Now this is just getting stupid!

Had a good morning down in the pottery, so thought I would tackle the front brake again. I took the caliper off removed and cleaned the pistons - nice and clean and smooth with no visible signs of wear. On re assembly I used a new O ring between the two halves.There is now a single Goodridge hose top to bottom with new copper washers. At the top there is a new master cylinder.I used a new method to bleed. I hooked up the syringe to the bleed nipple, with a bit of fluid in it, tapped the tube so it was full of fluid. Suspended the syringe above the bars so that all air bubbles would go skywards. Pumped the brake lever - air exited up the tube to the syringe along with fluid. kept going till all old fluid was ejected into the syringe which filled when lever pumped. After I was satisfied that all fluid was new and the bubbles had stopped (more than I thought there should be) I locked the nipple and pumped the lever a couple of times to get the pistons to grip the disc and brakes were great.Then set about bleeding the other linked brakes just to renew the fluid - all ok.Went back to front brake squeezed lever and it went back to the bars- nothing at all. Pumped the lever and they were back. What is going on?

No one talking to me?


jmee542013-09-07 16:38:04

Mm either air or master cylinder


When it did mine I ended up tying the brake leaver to the bars over night

Also rotating the calliper round in your hand to get any air out from behind the piston can help

you have a knackered master cyl or a small air leak on hose ,probbly where the end screws onto the hose,not the banjo’s

I would test the master cylinder by putting a plain bolt in the end , bleed it up and see if it looses pressure (remove from bike or take precautions not to get brake fluid all over your nice paintwork.
Another test, when the lever is hard keep pressure applied on it, if the lever pulls in over time the leak should be visible.

The master cylinder is new from Gutsibits, please don’t tell me it’s the third thing to go wrong from them!When I was pumping it did feel slightly graunchy if you know what I mean. Having said that it is the third one I have tried.The hoses have been changed, partly, three times too and now is a single hose, rather than split in the middle. It is now brand new Goodridge. Was brand new Venhill.I have swapped the brake switch.I have changed the washers twice.The only thing not replaced are caliper seals, what do yo reckon?I just cannot believe how something so simple is proving to be such a barsteward.I have tried reverse bleeding, normal bleeding with a jar, bleeding with a hose with slit, bleeding with a hose with a non return thingy, and as described above with the raised syringe.I have used new fluid.I have never had any trouble bleeding brakes before, in 40+ years on cars or bikes. This is just ridiculous. I will try testing the master cylinder as you describe HaydnR.Oh yes, I have removed the lot and bled it on the work bench too.


jmee542013-09-04 21:14:19

Totally stumped on this one.Have you transferred the seal kit from the old master cylinder to the new one?Do you have a spare caliper to try?Could there be a problem with your brake fluid? Have you been using the same bottle all the time? I would imagine you have probably got through several bottles by now.Are the seals fitted the correct way round on the caliper pistons? The faces are tapered, I seem to remember, as are the seals on the master cylinder.Going back to the start of this saga, what did you change that caused the problem in the first place?

New master cylinder had new innards.Don’t have another caliper unfortunately. Did have but sold them!Two new bottles of fluid.Seals in calipers still as they came when I bought the bike and it worked ok then.It all started when I put Cali bars on and needed to put a longer top section of hose on.The lever goes hard and stays hard whilst the bike is stationary in the shed. But, when I come to return it to the shed after taking it out to start it, down a slope, the brake fails and I have a fun time stopping it!(engine work in progress too)I have left it with rubber bands round the lever over night and all seemed great next day, till I had a near death experience reversing down the slope with no engine.

Bleed the front again. Do you get more air out? If so you may have had a bubble which didn’t want to come out, or there is air getting in somewhere.Have you tried lifting the caliperin the air with a spacer between the pads, so that any air will rise to the top.

You would have saved a fortune in time and money had you just taken the front brake off complete and taken it to a professional.

It is OK as a home mechanc “Having a Go” If it works fine once it doesn’t and you really do not know where you are going, save dosh get Pro advice.
To try and diagnose a problem on line is almost impossible.

Not having a “go” just making an observation based on 25 yrs of keeping a Convert/G5 on the road

Guzzi Brembo calipers as fitted to older bikes and BMW’s have a problem with trapping air behind the brake caliper which is almost impossible to clear using usual methods. I was shown how to reverse bleed the front brake years ago. It is the only way to ensure all air has been forced out.

IF that does not work then air IS getting in somewhere. JUST because a component is new does NOT mean it is working corectly.

Get it checked prove each part labourious but logical.
guzzibear2013-09-05 11:26:41

“The lever goes hard and stays hard whilst the bike is stationary in the shed” This is a bit more info. Suggests something else is going on, nothing to do with fluid at all. Warped disc? Pushing pads off when moved? Knacked wheel bearings ditto? You can try jacking up the sump to free fr. wheel and try checking brake action while you rotate it by hand?

remove the hose from caliper. put nut and bolt on the end if banjo type then nip up the bolt , place in a bottle of brake fluid and pump until no bubble remove and tighten nut and bolt, fully pump lever it should be solid now ,if not knackered master cylinder , I have a working cylinder to go on the new bike i can lend you to eliminate the item

Just a thought… Are you able to pressurise the brake line from the bleed nipple? If so, it would show up a leak where air could get in.
Admire your tenacity - I would have given up long ago! Good luck with this.

Call me stubborn, but I will not let this defeat me. It is so stupidly simple, that there must be a stupidly simple solution. I must be blind to something, I reckon it has to be either the master cylinder or the caliper.It’s times like these that I wish I was still in the Midlands.

as stated quite happy to send you one of each to try at least then you will know one way or the other

I had no end of problems once with a Triumph Speed Triple. Like you had never had a problem before in over 30 years of home maintenance. In order of issues one caliper had a damaged nipple seal, can only assume got a bit of grit in there when cleaning. Then could not get the after market copper seals to seal, had to anneal them after which they were fine. Lastly, my non return bleed tube managed to stick after 10 years of service, so was allowing no fluid through instead was welling up through bleed nipple threads. What are the chances of all 3 problems coming up at the same time ? I was close to madness. Oh, and before I even started the stainless steel lines came with the wrong thread pitch !

When my front wheel bearing went on the v50, the first I knew was when the brake lever came back to the bars.

I think you need to check your brake disc for wobble as it rotates using a clock gauge. The bike needs to be carefully pushed along with the clock gauge attached to the fork leg or caliper and detecting wobble on the surface of the disc. Maybe the disc is wobbling and pushing back the caliper pistons?
All the best,
David

Would that happen wheeling it in and out of the shed?It’s a new second hand spoked wheel. Not noticed anything untoward.

Leant over to put me plate on the table and my belly must have pressed a button!



jmee542013-09-05 20:36:37