CB125TDC brakes!

[artifact]

Hi

I have a CB125TDC year 1987, I'm after some advice about the brake caliper, the one on the bike is shot.

The metal that holds the first seal in is broken and the seal keeps coming out and jamming the piston, it's to thin to repair as it's only 1 mm thick, also the tread on the l/h side is mullered and will need helicoiling.

I have another (rear) caliper from a CB750 1982 which is in much better condition (either caliper will need new pistons/seals) the actual casting is identical and fits perfectly, it uses the same brake pads and all the bolts/seals/fittings look the same...

The difference is the piston size the 125's pistons are 30mm diameter, the 750 are 27mm diameter, which doesn't sound a lot, but looks huge!

https://www.2020creative.co.uk/calipers.jpg
The two calipers side by side, 750 on the left, 125 on the right, you can see the missing metal on the r/h opening top corner.

Anyone have any opinions on what the effect on braking would be if I use the 750 caliper cos I don't know, I don't want to pay Mr Honda £213.00 for a new casting (or £698.00 for the complete assembly, even if they were available!) and the ones on eBay don't look in any better state than the one I have.

Any thoughts, opinions, suggestions welcome!

[c_dug]

No idea on how much difference it will make, but if it was me I would have fitted it by now I reckon. I'd imagine good enough will be the answer.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Fisty]

InB4 a 43586383592672 word essay on everything BUT the calipers.

Fit it, see how it feels. If it feels poor look for a decent used one on the bay.
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Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Taught2BCauti...]

The diameter of the pistons in the caliper are only one half of the story - the other half being the diameter of the piston in the Master Cylinder.

The relationship between the two, determines how much pressure you need to apply to the brake lever, and how far it needs to travel, in order to apply the correct amount of pressure on the pads at the other end.

If you have bigger pistons in the caliper, the obvious danger is that you could apply the brake lever to the full extent of travel, and it won't shift enough fluid down the system to move the pistons in the caliper enough to make the brakes effective.

If you have to fit a caliper with larger pistons, try to also fit a matching Master Cylinder, or bad things could happen.
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Honda Varadero XL125(V8)
www.TheFutureIsHere.eu

[artifact]

Ha! you should have seen the unedited version, I was just curious and bored, obviously!

Once the new pistons and seals arrive I'll give it a go, if it doesn't work I'll get the wife to post a funeral invite!!!

[Fisty]

[artifact]

Damn, I'm more stupid than I thought, I can't get the 'quote selected text' thingy to work

I have read most, it not all the essays, which is what got me dragging my sons old "superdream" out of the garden and fiddling with it! (the 'dream, not the son!) before it rotted away. I don't know how one man could know so much about something and still have room in his head for other stuff!

As for brakes, I assume the man at honda decided on that size of piston for a reason, after all he gets paid far more than I do, I think the bigger the brake piston the more oomph you get for each squeeze of the brake lever, which I would guess also affects the progressiveness of the brakes?[/quote]

[Teflon-Mike]

The smaller pistons will move further for the same lever travel, but you'll get less pad pressure / braking force for the same effort on the lever. Ie the brake lever will be be a lot firmer, and take up will be a lot sharper.
On a rear brake, with full force you can put on the lever with your foot, this can be helpful; on the front? I doubt that it'll be so bad you cant stop, but could be a bit white knuckle. But give that the stock front brake is a 'bit' soft to start with, and more than powerful enough for the bikes weight & performance, might actually 'feel' better and still do the job more than well enough.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[artifact]

Thanks for all the thoughts, suggestions and help, once I get all the crap and rust of the frame/petrol tank etc, etc, etc I'll give it a go and see which comes first, skid-marks on the road or underwear!