Must Do Beta?

[dadof2]

The photo is the Grimeca caliper of the Front of an 2012 Beta on which brake problems started occurring at just over 18 months old.

Brake was grabby and disc was showing more wear than it should.

Caliper was removed from bike and pistons were found to be "seized". They would not move with 10 Bar (150 PSI) air pressure and had to be pumped out with a grease gun.

Pistons should move easily with less than 5 PSI.

When the pistons were out a band of corrosion was present where the black coating had worn or corroded off. The piston in the photo has had the corrosion polished off with solvol autosol.

The calipers were chemically cleaned (as shown on photo) Then the seal grooves scraped out, followed by polishing with fine wire wool, then solvol autosol.

The design of the cylinders is very poor. The fluid enters the cylinders just over 1/2 way up (slots can be seen in photo) meaning air is trapped above the fluid and does not vent to the bleed nipple or back up the hose to the master cylinder. Also the fluid hole drilling that connects the caliper halves is at the bottom of a larger hole meaning once again air is trapped above the fluid.

Hydraulics like central heating systems should be designed so that air collects at bleedable high points. Why Grimeca / Beta do not follow this basic good practice is beyond me.

Also the thin metal cover that has to be fitted between the caliper halves, why not an easily removable (to insect pads / wash out dirt) external plastic cover as used by Honda and Suzuki many years ago.

Come on Beta, you need to do better.

Edit - for those not familiar with this caliper on a Beta, when it is mounted on the bike the part of he caliper at the right of the photo is at the top, so to get a correct view rotate the photo 90 degrees anti clockwise

Edited August 4, 2014 by dadof2

[mags]

My wife's 2014 4T has a grabby front brake after only six months of use as a beginner (easy on brakes). I pulled down the master cylinder and still does it off and on.

I just know its the caliper pistons! When I say grabby its not that bad... you lift front wheel and spin it, it stops much quicker than when pistons return.

Strip down, clean and new seals is around the corner.

I was contemplating making a brake bleeding jig that bleeds system off the bike and does not have the loop of line down into master. Just make it straight on the jig and a 30 deg angle to make bubbles rise to master or reverse bleed from caliper nipple back up to master?

A small plate to simulate disc between the pads of same width as disc would keep pistons ok to lever bleed? A small bit of tube to simulate handlebars bolt master on? Another plate to attach caliper in any orientation?

Bleed on jig and get good lever feel and bolt back on bike? Could do Montesa one as well on the jig?

I removed the Beta stainless pad cover ages ago! I like to see in there and clean easier. The Braketec caliper on the Montesa doesn't have a dust cover standard. Cant see any downside but it must be there for a reason other than dust maybe???

Mags

Edited August 5, 2014 by mags

[lineaway]

The manufactures do not make the brakes. I would say all this happened when we lost AJP. The farce with Formula was even worse. In a day and age where the brakes are a main way of riding technique, no matter the brand they should get more attention. Ask a top team member how often the brakes are rebuilt, I think you will be surprised. On the other hand my 1990 Fantic has never had any attention to the brakes, besides new pads.

[totalshell]

the main consideration to the manufacturer will be price.. as the brake on a trials bike is unsophisticated due to its relative use, its not required to slow the bike down from high speed just to cope with speeds normally well below 30mph. you d probably find better brakes on a 1500 quid scooter or a 3 grand mountain bike

[paul_m]

As stated above its all to do with price, that means speed of construction, I spanner for a race team here in the UK, 99.9% of brakes are the same from the factory. they are dry assembled.

On receipt of a bike, I strip the assemblies down, clean thoroughly with brake cleaner, give every mating surface a sparing coat of red rubber grease, then re-assemble.

the nitride coating on the pistons hates direct contact with brake fluid. only use dot 4 as higher has a silicone content which perishes the oil and dust seals.

when you have ridden (and you have time) remove the caliper and wash in warm soapy water. remove the pads and place in a piece of 10mm wood and push out the pistons then re-clean.

its a simple task but one of those with we can never be bothered to do, but is so important.

I do them on a night between race days just to ensure we wont have that problem.

Paul

[dadof2]

When I rebuild brakes I thoroughly coat the cylinders and seals with brake fluid before putting the seals back in. This is so the seals can move easily to seat properly in the grooves. I do not use red rubber grease for this because I found on AJP calipers in particular the grease prevents the seals seating fully and then they put excess drag on the pistons. I do coat the piston with red rubber grease so it slips in easily and this fills the gap between piston and bore preventing dirt getting at the seal.

[mags]

I use artists brushes to apply rubber grease sparingly. The little ones can paint the seal groove without excess. You can paint it so you just get a shine if thats all you want.

I've come to terms that I may have to full strip, clean and reinstall brake systems on both bikes annually at worst, 6 months ideally.

Mags