Brake Gremlins

Hi All,

I have an issue with the front brake caliper, it is a standard lockheed system on a Mk3. I replaced the caliper seals, the pistons looked OK and I have bled the system using a clear plastic drain line, master cylinder high up and fairly level on the bars, no bubbles showing and have used 3 reservoirs of fluid trying to ensure no air. I don't believe there is air in the lines. However I still have a spongy brake feel until I pump it at least twice at which time the brake is normal and strong. This happens after the brake is left standing for more than a minute or so between applications.

I have had this happen on the move - pad "knock off" as some would have experienced before floating discs where the unit needed a pump along the straights before application at the corner due to the pads sitting back in the caliper. This is very similar but the bike is not on the move and it seems that the pistons are sucking back or something giving excess clearance after that minute or so standing.

Any thoughts or previous similar experiences anyone?

It may be air in the M/C.

Take the cover off and CAREFULLY lean the bike to the left (don't spill the fluid!) so there is an uphill run back to the master cylinder.

Then very gently tickle the brake lever so it moves a few mm in and out.
You may see some bubbles coming back into the reservoir. If you do, continue until they no longer appear.

Beware: this can be a tricky operation and if the reservoir is full you probably won't be able to do it without spilling fluid, probably onto your favourite bike's beautiful paint job!
It's probably a good idea to get someone to help you....sorry I'm in Brisbane.

Does indeed, as suggested, sound like air somewhere, a leak at one end or the other...or a really nasty, old rubber brake line that needs to be pumped up to it's full ballon/deformation before it will tranfer enough pressure to the master cylindar to get it to feel firm. One way or the other, not many things it can be. Do as suggested and redo the bleeding, but if you worry about the paint...look into silicone DOT 5. That won't ruin your nice paintjob.... :wink:

Try a reverse gravity bleed. Jockey the front end so as to get the mastercylinder high as posible. Use a tie wrap to hold the lever full on brake, let it sit over night. Air given enough time will find it's way up thru the system. norbsa

Hi All again,

Thanks for the replies to date
I did some more bleeding and tried the suggestions by norbsa and pommie john, unfortunately to no avial.

In desperation I swapped front caliper to rear, would you believe same result now at the rear? It now appears that air isn't the problem as the rear caliper on the front bled fine but the original front is still needng pumping up on the rear.

I wonder if it is possible the new seals are grabbing the piston, flexing with it and pulling it back when pressure released. I fitted them as per the manual,ie, smeared with brake fluid so it's not as if they are dry.

I'm submitting this just in case someoine has had a similar issue.

Rgds Vince