Hope Mini caliper weeping

wheely73

Just swapped a number 3 caliper half for a number 5 to suit my front brake/forks/rotor and when I bleed the system up there is a slight weep of brake fluid emiting from where the caliper halves join.

I put a new seal in the caliper when I changed it and have checked and double checked the alignment.

Stopping power is pretty good and the lever feel is reasonably firm but I'm not convinced fluid should be weeping between the caliper halves.

Any suggestions?

Cheers

nicklouse

is it actually dripping oil?

the remains of the fluid between the two half can give the impression of a leak but it is not doing so.

wheely73

It's not dripping a massive amount, but when I apply pressure to the lever you can see a small amount of brake fluid oozing out along the joint between the 2 halves.

There is enough to almost create a small drip on the bottom of the caliper.

cycletech

In most cases the caliper is not actually leaking oil. In these cases, residual oils are trapped inside the two halves of the caliper body. If the caliper was assembled with some residual oils trapped inside, a very small amount of this trapped oil may continue to seep out from the joint when the lever is squeezed during initial usage until the oil completely dries out.

If you see traces of oil on the caliper body, you should also check the brake pads and rotors for oil contamination. If the pads are contaminated, you may experience some noise and poor braking power. If the pads are contaminated with oil, clean the caliper and replace the brake pads. If the rotor is also contaminated with oil, wipe it off with a clean rag using brake cleaner.

Although most cases are due to residual oils, there may be cases of actual leakage.
If the brake leaver becomes spongy, there is a leak. You will need to strip the caliper, clean and inspect the 2 face half’s of the calliper and the seal. On reassembly do take care not to scratch the caliper surface/piston bore. Dip some DOT fluid and run it around the recess’ for the seals. Also apply a thin layer onto the whole of each seal. Carefully push the each of the seals into their recess’, making sure they are properly seated. Apply a thin layer of DOT to each piston and push it slowly into its piston bore. Rub a thin layer of DOT to the ‘o’ ring and its recess’ and drop it in. Note that one half of the caliper has a deeper recess for the ‘o’ ring. Thouroughly clean the facing surfaces of each caliper, ensuring there is absolutely no dirt or grit which may prevent the two halves mating up cleanly. Push both pistons fully into the bores and bolt the two halves back together. Don’t screw one bolt in then switch to the other; thread one in a little and then do the same with the other so that compression is similar on each. When the caliper halves are fully torqued together the pistons will need to be pushed fully into their bores in preparation for bleeding the brake. If you are unsure, have a skilled bicycle mechanic have a look.

wheely73

Thanks cycletech. There was only a slight spot of fluid on the rear of one pad. I presumed this was a drip from where it had weeped out. I fear they may be a touch contaminated but have used the cleaning method from the FAQ's on here to make them better. (i didn't want to invest in new pads untill I was sure there wasn't a leak)

I have stripped and dried everything twice, and even applied a small amount of gasket sealant to the 2 faces of the caliper halves.

Having taken it for a 24 mile ride on Tuesday, braking power seemed to be consistent and feel at the lever was too. As it only got a cursory clean in the dark, I couldnt tell if it was still weeping. As brake fluid is notoriously hard to dry off completely, you may be right that there was a small amount of residue between the 2 halves.

I will monitor it and have a good look at the weekend when I have finished work. My other option, is to whip it apart, pop the old No 3 caliper half back on and see i I have the saem problem. If not, it may be that my new claiper half is marginally out of true.

Thanks for the help.

Neil

nicklouse

wheely73 wrote:

I will monitor it and have a good look at the weekend when I have finished work. My other option, is to whip it apart, pop the old No 3 caliper half back on and see i I have the saem problem. If not, it may be that my new claiper half is marginally out of true.

you will have the same problem.

Like i said it is normal and has been worried about since the first Minis were made.

wheely73

Guess I'll save myself the job then, unless they start to fade.

Cheers guys