An Ode to brake bleeding

[Timmeh]

Hello Workshoppers

Whilst I am certainly not in the category of professional bike mechanic, I do consider myself fairly competent, having completed multiple engine and bike rebuilds over the few years that I've been pursuing my hobby. Well, I thought I was fairly competent, until I was presented with the task of getting my RVF's front brakes back together and working. Having tried numerous methods, over best part of a month or more, and having gone through well over two litres of DOT4, most of which ended up either the garage floor or in a gazillion rolls of tissue paper I thought I'd write a little essay here whilst celebrating over a can or two. Hopefully my efforts will help others so that they don't end up like me, tearing my hair out and crying in a heap on the floor (ok, that's a mass over-exaggeration but you get the gist).

I'm certainly not trying to teach the old dogs new tricks, and I know that some of you will have heard this before, but it might help someone somewhere. This forum has been awesome for me in the tips and tricks I've learnt from other users, so it's always nice to try to give something back to others.

Types of bleeding

There are several different ways of achieving the same goal, which is to expel all the air from a hydraulic system and generate pressure so your brake lever causes the pistons force themselves against the pads and disk(s). The simplest is gravity or 'standard' bleeding, where you stick fluid in the res and it comes out of the bleed nipple at the bottom. Then there's reverse, closed-loop, pressure and reverse pressure bleeding, which uses a variety of tools and instruments that offer varying advantages over the standard method, mostly that you don't end up with puddles of fluid over your tyres. Each method has its own pitfalls, and each can hide problems which can affect you down the road. I'm going to concentrate on the only method that worked for the RVF, and given that's its the only bike I've ever had such a polava to sort out, then it must be the best way. Once again this is based on my own observations so might not be the greatest for all, but it encompasses the advantages from the above and got my brake lever harder than a virgin window-shopping in Amsterdam faster than anything else I've ever used to bleed brake systems.

The Master Cylinder Reverse Pressure Bleeding method

Bit of a mouthful, but it's an accurate description of what's about you're trying to do. This method relies on you getting hold of a MC banjo with a magical bleed nipple like this one. NB; epic karma to CHR1S who pointed me in the right direction:

https://images.wemoto.com/full/BRAKE_FITTINGS/10031457.jpg

Goodridge/Wemoto make single and double-hose versions, and I got mine off eBay for around 30 quid, although I bought the tarty stainless version. Plated steel ones go for about 15 notes. Install this with the new copper washers (one should always use new ones when fitting brake components) and you can do some rather clever things with it.

What you'll need

Couple of things you'll need. A big syringe, 60ml is good - 100ml is best - a fair length of 6mm plastic tubing (get this from a pet shop as it's what they use for aquarium filters) and a big container for your brake fluid. I use a glass vase as its heavy and won't tip over easy. Connect lengths of tubing from the bleed nipples of your brakes so that they go into the fluid. A third piece of tubing connects between the syringe to the nipple on the MC bolt. You can compensate for syringe capacity by making the tube longer.

Testing for leaks

It's fairly obvious but any leak in any of the seals/banjos/hoses/etc will ultimately spell disaster for your bleeding efforts. With everything tight, pull on the syringe. If you haven't got a leak then you'll generate a vacuum and the syringe will fight you all the way. Pull and hold. It shouldn't loosen off and will fly back towards the MC when you release it. If this is the case then you've got a good base for carrying on.

Testing the Master Cylinder

Muchos Gracias to Marki for some insight here.

It's an odd truth that a brake system can sit for years and not degrade much, unless its exposed to air. This was certainly the case with the RVF where the seals in the MC piston had shrunk and the internals had corroded. This is where your special bolt comes into play.

With the lever relaxed, open the MC nipple slightly and pull on the syringe. You should be able to draw fluid from the res. Now try to push the fluid back into the res. Success here means that the input port is not blocked and that the primary seal is sound. A blown seal here will result in no fluid leaving the res, or it spurting out at the lever end when you push the syringe back in.

Now pull back and tie the lever so it's all the way against the twist grip. Again, try to pull/push fluid in and out of the res. This time is should be impossible as the piston's position means the seal has traveled past the input port and sealed the res. If you are able to force bubbles / fluid into and out of the res, then an MC inspection and rebuild should be considered (as was the case with the RVF)

Preparation for bleeding

Air bubbles are a funny thing. They will and can hide anywhere. Calipers are a network of lines and pressure fittings and any trapped air will result in spongy lever syndrome. The bleed nipple on calipers is usually at the highest point of the system, which aids gravity bleeding but can leave air pockets in there somewhere. In particular you can get bubbles trapped behind pistons (cheers BudgetBoy) , so it's always a good idea to push them out.

To do this you'll need to take the calipers off, crack the bleed nipple (unless the system is full of air) and push the pistons back out so they are flush with the caliper body. Use your plastic tube to drain the old fluid into a tissue to be discarded. Do this carefully, and evenly. Never apply any pressure to a brake disk else you might warp it, and never apply uneven or sideways pressure to a caliper. If your pistons are in good nick then pushing on the pads with your bare fingers or use of a non-metallic tool (like a plastic ruler) should be enough to get them to move back. Once that's done, put the calipers back on the bike and tighten the bolts to the right torque.

Now you're ready...

Bleeding

Crack the bleed nipples on your caliper(s) and dunk the end of the tubes in the container filled with new brake fluid. Tie the brake lever back all the way and fill the res with fresh fluid up to the top. Squeeze the hose from the res to the MC to fill the piston with fluid; you should see an air bubble or two come out. After you've expelled the air top up the res again.

Now take your syringe and start to pull. You should see fluid get sucked up into both calipers and air being pulled into the syringe, which should offer you a fair amount of resistance. No resistance means you have an air leak somewhere, so double-check your connections. It is possible to have air introduced into the system from the bleed nipples, so beware of loosening them excessively. Once the syringe reaches the end of its travel, pinch the end of the tube and empty the syringe back into your container. Then repeat until you're just pulling fluid around the system.

As a double-check for the MC, the fluid level in the res shouldn't change. This reaffirms what we should have found earlier in that there is no fluid leaking past the input port.

Got it right?

Once you've managed the above, and are just pulling fluid from your system (you may get some teeny tiny bubbles but they will be from the nipple threads leaking air) close up all the nipples on the calipers and on the MC bolt.

On some bikes (i.e. RVFs) the res sits at an odd angle which means that the hose sits higher than the hole at the bottom. This means that the MC piston might not get a mouthful of new fluid when you pump the lever. Because we've moved the caliper pistons in, the system needs to charge and more fluid is needed to allow for the piston travel before they strike the pad and the disk, so stick the cap on, unbolt the res and hold it so that it's a straight line down into the MC.

Now start to pump the lever. There should be a modicum of resistance as hopefully you're starting to move the pistons. On bikes with more than one caliper/piston you might find they move out sequentially as one travels out and then the others follow suit. With the system in good condition and bled properly it should only be a few squeezes of the lever before you've got the pistons travelling towards the disks.

Check that you're not running the res out of fluid and keep pumping until all the pistons are against the pads. At this point the system will pressurise and the lever will suddenly go hard.

Checking your work

It's possible to get a firm lever which will then go spongy over time due to a leak somewhere. Whilst this method aims to reduce the risk by testing each part along the way, I usually tie the lever off overnight and make a note of the angle of the lever or distance to the the twist grip. Come back in the morning and make sure it's the same. Any noticeable difference and you should really make another attempt as you might find your brakes not working properly, usually when you need them most.

I will try to add some pictures later but I have crapola phone and no camera. But I think it's fairly self-explanatory.

As a final note the reverse-bleeding methods tend to work better than the others; as air is lighter then fluid you're less likely to leave trapped air anywhere as it will be forced up and out. Bleeding from the MC banjo eliminates any chance of air being trapped in the hoses and gives you a useful test point to check MC operation. It also offers the advantage of closed-loop bleeding as you can put any captured fluid back into your container for reuse and not spilling it anywhere.

Using this method on the RVF's brakes got me results under ten minutes which is infinitely better than the other methods I had tried.

Hopefully this will be of help... Once again many thanks to Chr1s, Marki, BudgetBoy, Keith and any one else who spared some time for me in my RVF brake fail thread and also those who've managed to instill a bit of biking knowledge in me.


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GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[Casper]

https://images.wemoto.com/full/BRAKE_FITTINGS/10031457.jpg

If anyone is looking for one of these do pay the extra for stainless steel. I got the zink one a couple of weeks back and when tightening up the nipple the bajo just snapped. Trust me, i was not using exess force.

[Pete.]

Must be a manufacturing fault rather than material. Stainless steel is not as strong in tension or shear as mild steel.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Casper]

[Pete.]

Karma to Timmeh for doing the write-up. Brakes can be troublesome to bleed up and some are hassle even for old hands.

I have a few bits to add:

If you are having problems getting a firm lever, clamp off the brake line using a brake pipe clamp (not mole grips) right above the caliper. If you now have a solid lever you have air in the caliper, if your lever is spongy you have air in the pipes or banjos. Pipe clamps are cheap, I just bought one for £7 in the motor factors down the road. Also works with braided lines.

I once thought I'd be clever and connected a vacuum pump to the brake bleed nipple with a pot in line to catch the fluid. I figured I could use the pump to draw oil right through the system in one pass whilst re-filling the reservoir and be all done and bled in a few minutes.
The reality was that the vacuum pump worked too hard for bleeding and dragged air into the system past the back seal of the master cylinder. Total failiure and something to remember if you're trying to draw oil from the system with vacuum though I doubt you could do it with a syringe. A mityvac might be able to mind.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Casper]

I used a foot bump. Bleed from the nipple up. Fill up about a foot and a half of tubing with fluid and push in using the pump. Worked first time. I would have used a big syringe but i an still yet to order one. Only problem i had was i forgot to put the rubber on the reservoir and the fluid shot out over my head.

[chris-red]

I've tried various ways, however I feel you can not beat the jam jar/plastic tube method.
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Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.

[MarJay]

Its worth noting that if you have a double banjo bolt at the master cylinder end of the system and you can't get that last bit of air out, it is often worth cracking the double banjo open whilst slowly squeezing the brake lever. Obviously pad around the area with a rag so that brake fluid doesn't fall on anything important, but often you'll hear a little 'bloop' noise. Then tighten the banjo while there is still movement left in the lever and you might mysteriously find that your brakes have firmed up.

Happened to me at least three times.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.