R1100GS Rear Brake...works...not work...works...

[Grazoid]

Okay , can anyone solve this riddle.

'97 R1100GS rear brake decides not to work on a long run that involved a very wet ride down Birdlip Hill Whit weekend fully loaded with luggage and loads of lorries braking...scary... totally floppy pedal and no pressure. Left it sat on the rally site all weekend while I decide what to do next. Buuger me, it was all working okay again on the Sunday morning , but not by the time I had ridden from Forest of Dean to Derby.

Bled the rear caliper through... no air fluid was clear, so hadn't boiled it or got water in. Cleaned everything up then tried it again... no probs. Two weeks ago had to make a trip up to Liverpool and it stopped working AGAIN! Got back home... worked! Been riding it around town since and it was still working , went out today. 30 odd mile blat around the back lanes to a bike show , pulled up in deep gravel car park... so used rear brake and it worked.

Spent a couple or three hours looking at the bikes and spraffing with old friends , then got back on the bike...NO REAR BRAKE!!

So far there has been no common denominator for it working or not working.

My question is where do I start looking as I need it for next weekend as I have a ticket for the Farmyard Party... suggestions please of potential things to replace or look at!

 

[Tarka]

There`s a chance that while you`re riding the bike you may have your foot postioned in such a way that you`re pressing the brake pedal down without realising it....and 'boiling' the brake fluid so that you lose all brake pressure.
The fluid then cools when you`re stopped.

Is your rear brakelight switch working ? Get someone to ride along behind you to see if that`s happening.

Just an idea....seeing as I overused my rear brake on the madass twisties down the mountain to Susa and it lost all pressure until it cooled.

Failing that,perhaps the piston seals in the rear master cylinder need replacing.

 

[Grazoid]

There`s a chance that while you`re riding the bike you may have your foot postioned in such a way that you`re pressing the brake pedal down without realising it....and 'boiling' the brake fluid so that you lose all brake pressure.
The fluid then cools when you`re stopped.

Is your rear brakelight switch working ? Get someone to ride along behind you to see if that`s happening.

Just an idea....seeing as I overused my rear brake on the madass twisties down the mountain to Susa and it lost all pressure until it cooled.

Failing that,perhaps the piston seals in the rear master cylinder need replacing.

Hmm a thought... will have to check it tomorrow... but the fluid normally goes honey coloured when you do that and mine is staying clear. But I have had the backend off to fix the clutch seal so it m=ight have moved position slightly when it was replaced. For reference I had already done several miles before it showed up after replacing everything...but you never know...

Yes the twisties down to Susa... would have been fun that day if I had remembered to turn the ABS back on and not tried to do the front brake drift round the first hairpin with NO ABS! 2007 Stella weekend was quite notable for ABS on/off issues wasn't it

 

[Grazoid]

Checked this morning and working fine!

Rear brake pedal is not in a position where it can be accidentally fouled. Caliper can be seen to freely move when brake is applied. Fluid levels are not dropping so no leakage.

What the feck do I check next ! ?!

 

[Stewart H]

Do you have a little free play between the brake pushrod and the master cylinder?
Stewart

 

[Grazoid]

Do you have a little free play between the brake pushrod and the master cylinder?
Stewart

Depends on what you mean... normally there is a slight freeplay before the pedal starts applying pressure upwards.

When it's not working it's all freeplay!

 

[Ogmios]

temporary 'repair'

....seeing as I overused my rear brake on the madass twisties down the mountain to Susa and it lost all pressure until it cooled. ....

piss on the disc
it cools the components down...
oh - the resulant 'rich aroma' when you next apply the brake will remind you to do a proper job when you get home.

while this is not a method found in any manual and is entirely at your own risk i found it useful while in the Pyrenees on a Guzzi and must thank my technical advisor (Mrs Og! - that woman never ceases to amaze me ) for the suggestion

 

[Grazoid]

piss on the disc
it cools the components down...
oh - the resulant 'rich aroma' when you next apply the brake will remind you to do a proper job when you get home.

while this is not a method found in any manual and is entirely at your own risk i found it useful while in the Pyrenees on a Guzzi and must thank my technical advisor (Mrs Og! - that woman never ceases to amaze me ) for the suggestion

A fix I have ...er ....applied before, but this time round the caliper was not the issue, first thing I checked was for caliper binding...

 

[Grazoid]

Okay... think I may have sussed the issue. The fluid reservoir has a quite small capacity and has an offset feed to the master cylinder. I was looking at it this evening when I got home and realised I could not see the Max/Min marks on the outside... this was because they had been turned inwards , evidently when we refitted it after the clutch replacement.

With the pipe on the side away from the frame, when you put it on the side stand it slops ALL the fluid away from the feed and if it goes way over ( like it did with the side stand sinking into the gravel of the car park on Sunday) it leaves an air gap similar to having no fluid!

Moving the pot so that the pipe is against the frame and rubbing against the bit of clear plastic, that is evidently on the frame to protect it, the feed is always under fluid!

The couple of times recently it has stopped working suddenly have involved roads with quite steep hills or getting off the bike when parked on steeply cambered roads... so I have been allowing an air bubble into the master cylinder. Hence when it gets left overnight on the centre stand the air will rise and the pressure return.

So a warning , if you move or check your rear brake fluid reservoir make sure you replace it with the feed pipe against the frame and the Max/Min marking visible!

Off to the Farmyard Party this weekend so will confirm when I get back.

 

[Grazoid]

Forgot all about this one... as I have had no further issues with the rear brake. Ergo problem solved!

Also spoken to a certain Bowser of this parish who saw a similar issue on another 1100, and he concurred it will cause the issue.

So pay close attention to replacing the rear resevoir if you move it.

 

[Tarka]

So pay close attention to replacing the rear resevoir if you move it.

It does,however,take a particular grade of klonk to refit the fluid reservoir with the level indication mark and writing on the inside and thus illegible.