Another step needed for brake bleed?

[peteinpa]

I just changed the brake fluid on my FJ-09 for the first time. 

With the bleeder and the hoses on top of the front calipers how do you get the fluid out at the pistons? 

Do I have to remove the calipers,  open the bleeders, and push the pistons in a few times?

I don't think that old fluid will get out any other way.

Does anyone do this besides during pad change?

Also...Why doesn't Yamaha put a shield at the bottom of the reservoir to stop the geyser like Honda does?

Edited February 4, 2021 by peteinpa

[koth442]

Dave Moss will recommend removing the calipers, popping the pistons out & draining the calipers. The other 99% of the internet will tell you you're fine as is. I'm in the 99% percent. 

[betoney]

15 minutes ago, peteinpa said:

I just changed the brake fluid on my FJ-09 for the first time. 

With the bleeder and the hoses on top of the front calipers how do you get the fluid out at the pistons? 

Do I have to remove the calipers,  open the bleeders, and push the pistons in a few times?

I don't think that old fluid will get out any other way.

Does anyone do this besides during pad change?

Also...Why doesn't Yamaha put a shield at the bottom of the reservoir to stop the geyser like Honda does?

If you were worried about getting every last drop of fluid out of the calipers you could remove the calipers and push the pistons in all the way (make sure you have room for the fluid to go back into the reservoir).  Put a bar or block of wood in each caliper where the pads would go to hold the pistons in, and then bleed the system but I don't think that you need to go to that extent.

The new fluid should displace the old fluid, just like a car or truck, the brakes get bled with the calipers in place. 

When I used the stock master cylinder I found that you had to pump the lever very slowly with the lid removed or like you said it would shoot up like a geyser.

[knyte]

36 minutes ago, betoney said:

pump the lever very slowly with the lid removed or like you said it would shoot up like a geyser

After having just flushed the entire system a few weeks ago, I can deeply concur with this statement...

What worked well for me was to have a helper manage the fluid in the reservoir, along with some rags on hand as well as some packed around the reservoir to catch any splatter.

[NormR]

IMO there's no reason you should worry about the little fluid left in the calipers after bleeding your brakes with new fluid. The way I do it is siphon most of the fluid out of the MC (not all or you will get air in the system) and refill the MC. I usually start bleeding the calipers and will refill the MC at least 4-5 times for each caliper. After I'm done I don't fret too much about any residue. Only time I actually disassembled the calipers is to do a complete rebuild with seals etc..

[peteinpa]

I also still have to do a few ABS stops to get the old fluid out of the ABS unit. That and the TB sync will have to wait till Spring weather so I can get the bike out of the basement and run it outdoors.

I'm all caught up with mods and maint.!

 

[texscottyd]

12 minutes ago, peteinpa said:

I'm all caught up with mods...

That sounds like a challenge!  😳

[Manxkiwi]

I think pushing the pistons back is a good idea when flushing new fluid through. You can bleed a couple of reservoirs through with pistons still back. Then, when you think the new fluid is coming through, put the calipers back on and pump back out, while topping up the reservior. That's what I do anyway, calipers will then be largely full of new fluid.

I also don't think activating the ABS unit will flush any fluid through. It doesn't circulate any fluid, it merely modulates pressure. You may however, possibly get an air bubble out though?

[peteinpa]

Which direction does the fluid take internally in the caliper?

Does the fluid enter at the hose connection, go down to two pistons, cross over to other 2 pistons, then go up to bleeder? If that's the case, it's bled fine.

If on the other hand there are 2 paths that go down to the pistons then dead end, there is fluid untouched.

Anyone know the internal passage construction?

[Manxkiwi]

Good thought, would be very interesting to know that. Although it may not matter as the bleed nipple would deal with the inner half and the hose would allow any air directly up the line for the outer half.

[peteinpa]

1 hour ago, Manxkiwi said:

Good thought, would be very interesting to know that. Although it may not matter as the bleed nipple would deal with the inner half and the hose would allow any air directly up the line for the outer half.

I agree with the air, but nasty old fluid that never leaves the worst place, at the pistons.

Really would like to know the fluid passage route.

[Manxkiwi]

Yes, my last comment related to air. I think as already said pushing the pistons right back and flushing will get the most new fluid in, short of a full disassemble job. Still keen to hear about the flow though.

Thinking about it; they are mono blocks, so I doubt there would be crossover hole at the bottom of the caliper. Now I'm going to have to take a close look at them! Ha ha.

Obviously where the banjo hole is, it would be drilled through to the bleed nipple side. But the bottom would be difficult I'd think?

[peteinpa]

I wonder if the silver do not touch "bolts" are how they do all the drilling.

Having the fluid travel in a "U" through the caliper makes the most sense.

[Manxkiwi]

Yes the piston bores are machined through from the outside and 'capped' by the silver inserts. Other monoblocks are machined from within the gap. Brembo won't disclose how they do theirs, but they clearly must use a clever sort of 90 degree machining head of some sort.

Obviously a two piece caliper can have a channel put in below the pistons. But monos would require blanking off after machining if this was done and I don't see any evidence of this.

[peteinpa]

Looks like it's going to remain a mystery.☹

After I changed my fluid and tied the lever back overnight I've got a solid lever.  I'm good.