Brake lever goes soft.

[johnsmith222]

Hi guys.

I have had my ZZR 600E for a few years and I have been riding it daily. Now, I am no stranger to stripping and overhauling my brake calipers and bleeding brakes and I believed I had it nailed with this bike.

After bleeding my front brake to the point where the lever is all tight and ticklely, (I am talking nice 1 finger breaking) within the space of a few days, the lever will start to deteriorate and within a few weeks it will be really bad again. (before my last bleed, the front brake got to the point where it was nearly non existant.

Now, in the past week I spent a good couple of hours both reverse bleeding using a syringe and also just the standard bleeding from the caliper and the lever has already started to deteriorate.

What is the likely cause of this? I believe I am clearing all the air in the system as I can get it perfect, but it deteriorates so rapidly.

It was never like this before.

I am using the stock 2001 rubber hoses and the hoses come from the calipers, up to a splitter and a single hose to the master cylinder.

Thank you for any help.

-David.

[fatpies]

Can be three (maybe more) things

One your brake pads are wearing away at an alarming rate, which I doubt. Thus sucking the fluid through making a gap.

Or that you're really hard on the brakes boiling your brake fluid, so it causes internal bubbles, after a ride get off and feel the caliper and the disc brakes. If they feel warmish its OK. If you get burnt then its cooking off your fluid. Though this tends to correct itself for the next ride and warps your discs.

The other one is that you've got some sort of leak SOMEWHERE in the system which seeing as a tiny amount of air can get in and turn the brakes to jelly are difficult to find.The tiny amount of air means you won't get visible amounts of brake fluid.

I would do cheapest to most expensive checking first.

The brake seals themselves and if the grooves are in order and that the pistons don't have any obvious grooves in them which might let air into it.

Then the crush washers on the bits with go into the caliper the banjo bolt etc.

Then the master cylinder rubber bit at the top then the hoses themselves.
____________________
"It's easy to attack and destroy an act of creation. It's a lot more difficult to perform one"

[Mikey3]

My brakes are the same as this, but the deterioration not quite so severe.
having spoken to an old friend, he said to me there is the possibility of condensation in the lines, providing it isn't one of the things mentioned in the above reply.
as you work the brake fluid it can warm up and the heat generated can condense up on the inside wall of the line (i questioned this but i did get it verified)
This can make the brakes go spongy and lack bite, in a similar way to that you suggest - leaving no obvious signs or clues as to why it is happening.
this may be the same as the boiling fluid comment, but as i was told it and haven't experienced it myself, i'm not sure if it's the same or different.
hope it helps a little


on the other hand, i have had spongy brakes and my hand's been burnt touching the discs a few times before.... how is this solved?

mike.

[totalllama82]

Possibly the master cylinder seals that are worn or the brake hoses are perishing?

I had an issue with a soft lever on my Thundercat, turned out the hoses were bulging under pressure.
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Gone: Haotian HT125-8 / Yamaha YZF 600R Thundercat / Kawasaki ZX9R C2
Current: Kawasaki ZZR 1400 A7F

[Howling TerrorOutOfOffice]

[iooi]

I wonder if you have been bleeding the brakes so much that you have knackered a bleed nipple and its not sealing fully.
Try a bit of PTFE tape on the threads.

How old are the lines. Might be worth looking at replacing them if they are over a few years old.

Replace all the seals in the calipers.

As someone else said. Could be master cyl seals that are going.
____________________
Just because my bike was A DIVVY, does not mean i am......

[Mikey3]

[Kickstart]

Hi

If this is happening over a week or 2 then it is a bit strange. Water boiling giving a spongy lever would probably happen immediately that water got into the system, and would also only change things when the brakes got hot (it would behave just like brake fluid when just trying the brakes cold and not moving).

Worn hoses would do the same and also if the piston seal in the master cylinder is worn (it would just leak to behind the piston which is part of the reservoir).

If the outer seal when on the master cylinder then it would leak fluid, which might drop the level of fluid to cause problems. Same if the diaphragm in the reservoir is missing / damaged.

To me the most likely thing is a very very slightly damaged caliper seal allowing a tiny air leak.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[totalllama82]

Another thought is, for test purposes, remove the dust seals from the calipers leaving the piston seals. During my time diagnosing a similar issue a train of thought was that a slightly perished dust seal can catch the piston and prevent it moving back naturally when the lever is released. This would cause a soft lever until the pressure overcame the seals grip on the pot.

Riding about without the dust seals in this weather WILL bugger your pots so do it just to eliminate this problem and prove a point.

If it were me, this is the order I would attempt to resolve the problem in.

1. New bleed nipples (calipers and if applicable MC), put a slip of PTFE tape around the threads to prevent air ingress down the thread when bleeding.
2. Try removing the dust seals as above.
3. New MC seal kit.
4. New set of SS lines. I prefer the racing setup which tends to remove any splitters in the lines and replaces them with 2 lines from MC -> Calipers.
5. Replace the piston and dust seals on both calipers.

After this you pretty much have a completely new system so its now down to bleeding...

Cheers J
____________________
Gone: Haotian HT125-8 / Yamaha YZF 600R Thundercat / Kawasaki ZX9R C2
Current: Kawasaki ZZR 1400 A7F

[Walloper]

Heating fluid to boiling point on a vehicle on public roads is a bit extreme.
Unless you are hammering the bike/car.

I would put all my pocket money on air in the system.

Cover the tank and any exposed paint with rags to prevent fluid marks on the paint (cover with polythene if possible too.)
Remove the brake (Not Break) lever and brake master cylinder housing.
Loosen, but do not open, the banjo coupling
Turn the whole assembly until you get it in a position where the banjo coupling is at the topmost position.
Press the lever slightly to pressurize the system.
Open the banjo coupling and ensure that all/any air is squeezed out.
When all the air is out refit the brake lever assembly.
Bleed the callipers.
I use a pressure bleeder for bike brakes.
Works every time for the most stubbornest-est systems.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[iooi]