Reverse brake bleeding question

[Michael0124]

I want to flush the brake fluid and replace the lines on my FZ8. Non ABS models.

I was planning on getting a reverse bleeder kit until I realized I can make one out of syringes and clear tubing for a fraction of the price. I've bled many cars but never a motorcycle and am wondering about the dual front brake system.

The question I have for the more experienced diyers here is can I bleed one front caliper at a time or will I need some kind of tee fitting to force fluid up through both calipers and lines at the same time?

The system will be dry because of the new lines so I'm more concerned about air getting pushed back between calipers, but if I wasn't replacing lines would bleeding one side at a time force dirty fluid back and forth?

 

[TK4]

One at a time will work - let gravity do the hard part.

 

[Mad Mike]

Steps I use to flush bike brakes. You should have a lot less trouble than bleeding as ther should be no air in the system, and if you flush correctly it should stay that way.

you need a clear tube, 1 pint mason jar or equivalent, fresh brake fluid. Connect the tube to the bleeder, leave the other end in the jar. put enough fluid into the jar to covet 1” of the tube.

Stand bike straight up, not side stand (less important for flushing than bleeding).

Start with the left front caliper, pump lever 3 times then crack the bleeder. Close bleeder and repeat till the clear tube is cleared of air. After that you should not need to pump/crack, just open bleeder then slowly squeeze and release leaver repeatedly until fluid runs clear. Close bleeder then do same on right and rear.

be sure the reservoirs never run low.

 

[Trials]

Push the pads and pistons all the way open and keep them there, start filling the one that only has one hose connection. If the calliper is removed and held lower then the rest of the system the air will rise and go right past the second calliper, if not then you will have a high spot in the line and still might need to fight with bleeding that air out.
... sounds like you have a good handle on it confidence it high.

 

[Mad Mike]

Push the pads and pistons all the way open and keep them there, start filling the one that only has one hose connection. If the calliper is removed and held lower then the rest of the system the air will rise and go right past the second calliper, if not then you will have a high spot in the line and still might need to fight with bleeding that air out.
... sounds like you have a good handle on it confidence it high.

Why remove calipers? It’s just a flush, simpler than a bleed.

 

[Trials]

Why remove calipers? It’s just a flush, simpler than a bleed.

I have a hunch he has a short line that goes from one side to the other and that would make a high spot in the line. If he has 2 separate lines that tee off higher on the bike or right at the master cylinder, it won't be a problem.

I figure he is looking at scenario 2O

 

[Mad Mike]

I have a hunch he has a short line that goes from one side to the other and that would make a high spot in the line. If he has 2 separate lines that tee off higher on the bike or right at the master cylinder, it won't be a problem.

How would that impact a flush, the system is starting out air free?

 

[Michael0124]

Thanks for all the quick replies.

I'm going to replace the lines so it's going to be a complete bleed not just a flush.

There is only one line per caliper, both go into a block that has a line going up to the reservoir, see attached picture please. The lower line is the left caliper.

If I remove the caliper, how do I keep the pistons from shooting out when I force the fluid up through the calipers/lines? 4 piston calipers, im guessing use a pad spreader to hold the pistons in?

 

[Trials]

How would that impact a flush, the system is starting out air free?

In a flush you want to force all of the old fluid out of the reservoir, in a fill you want to force all of the air out of the reservoir.

 

[Trials]

... your bike looks like scenario 3T

I put a wedge shaped chunk of softwood between the pads to keep them wide open until they pump up solid. Then keeping the reservoir relatively full of fresh fluid pump the brakes once they are re-installed on the disc. Now you only have nice fresh fluid behind the pistons.

 

[Trials]

BTW your brake lines don't even look like steel braided lines unless there is steel inside that rubber hose and not nylon. Definitely room for an upgrade if your front brake currently feels at all mushy.

 

[Michael0124]

They are the original lines, 8 years old and looking faded so definitely time to upgrade. Front brakes feel good but the rear feels squishy and not much braking power to it, hoping some fresh fluid and steel braided lines will help.

Thank you for all the advice, appreciate it!

 

[Trials]

Easy to identify a non steel brake line, you can cut it with a knife, if it's a steel reinforced brake line your pocket knife is not going to cut it.
Nylon-reinforced brake lines blow up like a balloon and you lose much of your hydraulic pressure to that stretch in the lines.

 

[Mad Mike]

They are the original lines, 8 years old and looking faded so definitely time to upgrade. Front brakes feel good but the rear feels squishy and not much braking power to it, hoping some fresh fluid and steel braided lines will help.

Thank you for all the advice, appreciate it!

OK - so it's now a bleed situation - that's more work than a flush.

If your are replacing the brake lines, the best setup is to run full length lines from the master to each caliper (remember a longer banjo is needed up top), delete the OE splitter.

Bleeding Yamaha 4 piston fixed calipers is normally an easy job, you can leave them on the bike unless you are doing caliper service.

 

[Michael0124]

Easy to identify a non steel brake line, you can cut it with a knife, if it's a steel reinforced brake line your pocket knife is not going to cut it.
Nylon-reinforced brake lines blow up like a balloon and you lose much of your hydraulic pressure to that stretch in the lines.

I'm guessing I should have the replacement lines before I try your method of determining if it's steel or not?

I was thinking to attempt to bleed the brakes on my vfr, spent hours researching it and was still nervous...7 bleed points on the combined abs system with a very specific sequence needed, I'm going to assume this basic non ABS system on FZ8 is going to be a bit easier lol.

 

[Michael0124]

OK - so it's now a bleed situation - that's more work than a flush.

If your are replacing the brake lines, the best setup is to run full length lines from the master to each caliper (remember a longer banjo is needed up top), delete the OE splitter.

Bleeding Yamaha 4 piston fixed calipers is normally an easy job, you can leave them on the bike unless you are doing caliper service.

Curious why you suggest eliminating the splitter? Not sure what benefits/downsides there are either way with or without it.

I'm pondering between the Galfer kit or the Spiegler kit (that one is more expensive but comes in fancy scene point acquiring colours) and they both claim to come with everything needed to swap, I was assuming it included the splitter.

 

[Mad Mike]

Curious why you suggest eliminating the splitter? Not sure what benefits/downsides there are either way with or without it.

I'm pondering between the Galfer kit or the Spiegler kit (that one is more expensive but comes in fancy scene point acquiring colours) and they both claim to come with everything needed to swap, I was assuming it included the splitter.

Performance benefits -- none, a hydraulic brake system relies on pressure not flow. In theory the longer the line, the harder it is to maintain pressure, but over the lengths we are talking about I'd say the loss would not be measurable.

Maintenance is the primary benefit. The lines run up and down making them a lot easier to bleed, any trapped air will always rise to the top of the system.

I think both the kits you mention will delete the splitter, replace he master banjo, and run each line straight from the master to the caliper.

 

[Michael0124]

Maintenance is the primary benefit. The lines run up and down making them a lot easier to bleed, any trapped air will always rise to the top of the system.

.

Instead of possibly getting air bubbles caught in the restrictive splitter, got it. Thank you.

 

[Mad Mike]

Instead of possibly getting air bubbles caught in the restrictive splitter, got it. Thank you.

That and the extra curves in the splitter line setup.

 

[Michael0124]

Circling back to this, I'm about to order the Galfer lines and Motul dot 4 fluid.

Noobish question...never done this on a bike before and I have no clue how much fluid I will need, would 500ml be enough to flush and fill front and rear systems or do I need two bottles?