Caliper Rebuild (or not?)

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Merecat
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Postby Merecat » Thu Jun 25, 2015 6:58 pm

Corvus wrote:
Merecat wrote:I don't think any fluid returns. You release the pressure and the pads release the grip on the disk. No pressure no braking effect although the pads will probably be in contact with the disk to some small degree........
Maybe


What would happen, even in the short term, if the hole was blocked? If no flow into or out of the reservoir occurs, then we don't need the hole.


The hole is blocked when the brake is activated. The piston closes the vent hole to the res when the master cylinder is operated. The resavour is just that, to replenish the fluid that is required for the system as the pads wear. There is no flow as such. Pressure is transmitted equally to all parts of the system. This pressure acts on the caliper piston and clamps the disc. The fluid will move to fill the void. Moves as opposed to flow because the fluid is incompressible and acts almost like a solid.
When the lever is released it relieves the system pressure, venting to the resavour which is at atmospheric..
If the hole was blocked, the brake would still work, but more likely than not release the pads from the disk more slowly
Mick

2001 R1100s Frost Blue

Its not going the fastest,

Its stopping the quickest

Corvus
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Postby Corvus » Thu Jun 25, 2015 10:32 pm

Merecat wrote:
Corvus wrote:
Merecat wrote:I don't think any fluid returns. You release the pressure and the pads release the grip on the disk. No pressure no braking effect although the pads will probably be in contact with the disk to some small degree........
Maybe


What would happen, even in the short term, if the hole was blocked? If no flow into or out of the reservoir occurs, then we don't need the hole.


The hole is blocked when the brake is activated. The piston closes the vent hole to the res when the master cylinder is operated. The resavour is just that, to replenish the fluid that is required for the system as the pads wear. There is no flow as such. Pressure is transmitted equally to all parts of the system. This pressure acts on the caliper piston and clamps the disc. The fluid will move to fill the void. Moves as opposed to flow because the fluid is incompressible and acts almost like a solid.
When the lever is released it relieves the system pressure, venting to the resavour which is at atmospheric..
If the hole was blocked, the brake would still work, but more likely than not release the pads from the disk more slowly


Ok, I see the reluctance to call it "flow" because it's slight and not very long lasting, but that's the nature of the system. Displacement, movement, flow. We're singing off the same hymn sheet.

I would go further, however, and suggest that the system wouldn't work very long with no hole, or even with the reservoir topped to the very brim. Not only does the hole top up the system, but it caters for expansion of the fluid. I wouldn't think it would take too many firm applications of the brake to lock up the system. With the bike travelling obviously, not stationary.

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R-man
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Unsure about calipers

Postby R-man » Thu Jul 02, 2015 3:09 pm

1100 S's were fitted with three different calipers at the front. It makes a big difference to how you go about overhauling - see James Sherlock, Motorworks, MotoBins websites for parts.

Early bikes had Brembo opposed 4-piston calipers, which look sort of triangular from the road side. These are fully rebuildable, ie you can sometimes buy the o-ring that seals the two halves, making a full cleanup a doddle. Seal-and-piston kits are around £60 per caliper, AFAIK you can't buy only piston seals, without new pistons.

2000-on bikes mainly had Brembo EVO calipers which are much larger and marked BMW or BREMBO on outside face, and run on 320mm diameter discs. Although a couple of specialist dealers will recondition these for you, I have never been able to get the o-rings to split these calipers. Seal-and-piston kits are around £70 per caliper, and expelling pistons once their seals have become sticky is a fiddly job.
Beware the piston face against the back of the pads are a disc of ceramic, to slow heat transfer - and this is fragile, so do not lever against it.

2002-on some bikes fitted Japanese calipers by 'Tokico' and these again are larger, and seal-and-piston kits around £70 per caliper.

Pads for each type are quite separate and not interchangeable.

As your bike has covered 36,000 miles I suggest you will get biggest bang for buck from a thorough clean up (brake cleaning solvent and toothbrush around the piston outer seals; then changing fluid lines to braided. Full overhaul is the priicest option!
Read the many threads here on brakes, and go carefully, help is at hand.
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-in the 70s & 80s there were lots more...

Motocod
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Postby Motocod » Thu Jul 02, 2015 4:59 pm

The latest edition of Performance Bikes magazine has an article which steps you through rebuilding calipers. In spite of being fairly adventurous with mechanical stuff it's not a job I've ever attempted, but it looks pretty simple.

I expect the biggest faff might be getting rid of airlocks when you bleed new fluid through, but it might be possible to get round that by using a syringe to suck the fluid through (again, this is not something I've tried, but seems like a good approach).

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boxerscott
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Postby boxerscott » Thu Jul 02, 2015 9:32 pm

Wot tanneman sed.

If both calipers are binding equally then it is something common to both. That could be a flattened hose that serves from mc on handlebar to bridge splitter. It is acting as a non return valve ie when you release the lever the hydraulic forces are prevented from returning.

Hoses do flatten. pressure and the temperature of the hydraulic medium affect them.

Can not understand why your garage techy has not been more helpful?

Reverse bleed your calipers see if fluid freely fills your MC on handlebar?
I am the Village Green Preservation Society. God Bless Strawberry Jam and all it`s variety.


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