Brake bleed 101 - retracting caliper piston

[Scott9999]

Brad ( @Boxflyer) talks about compressing the caliper pistons when doing brake bleeds in his videos.  That's honestly how I usually do it, evacuate most fluid from the master cylinder,  i.e. clean off the caliper boot and piston, use a press (shop clamp works for me) to retract the piston back into the caliper, release the clamp, and then conduct the brake bleed, thereby ensuring that all the brake fluid is refreshed.   However, I've only done this while working on the brakes, meaning that the caliper was off the bike (or car).  Has anyone done this without removing the caliper?  It's not that tough to do, i.e. remove caliper, brake pads and backing plate, etc., but it just makes my bleed task (and propensity for screw ups) that much larger.  The other alternative that I can think of is removing the wheel, leaving the calipers on the bike, putting a clamp (or proper brake tool) between the brake pads and caliper, but that doesn't seem much easier than just pulling the calipers, as in doing an entire brake job (sans parts replacement).

 

Of course, I could just skip this step, which is certainly what the dealer's shop did last time they bled the brakes. 

 

Thanks.

[Hosstage]

I've not pulled calipers on a BMW, but I have found it easier to remove calipers than remove wheels on the bikes I have worked on.

One difference is older Harleys need the rear wheel removed to pull the rear caliper. My procedure there is to slip a putty knife between the pad and rotor, then work a screwdriver or small pry bar in there and gently push the pad back. This allows enough room for the pads to drop when the pins are removed, slip the new pads in and install the pins. This would retract the pistons and the fluid could be removed from the master. This only works if pads are being replaced as they take some damage usually. It may be possible to just pry on the lip of the pad avoiding damage to the pad surfaces. But if calipers can be removed relatively easily, that's the way to go for me.

[dirtrider]

8 hours ago, Scott9999 said:

Brad ( @Boxflyer) talks about compressing the caliper pistons when doing brake bleeds in his videos.  That's honestly how I usually do it, evacuate most fluid from the master cylinder,  i.e. clean off the caliper boot and piston, use a press (shop clamp works for me) to retract the piston back into the caliper, release the clamp, and then conduct the brake bleed, thereby ensuring that all the brake fluid is refreshed.   However, I've only done this while working on the brakes, meaning that the caliper was off the bike (or car).  Has anyone done this without removing the caliper?  It's not that tough to do, i.e. remove caliper, brake pads and backing plate, etc., but it just makes my bleed task (and propensity for screw ups) that much larger.  The other alternative that I can think of is removing the wheel, leaving the calipers on the bike, putting a clamp (or proper brake tool) between the brake pads and caliper, but that doesn't seem much easier than just pulling the calipers, as in doing an entire brake job (sans parts replacement).

 

Of course, I could just skip this step, which is certainly what the dealer's shop did last time they bled the brakes. 

 

Thanks.

Morning Scott

 

It probably isn't required on every service if the brake service is done in a timely manner. 

 

But it also isn't a big deal to do it the correct way as you can just pry the brake pads back then use tapered shims between the brake pads & brake rotor to hold the pistons retracted. 

 

If the brake fluid looks dirty, dull yellow, or brown then probably shimming the pistons back is a good idea as it does help get more of the old fluid bled out.  

 

The other thing to consider is that holding the pistons retracted, or shimmed back, is the proper way to get the correct fluid level in the master cylinder reservoir (this could very well be part of the reason for BMW requesting the piston retraction during bleeding service).

 

If your motorcycle has worn brake pads & you don't retract the pistons at brake service then it is easy to overfill the fluid reservoir.  If the front brake reservoir is filled with the pistons out farther due to worn brake pads then at next tire change when the pads are pushed back for wheel removal the reservoir can become overfull. Same with worn brake pad replacement, if the front master cylinder was filled after service without retracting the pistons. 

 

 

 

 

[9Mary7]

3 hours ago, dirtrider said:

If the front brake reservoir is filled with the pistons out farther due to worn brake pads then at next tire change when the pads are pushed back for wheel removal the reservoir can become overfull. Same with worn brake pad replacement, if the front master cylinder was filled after service without retracting the pistons

One of the reasons I crack the bleeder as I retract the pistons during a pad change.....

[Geekmaster]

If you want an easy way to push the pistons back into the caliper while on the bike, you could get one of these:

 

Disk Brake Spreader

 

Yeah, it's $30 and another tool to store, but it will do what you want.

[MikeB60]

21 hours ago, Scott9999 said:

The other alternative that I can think of is removing the wheel, leaving the calipers on the bike, putting a clamp (or proper brake tool) between the brake pads and caliper, but that doesn't seem much easier than just pulling the calipers, as in doing an entire brake job (sans parts replacement

Scott, You cant remove the front wheel without removing the calipers. There are only 2 bolts (T45 if memory serves me) and be careful not to nick the paint on the wheels, it's a tight fit between the rotor and wheels.  I make sure to clean the pistons with some brake clean before pushing them back. 

[Audi403]

2 minutes ago, MikeB60 said:

Scott, You cant remove the front wheel without removing the calipers. There are only 2 bolts (T45 if memory serves me) and be careful not to nick the paint on the wheels, it's a tight fit between the rotor and wheels.  I make sure to clean the pistons with some brake clean before pushing them back. 

 

This is a good point. I put some masking tape on the wheels while removing the calipers.

 

3 hours ago, Geekmaster said:

If you want an easy way to push the pistons back into the caliper while on the bike, you could get one of these:

 

Disk Brake Spreader

 

Yeah, it's $30 and another tool to store, but it will do what you want.

You can fit that tool with the calipers still bolted up?

[Audi403]

I don't know how necessary it is to remove the brake pads. I guess it would be easier to clean the sediment out that's stuck in the wear indicator grooves. I've always just pressed the pistons back using the pads.

 

I may buy that spreader tools for the next time.

[Skywagon]

Spreader...  $6 at Harbor Freight if you don't already have a drawer full of them.  About

99% of the time I can just push them back with my fingers..  I use a small block of wood to cover the pistons.

 

[Scott9999]

3 hours ago, Skywagon said:

Spreader...  $6 at Harbor Freight if you don't already have a drawer full of them.  About

99% of the time I can just push them back with my fingers..  I use a small block of wood to cover the pistons.

 

Ol' #2 C-clamp, trusty and sometimes, rusty, but it does the job. 😁

[Paul De]

If not removing the calipers, then I go to my wood shop supplies and use these between the brake bad and disc to push the piston back into the caliper.

 

 

Or if I have them on hand, these are more robust with less risk of leaving a piece stuck in the gap

Rip off price is anything over $2 for either type

[Bernie]

5 hours ago, Paul De said:

If not removing the calipers, then I go to my wood shop supplies and use these between the brake bad and disc to push the piston back into the caliper.

 

 

Or if I have them on hand, these are more robust with less risk of leaving a piece stuck in the gap

Rip off price is anything over $2 for either type

The shims will also work great if you remove the calibers. 

[Scott9999]

24 minutes ago, Bernie said:

The shims will also work great if you remove the calibers. 

LOL!  Heck, they work great for just about everything in my garage.  After building my house circa 2016-2017, I had a big box of shims left over from setting doors, windows, etc.  I kept moving that box around, not really having a place for it, but I didn't dare dump it.  Last year, I was installing stone around our foundation and my garage face (oh, yeah, I had a pro there to help!), and needed to shim between the drip edge and stone work, so I grabbed the box.  Almost empty!  Of anything other than scraps.  So, I bought 3 or 4 stacks of shims, including some of those composite types, which filled that 7 year old cardboard box right back up.

 

There are all kinds of things like that in my garage, that I have no earthly idea what to do with, but at certain times, are essential to getting anything done.  I have a pile of covered lumber from that build, too, some 2x8's, 2x10's, plywood, i.e. other construction materials that have been used and reused for platforms and such.  I'm real tired of having that wood pile over there out in the weather, but don't dare dump it.  Even if I don't touch it for a year and a half, then it becomes essential to some task.  Heck, I went out and bought a half dozen overpriced 2x4' last year for the stone project.  I had a few in the pile, but not enough, and digging through that wood pile was such a hassle that I just gave up and picked up some new ones.  Which, at the start of last winter, went into the wood pile.

 

That's why a 2 car garage (actually, 1.5 car, because of the stairs coming down one side) just seems impossibly small.  No matter how much stuff I sell off or take to the dump, I just have every nook and cranny stuffed with things I can't do without.

 

Shims are like that ... JUST like that.   😁

 

/end rant

[Skywagon]

36 minutes ago, Scott9999 said:

I have a pile of covered lumber from that build, too, some 2x8's, 2x10's, plywood, i.e. other construction materials that have been used and reused for platforms and such.

Shsshhh .. now you’ve done it. Roug will be by and the next thing you know you will have an addition on your house. Richard never met a board he couldn’t Mc Giver up something with😁

[Geekmaster]

21 hours ago, Audi403 said:

 

This is a good point. I put some masking tape on the wheels while removing the calipers.

 

You can fit that tool with the calipers still bolted up?

No, you need to remove the caliper, but that takes about 2 minutes, not a big deal, since you probably want to lube the slides, maybe put some copper grease on the back of the pads, and check the wear.  Maybe I missed something about someone wanting to do it while still mounted.

[Audi403]

Yeah, he mentioned not wanting to remove the calipers. I may buy one of those fancy spreaders. I like new tools...

[LAF]

Yes while I take mine off and stack plastic "bones" we used in the glass industry you could just drive shims in each side to retract the pucks.  When I have mine off and clean, you can move all the pucks with finger pressure.

 

 

[Audi403]

On 3/20/2023 at 7:37 PM, MikeB60 said:

Scott, You cant remove the front wheel without removing the calipers. There are only 2 bolts (T45 if memory serves me)

I can confirm this. I've tried to remove the front wheel wuthout removing the calipers. The wheel hits them and won't come out. I believe my calipers have bolts with a 13mm head holding them, definitely not torx. They are Brembos on a 2019.

[MikeB60]

6 hours ago, Audi403 said:

I believe my calipers have bolts with a 13mm head holding them, definitely not torx.

You are correct confused my GS which has the 13mm head with the GT which has torx!