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Help, front brake won't build pressure during or after bleeding

S

Stolenfant

Husqvarna
A Class
Bought bike few weeks ago. Lots of things just weren't maintained, but nothing badly broken. The brakes were working but the rear fluid was so badly burnt brown that I figured I'd flush and bleed both. Front resivoir looked clouded over, but upon opening I discovered a fluid that was the cloudy color of clear silicone, and the viscosity was more like 90 wt gear oil. Again the brakes worked. Judging from the number of times I dumped the little bleeder bottle, I flushed about 375 ml through. That's enough for more than three full drains and refills. However, I can't build pressure now. I've pumped a couple hundred times and only clear fluid bleeds, but it just won't build pressure. Any ideas?

Should I go ahead and disassemble the front caliper entirely and flush that too? I'm getting low on 600 degree Motul brake fluid, and was hoping to avoid that since it has to be ordered.

I've rebuilt brakes on my WeeStrom, old Triumphs (autos), so have a clue, but this one's got me stumped. It's as if the system is sucking air in somewhere, but it isn't leaking fluid anywhere except bleed valve.
 
I just tighten everything up and keep on pumping till I get all the air out. I´ve never been able to bleed all the air out before tightening the bleed valve on a bike.
 
Use an injection (big one), and push the fluid from bottom to top, all air will be pushed out at the top.
Air bubbles tend to rise, pushing them outwards especially when the system was empty, is cumbersome.
 
Bart said:
Use an injection (big one), and push the fluid from bottom to top, all air will be pushed out at the top.
Air bubbles tend to rise, pushing them outwards especially when the system was empty, is cumbersome.
Click to expand...
I need to change the fluid on my 2006 TE250's front brake, and that is my plan - I've yet to do it though.

Bought syringes at Ace Hardware.
 
I bought a vaccuum bleeder, that works pretty well... I've had the exact same problem 2 times on my wr125, and different things solved it each time. The first time, I had to lean the bike way over, and give the front caliper a little tap. Seems there was an air bubble trapped in there.

Second time it took me leaning the bike over again, to the left, and tapping on the resivoir with a screwdriver handle. There was little bubbles caught up in there. And both instances are after fully bleeding the system (so I thought).

Good luck!
 
Issue Resolved! Removed caliper, brakehose, master cylinder, lever, et. al. and laid on bench and blocked everything up so bleed nipple was lowest, master cylinder and a catchpan were highest, but not by much. Then pressed pads out far as possible and blocked w/ a piece of 3/16 aluminum flat stock incase calipers closed. Then started a Jamaican steel drum serenade of the wrenching gods on all metal parts. Evidently the bubbles loosened because after pumping the first 2 oz of fluid in, the lever was able to close the caliper. I ran another 1.5 oz in before tightening the bleed valve, and reinstalled everything. Opened the mcylinder back up, topped off and after second round of pumping it started to build pressure. Checked mcylinder and it was still full. Job done, checked torque on everything, and will test tomorrow. Thanks all!
 
I've had the same problem, used a Gunson's Eezlibleed for a car, reverse bled it from the caliper valve and just fluid comes out of the return valve in the master cylinder.

Still no pressure at the lever and only a slight effort from the caliper. Used over a litre of brake fluid, getting quite expensive and frustrating!

Not to mention the garage floor is drenched in brake oil.
 
I am considering that but there is no reason why my efforts haven't worked. Every time I have reverse bled the system from the caliper bleed nipple there is plenty of brake fluid coming out of the master cylinder like a fountain, no air bubbles at all. I am going to take the caliper to a garage and have them pop the pistons out with their air line so that I can check the seals. If the seals are obviously damaged I will replace them, if not I will also ask the garage to bleed it again.

But they will only pressure bleed it which is what I have been doing anyway. From the symptoms it does seem as though there could be a small leak in the caliper pressure seals although I have not noticed any fluid loss from the master so it would have to be very small.

I have found a rebuild kit on eBay but it is £34 so not cheap at all.

I have bled the brakes before and it only took a couple dozen pumps with the master cylinder cap off to get rid of the bubbles and a few further pumps with the caliper bleed nipple open to remove the rest of the air but even with some air in the system I have getting more effort of of the caliper than this.

It's turned into one of those sagas, very unexpectedly.
 
One thing you could try: Lock the front brake lever in the fully pulled in position (use rubber bands, or pliers, ...) and leave it that way overnight.
Sometimes that is enough for the air bubbles to make their way out of the system.

If not, the syringe method is cheap and it does work.
I started using it back when I had a yz250 and Yamaha was too cheap to pay Honda to use their patented direct brake line routing.
So my YZ front line had a big loop around the caliper, which means that if you ever got air in the line, there was no way to get rid of it by just bleeding the brakes in the traditional way.
 
Right, I have resealed my brake caliper and it has resulted in a slight increase in braking effort without any air bubbles at the seal but the lever is still going all the way to the bar.

I have pushed the pistons back in on the caliper and it is just wasting the fluid out of the master cylinder as no bubbles are coming out.

I have removed the caliper from it's mounting and actuated the brake lever and I have observed that it seems the pistons are pushing out to a certain point but before the pads are fully sandwiched together, pulling the lever results in the pistons coming out and then releasing the lever results in them going back in again, slightly before the pads are fully sandwiched together.

When I stripped the caliper the pistons and bores were in perfect condition, so unless it was a combination of the caliper and the master cylinder I am stumped. I could try the TE master again but I am getting through copious amounts of brake fluid so I don't want to do that.

I will make a video of what is happening and upload it.
 
Another update time! I have contacted the seller of the Brembo seals and he said that there shouldn't be any air bubbles around the caliper pistons at all. I have disassembled and re assembled the caliper three times now and tried it with both the SM master cylinder and the TE one, the lever goes back to the bar on both, but it doesn't feel like there is any air in the system. There is moderate braking effort but not the stoppie pulling power I am familiar with. It could be that both master cylinders are worn out and the bubbles around the caliper are a red herring because the caliper isn't designed to be operated off the bike but I doubt it!

Kinda typical, whenever I decide to do something fiddly like this instead of replacing the whole part it normally ends up with complications!
 
As far as I know about fluid dynamics, if the master cylinder of the TE has a smaller diameter, it will have a longer stroke. The stroke also depends on the ratio of the lever.
I don't know what the problem could be, sorry I can't help you.
BTW, have you disassembled the caliper opening it in two halves? Did you have to replace any gasket? Someone says you can disassemble and reassemble it reusing the inner gaskets and I'm asking just to double check because maybe I'll have to do that in the future.
 
Another update. I don't know what to think now, after swapping the brake hose for the one from my TE setup, the lever goes all the way back to the bar but only with a good squeeze, almost as though the linkage between the lever and master cylinder isn't long enough to squeeze the master cylinder plunger all the way to where it is at full pressure. What doesn't help is that I can't remember what it was like before! It is good enough to do a small stoppie at the end of braking now and my brake pads aren't the best after getting so much brake fluid on them either. I figure I will leave it how it is, still stronger than the TE setup when that's working properly.

Theo, yes to both of your questions. There is a small rubber O ring on the top part of the caliper where the hose goes in, sealing the two halves. I was careful to make sure that had not fallen out on each disassembly. This O ring does not come in the rebuild kit so you have no choice but to reuse it.
 
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