Bleeding rear brakes

[John Roberts]

First off, I've done a search on this, first on Airheads, then on on All Open Forums, and then in The Font of all Wisdom, so I have tried, god knows how I've tried. Right then. Bleeding rear brakes.

I've changed the rear brake tubing and hose but even though I've followed the Official BMW manual and the Haynes manual, I'm getting nowhere. I've tried pumping the brakes and putting my gob over the reservoir and blowing and turning puce while bleeding. It didn't work. I've tried filling a syringe with fluid and trying to push it in reverse from the bleed nipple, and also I've tried sucking it through the system with the syringe at the bleed nipple.

I had this palaver the last time I did it five years ago- I must have managed it, but I've no idea how by now.

How should it be done?

EDIT: The bike has been off the road since November- any connection??

 

[John Roberts]

On a slightly different topic, still brake-related, is there any reason why the bleed nipple is at the back and the hose at the front of the Brembo caliper? With the rear brake it's a bugger to get a spanner at the nipple as it is, and once the hose has been fitted there should be no reason to disturb that until you replace it. Any reason not to swop them? Here's a photo from the official BMW manual, they seem to be as they left the factory.

 

[PW Cymru]

I take it its your RS your talking about, if so try removing the caliper and bleeding it with the caliper raised to assist the bleeding process. The air will naturally want to travel to the highest point.

Obviously you'll have to stop the pistons from popping out by simulating a disc between the pads and it is easier with an extra pair of hands.

Worked for me a treat.

Good luck

 

[John Roberts]

Yes, it's the RS, Brembo rear.

Fair enough, it does make sense that, but why doesn't the fluid come out at all when I pump the brake pedal? I can see that the air puts some springiness in the system but I don't understand why it wouldn't come through eventually.

Oh, and the axle spanner (22mm?) is handy for putting in between the pads while effing about with the brakes.

 

[PW Cymru]

I've been told that the air is just moving when you press the pedal then resettling at the highest point when you stop, which is the solid pipe to flexi pipe joint area.

As soon as I raised the caliper above the pipe work it bled first time. (Tip from an ex BMW mechanic)

To be honest I was supprised how good the rear brake works after being told it was supposed to be crap.

 

[fayeslane]

Have you removed the bleed nipple and checked that it is not blocked? Had a couple that were gummed up after periods of inactivity.

 

[John Roberts]

Nipple cheched and it's clear, thanks. While removing the caliper from its mounting plate to get it as high as possible as PC Cymru said I took the hose off the caliper to swop the connections with that of the bleed nipple just to make the nipple easier to get at (see my second post above, the one with the picture from the BMW manual.)

When the hose was disconnected from the tubing I pumped the pedal and the fluid came out fine, and when I released the pedal the fluid got sucked back in, all well and good, but the worrying thing was that when I put my finger on the end of the tube to stop it sucking air in, then no matter how long I kept my finger on it sucked air back in when I took my finger off. Should that really be happening, will it ever bleed like that?

Sorry, but please bear with me on this, I accept that I may be puddled and not thinking straight, but I haven't ridden for six months and the bike's nearly ready apart from the rear brakes, and it's promising the best week-end for ages. I SO want to ride!

 

[Steptoe]

but the worrying thing was that when I put my finger on the end of the tube to stop it sucking air in, then no matter how long I kept my finger on it sucked air back in when I took my finger off. !

Check that the master cylinder is returning to completely closed.

It sounds like the rear brake pedal isn't fully returning and keeping the master cylinder slightly open.

 

[VAL. H.]

I haven't ridden for six months and the bike's nearly ready apart from the rear brakes, and it's promising the best week-end for ages. I SO want to ride!

Who needs a back brake to ride??? Blank the bugger off and ride it anyway. sort it out later


On a more serious note. Have you checked the hose for cracks etc? and can you be sure the fluid passes through the actual caliper (without the nipple in)?

Fluid being sucked back sounds like the peddle is floppy. ie the return spring doesn't have enough tension in it to hold the peddle up properly as Steptoe said above.


Val.

 

[John Roberts]

Thank you Steptoe and Val, although I haven't had the opportunity to try your suggestion, it does look likely that the pedal was not returning fully.

Let me tell you a story; as everyone knows, this is really a two-man job. So what smart-arse here did was to tie a bit of string to the pedal with the other end to a piece of wood that had its other end resting on the floor. It was then a lot easier to pump the brake by pressing on the piece of wood at floor level. I could lean over the bike and undo the nipple and so on while pumping the brake. And so, of course, the extra weight of the wood was enough to stop the pedal from fully restoring to its normal 'rest' position, hence all the grief.

Gentlemen, I thank you.

There's more, unfortunately. In my second post, the one with the picture showing the position of the hose and nipple (Nipple. Nipple. Mmmm that's such a nice word. Nipple.) I mentioned swopping the connections to make it so much easier to bleed. I took the caliper off the bike and split it to see if there was anything obvious that would be a problem with such an alteration. Couldn't see anything, so I'll go ahead. Then I realised while putting the two halves back together that there was room for a washer or O-ring between the two halves to seal the interconnecting fluid passages. It's on the floor of the workshop somewhere, I'm never going to find it in a month of Sundays.

Where can I get one? I suspect they are not included in the caliper overhaul kit, I still have the instructions from a few years ago and there is no mention of splitting the caliper, so the chances are that this O-ring/washer/seal may not be included in the kit. I did call my local BMW agent, they couldn't tell me. Where can I get this seal, or find out whether it's included in the kit? As it happens I do have a selection of O-rings, can anyone give me the size?

This is so sad. Two o'clock on a hot summer afternoon and I'm pissing about on my computer. Sigh.

 

[Kenny]

I bought this a few years ago for £20 complete with newish brake pads (+ postage )as it was for a never ever ever started special..is it any good for your bike? I'm on the Wirral

 

[VAL. H.]

Then I realised while putting the two halves back together that there was room for a washer or O-ring between the two halves to seal the interconnecting fluid passages. It's on the floor of the workshop somewhere, I'm never going to find it in a month of Sundays.

Where can I get one? I suspect they are not included in the caliper overhaul kit, I still have the instructions from a few years ago and there is no mention of splitting the caliper, so the chances are that this O-ring/washer/seal may not be included in the kit. I did call my local BMW agent, they couldn't tell me. Where can I get this seal, or find out whether it's included in the kit? As it happens I do have a selection of O-rings, can anyone give me the size?

This is so sad. Two o'clock on a hot summer afternoon and I'm pissing about on my computer. Sigh.

If you buy a complete caliper/piston overhaul kit the 'O' ring will come with it. However if you have a selection of 'O' rings take the caliper to them and find one that fits. Or measure the hole or grove where the ring was and go from there.

I'm told it's going to be sunny tomorrow too so no panic


Val.

 

[bustupbiker]

I bought this a few years ago for £20 complete with newish brake pads (+ postage )as it was for a never ever ever started special..is it any good for your bike? I'm on the Wirral

If you go for this option John, and if Kenny gets it to me, i will get it to you on Monday/Tuesday, depends on Kenny. It's all Kenny's fault anyway.

BTW. Kenny, whats (Appening) Re: the week-end! is Roger over here and meeting up, cos John will want company too!
Lyn.

 

[John Roberts]

Kenny: thanks very much for the offer but the caliper itself is fine, all I need is the pesky O-ring which VAL. H. says will be included in the overhaul kit, so I'll be ordering one by email from Motor Works.

As for the Wee-kend, I will certainly be coming if I can, but there is a possible snag with that, something about having the whole house rewired. 'Course, I can't make it anyway if I haven't finished the first batch of 737's, Kenny!

PS I'll be in touch, Lyn.

 

[VAL. H.]

I bought this a few years ago for £20 complete with newish brake pads (+ postage )as it was for a never ever ever started special..is it any good for your bike? I'm on the Wirral

Kenny,

Looking at the photo of your caliper and the one in Johns manual, they are opposites of each other. Or is it my imagination?


Val.

 

[Kenny]

Kenny,

Looking at the photo of your caliper and the one in Johns manual, they are opposites of each other. Or is it my imagination?


Val.

Fixed it for you

I actually meant he could use the rubber inner ring, the pads etc etc if his was bladdered. The caliper is (was) for a left g/s fork when I was going to do a dual disc conversion but TBH a larger single 320mm disc is well up to the job
Caliper is off an earlier RT

 

[Rob Farmer]

Just gone through exactly the same hassle with my R100RS. I ended up taking the whole lot off the bike and bleeding it on the bench. Paul's suggestion of getting the calliper as high as possible is spot on

 

[John Roberts]

Still it goes on...

At last I've got the missing bits for the caliper, bleeding them should have been a doddle with the help I've had from here.

Well, I'm still having problems. The root cause seems to be that when I release the pedal the air is still sucked in, despite Steptoe and VAL. H.'s suggestion- I now pull the pedal up all the way, and presumably this should open some port or other in the master cylinder, thus releasing the suction in the system. It does push the fluid through OK, it's just that it isn't pushing the air out of the system by pushing in more fluid at each stroke but it's immediately sucking air back in when I open the nipple. And it's bloody annoying.

 

[PW Cymru]

Still it goes on...

At last I've got the missing bits for the caliper, bleeding them should have been a doddle with the help I've had from here.

Well, I'm still having problems. The root cause seems to be that when I release the pedal the air is still sucked in, despite Steptoe and VAL. H.'s suggestion- I now pull the pedal up all the way, and presumably this should open some port or other in the master cylinder, thus releasing the suction in the system. It does push the fluid through OK, it's just that it isn't pushing the air out of the system by pushing in more fluid at each stroke but it's immediately sucking air back in when I open the nipple. And it's bloody annoying.

Assuming you have "Some" fluid in the pipe to the caliper and you are closing the bleed nipple prior to releasing the brake pedal, then no air should be able to re-enter the system unless you have a large leak somewhere, which should be visible by the pool of fluid below it.

Is the master cylinder in good condition?
Does the pedal pressure increase after pumping?
Are you getting any fluid out of the bleed nipple during the bleed procedure?
Have you raised the caliper above the level of the cross pipe to prevent an air lock?


Sorry if it sounds condesending.

 

[John Roberts]

1. Is the master cylinder in good condition?
   
2. Sorry if it sounds condesending.

In order:

1. I've ordered an overhaul kit for the master cylinder, there was some gunge in it. I overhauled it a few years ago and really didn't expect any trouble. And assumption is the mother of all fuck-ups (as any fule kno). It's difficult to take off and far harder to get back on, I'm not looking forward to it, I think that's why I dodged biting the bullet.​

2. It doesn't, not in the least. And thanks. ​