Caliper question

[erik]

Short Version:

Does anyone know if replacing the seals in the calipers is likely to pull the pistons back further (to get more clearance between the pads and discs when the brakes are released) than the old seals that are in there now?



Long Version:

I've recently (about 2 months ago) put new discs and pads on my bike and disassembled and cleaned the calipers.

Something I've noticed in the last few weeks is that the pads don't retract very much from the discs at all and that the high points on the discs brush against the pads when you rotate the front wheel (the RH disc actually squeaks/hums a bit at really low speed).

I've checked the run out, it's about the same as when the discs were new (about 0.10mm LH and 0.14mm RH).
The RH disc thickness varies by about 0.004mm (ie 4µm) and is thinnest at the point where the disc rubs against the pads.

I'm worried that if the pads continue to rub on the disc's high point that this point will wear more than the rest of the disc (as seems to already be happening) and that I'll end up with pulsing brakes again. I had to replace my last discs because the RH disc varied in thickness by 0.025mm which made the brakes pulse.


The only thing I can think to try is to get new seals for the calipers and hope that they'll pull the pistons back further than the current ones do.

Does anyone know if it's worth a try or have any other suggestions?

I'm guessing the seals that are in there now are the original ones (bike is a 1993) so maybe they're not as elastic as they were when new?

[FROSTY:Me]

mate id do a strip polish the pistons and rubberlube the seals

[erik]

With just the original seals?

When I stripped the calipers before, the pistons looked to be in good condition. I only used brake fluid to lube them when I put them back together though.

[Brian d marge]

Eric

the piston is pulled back away from the disk as by the deformation of the Rubber ( I think that the Honda clearance is 0.7mm between rotor and pad off top of head )

Think of it this way , that 17 year old gymnastics student you pick up at the university is a damn site more flexable and bendyable than Your aunt Maude who must be touching fity odd and still think she looks hot in tight denim


Also the distance the seal is from the piston also has an effect on the force at which it is retacted ( up to a point )

Change the seals they are cheap

If help needed I have some in stock ,,,( for a cr of course!!)

Stephen

[erik]

Change the seals they are cheap

Just got the price from Coleman's Suzuki...

$97.40

per caliper

from Japan!

If anyone knows of cheaper options, please let me know.

I'll try phoning a few other shops and ask on the banditalley website

[imdying]

What diameter at the pistons? Seals are about $3-5 each.

[Brian d marge]

100 bucks for seals .......No way !!! imdyings right measure the piston dia , and Ill have a nosey !

Stephen

[imdying]

It's actually not that bad a price. Those kits generally come with the bleeder covers, orings for between the bodys, and the dust seals etc as well.

[erik]

That's good to hear.
I'll have to measure the piston diameters, the top pistons are larger than the lower pistons.
I've got exams next week and the week after, so I think I'll chuck the old pads and discs back on so as to avoid damaging the new ones more and then pull the calipers apart after exams.

Will I only need the piston diameter or will I need the groove dimensions for the seals? Are the dust seals also more cheaply available than through the kit?
Where can I get the seals from?

Thanks heaps.

[imdying]

You can probably only get the dust seals in the kits... but that's ok, unless they're swollen you can just reuse them. Measure everything, you can't have too much info.

[erik]

Finished my exams!

Disassembled one half of one of the front calipers today and got the dimensions:
big piston dia: 33.9mm

small piston dia: 30.2mm

the seal cross section is 3mm difference from inner to outer radius and 3.4mm thick. Both seals are the same cross section, as are the slots they fit into (see pic).

The old seals still feel fairly elastic, but it does look like they've taken on the shape of the slot a bit (assuming they were just rectangular to start with).

[imdying]

Anybody on this list should be able to help:
http://nzbcsa.org.nz/indexmain.asp?p...berprofile.asp

Try Atlas, Automotive Supplies or Sterlings.

[erik]

Cheers, I phoned all the ones in auckland except for masterpart and pitstop, the only place that said they might be able to help was Just Brakes Protect Parts. It turned out they had the right seals and only charged me $25 for 8 seals. Not only that but when I showed up there late on friday afternoon (they were closing) and only had my eftpos card (they haven't got eftpos), the guy gave me the seals and said I can drop the cash off later!

I installed the seals in the right hand caliper today, but I don't think they're making much of a difference to how far the pistons are being pulled back. Compared to the left, it looks like they move about the same. You can still hear the disc rubbing against the pad when you spin the wheel.
Not only that, but I went on a decent ride with the old discs yesterday and didn't really notice any shuddering. They only pulse slighty when coming to a stop.
So I think maybe that's just how they are and I was worrying about nothing (and wasted the money on the new discs - although I guess it's been a learning experience).
I'll just stick with the old discs for now and use them till they're below the thickness limit (should be another 10,000km or so away I think) then change over to the new discs.

[SimJen]

When I've rebuilt my brakes with new pads etc, I usually find the pads rub for a while.
Im a hard braker anyway, so it usually beds the pads in quite quickly and the rubbing goes away after a few hundred km's. They don't have to be completely free running though, most bikes will have some pad/disc drag.

[Motu]

Just Brakes (or Protec Parts) are really trade only - they do the cyl overhauling for nearly everyone in Auckland...Autostop,BNT,Sterling,they all send their cyls to them for resleeving.You can tell their work because they paint the cyls arfterwards.Great guys,I remember going in their on fridays and they'd have their bikes in the shop getting ready for a weekend trail ride.