Caliper not releasing

Rigez · Postby **Rigez** » Sun May 18, 2014 11:52 pm

Hi. Been upgrading my brakes and more dramas. Nearly done but after bleeding and getting a good firm pedal, the front left brake is not releasing. I've taken the caliper apart twice since the initial overhaul to re-check, regrease etc, but it's still not releasing. I've tried a new inner piston seal and piston, and also re-installed the older seal/piston but all with the same result. All equipment looks in good working order, so I can't figure out why I have this problem.

I've got new fluid/lines/rotors/pads.

Any thoughts? Thanks.

manga_blue · Postby **manga_blue** » Mon May 19, 2014 3:32 pm

I can't tell whether you mean the caliper is binding just after you assemble it or after being dríven.

There've been a few cases on this forum where brakes have been binding while driving. Basically pressure is not being released from the system, so the pads drag a little, which heats up the fluid, which expands, which causes the pads to drag a little more, which causes more heat, .... Sometimes it's caused by not enough free play on the brake pedal. More often it's been a faulty booster unit. In all cases so far it has affected all four wheels. Yours doesn't fit the pattern but I suppose there could be a case where it only affects the front circuit and it happens on one side first.

If it's got nothing to do with driving then have you checked that the caliper moves freely on its sliders. MX5 brakes are pretty sensitive to any sort of binding or sloppiness in the sliders. Grease them well.

Rigez · Postby **Rigez** » Tue May 20, 2014 1:29 am

Sorry - the car is still in the air - so nothing has been road-used yet. Thinking it might be the slider bolts. Have stripped it all down again so I'll see how I go.

Thanks.

manga_blue · Postby **manga_blue** » Tue May 20, 2014 5:03 pm

Sometimes it's worth replacing the sliders, whether or not you can see any wear in them. I had braking stability problems, couldn't see or measure anything wrong with the sliders, except that they were 180ks old, replaced them anyway, fixed 90% of the problem. Normally you only need to replace the big sliders, the little ones only run inside a rubber sleeve.

http://www.mx5parts.co.uk/front-caliper ... p-897.html

hks_kansei · Postby **hks_kansei** » Tue May 20, 2014 6:23 pm

Can you see the caliper grabbing the disc? (the pads will often rest on the disc lightly at rest)

if it's just hard to turn have you confirmed that it's not something like a siezed wheel bearing instead? (or that the bearing is worn and soon to die)

It most likely is the caliper, but no harm checking that while it's on stands.

Rigez · Postby **Rigez** » Mon Jun 16, 2014 1:47 pm

Hi, just realised I hadn't posted after sorting this problem. The banjo bolts that came with the Goodridge Stainless Steel Brake Line kit are about 5mm longer than the OEM bolts. So when I torqued them up, they were protruding into the brake caliper bore and then making contact with the piston. Then after applying the brakes there was enough force to push the piston out to produce braking, but then as the bolt was still tight against the piston, the piston would not retract.

I took about 5mm off the ends of the front banjo bolts, re-installed and it all works perfectly.