Tank Slap - Motorcycle Forum

I've been replacing brake fluid and pads on the CBR600rr. The new fluid is brand new unopened stuff i bought last month.

I've cleaned the calipers, changed the pads, flushed out old crappy fluids and completely bled the brakes yesterday. Once there was no air in the system, i zip tied the lever to the bars (good pressure) and left it overnight.

This morning, i went to finish the job. No visible leaks from banjos etc, so I released the lever which had pressure, left it for a few mins while i finished the chain tension and a few other things then tried the lever - no pressure.

Pump the lever twice - pressure again.

I bled the brakes again, a couple of tiny bubbles but nothing else.

Lever holds the pressure until the bike moves. Ride it round the drive - looses pressure until you pump it a couple of times. Move off again - no pressure.

Anyone seen anything like this before. I've bled the lines within an inch of their life - no air.

Any ideas fellas?

Sounds strange! Is there a third bleed valve on the brake lever itself you've bled too? Iirc you should start at the valve furthest from the cylinder and work back. Are you using an easy bleed system or the old fashioned 2 man pump and close method?

Sounds almost like this pistons are retracting to far, but no reason they should. Indeed strange. The only other thing I would try is unbolting them brake units from the fork and holding the up higher than the master cylinder while you bleed them again.

Twin lines?

No leaks from the master cylinder?

Given the age of the bike I would be checking anything that's rubber to make sure it's not started to degrade.

Does sound strange.

If you had a leak the reservoir fluid would drop. Pump the lever alot and see if the level drops. If not a leak can only say you still have air in there. Been in the same position and bled to with an inch of life and it was still air. Some times it is a real bastard to get it all out.

Can you bleed at the master cylinder? If no nipple just crack a fitting. Remove calipers to highest point as kiwi suggests but ensure nipple is at high point. I remeber my B1 had the nipple 1mm lower than the highest point of the caliper so always a bubble in there above the nipple. Trick was to rotate the caliper so nipple was high point.

Try reverse bleeding from the bottom using a syringe at the caliper to force fluid up, that some times helps.

Kwacky wrote:No leaks from the master cylinder?

Given the age of the bike I would be checking anything that's rubber to make sure it's not started to degrade.

Good shout. My kawasaki manual suggests changing rubber brake lines at 4 year old.

Are there any cracks or splits in the hoses that could be sucking air in ?

Thanks so far. i went back down to the bike after leaving it for an hour and the lever was solid - move the bike forward a metre or so - lever goes to the bar

I'm thinking the master cylinder is either air bound or knackered. its a ten year old bike, so i might have to refurb the mc or replace the lines. My suspicion is that the pads are pushing back and the MC isn't stopping the fluid flowing backwards.

I don't think there is a bleed valve on the MC as its the stock honda one.

Bleed wise, I've used the old skool method and i also have a big syringe to push or pull the fluid.

I can't see any leaks after clamping the lever overnight. I always do that to check my work.

Keep any other suggestions coming. I'll leave it for today and have a go at the MC tomorrow afternoon when i have time unless someone comes up with a magic solution. Fecking thing ..!

Is the rear wheel on straight and tight? It does sound as though something is pushing the pads away somehow.
Edit you're talking about the front brake doh!

http://www.cbr600rr.com/forum/index.php?topic=5297.0" onclick="window.open(this.href);return false;
the water in the drain bottle to stop air getting in may help?

Split rubber lines on a bike over 10 years old? They need replacing regardless IMO.

As Blade says, kwak advise replacing them after 4 years.

If you don't want to replace the master cylinder for a bling unit there are loads of nearly new stock Honda master cylinders for sale. They're very cheap.

If you're going to replace the brake lines follow Goodridge on Facebook and enter their competition. You won't win but you'll be offered a 25% discount. That's what I did with the SX.

I'm wondering if leaving the lever fully displaced overnight could be the cause.?
- That never happens in normal use, and may have caused the piston to stick or a seal to distort.
Perhaps leaving it alone for a while would then sort the problem.

Fwiw I had a problem with an airlock in the master cylinder on my RS250 when I replaced the fluid in that, that produced almost exactly the same symptom.

What does holding the lever on over night actual do ?

Anyone have a factual answer ?

I've never understand the reason why tbh and have never found a good reason to do it.

Is it just one of those myths everyone suggests doing but has no effect ?

All advice welcome ?

When the lever is open the fluid in the lines is sealed. Holding the lever closed opens the path to the cylinder and then overnight any trapped air bubbles are supposed to rise to the top... I think!

That's what I ve heard also Andy and thanks for the reply but would it happen ?

Surely the bubbles cannot rise back to the reservoir as otherwise it would be open pipe from caliper to reservoir and then there would be no pressure increase generate by the master cylinder.

Not saying it doesn't just I don't understand how

I'm probably being tick sorry

From what I've read tying the lever up overnight is nothing more than a temporary feel on the brakes. Given the pressure in the system, the direction of that pressure and the viscosity of the fluid the air won't move.

I think you have a very small leak this is what i had on the gsxr. the lever felt ok but a bit spongy you pumped the lever you got pressure just fine then over time it would get worse especially over night. Still ridable but and the brakes worked strong but you had to pump the lever sometimes to get pressure. I believe mine was in the calliper as it was the only thing i did not replace for a working or new item. There was no visible leak. i Wrote it off before i could fix it :-P

Replace the lines first Cookie as a cheap and decent mod as well as good maintenance on a 10 year old bike.

I would also consider replacing the caliper seals or at least stripping and lubing them to check their condition.

Both cheap and simple jobs.

I would take the calipers off one by one, put a piece of wood between the pads and check the pistons are moving freely and there is no leak around them.

Did you flush new fluid through the system or drain the fluid out and refill?

I would get Brembo M50 calipers and matching radial Brembo MC it's the only solution

Right, I've had a good look at the MC and it looks ok.

The fluid when i first bled it was very dark, almost milky black, so i do maybe suspect the brake lines.

I've ordered a set of braided hoses and gone for a race setup as i don't like the over the wheel single line stuff anyway. Probably get those at the weekend fingers crossed and see what that does.

As has been said, not worth having any doubts.