Stupid bleeding question

[Phil50]

I've just been looking through the brake bleeding tutorial here http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=9225 and was wondering why do we remove the callipers and shim them out with wood? Why not just bleed the brakes with the callipers in situ?

 

Thanks

 

Phil

 

 

[dirtrider]

Afternoon Phil

 

Some do it that way, I don’t.

 

Two reasons are:

 

First- it moves the caliper pistons out so no old fluid gets trapped behind them when the system is bled. (you can accomplish the same thing by just prying the pads back while in place then wedging shims or something between the pads and rotors to hold them there through the bleeding process)

 

Second- It holds the caliper pistons at a set distance (set volume) so when the reservoir is filled it will be the correct level if new brake pads are installed at a later time. (this isn’t a big deal for an at home brake bleeding)

 

[Skywagon]

They do it to get that last little bit of fluid in the caliper. I don't.

[OoPEZoO]

The idea of pushing the pistons back in is so none of the old fluid gets caught out in the caliper. Pushing them back in and blocking them should give you a "better" flush.

 

Not exactly necessary, but good practice.

 

FWIW.....I have never blocked mine either. I just leave them on the rotors.

[AndyS]

I push my pistons fully into the caliper housings and then insert a block of the correct thickness to keep them in that relationships.

I like it as it keeps everything at the correct levels and removes as much of the old fluid as possible and it also means there is less volume to fill and potentially a few (very few)less places for air to get trapped during the bleed process.

It really isn't a lot of hassle. It also means I can clean the pistons before I push them in, and also clean the caliper internal parts. To me that is just as important as bleeding. It is all part of the brake system and I have seen more than a few knackered callipers due to corrosion on housing (less common) and pistons (more common).

Andy

[Boffin]

I push my pistons fully into the caliper housings and then insert a block of the correct thickness to keep them in that relationships.

I like it as it keeps everything at the correct levels and removes as much of the old fluid as possible and it also means there is less volume to fill and potentially a few (very few)less places for air to get trapped during the bleed process.

It really isn't a lot of hassle. It also means I can clean the pistons before I push them in, and also clean the caliper internal parts. To me that is just as important as bleeding. It is all part of the brake system and I have seen more than a few knackered callipers due to corrosion on housing (less common) and pistons (more common).

Andy

 

I agree about the importance of cleaning the callipers and pistons, especially in our climate, more so if you ride when there is salt on the roads.

 

After cleaning the pistons and callipers, I lube the pistons with a thin smear of brake-fluid before pushing them back into the calliper.

 

Andy

[AndyS]

After cleaning the pistons and callipers, I lube the pistons with a thin smear of brake-fluid before pushing them back into the calliper.

 

Andy

 

Me too. but just the tiniest amount as it can get blown around and make a mess of nice shiny bits!

[Jim VonBaden]

I use a pair of plastic window shims and push it back. It is a bit of extra work, but if you ever did a servo-bike you will see how much fluid is pushed back when you do it as the fluid rises in the funnel. This is a significant amount of fluid IMHO.

 

The shims make it easy, and this minimizes contamination of the new fluid with the old.

 

Jim

[Phil50]

Thank you for all of the helpful comments and suggestions. On balance it sounds like I don't need to remove the callipers but if I'm in the mood to do it then I'll make a better job of the fluid change. I'm thinking it would be a good idea to go the whole hog this first time I do the job and then I'll be in a better position to decide whether to do it in future. I have most of the bits and pieces I need together and hope to get on with this job this weekend.

 

Thanks again

 

Phil

 

[AndyS]

Well Phil, the choice is yours, but if you do it without pushing the pistons back, next time you do, you may find some paint missing from your torque arm....just sayin'

Andy

[Solo6]

One a related note, is there any reason to not modify the caps on the ABS so that they can connect to an external reservoir?

 

My idea is to put tubing nipples on the caps, then connect tubing to a common reservoir which can be topped off without stripping the Tupperware.

[4wheeldog]

One a related note, is there any reason to not modify the caps on the ABS so that they can connect to an external reservoir?

 

My idea is to put tubing nipples on the caps, then connect tubing to a common reservoir which can be topped off without stripping the Tupperware.

 

Unless some part of the system has failed, their should never be a need to fill the reservoirs between flushes. Plus, brake fluid is nasty stuff, so overfilling/overflowing the system can do some damage to paint work. I believe this falls in the category of "Fixing a problem that doesn't exist". Good luck.

[dan cata]

FWIW.....I have never blocked mine either. I just leave them on the rotors.

 

+1 on that

 

Dan.

[dirtrider]

Afternoon Solo6

 

I suppose with enough engineering you could rig up some sort of external reservoir. It would have to be vented so as not to pressurize the ABS controller sump in any way. The external reservoir would also have to be a bit higher than the ABS pump or so well sealed and plumbed without any air trapping loops that only air free fluid would be pulled into the ABS controller. (doesn’t sound worth the effort)

 

If just filling is the idea you can already back fill the “under tank” ABS internal controller reservoirs without removing the tupperware from a front or rear caliper bleed nipple. As long as the fluid is air free and the bleeder is sealed at the threads it’s real easy to force some fluid back into the ABS controller reservoir’s through a caliper.

 

[Phil50]

Even if you ever needed to add fluid between flushes how would you know how much to pump in to get it to the correct level?

 

Best wishes

 

Phil

[AndyS]

...because you push the pistons fully into the calliper...nd then you fill the Servo resevoir do the leveel marks ad then you have enough fluid in there...even when the pads have worn down.

However, doing it the other way ie filling the Servo resevoir with worn pads can result in jettisoning it out of the breather and pad renewal time.

Andy

[dirtrider]

Evening Phil

 

Not sure there is an exact way.

 

Good question as it’s not precise, just quick & easy.

 

IF the ABS lights flash a low fluid code I first pry the rear brake pads away from the rotors (pistons all the way into the calipers). If the lights go out I add fluid to the rear. If the rear pry back has no effect I do the same to the front pistons (pry all the way into the calipers). One end or the other usually puts the flashing lights out. I add a little fluid (maybe an ounce) to end that is low then ride the bike, if the low fluid warning goes away that is all I do.

 

 

 

 

 

[Phil50]

Interestingly BMW are anal about pushing the pistons back. The repair manual says:

 

Remove front brake pads.

• Wrap cloths around the left and right brake calipers.

• Use resetting tool, BMW No. 34 1 531, and

locator, BMW No. 34 1 532, to force the pistons

in the left and right brake calipers all the way

back and hold them in this position.

 

I guess that tools 34 1 531 and 34 1 532 are just crude alternatives for the superior bits or wood or window wedges that members here use

 

Cheers

 

Phil

[nrp]

Don't do this as the existing brake fluid reservoirs are all bladder isolated from the atmosphere. You would be introducing a path for moisture to get into the system.

[dirtrider]

Don't do this as the existing brake fluid reservoirs are all bladder isolated from the atmosphere. You would be introducing a path for moisture to get into the system.

 

Evening nrp

 

Not on the I-ABS wheel circuit side. Those internal reservoir’s are vented through a simple catch container directly to atmosphere. Not sealed like the control side is.

 

[Phil50]

First of all I'd just like to take the opportunity to thank all of you who have encouraged me to have a go at bleeding my brakes. It's the first time I've had the tank off and it is amazing how much you learn about your bike just be doing that simple procedure. Once you see with your own eyes where the alternator fits, and the Servo ABS etc etc are loads of other stuff you guys talk about starts to make sense.

 

I've only done the front wheel circuits so far but it was so easy I wonder why I paid someone to do it for me all these years.

 

The only gear I bought was a Vizibleed. Basically a bit of pipe with a none return valve on the end. I don't think you need one of these but it gives you confidence to take your time closing the bleed nipple once you have finished flushing through.

 

 

On the picture guide in the bmwsporttouring.com FAQs it explains how to make a "mini Stan" with a special order part from your BMW dealer but in fact a 40p ASDA funnel with some self amalgamating rubber tape carefully screwed into the relevant orifice (as suggested by Andy Long and others) works perfectly.

 

 

Thanks again, I'm off to do the rear and then the control circuits.