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Discussion Starter · #1 · (Edited)
First of all, regards from Spain to everybody here, I've been reading the forum since some time ago and this is my first post :)

Now, my problem: I have a Oro K18 brakeset and I was having problems with the rear brake, making weird sounds and producing vibrations. I decided to try new pads and I bought genuine Formula ones (supposedly the same as the old ones).

Here is where my problem really begins: with the new pads it is nearly impossible to mount the caliper, the rotor has no room between the pads. I 've pushed the pistons back as much as possible using a screwdriver and the old pads (as the manuals in the website says) but no way, the wheel is totally braked and the lever has near zero travel.

I've sanded down a bit the new pads, but only helped a little. With the old pads (not totally worn, I would say more than 50% life) everything is ok.

Could the new pads be defective and have too much material? Maybe the circuit has too much fluid and that's the reason pistons can't be further pushed back? If so, is there any way I could I empty it a bit without full bleeding process?

Thank you very much in advance & best regards!
 

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Meh.
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Does the backing of the pad sit flush with the caliper? If not, the piston is not all the way back in. If it cannot be pushed all the way in, the system may be overfilled. To remedy this, level out the lever on the bars, open the bleed port, push the pistons in. Excess fluid will come out the bleed port. Close the bleed port. Clean with plenty of water to de-activate the DOT fluid. You should be good to go.
 

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Discussion Starter · #3 ·
Thanks for your reply...

The pads do not sit flush against the caliper (the distance is about 1mm or so) so you might be right: too much fluid. What's weird is that with the factory pads the lever travel was normal and the fluid is the same since I bought the bike and the circuit has not been opened or refilled. Could the fluid expand a bit over time? Maybe due to humidiy or something?

I think that I've used more than enough force to think that the pistons won't go further back, so tomorrow I'll try what you've suggested.

Anyway, any other ideas or suggestions are welcome.

Regards!
 

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Hi _lalala_,
There are probably several explanations for what you are experiencing:

1. As XLS_Will says, the system is likely overfilled. Even though you have never opened the system, because DOT fluid is hydrophilic, you most likely experienced some swelling. This would be particularly true if the brake is over a year old and you have not changed the fluid during that time or if you live in a particularly humid area.

2. The second contributing factor is this: The caliper pistons on brakes which use a fluid reservoir to compensate for pad wear ("Open System...which is about every brake on the market today) will have a range of motion based on how much pad material you have left. When your pads are new, the resting position of you caliper pistons is further into the caliper than when your pads are worn, as your pads wear the pistons move further towards the rotor. Each time you squeeze your lever and actuate the caliper pistons they move a given amount until the pads contact the rotor. This means that the portion of the caliper piston which was in contact with the caliper piston seals when the pads were new is now positioned outside the caliper and exposed to the elements. The caliper pistons range of motion no longer put that area in contact with the caliper piston seals which effectively lubricate each time the caliper pistons move. Now that you put the new pads in, and forced the pistons back into the caliper, the piston seals are in contact with an area of the caliper piston which they have not been in quite some time. This area is dry and unlubricated causing sluggish movement and the migration of the caliper pistons back into the position they were used to when you had the worn pads in there.

The solution to you problem will be this:
First you should reset your caliper pistons but before you do this you will need to remove the excess fluid from the system.

1. Remove the brake from the bike and on a workbench position your brake lever with the MC above the Caliper and with the bleed port on the MC pointing vertical. Be sure that the caliper stays below the level of the MC bleed port at all times.

2. Remove the bleed port on the MC and place a rag around it to catch the small amount of excess fluid you will push out.

3. Put your old pads back in the caliper and with a flat head screwdriver or tire lever pry them apart forcing the pistons back into the caliper and purging the excess fluid out the lever bleed port. NEVER USE AN OBJECT (METAL OR PLASTIC) DIRECTLY ON THE CALIPER PISTONS!

4. Squeeze the brake lever 3-5 times, moving the caliper pistons inward. Make sure that both caliper pistons are moving and BE CAREFUL NOT TO POP A CALIPER PISTON OUT COMPLETELY. Then pry the pads/pistons back into the caliper fully. Repeat this process 2-4 times or until the caliper pistons are moving smoothly and staying set in their position fully inside the caliper. Each time you do so, you are lubricating the caliper pistons and effectively preventing them from wanting to migrate back to the position they were in when the pads were worn.

5. Bleed your brakes following these instructions:
http://www.formulabrakeusa.com/tech/Formula Bleeding Procedure.pdf

6. Remember to reset your caliper pistons all the way back into the caliper before closing off the lever bleed port at the end of the bleeding process.

7. Replace your old pads with the new ones and make sure the brake is functional and the bleed is good before you reinstall the brake on your bike.

8. Before riding your bike again: 1. Make sure ALL fasteners are torqued to spec!!!!!. 2. Make sure you have the E-clip on the pad retaining screw. 3. Make sure all DOT fluid has been cleaned up using denatured alcohol.

I hope that gets you going. If you are still having problems please bring your brake to a Formula Dealer in your area.

Thanks,

Chris Costello

Formula Brake USA
 
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