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Bleeding dry brake system

2K views 19 replies 5 participants last post by  RIDER675 
#1 ·
Dry system after replacing a caliper banjo bolt, can't build much pressure but no bubbles (hear the discs creak a bit). Used a harbour freight vacuum bleeder to get it started then bleed the MC etc by hand over 4 hours yesterday. Vacuum had no effect on lever.


Ran a line to a nipple from the reservoir and pumped a thousand times until fluid was pumping into the res. No change.

Next tried pushing fluid through one side. On other side most of the fluid leaked out the hose or bleeder threads could be because its a banjo bleeder. Tried using the syringe to suck the res empty from the caliper nipples. Replaced MC crush washers. Replaced a bleed screw and put grease on the threads. Left rubber band on the lever and reservoir cracked open.

Getting pretty desperate spent all of yesterday and today is last chance to make my track days.
 
#2 · (Edited)
Not sure what your specific problem is, but with completely empty lines I'd just let gravity do the work. I'd even recommend you empty the lines completely and start from scratch with fresh brake fluid, as the one you've spent so much time on is probably aerated to the max by now.
Close the MC bleeder, open the bleeders on the calipers and attach vinyl hoses pointing skyward. Push in all the caliper pistons to reduce any potential room for air pockets. Slowly fill up the reservoir, then wait, refill fluid when the level gets low. After 15 minutes or less you should see the fluid rising in both vinyl hoses. If not, the caliper bleeders are not open enough.
Then close the bleeders and get the remaining air out conventionally (pump lever SLOWLY, open/close bleeder, repeat). Zip-tying the lever only makes sense to get the very last tiny bubbles out in the end.
I say be slow with your movements on the lever, so the air bubbles have more time to rise up to the reservoir or the MC bleeder, and won't brake apart into tinier bubbles, which will be even harder to get rid off.
 
#3 ·
Looks like the RH bleed nipple is leaking, when I pack grease on it the pressure increases for a few pumps. I tried the old bleeder again and the newer one is just a yr old. Is the anything I can do without replacing the caliper? Are gen1 calipers compatible w gen2?
 
#4 ·
I trick I came up with some years ago to get the MC primed when the level has dropped too low whilst bleeding may help.

Have your right side bleed nipple open and I use the Old-School piece of pipe into a Glass jar with some Brake fluid in it as a one-way valve.

Fill up the MC to the Top line.Now spit on your hand and place it on top of the MC and press to make an Air-tight seal and then slowly pump the lever and keep an eye on the Jar and the level in the MC.With luck you should feel a bit of suction on your palm and fluid starting to flow.

Top-up MC as you go along and repeat.When satisfied you have pressure alternate bleeding right and left sides until happy there's no air left in the system but keep an eye on the MC fluid level.

HTH :)
 
#5 ·
Actually doesn't seem like the bleeder, teflon had no effect on it. As for bleeding the MC, how is that different from just cracking the banjo? I have enough pressure to get fluid out there and make the brake discs creak.

One odd thing is a rubbery or sucking noise from the MC, most likely the dust boot.

Also when I start to bleed sometimes it build up a bit of pressure, then as I continue the pressure drops off.
 
#10 ·
Got a proper syringe, the other didnt fit the hose tight enough. Didn't help I got better results bleeding normally, but is it odd that I get a drip through the bleeder threads using the syringe?

Swapped the MC, feels the same. Starting to wonder if the replacement banjo with bleeder leaks.
 
#13 · (Edited)
Just picked up new bleeders. Only things ive noticed, the bleeder has some play up/down when fluid flows at 1/8 turn out or less. Also can't get much fluid off of that side at all. This is weird, the vacuum bleeder on this side only pulls bubbles towards the bleeder opposite the other side.

Removed the new banjo bleeder and just bled using the caliper bolt. Now everything is new except that and the crush washers on the side that haven't been moved.
 
#17 ·
I found this sleeve to replace the bleeder screw, that has its own seat and smaller bleeder. I don't think there's much chance I can drill out the bleeder and tap it though. Seems like it would require a drill press and some way to clean the caliper afterwards.

Considered taking to the dealer but I don't think they can do anything different than bleed and inspect it. Anyways thanks for the suggestions, guess this is why track day orgs offer insurance.
 
#18 ·
Just wanted to update this if anyone has similar issues, I believe the caliper is leaking air. Managed to get the brakes going, did 3 sessions before they faded a lot. Flushed the fluid got a good lever again, then nearly ran out of lever the next session coming into the pits.
 
#19 ·
Have you found out where the air leak is? I might have a similar problem. After a day of hard street riding, the lever travel increased over 50%.
I suspect the bleeder valves threads on the calipers stretch out over time. I may try to put some thread lock on next time I flush them or replace them with speed bleeders (who come with thread lock).
There should be no leaks if the washers and seals are new and pistons smooth, since there's no other way for air to enter...
 
#20 ·
Waiting for new calipers but I suspect its the bleeder. I figured before that if air was leaking in bubbles would show or a fluid leak, but from talking to a mechanic it seems that it's possible for an air leak to have no visual symptoms. Also my lever felt weird, but only if you had felt it when it was well. It would be firm but spongy during initial travel and let off.
 
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