Just replaced the front caliper on sons cg125 and, after 1 litre of brake fluid being pumped through, still getting air bubbles in various quantities and sometimes a huge amount - master cylinder knackered or could it be something else?
Cheers
Start with the basics:
Why did you replace the caliper?
Where the brakes actually working before the swap?
To Bleed, push the piston fully home in the caliper (hold in place with a G clamp or similar. Get a large syringe and a piece of tubing that is a good tight fit on both the syringe and the bleed nipple on the caliper. Fill syringe with fluid, attach to bleed nipple via tube, hold syringe vertically and gently pull back on the plunger to get all to air in the syringe to the top, crack open the bleed nipple and push fluid into the caliper and up the system with the syringe (you may need to remove fluid from the master cylinder, keep pushing until no more bubbles come out. lock off bleed nipple. top up master cylinder with fluid, carefully pump the piston out of the caliper using the brake lever (not so far you push it out of the seal) now slowly push the piston all the way back into the caliper, check for bubbles in the master cylinder.
Now refit the caliper and brake pads, pump brakes till the pads are in contact witt he disk, if you still have a spongy lever the next step is to overhaul the master cylinder.
Simples :azn:
Caliper piston was seized and the allen bolts to remove it from the sliding bracket were seized solid and rounded off, so got replacement caliper off ebay.
Pistons were pushed fully home and kept there, courtesy of wide spanner, during bleeding, didn't try the syringe method as have always managed to bleed brakes ok the normal way, even the infamous tokico six pots.
It was the sheer volume of bubbles that kept appearing, it would be down to next to none and then a huge stream would come out; this was over the period of a couple of hours, including leaving it to let any bubbles settle and try again, including having the caliper raised above the master cylinder. It's on a CG125 so hardly a a large volume system. Can only think that somehow air is getting in at the master cylinder, but wasn't sure how likely that was.
To get stubborn bubbles I've pumped the brake until the piston is almost out, then pushed it back into the caliber to push bubbles out of the master cylinder at the top. Be careful though because it squirts everywhere I you're not.
Are you bleeding "by hand" or using something like a Mityvac? If the latter then it has a tendency to pull air down the thread of the bleed nipple making you think there's more air in there.
Using the one person bleed kit so non return valve on the end of bleed pipe. Did wonder if air could get dragged in around the bleed nipple somehow as couldn't see how air could get into the master cylinder and not leak under pressure
PTFE tape on the bleed nipple to stop air being sucked in.
I tend to use my Mityvac to get the fluid through then just bleed normally.
Also try turning the bars so the reservoir is at the highest point then wiggle the lever through about 1/8th of its travel, was amazed how many bubbles this got out last time I did it.