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Discussion in 'Parallel Universe' started by The Jinx, Nov 2, 2010.
The first problem I had with the bike was a dead battery
That makes the most sense Gary. Because the next day when I tried to pump the brake without the one pad in place it moved with ease and I was able to push it back open with my thumbs easily. When I had the calliper pushed open I could re-install the brake pad with out any trouble. I need a square piece of wood the width of the space between the brake pads at full open maybe 4" long to hold the brake pads in place as you slip in the rotor, pull the piece of wood out, push in the axle, and your done. Let's see two hands to lift the wheel, one hand to pull out the piece of wood and one hand to slip in the axle. That's four hands, that's right you need two people to replace the rear wheel on one of these things.
At home in the garage I use a 1"x 4" 2 foot long piece of wood under the wheel to use as leverage to lift the wheel, that frees up one had and you can replace the wheel easly by your self as long as the brake pad stay put.
I would agree that the most probable cause for him not being able to spread the pads (and thus force the caliper piston bake) is some sort of mis alignment causing them to jam.
The hypothesis on air in the system causing the problem is completely a falshood. Yes air in a hydraulic brake system is bad because air is compressable. That means if you squeeze the lever, your effort is expended compressing the air with little increase in the system pressure to push the caliper piston out and apply the pressure to the pads. Fluid is uncompressable and thus will transmit all apllied force at the lever to the caliper.
Expansion of the fluid and air if it were in the system (not that this would be your problem as outlined previously) is managed by the master cylinder. If the system is in proper working condition, as the fluid expands due to heat, it is allowed to be displaced back into the resevoir by a small relief port which is opened at the full release of the brake lever. At no time does fluid pressure in a properly functioning brake system ever rise above atmospheric pressure except when the brake lever is actuated.
And yes, the rubber diaphram in the cap is there to allow for fluid movement wether it is the return of fluid to the resevoir due to expansion or for the gradual transfer of fluid to the caliper to account for pad wear without allowing atmospheric contamination of the fluid.
Bayner touched on the facts behind the caliper piston being drawn back into its bore when he mentioned the square cut o-ring seal. How that works is that the pressure of the fluid actually causes the o-ring to deflect outward with the piston as the brakes are applied. When the pressure is released, the o-ring returns to its normal state and draws the piston back with it. It is a very miniscule amount of travel, but is sufficient to free up the disc to spin freely between the pads.
The piston is often pushed further back into the bore due to variations in the rotor. No rotor is ever perfectly true (or at least not for long) and the wobble in the rotor pushes the pads back as it spins. If this is excessive, it causes what we know as low brakes, it takes more lever travel or even multiple lever strokes to pump the fluid back down to the caliper to push the pads back together sufficiently to apply braking force.
As Bayner noted, corrosion and contamination can cause the system to not function as designed. If the master cylinder is corroded or contaminated, the pressure return port may not be opened and then pressure will remain in the system. Oil contamination can also cause the seal to swell and not allow the port to open. However, if this happens, not being able to push the pads back to replace the wheel is not your real problem. What will most likely be your problem is that as the brake fluid heats and expands the pressure that is not allowed to escape will actually apply the brakes even up to the point of locking the wheel.
Oh, and the reason your cars brakes feel firmer in the morning after it has sat all night is actually not a problem with the hydrualic system at all. It is actually the vacuum assist servo that is losing its vacuum as the car sits and thus you have old fashioned unassisted brakes when you step on the pedal prior to starting the engine. There is a check valve to hold the vacuum in, but they often leak down and create this symptom.
Now where is my gold star.
They've got such a woody for going electric with everything they can. While I readily understand the benefits 'in theory', I just can't understand why they want to do this, because in reality, mechanical failure is becoming much less common than electrical failure. How many power window motors have had to be changed versus a master cylinder?
There is no way they would go with electric brakes!!! Maybe an electric assist but brakes have to be actuated without electric power, that is a "user need" for us consumers.
In my industry we are using electromagnetic brakes but the default condition is "on" not "off" so if there is no power it will act as a friction brake but won't let the equipment swing wildly out of control! :eek1
Here is an alternative to consider. I have a friend using this system and he loves it. Having said that, I think he is kind of a goofy guy i.e. he has a Rekluse in his 990A, and also owns an Aprilia.
This would mean you have to replace both front and rear rim (and therefore spokes) with narrower ones - ideally 1.6" front and 2.15" rear for it to work as designed. That is very narrow for riding on the road and doesn't give all that good of a contact patch as the tire gets pinched together.
for getting things back on track Tmex
can someone please tell me why you guys with the 8 just can't buy rims like on the new yamaha s10?
Did anybody say you can't? You'd have to look at the number of spokes, lace pattern, angles etc to figure out if it would work.
I doubt they will hold up well however, just like the Aprilia Capanord rims some guys are having put on their 950/990 Adventures.
By the way, since I don't think these have been mentioned yet in this thread:
Not exactly a bargain for about $2200 a set.
This is a good post and is spot on. Your knowledge of brake systems is a great asset to this forum. I still deserve at least one of those five stars though.
well ALMOST anything,,,FYI ...BWOE,,,i have not yet been able to use mismatched rim and hubs,,,ie 36 hole hubs with 40 hole rims or vice versa....another thing is using radically mis-matched angles between rim/hub
FYI,,the HP2 a fun ''parts-bin'' bike uses the same rim combo as their R100GS and GS/PD laced onto R1200GS hubs [the front having it's right side brake mounting lugs machined off]
FYI....all BMW wire wheels in recent time are derived from 3 basic rim width extrusion dies which get rolled into these available diameters:
2.5'' x 17 and 18 and 19
4.0'' x15 and 17
Hence i've figured out that these can be x-laced/swapped to any front or rear x-laced hub
BWOE,,,,common swaps are going from 19'' front to 21'' on all the GSs,,,going from 2.5x17 to 2.5x18 on the rear of HP2s for better rear tire selection and handling ,,,,then there's reverting from 21'' front to 19'' on all the HP2s and R100GS & GS/PDs for better on road performance
FYI,,,the rear F800GS can be made tubeless using known and reliable sealing techniques,,or the Alpina 'O'ring seal system or by using genuine x-laced technology ala transforming/marrying Aprillia CapoNord rims onto Billet hubs,,,OBTW only available in 2.5x19/4.0x17,,,, in this case the oem hubs do not lend themselves to the conversion because the indexing and spoke angles aren't compatible
some comments on a variety of posts...
there are more than 50 sets of KTM 640/690,,,950/990,,,bmw F800GS CapoNord conversions out there trouble free and not one save the prototype has been back for truing,,and that one was actually within specs [analysis revealed the same shoddy manually trimmed /ground weld area divots found on most BMW x-laced wheels..of course made by the same company=Behr]
earlier the discussion centered on how much simpler just putting a tube in to your punctured tire was as good as putting in a plug on a tubeless tire... yes i've seen folks run on a plug as well those who continue with a new tube in their tires....i've also seen more blowouts caused by the tube being eaten/chafed in the spot where the nail came through as well as leaks coming from the plugged hole...
all the tech literature and my common sense/experience speak the mantra of putting a T-patch into the nail hole of your TT tire to prevent your tube from chaffing and having a blowout and swapping your plug for a T-patch in your TL tire....IMHO,,the T-patch is a superior and permanent Rx .... you not only physically patch AND plug the hole you also provide a smooth surface for your tube to rest against.
Guys, DID makes tubeless rims, they are called 'easy tubeless' and they work really well. In 17" size they do come in 3.5 and 5.0, maybe 5.5 too.
I am running the 5.0 on my SE and does not leak any air for the last month.
They don't make a 21" front though.
There's no way I'd go down in size in the front.
So, what? Out of the 10 times in my 300,000 kms of biking experience I had a flat, not one time it was on the front and I bet that similar statistics apply to most of us.
Flat tires have nothing to do with it. Where did that come from?
BMW put the 21" front wheel there for a reason. The larger 21" front wheel rolls over uneven terrain much easier and smoother than a 19" or 17". I like to ride my F8 on gravel, fire roads, and trails. The 21 incher is essential.
Put it this way: That smaller the wheel, the harder time it has rolling over things.
I had a front flat on a dirtbike once. I wasn't done for the day yet so I went out for another loop at the OHV before loading up for the night.
Come to think of it...I had another front flat on that bike too...couldn't get the bead to seat, so I just hit the trail and the bumps and ruts sorted that right out!
This is obvious Griz, but my point is that you need more a tubeless on the back than on the front. And for your bikes, you have to choose between a 3.5-17 and a 5.0-17.