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Discussion Starter #1
I've re-built the front caliper on the XR600 (1989 RK bike) and I can't get all the air from the system.

Yesterday was getting fluid into the caliper and brake line, and now i have some resistance to the lever but it still comes back to the bars and I've not got any air bubbles coming from eith the caliper bleed valve or the lever bleed valve.

Last night the lever was pulled back to the bars with a cable tie and the pistons are pushed back into the caliper with a block of wood throughout the whole process. I've checked and I don't have any leaks, and now i've run out of Ideas...

HELP :confused::confused::confused::confused::confused::confused::confused::confused::confused::confused::confused:

Cheers
 

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I know nowt about Xr 600's but whenever i've had trouble bleeding a brake i find reverse bleeding from the caliper upwards usually sorts it (use a big syringe full of new fluid and a bit of pipe on the caliper nipple, remember to have someone at the handlebar end to 'mop up' or extract the excess)

My son once had a bike whose back brake just wouldn't bleed when on the bike (yz250f) and we had to remove the caliper and hold it higher up than the master cylinder with the bleed nipple facing up (nipple at the highest point)

Aprilia Tuono's have a similar problem sometimes requiring the caliper to be rotated into a couple of un-natural positions to get the air out from the pockets behind the pistons and ending up with the nipple uppermost to get rid of it from the system.

I suspect a pocket of air trapped inside the back of a piston or inside the chambers of the caliper so i would try unbolting it from the fork leg and holding it higher up than the handlebars. Try normal bleeding it in various positions to try and encourage the 'bubble' to travel up to the nipple.

Hope this helps
Ian
 

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Discussion Starter #3
Well, tried the caliper in a lot of different positions and I've cycled the pistons in and out a number of times no air from any of the two bleed nipples and I have a front brake that locks the front wheel and will slow the bike down with easy, but and this is the real issue, if i squeeze real hard I can still get the lever to come back to the bars, is this normal?

Sorry of all the questions but my other bike is a 1954 BSA with a cable operated TLS drum up front, so this is all a little new to me...
 

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I think you need to install a braided brake line as that explanation sounds like the walls of the original one are 'bulging' under pressure.

I think the OEM brake lines are only supposed to last about 3 years?:confused:
 

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Hubby says to try putting a ziptie round the brake lever and the handlebars and leave the brake fully on for a day or so, it gets all the micro bubbles out of the master cylinder
Tracey
 

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On my XR400 there's a loop of brake hose that goes higher than the front master cylinder (m/c)...so I use a clothes peg to hold the loop outwards from the fork leg so that the line is lower than the m/c. I also do the front brake bleeding with the bike on the side stand so that any air in the system has an easier chance of getting to the top.

When bleeding, look for any small bubbles that appear when you pull the front brake lever in by a few millimeters. Let these escape before bleeding the brake as they are so small but have a big affect on the way that the brake is bled.

On my XR400 I replaced the brake hose with an Aeroquip braided hose. When I came to dismantle my original so's to reuse the outer sheathing I found that the hose wasn't just like any other hose but a much higher quality than one from say my old 750 Honda. So don't be in too much of a hurry to replace the hose as it may not be that. I didn't need to do my ones on the XR...but I was racing it in enduros at the time & I thought that the armoured braided steel one might not come out so badly in an off than a rubber one.
 

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some times you can get a air pocket at ther top of the brake line where it meets the master cylinder. try pulling the front lever in all the way and then just un-nip the front brake line from the master cylinder at the top and then do it back up, that can release any air in there, i had that problem on my old Transalp 650.

or get one of these, they make bleeding brakes sooooo easy :D
but are expensive :mad:

SEALEY Brake Clutch Bleeder, Vacuum Type RRP£82 VS020 on eBay (end time 12-May-10 21:27:28 BST)

or maybe one of these all though i havent tried them :confused:

Speed bleed valves / brake bleeder TIGER 955i M8x3 on eBay (end time 26-Apr-10 22:13:50 BST)

good luck with what ever you do to sort it out! 'spongy' brakes are rubbish!
 

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Having just replaced/serviced both my brakes on my XL600V, I'm another candidate for the reverse bleeding method. I found that I had lots of air trapped in the system when doing the front brake, and when pushing the fluid in from the caliper, after about 3-4 fills (taking the fluid from the reservoir with the syringe, and pushing it back into the caliper... this way you don't have to worry about over filling the reservoir), I heard a mass of bubbles come from the reservoir when I pushed the fluid in the caliper.... and after that the brake lever went hard, and now only travels about halfway into the handlebars.
I would have to aggree with going for braided hoses though, as they seem to hold the pressure better than just the OEM rubber hoses.

Bare in mind though that I had lots of trouble bleeding up my rear brake, and ended up replacing the master cylinder seals, caliper piston seals, new braided line and all copper washers, so depending on how old your bike is, it may be worth changing them anyway, as at least then you know that they are new and will last for a while.

Hope this helps,

Titch:thumbup:
 

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Discussion Starter #9
I've made my own pressure bleeder and forward and reverse bled it, still not a good deal better. I took the bike for a ride though and I can lock the front wheel at 40mph so i guess its working ok.

But and this is it for me, If I pull hard I can get the lever back to the bars, so I'm assuming that there is some give in the brake line. Plan X will be to get some Goodridge between the lever and the caliper and see what that does to help...

All the same, flipping awesome brake, well I am used to a 8" tls...
 

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I've made my own pressure bleeder and forward and reverse bled it, still not a good deal better. I took the bike for a ride though and I can lock the front wheel at 40mph so i guess its working ok.
Thats sort of how my front brake started to go soft, and my problem was the 'Master cylinder' seals had gone/on their way out.... about £20 from Ebay to get new one, and easy to replace.

But and this is it for me, If I pull hard I can get the lever back to the bars, so I'm assuming that there is some give in the brake line. Plan X will be to get some Goodridge between the lever and the caliper and see what that does to help...
As above, but agree would first rule out the line itself, as sounds like you have pressure but either a small leak somewhere or a bulging line. Got my goodridge line from of all places my Honda dealer, and at a reasonably cheap price too.

Titch.
 
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