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'99 Gas Gas Tx250 Rear Brake Cylinder


dickiem
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Think my rear brake master cylinder is shot, can't get any pressure to build up, although the pads move very slightly when the brake lever is pressed, the lever 'bottoms out' on the frame.

How much am I looking at for a replacement...or can you get a refurb kit? Where's the best place to source one?

Edited by dickiem
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Hi Dickiem, is it possible that you may have had some air enter the system and it just needs bleeding? if not the place for AJP brake spares seems to be www.bvm-moto.co.uk, if you are in the UK that is.

Hope this helps Andrew.

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Hi

It might not be something wrong with it. The rear brake cylider is a hell to bleed. Just keep trying.

Some advices that might work is:

-Use a syringe to both push and pull brake fluid from the rear end.

-Put the front wheel against the wall or something to get it vertical and the master cylinder high

-Put the rear end high to get the slave cylinder high

-The "pin" that goes into the master cylinder is short. Make it longer or take it off and use a screwdriver or something to pump the master cyinder

-Jan

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Hi Dickiem, as Jan rightly points out the rear brake is a real bitch to bleed and it can take several attempts to get the feel just right, the way that works for me is to remove the rubber feed hose from the reservoir and force feed new DOT4 fluid or 5 in the right direction and out through the bleed nipple and then reconnect the reservoir and top up. I tend to change my front brake, rear brake and clutch fluid every 4 months with it being hygroscopic it takes in moisture (water) and loses it effectiveness in time.

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Tried bleeding it but from what you're all saying, perhaps a bit more perseverence is needed. Will try it again tomorrow. The fluid level was low which led me to believe there was a leak somewhere, strangely, I couldn't find any signs?

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put the long piece of silicone pipe from model shop on your syringe put into bottle of fluid and draw syringe and tube full of new brake fluid then connect to bleed nipple on rear caliper open the nipple and back fill the reservoir with the cap off and make sure that you are NOT pressing the brake leaver down, only crack the bleed nipple open 1/4 to 1/2 turn when syringe and pipe empty shut the nipple.

Tried it but the fluid just seems to squeeze out from around the threads on the bleed nipple (1/4 to 1/2 turned out), no fluid is being forced back into the reservoir :D

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make sure there's no pressure on the MC and the cap is off ect ect

i had a mare of a time doing mine, one piston was stuck you see, split it once i'd un stuck it and rebuilt it.

one thing i did, was put pressure on the lever and crack the banjo bolt on the MC just to get any air out from there, tighten and release lever.

also, remove the resivoir tube and pinch it to stop all your fluid coming out on the floor (opps) then connect you syringe and tube here and open the bleed nipple and push your fluid in at the MC and out the nipple, worked for me and mine will now do skids!! and actually slow me down!!

best remove pads when fiddling and place something in there to stop the pistons coming out,

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Tried it but the fluid just seems to squeeze out from around the threads on the bleed nipple (1/4 to 1/2 turned out), no fluid is being forced back into the reservoir :D

Usually if you pressurize the system and no fluid is forced back into the reservoir, that's a sign that the piston has not retracted back (or down in this case) to the stop at the circlip, and the bleed hole from the line to the reservoir is not opened (the system is not able to equalize itself).

Generally there are two causes for this (1) the rod at the back of the brake lever is adjusted too far up and/or (2) the piston return spring (in front of the seal) has sacked or broken (usually caused by rust in the system as water collects in the M/C bore or by wear on the sides of the spring, which gradually thins it to the point of breakage). You might want to pull off the rubber boot on the M/C and be sure the piston rod is back against the circlip.

Jon

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Usually if you pressurize the system and no fluid is forced back into the reservoir, that's a sign that the piston has not retracted back (or down in this case) to the stop at the circlip, and the bleed hole from the line to the reservoir is not opened (the system is not able to equalize itself).

Generally there are two causes for this (1) the rod at the back of the brake lever is adjusted too far up and/or (2) the piston return spring (in front of the seal) has sacked or broken (usually caused by rust in the system as water collects in the M/C bore or by wear on the sides of the spring, which gradually thins it to the point of breakage). You might want to pull off the rubber boot on the M/C and be sure the piston rod is back against the circlip.

Jon

Hey Jon, send me a PM or something to remind me, and I will send you some samples of the DC-111 compound. Seems really good for packing the backside of the boots to prevent corrosion and water. Good assy lube too! MC

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Usually if you pressurize the system and no fluid is forced back into the reservoir, that's a sign that the piston has not retracted back (or down in this case) to the stop at the circlip, and the bleed hole from the line to the reservoir is not opened (the system is not able to equalize itself).

Generally there are two causes for this (1) the rod at the back of the brake lever is adjusted too far up and/or (2) the piston return spring (in front of the seal) has sacked or broken (usually caused by rust in the system as water collects in the M/C bore or by wear on the sides of the spring, which gradually thins it to the point of breakage). You might want to pull off the rubber boot on the M/C and be sure the piston rod is back against the circlip.

Jon

Mmm, the MC piston only returns to within about 12mm (1/2") of the circlip. Total 'travel' from rest to fully compressed is probably only about 10mm (3/8"). Would appear that the piston is jammed at the top of its bore/stroke. Removed the circlip but can't get anything into the bore to 'grab' the piston to remove it.

Edited by dickiem
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