Rev 3 Rear Brake Problem

[scorpa250]

Thanks again i have ordered a set of pads ...will keep you all updated on the progress..

Regards Paul

[yoyo]

Or you could just do what I did with my 06 Rev 3.

CHEAT!

I just handed the bike over to my local friendly bike shop and asked them to sort it! It only cost me an hours labour and a new M/C seal kit and I was away!

I had been going through various processes and just got pee'd off with it in the end.

I'm normally very patient but not this time!

[wanariot]

Hi scropa 250, I too am having exactly the same problem, Ive had beta rev3's for 6 years and this is their No1 problem and why some off road/engineering firm hasn't come up with a mod kit is beyond me,,,,,,,,,,,,why is it the off road market is so full of s@hit like noisey exhausts yet you can't buy want you really need,,,,,,,,is there anybody out there??????

Anyway mustn't grumble,,,,,,,,,,,,cant expect brakes to work to the year 2008.

True; you do need plenty of meat on your rear pads to get the brake to work well once they are half worn replace them, and there my friends lies the problem, the bike industry loves selling profitable items so why would they want a decent brake set up that gets a reasonable wear out of your pads????

BUT i do find I can put well worn pads in the virtually identical front brake with no problem ( year 2000 to 2004), so use them there and get your moneys worth.

What happens is this; rear brake usually get more covered in crap and we tend to use it more than the front so it gets hot. Once the pads are part worn they are not capable of obsorbing the heat due to lack of mass and the brake overheats and goes all weak and floppy, similar to when your watching Racheal Stevens on strickly come dancing.

BUT this doesnt explain the not being able to bleed the brake problem, I ve pumped about a litre through mine with no joy. Ive tried removing the master cyl and lying it flat with the caliper and reservoir higher ( too avoid the 'raised' section off the brake line) and pumping the master cyl with suitable tool (whilst thinking of Racheal Stevens) but still no joy.

I have now taken complete brake system to brake speciallist and will report on his findings soon.

P.s. i have fitted new caliper seal kit and another master cly and still no joy.

The thing is even when this brake is working they are still s@hit. I only realised how S@hit they are when I rode a pre 65 BSA with a standard rear drum brake, fantastic power and feel, weve spent 40 years going backwards.

[grahamjayzee]

Been watching this with a bit of interest.

I bought a 2001 Rev3 a few months back and have not had much chance to use it. However, first time out at the Yennards I lost my rear brake completely. It flet like a stone had lodged the pads but that wasn't the case. The disc was very hot though so I assumed that I was slightly dragging the rear brake (I ride with a lot of rear brake anyway) and I also felt that the pedal needed adjusting slightly as it was a bit high for me.

Anyways, I thought at the time that the fluid had boiled. Sure enough, after a while to cool down the brake returned. I NEVER had a problem with the brakes on my old 1992 Zero, and that had much larger pistons. It would seem to me that the brake circuit cannot dissipate the heat and the fluid boils. If this happens it soon denatures the fluid and may cause it to absorb air. Certainly on the race bikes with racing fluid, you need to change it very often to avoid fade. This also concurs with those who have noticed that new pads ease the problem. More pad = more to absorb the heat.

I wonder, has anyone experimented with brake fluids? What are we all using?

As regards the bleeding, I don't know at the moment, but if there has been air absorbed into the fluid, only changing the lot will work. If you just bleed a few ccs, you'll still have a large percentage of spongy fluid!

Graham

[stork955]

Gday, Brake fluid (aprt from the silicon type) is Hygroscopic, which means that it absorbs water from the atmosphere by nature. It gets in through the hoses and is present in the reservior. If you look at any maintenance manual for any vehicle you will see that Brake fluid should be changed at least every 2 years because of this. I dont think that this is the problem we have here however although your fluid should be changed regularly!

I dont have a Rev 3 but I'm beginning to suspect that the reservoir can not compensate for the pad wear by allowing the fluid inside itself to get into the master cylinder. This is caused by the rubber diagphram thing that goes under the cap - it is designed to allow atmospheric pressure to act upon the fluid but not actually allow air to directly contact the fluid for the reasons above. If the pads wear somewhat and the pedal begins to go spongy this is symptomatic of this effect - the fluid is not replacing that which has gone into moving the pads further out. Usually the cap has either a small air bleed hole or in the case of front m/cylinders a passage thet runs from the outside of the cap to above the rubber bellows. An interesting experiment would be for someone who is experiencing this to remove the rear filler cap, pump the brake back up and top the fluid off, and replace the cap again, then see if the problem is solved.

I hope all this makes sense.

Cheers,

Stork.

[grahamjayzee]

Light bulb!

That makes good sense Stork. I'll investigate this.

However, mine certainly went off because it was hot! When it cooled down it was fine so there is an issue here elsewhere.

Graham

[scorpa250]

Pads arrived today from BVM ...........The wrong ones !!! o well i could be writing that that did'nt work !!! another set on there way .will i ever get to the bottom of this.??

[stork955]

Light bulb!

That makes good sense Stork. I'll investigate this.

However, mine certainly went off because it was hot! When it cooled down it was fine so there is an issue here elsewhere.

Graham

Gday, If the brakes change when they get hot it would either be that the fluid is boiling (you cannot compress a liquid but you can compress a Gas) due to the fluid being old, or that the transfer port in the master cylinder is blocked (either the old fluid again has blocked the hole with rubbish, or the pushrod from the pedal is adjusted too long and holding the piston in the m/cyl across the port). Both quite common. There must be some small amount of freeplay between the end of the pushrod and the master cylinder piston.

Cheers,

Stork.

[grahamjayzee]

Hi Stork,

I think a bit of both in my case. Since I bought the bike I have been going through and make each aspect tip top, but hadn't got as far as the rear brake yet! I had noticed that the lever is too high for me and suspect there is no clearance between the pin and piston. Also, given the state of the fluid I flushed out of the front brake, I suspect the rear circuit is full of cold tea too!

I'm going to replace the pads and fluid this week and get it set properly. Hopefully that will make the recent failure a one-off.

Graham

[wanariot]

I've had a brake specialist look at my 04 rev 3 rear brake system, he reckons the new seals are at fault in the caliper as they are too tight a fit and do not allow the pistons to push and return freely which contribute/start the overheating process. The recesses for the seals where clean before fitting. There has to be some fundamental design flaws in this system with the number of people who have on going problems and maybe this is one of them.

Does anybody know of any upgrade kit?

[grahamjayzee]

Wanariot, I'm not 100% that's likely to be the cause. I bow to your chap's knowledge, but my understanding of the brake concept is that the square profile of the seal is designed to GRIP both the piston and caliper so it pulls the piston back in after it has moved out. It is the size of the seal that governs how much forward movement can be retracted. Brakes often bind because a seal expands in the recess due to corrosion behind the seal and this then prevents free movement of the piston. As a result, the rubber does not have enough grunt to pull the pad back in. The piston only moves past the seal as the pad itself wears.

However, there may be something in what you are saying; if the size and shape of the seal are inappropriate for the amount of movement, it will not be able to retract far enough to prevent some degree of brake drag. I still think that the master cylinder looks like a more fundamental cause. Particularly i the breath hole/ disphragm is not able to provide sufficient fluid to keep the system fed.

I shall investigate further though!

[stork955]

Gday, I agree that the seal profile is unlikely to cause problems, considering that these are a fairly common caliper design fitted to a few different bikes. ( I assume they are AJP - possibly wrongly....) It is vital that the m/cyl releases correctly and uncovers both ports inside (the pushrod thing). The caliper seals are designed to flex and pull the piston back a few thou, which is all they need. Most are fairly tight when new and it is very unlikely that genuine parts are going to be incorrect. Notice I said "unlikely" :-) I'd be having a very close look at the breather hole in the reservoir cap - this is most likely the trouble, and the the pushrod clearance next - in order of "easiness".

Have you got your new pads yet Scorpa250?

Cheers,

Stork.

[scorpa250]

No not yet stork,just a thought is there any advantage if i take the whole braking assy off and do it on the bench with the master cylinder a lot higher ??

Scorpa250.

[stork955]

Yep - almost - It can help in that you can roll the system around to work out all the air from corners in fittings and the like. Air likes to go up always so keep the m/cylinder low and the caliper and reservoir high as you want to push the air out of the caliper. You also need to prime the m/cyl first to get things started. Usually I do this on the bike by very gently just cracking the lever/pedal very slightly multiple times. After a little while you will begin to see air appearing in the reservoir, this is coming out of the m/cyl. The important thing is that the system is closed during this (bleeders done up) and the amount of movement is very small, just enough to move the piston a couple of millimeters -no more than that. Afterwards, when it seems most of the air is gone using this method and you begin to feel a "lever" coming on, I tap fittings etc with the handle of a screwdriver to help the process of removing air along and bleed in the "normal" fashion from the bleeder screw. (It might pay before you start doing anything to make sure that the bleeder screw is not blocked up - this has caught me out before...) Be very patient! Also make sure all of the other things we have talked about are OK before you start, just so you dont chase your tail around.

Good Luck,

Cheers,

Stork.

[scorpa250]

hello all... the plot thickens,i removed the whole brake system and set it up on the bench (master cylinder in vice ) started to bleed and noticed the was a small damp spot on the joint where the two caliper halves join i separated them, there is a "o" ring which must be the cause !!!!! of all my problems will get a new one in the morning,will my son ever ride it again ??

Scorpa250