Shimano brake bleed question

I bled my front and rear XTs today--my first time doing Shimanos and the first for this bike (6 months old). The pads still have life on them but the rear is worn more. Three different guys (2 mechs and one expert rider) said although worn, they still have some life left but they're close. Anyway, after the rear was bled and put back together with wheel on, the lever went to the grip when squeezed. It took a few pumps of it to get firm. Note, it was firm after the bleed with the brake block still in the caliper. I syringed it 2x, tapping the line, tilting the lever, tapping it, etc. Is there air still in there (hard to believe with two, 20 ml fills of oil) or is it just because the pads are so worn that the pistons have to close down a bit before the lever gets firm? Possibly related to that, I did notice that I had to push the pistons back in a bit so I could get the brake block in. Thoughts?

 

Pads were worn.

 

You didn't perform the bleed correctly you must have air still left in the line or not enough fluid. I don't think it is the pads.

 

That's normal in my experience. Any time you push the pistons back it will take a number of lever pulls to get the pads back to the rotor. As long as the lever eventually gets firm it should be fine. I just did this a couple days ago to change a rotor. Maybe 10 lever pulls for it to get firm? But you may have pushed the pistons back farther than I to get the bleed block in there, I just needed room to get the new rotor in.

 

After it firmed up, is it is "still" firm like it was before?

 

I agree with Dave (dcrfx). If it's still firm than you're on the clear. If your pads are almost worn out then it takes the piston to make up for the clearance compared to new pads.

 

CAREFULLLLLL. Once agin CAREFULLLLL. That happened to my brakes where they would get firmer the more i squzed the lever a couple of times. Then went for a ride popped a wheelie and no brake. You probably have air in them if it keeps going to bar after you let it sit for a while and squeze it .

 

I'll check tonight and see if it got mushy again. Thanks, all.

EDIT:

Just checked the rear--mushy again. I'll try bleeding again tomorrow. Do you guys do the plastic bag drip at the caliper after syringing like in their instructions? I saw a Shimano pro race mech's video and he skipped that part.

 

To get the clearances correct after a bleed I only bleed brakes with new pads or use that orange spacer that comes with the brakes when you buy them.

Dean

 

I am curious why you felt the need to bleed the brakes after six months when you did not need new pads? I would have just waited until I did the pads...

 

yes, definitely do the plastic bag step. I think its supposed to help remove air from the caliper.

 

Welcome to the world of Shimano brakes. These are some of the best brakes but you have to bleed them frequently. I never do the bag step. Only bleed using the syringe. Make sure to tap the lines, caliper, and lever. Air bubbles can be anywhere. The most useful thing that I have is done, is to tilt the bike up like you are doing a massive wheely. Helps to have a stand to do this. Make your lever parallel to the floor and then bleed using the syringe. At this angle the air bubbles will naturally work their way up to the lever through all the bends and curves of the suspension hose routing. The front brake does not need this as it is usually a straight shot with no drastic bends up to the lever.

 

I have had good results with brake bleeding by following the instructions Shimano provides.

NOTE: Be careful when pushing the pistions back into the caliper. They are made of ceramic and they are fragile. I learned the hard way.

 

I follow this video's method, which seems to work well, especially the part about moving the lever around and pumping it: http://www.youtube.com/watch?v=o2c6ezHY0A4. I do the caliper bleed too, but it's not clear to me that it actually helps since I never see any bubbles coming out of the caliper.

 

If you bled correctly here is what happened.

With the bleed blocks, the pistons are pushed in and the system is filled with the right amount of fluid with the bleed. When the used pads are installed, there is not enough oil in the system to push the pads all the way to the rotor.

At this point, when you pump the lever, fluid is taken from the reservoir and fills what is lacking. The system will be fine.

However, even after pumping the lever and you still can't get a firm feel, you will have to bleed again. There is air in them thar hose!

After bleeding so many systems, I have given up bleeding rear brakes on the bike. I pull them off and hang them vertically with the hose fully extended for the bleed. For the front, I take out the caliper and let it hang with fully extended hose. These tedious steps helps me avoid countless rebleeds

 

I bleed my XT's as well, when you use the provided orange block in between your pistons I've found that your effectively bleeding the system to accommodate a new set of pads as the orange block is similar in size/thickness. When your pads are worn, and possibly even your rotor, the brake system needs more fluid to accommodate the difference in pad thickness and rotor thickness. If using old pads after a bleed, I find something similar in size to the worn pads to use when bleeding, this will allow more/right amount of fluid into your system. Check your rotors thickness too, that can be another culprit.

Another tip for air bubbles when bleeding is to touch your caliper and brake lines with a vibrator to shake/unlock all the trapped air. Its the same process used when pouring concrete, a vibrator is lowered into the concrete to force the air bubbles out, works well for me. YMMV, Good Luck

 

If all is bled, in this situation, I usually take the wheel off and give the lever a few squeezes to bring the piston out a touch to reset its resting position closer to the rotor. Put the wheel back on and you should feel a difference. If not try again but be careful not to get it too tight. Not sure how appropriate this procedure is, but it works for me.

 

I guess I'm not following the thinking of lack of fluid when you bleed and then put worn pads in. If that was the case there wouldn't be enough fluid to ever use the full thickness of new pads (?). Or you'd have to top up the reservoir before you could use the full thickness (?) Anyway, I've never had a problem pushing pistons back, bleeding, and putting old pads back in...

Having said that, in the OP's case he must have some air hiding in there somewhere. Good tips from Bing and dmbfan and others to get the air out. I once tried to to bleed backwards towards the caliper to get some bubbles out, but it ended up being a problem with the piston seals and the bubbles just kept coming out. Good luck fongster, let us know how it goes!

 

Always bleed with the bleed blocks in (or at least with pistons pushed back in), regardless of how worn the pads are. Brakes are designed around a specific amount of fluid in the entire system and have the collapsible reservoir to adjust for wearing pads and to some extent, wearing rotors. When the brakes lever is squeezed the reservoir is closed off from the rest of the system. If you bleed with the thin worn pads in and pistons extended instead of installing the bleed block you will overfill and there is a slight danger of the brakes lever throw getting real small or even locking up completely if they get real hot. Fongster it is normal to pump the lever a few times till it firms up, as long as it then stays firm and has normal lever throw. If its still soft still air in teh system. If the pads or rotor are so worn down that the brakes dont work properly with full lever throw with the proper amount of fluid time for new pads and/or rotor. most brake manufacturers recommend not wearing the pads down to the bone.

 

Hi guys. Success! Your tips were great. I got the bike into a wheelie for the rear and also removed the caliper so it'd hang vertical. I tapped the heck out of it and also left the bike for an hour as I had a errand to run. Gravity worked and the bubbles went up. I had a great bleed on the rear. I even heard the air coming out into the funnel when I syringed it. I did the bag thing too but never had any bubbles come out the caliper end. I also redid the front with lots of tapping, flicking the lever, and line and got more air out so it's real firm now--the lever did pump a few times as the piston had to close the gap to the half-life left pads but the lever pull is firm. The rear pads were more worn than first thought, so I replaced them with new ones--no lever pump, just nice and firm. Thanks again for your help. *I passed on the vibrator suggestion, too kinky for me, lol. Made sense though!

BTW, here's my tip for making your bleed kit. The Shimano budget "kit" is worthless at $14. It's just a little oil, a hose and no instruction sheet. Their "deluxe" kit is a rip too. Buy some of this hose and share it with your friends http://www.socaltrailriders.org/forum/showthread.php?70114-Source-for-syringes (see post #12). It holds onto the bleed nipple much better than the Shimano, which falls off too easily. You will need to buy the Shimano funnel ($10) and a quart (liter?) of their oil for $28 from the LBS (the budget kit is a rip--you get a one time use amount for $14--2 oz?), get a free 20-30 ml syringe per that link for the other post and you're set with using the video mentioned earlier plus the instructions with the funnel.