside blocks, loosely held together with dowels and a pair of like wedges in opposition, free to slide within, will allow you to use the tool to spread the caliper pistons and then, with an additional little squeeze wedge the whole assembly in position. I've done it with just a pair of wedges many times.

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Like Ed, I ease the pads back manually then insert composite material carpentry wedges (harder, no split/splinter)to hold them back and, thusly, manage to keep my brake calipers in situ. Works just fine thumbsup.gif.

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russell_bynum

I'm sure someone will call me a Philistine for this, but is it really that important to push the pistons back into the caliper?

 

I mean...when you're filling the system the first time, or if air has gotten in there, I understand why it matters. But is there really enough brake fluid behind the piston to make a difference in a normal, routine flush?

 

And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?

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And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?
Actually BMW instructs that you should retract the caliper pistons before bleeding on the 1100 bikes as well. I share your doubt over how important this is though. I suppose it's possible that (depending on where the inlet and outlet holes are) the new fluid could go right out the bleeder screw without forcing all the old fluid out of the piston bore, but really... in even the worst case I gotta believe that most of it will be replaced (via dilution, etc.). If this is such a big deal why isn't it recommended for cars as well? They have a much larger piston bore volume so in theory they should suffer such problems even more readily than on a bike.
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russell_bynum
And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?
Actually BMW instructs that you should retract the caliper pistons before bleeding on the 1100 bikes as well. I share your doubt over how important this is though. I suppose it's possible that (depending on where the inlet and outlet holes are) the new fluid could go right out the bleeder screw without forcing all the old fluid out of the piston bore, but really... in even the worst case I gotta believe that most of it will be replaced (via dilution, etc.). If this is such a big deal why isn't it recommended for cars as well? They have a much larger piston bore volume so in theory they should suffer such problems even more readily than on a bike.

 

Yeah, that was my thought as well. You're certainly not going to hurt anything by doing that, but I'm having trouble understanding why it would make a noticable difference.

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Dear Mr. Philistine

 

I will fess up that I usually don't bother to push the pistons back on any of my bikes. I do, however, perform the brake flush on all my bikes on an annual basis, even on bikes that don't rack up much mileage.

 

As I've yet to have any brake related problems, it can't be too important.

 

Stan

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russell_bynum
Dear Mr. Philistine

 

I will fess up that I usually don't bother to push the pistons back on any of my bikes. I do, however, perform the brake flush on all my bikes on an annual basis, even on bikes that don't rack up much mileage.

 

As I've yet to have any brake related problems, it can't be too important.

 

Stan

 

I, too, bleed the brakes on all the bikes once a year.

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I'm sure someone will call me a Philistine for this, but is it really that important to push the pistons back into the caliper?

 

I mean...when you're filling the system the first time, or if air has gotten in there, I understand why it matters. But is there really enough brake fluid behind the piston to make a difference in a normal, routine flush?

 

And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?

 

Russell,

 

When I did my brakes a few months ago, I "kinda" pushed the pistons back, did the bleed and called it good. I noticed after the check ride around the block that both calipers were hanging up. I think got the wooden shims out from a door project I did, pushed the pistons back held by the shims, and was amazed at how much nasty fluid came out on the second try. Hanging calipers fixed, and pistons will be shimmed back from no on.

 

BTW, I've probably blead 100 sets of brakes in my days from cars, trucks, motorcycles...whatever. Never had one hang up until this last time.

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And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?
I think it's important on any flush and bleed on any vehicle. The fluid behind the piston is the fluid subject to the most heat and the most deteriorated in the entire system. I think it behooves us to fully retract the pistons and get as much of it out as reasonably possible.
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russell_bynum
And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?
I think it's important on any flush and bleed on any vehicle. The fluid behind the piston is the fluid subject to the most heat and the most deteriorated in the entire system. I think it behooves us to fully retract the pistons and get as much of it out as reasonably possible.

 

Is the fluid stationary? IOW...when you flush the system (without pushing the pistons back in) does that old fluid stay behind the pistons forever, or does it mix back in with the new stuff once the system starts getting used?

 

If it is the former, then I'd totally agree with you (and I'd wonder why pushing the pistons back in isn't standard practice on all brake bleed/flush procedures). If it is the latter, then I wouldn't think it would matter much.

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Is the fluid stationary? IOW...when you flush the system (without pushing the pistons back in) does that old fluid stay behind the pistons forever, or does it mix back in with the new stuff once the system starts getting used?

It's stationary and stays there. There is a small amount of mixing of new to old as the pads wear and additional fluid moves into the caliper behind the piston, but it's pretty minute.
I'd wonder why pushing the pistons back in isn't standard practice on all brake bleed/flush procedures
IMHO 'best practices' says that you do. Even if this manual or that doesn't spell it out.
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Joe Frickin' Friday
Is the fluid stationary? IOW...when you flush the system (without pushing the pistons back in) does that old fluid stay behind the pistons forever, or does it mix back in with the new stuff once the system starts getting used?

 

Think of how little the pistons move during normal riding. Very little fluid actually moves into/out of the slave cylinders during a normal braking cycle. Theoretically, through repeated mixing and diffusion, you'd mix the old fluid in the calipers with the new fluid in the lines, and eventually with the large volume of new fluid in the master cylinder, but I think it would take a long time. Might be less of an issue if you've got very new brake pads (i.e. pistons almost fully retracted into calipers, minimal fluid volume).

 

Maybe that little bit of mixing is enough to fight corrosion in the calipers, but I wonder if we're compromising boil protection? back in '01 I boiled my front brakes at a track day, despite having bled them only a couple of weeks before. I mean literally boiled: lever comes all the way back to the bar with zero resistance, and there's zero deceleration. eek.gif I don't recall whether the pads were brand new or mostly used or what, but I didn't (and still don't) retract the pistons back into the bores when bleeding. Is it possible that the old fluid remaining in the calipers contributed to my brake failure?

 

I can't tell for certain from the pics in the manual (and I don't have the bike in front of me), but it doesn't really look like the plumbing is set up to circulate new fluid through the caliper's cylinders before dumping to the bleed fitting.

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And if the answer is yes, then why doesn't anyone seem to feel the need to do this whole "push the pistons into the caliper and shim them there) routine with the non-servo brakes?
I think it's important on any flush and bleed on any vehicle. The fluid behind the piston is the fluid subject to the most heat and the most deteriorated in the entire system. I think it behooves us to fully retract the pistons and get as much of it out as reasonably possible.

 

I'm with Ken on this one. I also use the wedges, but I use two just to push the pistons back by wedging them together. It pushes the pistons back far enough.

 

I do not, however, bleed all six bleeders on the ABS unit!

 

Jim cool.gif

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russell_bynum
IMHO 'best practices' says that you do. Even if this manual or that doesn't spell it out.

 

I don't get it. In today's nanny state world where there's 15 warning stickers on the fuel tank of my motorcycle so that the lawyers can be absolutely certain that there's no possible way I can hurt myself in a way that they didn't predict and warn me about why would something that could cause your brakes to go away not be in the manual?

 

And why don't the brake shops do it when you get the fluid flushed on your car? If it is really that important, then it seems like a HUGE liability to not do it.

 

(FWIW, what you're saying about why it is important makes sense to me, but that doesn't seem to play out in real-life maintenance practices.)

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This is a thread about woodworking, for crying out loud.

 

It's not a thread about politics and the legal system. I humbly propose that you start your own thread if that's what you want.

 

I thought I might help somebody out, but apparently not. I'm sorry now that I even thought of taking photos and writing instructions for noobs.

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russell_bynum
This is a thread about woodworking, for crying out loud.

 

It's not a thread about politics and the legal system. I humbly propose that you start your own thread if that's what you want.

 

I thought I might help somebody out, but apparently not. I'm sorry now that I even thought of taking photos and writing instructions for noobs.

 

Hey, it's all good....no need to get offended.

 

I'm just trying to understand if this extra step is actually necessary, and to understand the seemingly conflicting info out there.

 

If it is necessary, then I'm going to start doing it...especially on my track bike where the brakes really get a workout.

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Joe Frickin' Friday
This is a thread about woodworking, for crying out loud.

 

It's not a thread about politics and the legal system. I humbly propose that you start your own thread if that's what you want.

 

I thought I might help somebody out, but apparently not. I'm sorry now that I even thought of taking photos and writing instructions for noobs.

 

Hey, it's all good....no need to get offended.

 

I'm just trying to understand if this extra step is actually necessary, and to understand the seemingly conflicting info out there.

 

If it is necessary, then I'm going to start doing it...especially on my track bike where the brakes really get a workout.

 

It seems very strange to me that this step wouldn't be necessary, at least on high-perf systems, if not on the family mini-van. But these guys seem to know stuff about brakes and racing, and there is nary a mention of retracting the pistons when bleeding brakes:

 

http://www.stoptech.com/tech_info/wp_howto_bleedbrakes.shtml

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russell_bynum

Hmm...

 

according to the pdf in the Hall of Wisdom, you have to push the pistons back into the calipers and hold them there during the flush in order to get the correct fluid level in the wheel circuit reservoirs. Failure to do that will result in an ABS fault.

 

So...I would guess that's the primary reason we see this proceedure on the servo bikes but nowhere else.

 

Can anyone confirm that this is true and you actually do get a fault if you don't bleed/flush the servo brakes with the pistons pushed back into the calipers?

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Seems that we are obsessing here about something that takes about 2 sec per caliper to do. So, why not do it and move on to the bleed job without any worry? wink.gif

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russell_bynum
Seems that we are obsessing here about something that takes about 2 sec per caliper to do. So, why not do it and move on to the bleed job without any worry? wink.gif

 

First, none of the people asking questions are obsessing...we're just asking questions and trying to make sense of the whole thing. That's called discussion and that's what this place is for. tongue.gif

 

Second, Why do something that isn't necessary? If it isn't necessary, then you will have spent the time building the shims, removing the calipers, shimming the pads, securing the calipers so they don't hang by the brake lines, then remove the shims, reinstall the calipers, find the torque wrench, look up the appropriate torque for the caliper bolts, etc....for nothing.

 

I'm not a fan of doing work when there's no reason to.

 

If, on the other hand, there is a reason to do it (which it seems like there is, if the wheel circuit fuild level thing is true), then I like to understand why it's important.

 

My bikes do not have servo brakes, but they do have hydraulic brakes. If the reason pushing the piston back into the caliper is important is because otherwise you leave a bunch of nasty fluid in there that negates the whole reason you did the bleed/flush in the first place...then I'm going to start doing that on all my vehicles. (And I'm going to start wondering why none of the brake shops do it when they bleed/flush brakes.)

 

If it is just to get the correct wheel circuit fluid level, then that's not applicable on my vehicles so I can ignore that step unless I just want to be really anal retentive about it.

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Seems that we are obsessing here about something that takes about 2 sec per caliper to do. So, why not do it and move on to the bleed job without any worry?
First, none of the people asking questions are obsessing...we're just asking questions and trying to make sense of the whole thing. That's called discussion and that's what this place is for.

 

Second, Why do something that isn't necessary?

Third, it doesn't take '2 seconds.' Bleeding the front calipers in place is so easy that the additional task of removing the calipers and futzing with it all will about double the time it takes to do the job. If there is a reason to do it, fine, if not I have better things to do.

 

And regardless of the necessity of this task, as for 'worrying' about it... believe me, I don't... grin.gif

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I think it's necessary. The fluid in the pistons is that which is mostly subjected to heat, and since DOT4 is hydroscopic, water in the fluid would be present there too by virture of osmosis. I've found that the nastiest stuff always comes out of the pistons of the systems I flush (especially the rear brake).

 

One possible consideration would be influenced by how the brake line and bleeder were arrainged on the caliper. If the brake line were on one side (preferrably the low side) and the bleeder were on the opposite side, it might be possible to flush enough fluid through to effectively change the content of the pistons. But, if they are adjacent to each other, you would likely not be able to put enough fluid through to get it all.

 

Retracting the pistons is specifically detailed in the manual, and I think it's reasonable to conclude that it should be done.

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Can anyone confirm that this is true and you actually do get a fault if you don't bleed/flush the servo brakes with the pistons pushed back into the calipers?
I don't think there's anything to it. The whole bit about using a block of a specific thickness is aimed at getting the fluid level in the ABS servo reservoir to a mid level that will provide the most latitude for the range of pad wear. And that only works if the pads used with the specific size wood block are new.

 

The ABS unit has has a fluid level sensor in it, if the fluid drops below that it sets a 'fault.' That's the only 'harm done.'

 

Rather, when doing a bleed on the servo brakes after done flushing, remount the caliper, seat the pads to the rotor, then top off the ABS reservoirs to their fill mark. That will accommodate any wear of pads and resulting drop of the fluid in the ABS reservoirs. If the pistons are pushed back (like when putting on new pads) at some future point, it might overflow out the vent tube bit, but it's no big deal and certainly harmless to the ABS unit.

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Dear Mr. Philistine

 

I will fess up that I usually don't bother to push the pistons back on any of my bikes. I do, however, perform the brake flush on all my bikes on an annual basis, even on bikes that don't rack up much mileage.

 

As I've yet to have any brake related problems, it can't be too important.

 

Stan

 

I read it three times to be sure what you meant. "it can't be too important."

 

Reminds me of when I was in the Army in GA. If you asked a local to do something, like come over to "burn" steaks, they would say "I don't care to." I thought it meant NO but it really meant YES.

 

So I guess "it can not be too important" really means "it is very important". wave.gif

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Well, it is important to take the very best care of our Beemer brakes. But the minivan isn't as important, as the wife just uses it to take the kids to school.....

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Anton Largiader

I started spreading the pads for brake bleeding long before iABS came out. Looking at the color of the fluid, it was clear to me that it was a half-done job otherwise. On most brakes, the clean fluid will go from the brake line straight to the bleeder without washing any of the dirty stuff out.

 

With floating calipers, I often just push the caliper to one side to compress the pistons (except on iABS where I set the distance).

 

With iABS, the fluid looks even worse, usually.

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How do you guys keep the crud on the pistons from fouling the piston / caliper seal when you compress the pistons?

 

I recently compressed my pistons and the pucks hung up, which then forced me to completely disassemble the calipers ( popped the pistons with compressed air and a wood shim in the middle).

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How do you guys keep the crud on the pistons from fouling the piston / caliper seal when you compress the pistons?

 

I recently compressed my pistons and the pucks hung up, which then forced me to completely disassemble the calipers ( popped the pistons with compressed air and a wood shim in the middle).

That can be a challenge. I some times wire brush around them, then blow it off before doing the compression. But the bottom line is sometimes you do damage a seal and have to disassemble and replace it.
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