Air in front brake system after major service

[xor_bot]

Hi All! So I did a service on my front brake system (disassembled and cleaned calipers, replaced piston seals, replaced brake master cylinder kit), and now there seems to be air in there somewhere that I can't get out. I have it bled to a point where things are working, but working badly. As in, the brakes bite, but I can press the lever to right up against the throttle grip. So extremely "spungy", and I can't get it better. I've bled at both caliper bleeding screws and at the master cylinder banjo bolt. Also checked that there are no leaks anywhere. The only thing I can think of now is air trapped in the loop that runs over the wheel between the two calipers, or somehow in the ABS pump. There is also a slight high point in the line where it goes from the ABS pump to the font calipers. Any suggestions? Should I just continue pumping and hope for the best?

The front brake system was standing without the front calipers (and any brake fluid) for about six weeks while I was waiting on the backorder for the piston seals.

[klx678]

Get a vacuum bleeder, like the Mity-Vac and have someone to help keep the master cylinder from running dry.  I did and it was worth every penny.

If you use one do not draw vacuum too high it can suck air in around seals, which are made to seal against pressure, not vacuum.  Saves a lot of headaches.  Harbor Freight in the U.S. sells them for $20, should be something where you're at to get a kit.  

The first time I used it was doing my double disc set up on my Zephyr 550, it was when I learned not to draw too high a vacuum.  Once I stopped drawing so high the brakes came in in minutes.   The second job was on the Zephyr rear brake, about 3 minutes.  Did the brakes on an XT225 took about 10 minutes working alone, and an MB5 done in about five minutes.   It's pretty quick when done properly.

Only problem I had was the gauge lens broke - no idea why they'd use glass in a tool that is almost sure to be bounced around a bit.

Edited April 24, 2021 by klx678

[Pursuvant]

Yep, a reverse bleed would have helped at the start of refill, here is a low cost one that (not as nice as KLX678's vacuum) but works every time I get it out.

Order of things. You are already into this, so just keep going unless you find a show stopper during this process. Get a couple more bottles of the Belray DOT4 or whatever you run. You work accumulated air at top of system, bleed from lever to left caliper, then lever to right caliper. Every day you can before you ride, and keep doing it, your problems will go away. How...

Accumulated air at top (where there is no "bleeder")

Test your brakes every night for a week after bleeding by doing this (to remove additional air from system AND show any "weeping" from banjo crush washers). At night you can use a couple zip ties (cable ties) to hold the lever under moderate braking pressure all night like you were squeezing the lever firmly - firmly but no need for crushing force pulling the lever. In the morning, hold the lever at this squeezed location and cut the zip tie, then slowly release the lever. It can "suck" any accumulated air bubbles at the top of the system back into the master cylinder where they travel up into the brake reservoir (if you have a bleeder banjo at master, give it a one pump bleed as well after slowly releasing lever). It helps get air out of the system AND you can go look closely at all the banjos, if they are leaking go slow but tighten them a very little amount until they stop leaking each time you check and find weeping.

Lever to left caliper

Just normal bleed down, but don't pizz around while you do it. Get ready, have an open bottle of brake sauce, and just do it. Don't pump a couple of times and get coffee, couple more pumps and play with dog. Get bizzy, bleed into an empty gallon jug of nonsense. From lever to left caliper.

Lever to right caliper

Nothing special about bleeding over a fender from caliper to caliper. It will come out if you don't "stroll". Get bizzy.

Just do these three every day before you ride, you will get those brakes bled and you will find any weeping banjos and tighten them up. Yes the ABS makes it more interesting. No, you don't need a new process (unless you have never reverse bled brakes at the start, that might be new for you but it's the cat's meow), give that a whirl next time you empty the system and want to fill the whole she-bang. Just my opin, ymmv

It's my impression air hangs out at the ABS and the high line on the out port, but when you ride it gets disrupted and accumulates up at lever, but I can't prove it without putting a banjo bleeder bolt at the ABS, and that's just a not needed headache

Edited April 24, 2021 by Pursuvant

[klx678]

You're actually calling a Harbor Freight bleeder nice?    Actually it is very functional for less than the MityVac unit.  I have no regrets on the $30 spent for sure.  Saved a lot of frustration the three or four times I've used it.  So cost-per-use at this point is less than $10, but cost-related-to-frustration-level is almost priceless.  

[Pursuvant]

1 hour ago, klx678 said:

You're actually calling a Harbor Freight bleeder nice?  ">  Actually it is very functional for less than the MityVac unit.  I have no regrets on the $30 spent for sure.  Saved a lot of frustration the three or four times I've used it.  So cost-per-use at this point is less than $10, but cost-related-to-frustration-level is almost priceless.  ">

Wow no idea that you found this bargain for $30, that reverse V5 bleeder is about $50. Spread da word

[xor_bot]

@Pursuvant Thanks for that clear how-to. I followed your procedure, but I had only 2 bottles of brake fluid and after going through both it was only marginally better.

@klx678 I'm going to try and procure a vacuum bleeder this week, and a couple more bottles brake fluid, and see if that helps.

Otherwise I'm taking it to the dealer. At this point I just want to ride

[Evill_Ed]

 

 

This video may help 

 

Ed

[klx678]

@xor_bot If you do use the vacuum set up remember, do not use too much vacuum.  I kept the draw low and consistent as possible keeping my eye on the fluid in the master cylinder, not running dry.   After all, what is being done is drawing the fluid through, pulling along any air pockets out into the vacuum bleeder.   Too much draw will suck air in through the bleeder threads and/or other seals that seal against pressure, not vacuum.  If you had a master cylinder apart you would notice the seal work one way - the direction of the cupping, toward the caiper(s).  Too much vacuum may suck air through.

I never messed with it, but what would be ideal would be to work the opposite way, pushing fluid up through from the caliper, although it could keep a pocket of air in the caliper because the bleeder is at the high point, not the low.  

[xor_bot]

Right. I got a vacuum bleeder and 2 liters of brake fluid. Wish me luck. Also @Pursuvant I kept a zip tie on the lever through last night and slowly released it this morning as you suggested. To my surprise it made about a 5mm difference in how far I can depress the lever - so I'll keep doing that anyway for a couple of days.

[xor_bot]

Went for a test ride yesterday and all seems back to normal! I did a vacuum bleed, regular bleed, and left a zip tie on the lever overnight. Thanks for everyone's input!