Ate brake calliper assembly

[jamestnewsonr65]

On installing them the pistons retract a millimetre or two when pushed, but then they spring back causing the pads to rub when installed in the calipers.

I filled the brakes with fluid over the weekend to see how they preformed and whether the pistons would miraculously work as intended by as expected they didn't really.

When I pull the brake lever the pistons do retract though again, but obvously not enough for them to not rub.

It is only slight though and the wheel still turns just not as freely.

 

[Tony Smith]

Take the pads out and then push the pistons as far into the caliper body as they will go.

Replace pads, go for a ride and heat the brakes up as much as possible, deliberately dragging the brakes as much as you dare will help this process. When the brakes are good and hot, release them, then slip a small screwdriver (or the back end of a clothes peg) between the pad and the caliper and then go have breakfast/lunch/several coffees.

The problem you are facing is that the dust seals (and possibly the seals themselves) have taken a "set" which is causing the pistons to come out in the bore and cause the pads to rub. By heating everything up (brutally - do not be gentle in this) the intent is to impose another "set" on the dust seal / seal

[Mike V]

James,

Based on your Reply "#28" on the previous page, it sounds to me as though you may need to correctly shim your caliper at the fork leg.  Or am I missing something?

-Mike V.

[Bob_Roller]

Try using a C-clamp with the fixed part of the clamp on the piston, then place a thin piece of wood on the caliper body, where the moveable part of the clamp will rest against .

Turn the adjuster on the clamp to press the piston back in a bit and see if that helps .

If your master cylinder is topped off, you may want to remove some fluid, so you don't get an over flow condition at the master cylinder, when the pads are pushed back into the caliper .

[Barry]

With rubber having some inherent hysteresis and allowing for the stiction in the piston movement to be overcome the self retracting action of the piston seals is not usually perfect i.e. it won't always completely eliminate drag of the pads on the disc and even if it does it is unlikely to last between service intervals.  

"Exercising" the pistons as has been suggested above usually works for me.  Some times it just moves the starting point of the piston a few thou and that is enough to resolve the problem.  This slight difference in piston starting point will occasionally work in the other direction causing too much retraction resulting in excess lever travel. It's rare but it can happen and it's worth being aware of as a possible cause of excess lever travel.  If this last paragraph doesn't make sense consider the relaxed position of the seal shown in the diagram will never actually be quite fully achieved in practice because the rubber is never going to fully recover it's relaxed shape while it is trying to overcome piston stiction. It's a balance of forces between piston stiction and tension in the rubber.

[Mike V]

Or am I missing something?

Obviously I missed the boat on this one regarding the shims, sorry James. I'll step out of the way and lurk.

Doh!

-M

[jamestnewsonr65]

Thanks for the suggestions. I will try these at the weekend when I get a chance to get the bike out on the road.

I think the suggestions about heating the brakes and then setting the rubber sounds like what I see happening, so hopefully this will fix my problem also.

Will report back on what happens and whether this worked.

Thanks again.

[jamestnewsonr65]

So I was getting everything ready to go out and get the brakes nice and warm, but couldn't seem to bleed the brakes fully.

I've changed from the original set up to running an individual line to each caliper from a double banjo bolt at the lever. When bleeding the right hand side I just kept getting air come through and ran about 1/2 litre of new brake fluid through it.

Could this be down to air maybe getting through at the bleed valve? The only reason i'm not convinced all the air is out is that the lever travels quite far before getting firm and applying the brakes fully.

I still have the problem of the rubbing brake pads though, but just wanted to bleed the system fully first.

Any tips on bleeding? Ive been using the open, squeeze, close release method with the end of the tube in about and inch of fluid.

[steve hawkins]

Two things come to mind:

1.  lightly 'flutter' the brake lever with the master cylinder refill cap off and watch the bubbles come up the little holes in the bottom of the reservoir.  We are only talking about small movements of the lever, the path is vertical, the air will eventually run out.  I have successfully bled my brakes using this method alone on new lines in 10 mins on my R100 most recently.

2.  Tie the lever back to the handle bar over night, not too tight to get the last bubbles out.

Cheers.

Rev light

[montmil]

Speed Bleeders ease the effort with bleeding brakes.

[Tony Smith]

Speed Bleeders ease the effort with bleeding brakes.

I have a "cheat" that has served me well over the years. A piece of flexible hose that is a tight fit over the bleed nipple, a "horse" syringe of 200mls capacity.

Fill syringe, fit hose over bleed nipple and crack open. Gently introduce brake fluid whilst "fluttering" [Pat Pending :- Rev Light] the brake lever. By the time the reservoir is full there is no air in the system. Takes about 3 minutes and you are done.

Works well for dual system as as well, fill the first caliper and by the time you get fluid appearing in the reservoir there is no air in that side from caliper to splitter - change to the other caliper and continue - takes about a minute longer than a single disc.

[Barry]

I do it the same way as Tony and it produces a usable brake lever straight off but I still tie the lever back overnight. The only slight problem is a a bit of leakage at the bleed nipple threads. A few turns of PTFE tape on the threads helps.

[jamestnewsonr65]

I will give the 'rev-light' fluttering technique a go and if all else fails then refill from the bottom with the syringe as that seems pretty foolproof.

[Tony Smith]

T's OK, some of us have never seen a "proper" caliper shim, we call them "washers"

[mrclubike]

It may be to late for the original poster but I started a caliper rebiuld untill I found the  Brembo F08 off a Guzzi and it is working perfectly.
 
Very Fast shipping also