HELP!!! I have always had a modicum of trouble bleeding brakes systems, but have usually got there in the end. 1) I have zero pressure on the 'pump' for both front and rear brakes. without a brake reservoir or pipe(s) fitted, both pumps squirt out residues of brake fluid when 'activated' So they seemingly work. 2) Front brake. Top up reservoir, open the 'pump' by tying back the brake lever with a rubber band. Open caliper bleed nipples. Leave overnight. Result = Leakage. So gravity is getting the brake fluid down to the Calipers and out of the open bleed nipple(s) 3) carry out the same procedure with the bleed nipples closed but the brake banjo unions cracked slightly open/loose. Leave overnight. Result = leakage, as above. so fluid is getting down there! 4) carry out the same procedure but have the caliper bleed nipples and Banjos firmly 'closed'. Crack open the bleed nipple on the brake lever pump and leave overnight. Result = Leakage 5) Rear brake, the same procedure but the brake 'cyclinder/pump' doesnt have a bleed nipple. same result with caliper bleed nipple and banjo bolt.... leakage as above. Brake fluid is getting where it should be. But try and bleed it conventionally, glass jar higher than the bleed nipple. Rubber tube fully submerged, slowly pump until no more bubbles come through. Absolutley zero pressure on the brake lever front and rear. pump pump pump, no resistance at all! WHAT am I doing wrong? I have successfully bled these brakes in the past. It cant be blocked caliper pistons, surely, as that would give me hard pressure on the levers? No?
Nope, at the 3 min mark...'Pump the lever to pressurise the system'.... that's the bit that my brake system won't do.... pressurise. There is zero resistance no matter how many times I pump and crack.
Not sure what bike you have - does it have a bleed nipple at the master cylinder? If so, I'd start there.
It's upgraded 900SS. The front brakes has a 'radial' Brembo racing master cylinder (with a bleed nipple yes), the rear brake master cylinder is standard (no bleed nipple) I guess Theres nothing lost in starting up on the master cylinder... but still won't help with the identical problem on the rear brake
the 749 master cylinder had a screw inside that needed releasing, otherwise very spongy brake, no matter how much it was bled.
What do you mean by leakage? Brake fluid or air in the system? Are your front and rear brakes interconnected like an ABS set up?
This is my vacuum bleeding kit. Fluid is sucked down to the calipers from the master cylinder by vacuum. Seems to work OK, quick and reasonably cheap. EBay it.
I leave first, the caliper bleed nipple open to see if fluid was making it to that point in the system, so it was fluid that leaked. Same as closing the bleed nipple and cracking the banjo bolt. If you keep the brake lever held back overnight (in the open position) and the fluid level in the reservoir drops, as the fluidd leaks, then you know that there is no hinderance in the system.
I I use the same on empty lines then once fluid starts to show I switch to the usual method. Can take a long time to get the air out otherwise.
I've never understood why people struggle to bleed brakes, I've had 15-20 bikes & 10-15 cars in the last 30-40 years and never had an issue on any of them and no need for any vacuum bleeding gear, hell I've had to bleed my clutch at the side of the road with no hoses, just washed off brake fluid from a water bottle after.... 1. Reservoir filled with fluid & all pads / pistons pushed back to the zero position 2. Prime the mc by bleeding the mc cracking a union or using a dedicated bleed nipple 2a. Pump the lever & hold in fully 2b. Crack the beed nipple 2c. Tighten the bleed nipple (just one finger on the spanner tight is more than enough) 2d. Release the lever slowly 2e. Repeat until fresh fluid with no bubbles is seen 2f. Check the MC reservoir all the time and top up where necessary 2g. Nip up the bleed nipple properly 3. Go to the furthest caliper from the MC and repeat step 2 4. Move to the next closest caliper and repeat step 2 5. For cars, repeat 4. Tips & tricks In the beginning try not to build up too much pressure when pumping to ensure you are flushing out all the old fluid from the slaves, if you build up pressure too soon you might not get all the old fluid out. Not a huge deal as there's very little left anyway if you fully push back the slave pistons. Sometimes a couple or so pumps on the lever helps before cracking the bleed nipple, you get a feel for it, pump feel the slight pressure, crack and pump the lever home, hold then tighten the nipple. Rinse and repeat. In the begining with new hoses / rebuild calipers etc and everything is empty, you won't build up any pressure due to compression of air, but just keep going it will get there. Always pump and hold then crack the nipple, then close the nipple before releasing the lever. Release the lever slowly especially in the beginning when everything is full of air. If you are struggling, check the freeplay between the lever actuator and MC piston is correct, you might not have enough freeplay to uncover the compensating port. If you are still struggling, strip the MC and check for blockage at the tiny compensating port - you'll need to remove the big rubber bung where the reservoir feeds in fluid to the MC to access it. On odd occasions I have seen Brembo rear MC pistons not floating properly in the plastic insert, dunno if the plastic swells over time or perhaps corrosion from behind, but in that case - time for a new MC. Sticking to this method, I have never needed anything fancy, no vacuum kits, no hanging calipers upside down, no tying the lever back overnight etc etc...
I once borrowed a super duper vacuum bleeder off a fiend of mine. Always seeing air bubbles in the drain pipe. When bleeding. Tightened the bleed nipples up no problems. Tested brakes fine, no spongebob or squarepants. Conclusion was the vacuum was so great it was pulling air from outside the loosened nipple through the nipple threads. Hence the bubbles. Not convinced with shake an vac bleeders.
One problem on many motorbike brake systems it the tiny amount of volume that gets shifted by the master cylinders. Sometimes it's just not enough to overcome the sticktion in the caliper seals. Every time you pump the lever the pistons move out a bit but get sucked straight back in by the seals. What helps is a little bit of friction between pad and disc. Let's assume you have most of the air out by the methods you've employed. Try building pressure whilst someone is rotating the wheel.
Vacuum bleeding will tend to draw air in passed the bleed nipple threads then out of the vac line so you can chase your tail waiting for a bubble free stream of fluid. So don’t waste fluid waiting for no bubbles. Pressure bleeding works great but can make a huge mess if it goes wrong. F1 teams pressure bleed their brakes. Huge wastage of fluid. But who cares?
