| Author | Post |
|---|
KevG
Super Moderator
|
Posted: Mon Jun 30th, 2008 04:30 pm |
|
Hi David.
Good points there.
Salty water is an excellent eletrolyte. Salt comes from the road of course.
The calipers suffer from anodic corrosion true.
However when the plating on the pistons wears they rust too.
Kev
|
David
Member
| Joined: | Sun May 25th, 2008 |
| Location: | |
| Posts: | 267 |
| Mana: |   |
|
Posted: Sun Jun 29th, 2008 11:15 pm |
|
Hi Kev thanks for that, with regards your comments;
Bike calipers are generally aluminium with steel pistons, so prone to electrolytic corrosion.
2. Bikes can be laid up over winter.
3. They are more easily cleaned with high pressure water.(Supplying the electrolyte).
Combine this with no movement when laid up over winter.
4. The forces involved are not as great as a car, so the calipers don't get as hot, and they are better cooled, so less thermal shock.
only a theory though
What do you think about;
Calipers are manufactured from Aluminium with steel pistons, so would I be right to say that only the pistons would suffer from electrolytic corrosion.
Does water supply electrolyte, where these are generally understood to be molten ionic compounds, or solutions containing ions, I thought that normally sodium sulphur cells where electrolyte.
With reference to your theory, point 4, maybe I would look more along the lines of thermal expansion and retraction, here we have two different types of materials which expand and retract at different rates and temperatures, and although a compromise is used between them, the protective coatings used on aluminium may be breaking down over time?
Cheers
David
|
KevG
Super Moderator
|
Posted: Sun Jun 29th, 2008 08:07 pm |
|
David wrote: In theory all brake caliper pistons slightly retract when the pressure is released, most cars never pose a problem with caliper pistons seizing, so why do bikes seem to suffer so much with this problem?
David
Several reasons David
1. Bike calipers are generally aluminium with steel pistons, so prone to electrolytic corrosion.
2. Bikes can be laid up over winter.
3. They are more easily cleaned with high pressure water.(Supplying the electrolyte).
Combine this with no movement when laid up over winter.
4. The forces involved are not as great as a car, so the calipers don't get as hot, and they are better cooled, so less thermal shock.
only a theory though
Kev
|
David
Member
| Joined: | Sun May 25th, 2008 |
| Location: | |
| Posts: | 267 |
| Mana: | |
|
Posted: Sun Jun 29th, 2008 07:51 pm |
|
In theory all brake caliper pistons slightly retract when the pressure is released, most cars never pose a problem with caliper pistons seizing, so why do bikes seem to suffer so much with this problem?
David
|
KevG
Super Moderator
|
Posted: Sun Jun 29th, 2008 11:35 am |
|
Tim wrote: KevG wrote:
(They do not retract when you release the brake).
Um! Yes they do. Otherwise they would bind. The piston seal being square in section causes the piston to retract slightly when the hydraulic pressure is released.
Read the rest of the post before you confuse the guy with comments like this.
I,m keeping it simple on purpose to make it easier to comprehend. We all now what happens, the guy thought that the pistons were completely retracted every time the brakes were released.
|
Tim
Member
| Joined: | Sat Jun 14th, 2008 |
| Location: | Southampton |
| Posts: | 16 |
| Mana: |  |
|
Posted: Sun Jun 29th, 2008 08:36 am |
|
KevG wrote:
(They do not retract when you release the brake).
Um! Yes they do. Otherwise they would bind. The piston seal being square in section causes the piston to retract slightly when the hydraulic pressure is released.
|
Tim
Member
| Joined: | Sat Jun 14th, 2008 |
| Location: | Southampton |
| Posts: | 16 |
| Mana: | |
|
Posted: Sun Jun 29th, 2008 06:53 am |
|
big..E. wrote: my mum also told me not to spit my dummy out aswell....
Hmmmm... I think the teddy bear got launched too
Seriously though, the first tester who MOT'ed the bike failed it because he obviously felt that the bike had a fault with the brakes. Then the garage who fitted them and took your money said they were OK. I think for your own safety, you should maybe get a third opinion?
BTW Its mummy not mommy. ( Another Americanism seems to have slipped past the safety net)
|
big..E.
Trade Member
| Joined: | Tue Jan 29th, 2008 |
| Location: | |
| Posts: | 218 |
| Mana: | |
|
Posted: Sat Jun 28th, 2008 08:54 pm |
|
| my mum also told me not to spit my dummy out aswell....
|
cbr65
Member
| Joined: | Tue Jun 24th, 2008 |
| Location: | |
| Posts: | 9 |
| Mana: | |
|
Posted: Sat Jun 28th, 2008 04:58 pm |
|
Pay attention Timothy 
The garage fitted the discs and extended the caliper mountings, I just changed the pads.
Anyhow Einstein! If you don't ask, you don't learn. Surely your mommy told you that!
|
Tim
Member
| Joined: | Sat Jun 14th, 2008 |
| Location: | Southampton |
| Posts: | 16 |
| Mana: | |
|
Posted: Sat Jun 28th, 2008 02:22 pm |
|
Is it just me. Or does anyone else's blood run cold. When someone with such obviously limited mechanical knowledge attempts to repair their brakes by asking questions on an internet forum.
|
cbr65
Member
| Joined: | Tue Jun 24th, 2008 |
| Location: | |
| Posts: | 9 |
| Mana: | |
|
Posted: Sat Jun 28th, 2008 09:02 am |
|
Ahh, I think I've got it now.
Then there must be some sort of one way valve at the master cylinder that only allows fluid to return to it when the system is unpressurised/at low pressure. Otherwise how would you be able to push the brake pistons back manually when changing pads.
Is that why the brakes are mushy after pushing the pistons back in until you pump them a few times ?
|
KevG
Super Moderator
|
Posted: Fri Jun 27th, 2008 07:49 pm |
|
cbr65 wrote: Well from a purely hydraulic pov it should do, less travel on the piston should mean less travel on the lever
Unnles I've got the wrong end of the stick
Hi cbr65
I think you may not have grasped the concept. But no problems.
It makes no difference how worn the pads are, The travel at the master cylinder (Brake lever end ) is a constant, given the same sized slave cylinder(s) (Or pistons in your case ). This is because
The pads are always touching the disc regardless of how worn they are , when you operate the lever you squeeze them onto the disc, they move a little, but not much, that amount is always the same regardless of the thickness of the pad.
As the pads wear they get thinner,The pistons in the calipers move out of the calipers as this happens, (They do not retract when you release the brake). The extra space created in the caliper is filled by the fluid in the master cylinder on your handlebars, The level in this will drop from full to empty as the pads wear out.
Hope this helps.
Kev
|
cbr65
Member
| Joined: | Tue Jun 24th, 2008 |
| Location: | |
| Posts: | 9 |
| Mana: | |
|
Posted: Thu Jun 26th, 2008 11:20 pm |
|
Well from a purely hydraulic pov it should do, less travel on the piston should mean less travel on the lever
Unnles I've got the wrong end of the stick
Last edited on Thu Jun 26th, 2008 11:21 pm by cbr65
|
KevG
Super Moderator
|
Posted: Thu Jun 26th, 2008 07:07 pm |
|
cbr65 wrote: Well the front pads are quite worn but I had them out two weeks ago to check the wear and there's still a good 3mm of pad on them. I have new pads and if I fitted them it should reduce the brake lever travel. Thinking about it, I'll fit the new pads it will give him one less thing to gripe about.
The thing about the lever touching the bar is a bit of a red herring imo, the front brakes on a 600RR are savage they start to bite after a few mms of lever travel and even under emergency braking you'd probably cartwheel the bike before the lever hit the bar
However if that's the regulations then I shall try to fix it.
I suppose the brembo discs could be narrower, which would have a similar effect to worn pads. The discs were the only parts non-standard, as the cbr has radials you just insert a couple of spacers on the caliper mounting to allow for the brembo disc's increased radius.
hi CBR65
The condition of the pads ie there thickness, or the thickness of the disc, has no effect on the travel of the Lever. So fitting new ones will make no difference to lever travel, In fact it may make it worse until the pads have bedded in.
I assume youre using a genuine Honda lever?
Does the lever still touch the bars
Kev
Last edited on Thu Jun 26th, 2008 07:12 pm by KevG
|
KevG
Super Moderator
|
Posted: Thu Jun 26th, 2008 07:03 pm |
|
Nik Nak.
You said ; Quote
"Its always the ones that do both"
We do both.
Thats when you said it.
Are you now saying those that do both are Ok?
Kev
|
nicknak
Trade Member
|
Posted: Thu Jun 26th, 2008 04:38 pm |
|
| Kev, I missed the bit where I said it applied to your vts?????????
|
cbr65
Member
| Joined: | Tue Jun 24th, 2008 |
| Location: | |
| Posts: | 9 |
| Mana: | |
|
Posted: Thu Jun 26th, 2008 04:33 pm |
|
Anyhow I went back today after fitting new pads and another examiner passed it
|
cbr65
Member
| Joined: | Tue Jun 24th, 2008 |
| Location: | |
| Posts: | 9 |
| Mana: | |
|
Posted: Thu Jun 26th, 2008 10:33 am |
|
KevG wrote: Hi CBR65
2-3 mm Lateral play is qite a lot, I just checked one of my bikes that has Brembo floating discs on it and it has about .5mm of play where the inner meets the Rotor.
However as Stealth rightly says this is not a reason to fail if all else is OK.
Hi Kev
I'm measuring the 2mm at the edge of the disc in relation to the wheel. I put a ruler up against one of the spokes and move the disc from as close to the wheel to as far from the wheel as I can move it.
Also they do tighten up once they are at operational temp. Pulling over after a few miles in heavy traffic where the brakes are used a lot and the amount of play is roughly halved. One problem was that the discs were cold by the time the examiner looked at them.
|
cbr65
Member
| Joined: | Tue Jun 24th, 2008 |
| Location: | |
| Posts: | 9 |
| Mana: | |
|
Posted: Thu Jun 26th, 2008 10:26 am |
|
Well the front pads are quite worn but I had them out two weeks ago to check the wear and there's still a good 3mm of pad on them. I have new pads and if I fitted them it should reduce the brake lever travel. Thinking about it, I'll fit the new pads it will give him one less thing to gripe about.
The thing about the lever touching the bar is a bit of a red herring imo, the front brakes on a 600RR are savage they start to bite after a few mms of lever travel and even under emergency braking you'd probably cartwheel the bike before the lever hit the bar
However if that's the regulations then I shall try to fix it.
I suppose the brembo discs could be narrower, which would have a similar effect to worn pads. The discs were the only parts non-standard, as the cbr has radials you just insert a couple of spacers on the caliper mounting to allow for the brembo disc's increased radius.
Last edited on Thu Jun 26th, 2008 10:27 am by cbr65
|
KevG
Super Moderator
|
Posted: Wed Jun 25th, 2008 06:50 pm |
|
Hi CBR65
2-3 mm Lateral play is quite a lot, I just checked one of my bikes that has Brembo floating discs on it and it has about .5mm of play where the inner meets the Rotor.
However as Stealth rightly says this is not a reason to fail if all else is OK.
As the discs are not std. fit to your bike I would pay carefull attention to them whilst testing your bike.
The F.Brake Lever should not touch the bars under test. mover the lever to the max span before its re-tested. Did You Fit new calipers with different size or number of Pistons when the conversion was carried out?
If so the Volume of your Master Cylinder may now be incorrect. This Might be why the lever is coming back to the bars?
Kev
|
Current time is 02:01 pm | Page: 1 2   |
|
