Brake problem after tire change.

[mike72903]

Not on my Valk but I figure front hydraulic brakes are pretty much the same.  Anyway I put a new tire on my 04 Shadow Aero VT750.  Afterward it took a while to get the brakes to pump up but they eventually did.  A little later I was moving it out of the garage and the front brakes seemed to work fine and then they didn't. Lever went to the grip and refused to pump back up.  I've tried bleeding with no effect and see no bubbles when I do try.  There was an adequate amount of brake fluid to begin and I've kept it topped up as I tried to bleed.  Not sure what to think.  Only thing I did to the brake system was to force the pads apart a little bit before I put the new tire on.  Bike only has a single brake caliper and it was not necessary to remove it to change the tire. Is it possible my master cylinder has gone bad?
Thanks for reading

[Hook#3287]

Looks like a pretty simple system, it's got to be air bound somewhere.

The fluids going somewhere.

Try the "Holding the lever with a rubber band overnight" trick.

Rebuilding the M/C may be next, maybe something went wrong when you forced the fluid back.

[gordonv]

Not on my Valk but I figure front hydraulic brakes are pretty much the same.  Anyway I put a new tire on my 04 Shadow Aero VT750.  Afterward it took a while to get the brakes to pump up but they eventually did.

And this is all you did? Just changed the tire, no other brake work.

If you try the lever trick, make sure the reservoir is on the high side of the bar (handle bars turned to the left).

[mike72903]

Not on my Valk but I figure front hydraulic brakes are pretty much the same.  Anyway I put a new tire on my 04 Shadow Aero VT750.  Afterward it took a while to get the brakes to pump up but they eventually did.

And this is all you did? Just changed the tire, no other brake work.

If you try the lever trick, make sure the reservoir is on the high side of the bar (handle bars turned to the left).

other than forcing the caliper pistons back a small amount,yes.  I will say the fluid might not have ever been changed before I got it.  It was pretty dark before I tried bleeding.  Maybe pushing the pad back forced addition dirt into the master? IDK Weird that it pumped up originally then failed.  I'll go wire  my lever back but I'm not hopeful.

[Oldnick]

Just my 2c worth. and that's  about what  it IS worth.

If there was air in the brake piston cylinder and you forced it back into the system by pressing back the piston it would have been in a place like the cylinder, where a tiny bubble does not matter. But if for some reason it then moves to a small diameter place, suddenly it becomes a major patch of air that, being compressed, takes up"all the space".

Did you completely bleed the system until the fluid ran clear? Anyway, my rule after one failure years ago is to bleed, go for a careful ride frequently testing the brakes for 10-15 minutes, and have another go. Surprising how often a few bubbles appear.

Also, what I was taught by my mentors (my mate's racing father and uncle) was to use some clear tubing a tight fit over the bleed nipple, take it straight up in the air, where you can see its full length, and curved over into a jar for catching the fluid. Then you do not need to operate the nipple as you bleed, because you have a liquid trap that stops any air getting back into the system when you release the lever. You also see any bubbles. I always keep pumping for quite some time after bubbles seem to disappear. You can't (shouldn't) use the opened fluid bottle again anyway.

[Earl43P]

I agree with Oldnick but will add my 2 cents.

Dismount the caliper(s) remove pads. Use the brake handle to push the piston(s) out past where they were while in use. Should be a distinct line of crud. Using an old shoelace soaked in brake cleaner, clean the crud off the piston(s). If necessary I'll use a narrow strip of 400-600 grit sandpaper cloth to brighten it up just so.

After this thorough piston cleaning, place a good drip of brake fluid on the piston such that the seal gets well wetted. You'll clean the excess later.

Push the piston(s) fully retracted with a suitable size C-clamp with the bleed screw loose and fitted with a tube as Oldnick described HOWEVER I add a step of installing a small 10mm box end wrench before the tube gets put on the bleeder. Orient the caliper with the bleed port vertical and still open. Clamp the piston(s) fully retracted and leave them. I keep an old brake pad for this clamping, installed backward - pad against the piston, so steel is against the clamp.

Suction or rag out all of the old fluid in the Reservoir. Clean out the crud.
Lift out the spooge (return) hole baffle and thoroughly clean out that tiny hole. Use fine wire if necessary, usually just the jet of brake cleaner straw is sufficient. Refill with fluid to about the bottom line, this new fluid will be removed later. You should have your Master Cylinder as level as possible using the handlebars.

Using the brake handle, slowly squeeze/release the handle until clear clean fluid comes out of the caliper hose. It should take several refillings of the reservoir to do that. In between refillings, rag or suction out the fluid and refill with clean new fluid. You'll notice that the spooge hole will reintroduce dirtier fluid back into the reservoir. Maintain clear clean fluid throughout the process, fluid is CHEAP.

Once you have clear fluid, pick a stroke and close the bleeder just snug. Give a few strokes and see how you like the feel of your brake handle, remember you are pushing against the clamp so don't get too pushy. If it feels squishy the best place to look for bubbles now is at the master cylinder. USE RAGS Slightly loosen the banjo bolt there and do a steady stroke remembering to retighten the banjo bolt as you stroke pressure NOT after releasing! If you find air, repeat as necessary. Usually goes away quickly.

Once you feel good handle pressure and have the banjo tight, bleeder snug, remove the caliper clamp, clean the excess brake fluid in that area with a clean dry rag and then push the Piston(s) out a fur piece, install the (new) pads (remember the grease points on the spring clips) and remount the caliper. Stroke the handle until the pads contact the disc and assess whether you are satisfied with the feel or not. I do that with a pad-bedding test ride.

I rarely have to rebleed after the test ride using this procedure. If I was not quite happy, I would use the zip-tied brake handle trick a couple overnights before I'd crack the bleeder again, personally.

All that might sound like a lot of work, but once you get the hang of it, it goes quickly and you have full confidence in your brake job.  IMO pads are cheap and I replace them every tire change (sometimes BEFORE in the case of car tires on the back and rear tires on the front). I keep a set of new pads on hand, ordering them immediately after pad installation. 

The rear caliper and master cylinder method is similar, but does involve a great deal more work and mess to clean its spooge hole (making keeping CLEAN FLUID in there all the more important). Linked brakes, like my 93 has also presents challenges, but remains virtually the same procedure, but with two clamps, which dual front calipers also requires. If it has been a few years, it's a good idea to remove the brake line and bleeder to clean the interior of the caliper with brake cleaner.

My 2 cents typed out looks more like $2.

[mike72903]

Thank you all for your very knowledgeable suggestions.  I tried some of them before becoming convinced it was the master cylinder. Went to the local dealer but they didn't have the rebuild kit and had to order it.  It the meantime I disassembled the MC. It was really dirty. I cleaned it the best I could and reassembled.  Now I could get some resistance when pulling the lever where as before there was no resistance at all.  I could actually get the brakes to work but the lever would slowly pull to the grip. So now I'm waiting for the order to arrive. Just in case that isn't the problem I ordered off of eBay from a recycler a working set of master cylinder, complete caliper and brake line for less than the price I had just paid for the rebuild kit. Good to have spares I guess.

[Oldnick]

Wow! Must have been filthy to leak even after cleaning. Shot seals. Hope it all goes well for you.

[Oldnick]

earl43p thanks for that. My brake lever has been a bit stiff and jerky, until more pressure "cracks" it.. I was going to clean everything up and your description will be near me!

[falconbrother]

After owning a few Harley big twins I always do a reverse bleed on my brakes.  The traditional way will not work on Harley (ask me how I know) but, a reverse bleed works quick and easy every time.  That is force fluid from the caliper to the master cylinder.  Bubbles go up hill always so, trying to get them out at the lowest point can be an act in frustration. 

[Valkpilot]

My 2 cents typed out looks more like $2.

Worth every penny.  Excellent advice for anyone with spongy brakes.

[Earl43P]

earl43p thanks for that. My brake lever has been a bit stiff and jerky, until more pressure "cracks" it.. I was going to clean everything up and your description will be near me!

That ^ can be caused by a worn handle or (more likely) the bushing that the handle pushes into the master cylinder. To tell, simply spray some lithium grease where the handle goes into the Master. If that smoothes it for a short while, replace the $5 bushing.

[Oldnick]

earl43p thanks for that. My brake lever has been a bit stiff and jerky, until more pressure "cracks" it.. I was going to clean everything up and your description will be near me!

That ^ can be caused by a worn handle or (more likely) the bushing that the handle pushes into the master cylinder. To tell, simply spray some lithium grease where the handle goes into the Master. If that smoothes it for a short while, replace the $5 bushing.

Jeeze! OK. Far easier than getting stuck into the calipers. Many thanks. I assumed it was the bottom end because of the far greater contact surface, but yeah the sticking is pretty mild.

[Oldnick]

earl43p thanks for that. My brake lever has been a bit stiff and jerky, until more pressure "cracks" it.. I was going to clean everything up and your description will be near me!

That ^ can be caused by a worn handle or (more likely) the bushing that the handle pushes into the master cylinder. To tell, simply spray some lithium grease where the handle goes into the Master. If that smoothes it for a short while, replace the $5 bushing.

You were right. Bit of lube and all is well. Typical of me wanting to start at the difficult end....