CB125 TDC - rear disc conversion

[Martin125tdc]

Hi All,

I'm a new but old owner of a CB125Tdc [1982] project and thinking of carrying out a rear disc brake conversion.
Has anyone been brave or daft to have carried this out ?

I was thinking of a few options to do this:

- New swingarm that has fixings or caliper and pedal already fixed. Not sure which one yet, maybe a CBR125.

- Use my existing Swingarm but fabricate points for caliper and fit new wheel from a CBR125 and a pedal / master cylinder from same.

- Use a VF400 / VF500 rear wheel, swing arm and brakes, hangers.

I have seen a few enquiries on this topic buyt no-one has done this yet.

Id be interested to know possible combinations to get this on, id like to keep the original comstars hence while i have mentioned the VF approach.

Cheers

[Teflon-Mike]

OK......

Why?
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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?'

[Shaft]

[WD Forte]

Why and pointless were my immediate thoughts too.
I cant see much if any improvement and you'd probably spend as much as its worth doing it while reducing its value at the same time.
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bikers smell of wee

[Martin125tdc]

thanks for your replies,

Why?

well Why not, a lot of younger riders are making conversions, and making then at home of in a garage or in their work.

I think in the modern day we're in it isn't impossible. I was in a MUTT motorcycle shop yesterday and all of their new machines which are either 125cc or 250cc have rear disc, even with ABS>

Most new 125cc are disc, whether its a Honda, YAM, KWAK, SUZI or jap / china import.

These could be considered OVER BRAKED / OVER POWERED REAR BRAKE.

I really think this would be another way of keeping our bikes alive and on the road where others can admire.

[Martin125tdc]

could a wheel from a vf500 and a nsr125 [2003] swing arm work as an option?

[Speedy23]

No.

[WD Forte]

Martin
It's your bike, time and money
How you choose to spend it is up to you but were it mine
I would see no advantage in a drum to disc conversion.
Unless you're very skilled and/or have shit load of money throw at it
you could end up ruining it or have an ugly half assed abortion.


I really think this would be another way of keeping our bikes alive and on the road where others can admire
LOL!

Nonsense IMO.
so is comparing them to modern bikes

My bike is older than yours and I love to tinker and mod it
but a drum to disk conversion would not help keep it on the road
Good proactive servicing and maintenance keeps em going.
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bikers smell of wee

[Martin125tdc]

good question and points
, I'm really interested to see if it can be done. it has to be able right? I remember in the 80/90's readers specials where older bikes with sh1t brakes grew new rear dics. I know these where bigger bikes but why should it not be possible on the smaller bikes.

[Fisty]

This thread is going to turn into an autistic sperg off between OP and teffers.
____________________
Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Ste]

[redeem ouzzer]

Rear discs are shit and anyone who wants one by choice should drink bleach.
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Be a REAL MAN!

[Shaft]

[Teflon-Mike]

Oh-Kay... well if you look in the sig-line, I admit go owning half a dozen CB125TD's. If you look in profile, you'll find links to a couple of 125TD's I have ground-up restored!

Yes, I do keep these ruddy things alive and on-the-road... as to admired?!?!? Well, yeah... I'm almost half a century ancient, so take this relatively, I DO get the odd, and they ARE normally pretty odd, even compared to how odd I must be, pigging about with clapped out 125-twins!!! But I do get the odd 'old-boy' looking at one of the Super-Dreams, telling me they dont make'em like they used to, and how they had one when they were a Learner, and usually insisting, that despite the 125 badges clearly on the side-panels, it MUST be a 250.....

No, I have NOT done rear-disc conversion... why would I even want to?

VF400... it has disc-brakes... ish! They are actually the Honda patent 'inboard' discs, in a drum. Fantastic application of technology over common sense, to make something with pretty much all the draw-backs of both drum and disc and nie on impossible to change the ruddy pads in! Totally different wheel, and it's not even the same style as the Mk3 Comstar of the Super-Dream, it has slots not holes.

VF500... has more conventional disc brakes, 'some' models also had the same style round-hole Comstar as the 125 Super-Dream.. but in anodised black, not silver.... good luck finding a VF500, let alone a pair of wheels for one.

VT250? Inboard disc & slotted Comstars. VT500... inboard discs, usually chucked away for CX500 front ends by dispatchers to whom it was easier to change half the bike than the brake pads!!!!!

You are barking up the wrong tree... no, cut that, just barking!!!!

Yes, modern bikes have discs; this does not mean that they are 'better', and even less that the bike might slow-down any better.

Modern small bikes tend to have disc-brakes for two reasons; first the construction and use regs say that they have to, second its usually 'cheaper' for manufacturer to use 'standard' disc-brake components and wheels than it is make drum-brake assemblies... they dont have them for 'better' slowing down!

Have you done CBT? Tests? Do you remember the lesson on braking? in the dry, 75% front, 25% rear 'effort', in the wet, 50/50, front-before-back in all cases.

MOST braking force comes from the front brake; which is why super-bikes and the like tend to have two pretty enormous wheel-sized brake rotors on the front.... and a single tea-cup diameter rotor on the back. You brake hard... back wheel comes off the floor... and it dont transmit braking force too well... so what brake is on it matters not a lot!

What matters is the tyres! If you have crappy tyres, they dont grip very well. If you have really good brakes, they lock the wheel real easy, result is wheel locks up and you skid, not slow.

On a 125 Superdream, the standard drum back brake is more than powerful enough for the bike, and likely most tyres you could fit to its wheels. The OE drum, is sufficient; bits to recondition/overhaul are all cheap and available of the shelf, no engineering is required, and insurance salesman dont tend to frown at the suggestion! In short, its about the 'best' back brake you could fit to one!

A-N-D in the list of things where a 125 Super-Dream might be 'improved' or 'upgraded'... the brakes? Pretty much at the very bottom of the list!

The front brake; A hydraulic 'floating' twin-piston caliper design, for its era and even today, is, if in good condition, a pretty sophisticated and very 'powerful' bit of design.

But take note; only a crunt-locks-the-front... tyres are still the most limiting factor there, and decent tyres are a far better 'upgrade' for one of these things, and or so much more than just slowing down.

Meanwhile Honda 'floating' brake calipers are notorious; the calipers have a habbit of not 'floating' on thier mount-pins. This is NOT so much a design problem as a user-error.

Hydraulic disc-brakes are 'self-adjusting', so no-one pays them any attention until the pad backings start grinding on the disc, meanwhile the calipers are all gunged up, with brake pad dust that promotes corrosion, on both pistons and float-pins, and ham-fitsted DIY pad-changes shove that gunk back into the caliper with the pistons to get new thicker pads in, and make them even more sticky and prone to sieze.

Overhaul of the caliper; new fluid, new pads, and some contentious cleaning, IF you can get away with it, if not, full and proper overhaul with new pistons and seals in both caliper AND master-cylinder, and probably a new hose, will make the brakes as good as they are ever going to be, better than most and almost certainly better than the tyres!

Moving on....

Other top jobs on these bikes, is normally the engine/carbs/exhaust. Engines usually get looked at first, cos people like to hear motorbike noises, and then worry about going round corners and or stopping and stuff... engine is almost the last thing you need look at. Again, they tend to suffer numpty DIY servicing, and the unobtanium carburettor mount-rubbers usually get spilt or torn by foilk trying to get the carbs off, usually without removing the air-boxes first. Carbs themselves are then oft cleaned to death, as they seem less scary than looking inside the engine, and stickly float valves and wampy choke links are notorious niggles. 'Problem' though is usually that the engines fcuked. They have tiny little pistons, into which the piston rings are want to 'stick' with age, and cylinder and ring 'wear' is almost imperceptible, BUT to run half well these motors like decent bores and rings.... about £120 of there abouts for a barel kit to do a top-end rebuild, little point in messing elsewhere if you dont.... change the valve stem seals that are probably crusty flakey mess, if even still there, whilst you are at it, and check that the cam-chain isn't slack as a tart's nicker elastic.

Happy you have put-put-noises... starter motor, solenoid and battery, could probably do with attention, or again, you will be moaning about Honda Regulators and faffing with carburettors, and reaching for a can of etha.....

More happy... back suspension on these goes sloppy, and a sloppy super-Dream is simply horrible. Still more sophisticated than any current 125 on the market I know of, the back-suspension uses a full rising rate, multi-linkage, and short mono-shock. New mono-shocks are around £15o if you can get one.... unsurprisingly few do.... so neither do the probably seized links get reconditioned with from flakey-memory, about £120 worth of new bloody hard to fit new bushes.... BUT, a tight back-end is a joy, and a well fettled Super-Dream, with sticky tyres will handle superbly.

So make the front as good; pretty cheap comparatively; overhaul probably only takes about £30 worth of taper-roller steering bearings, £10 worth of fork seals and £15 worth of decent fork oil... and lots of cleaning.

A-N-D you may like to wonder about doing something with the electrics, and the likely rather rotten wires and rusty bullet connectors, and the indy flasher full of water.....

The torn vinal seat? The manky paint and mis-matched side-panels? Well. POR15ing the petrol tank early on, is well worth while; tanks do tend to rot on bikes this age, and it saves a LOT of carb cleaning. But otherwise, its just pretty bits, and that costs, takes time, and makes no difference to how the bike goes, turns or stops really.. its not all 'that' important.

B-U-T..... a well fettled 125 Super-Dream, on decent tyres, can be a pure joy.... ish!

As standard.... one can hold its own against any of the contemporary 'sports' 125's, or even big-bikes! It LOOKS like a humdrum 'commuter' like a CG or YBR, which doesn't garner great expectations, but, under that conservative styling, its light, tight and got as many if not more technical 'features', like proper multi-link rising rate rear suspension, like that twin-cylinder motor, and all 'restricted' to learner-legal power limits... its just as quick... and point to point, if ANYTHING will make a difference, its the bravery/skill/stupidity of it's rider.....

So take another 'look'.... audacious mods like a rear-diac or full fairing or or or... RATHER detract from what is the thing's likely 'best' feature, which is its rather conservative, dour, 'un-sporty' by modern-standards styling..... it dont look a lot, so no-one expects a lot from one, which means when it DOES it is all the more satisfying, and if it dont.. well no-one expected much any-way!

And there is simply LOADS on one of these things to keep your fiddle-fingers occupied IF you are so inclined; most of it hauling something out of thirty odd years of basic maintenance overdraft just to make it 'standard' let alone try and make it better than standard, even less, do daft ill-considered things to it that wont make it any 'better' for it, and likely a lot worse in so many ways.

Your call.... B-U-T.... you really do seem to be barking to think it's even worth contemplating, let alone pursuing! IF just owning a CB125TD isn't proof enough you are already a long way down that road of delusion! Hey, yup, I'm nuts, I have half a dozen of these things, but I am still not quite SO nuts as to think that any of them need a disc back brake!
____________________
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?'

[Martin125tdc]

Hi all.

After a few weeks of stripping and a lot of reading comments on this thread I realised these bikes don’t need to be hacked or mauled into a cafe racer if they are altogether there. This bike I have is totally original, after 27 years Since last mot and tax I cleaned the carbs , tank and changed the fluids she started.

I’m keeping her original, I realised that a lot of us loves these bikes and grew up with them. This was my first bike as a 17 year old.

Painstaking I’ve sourced the odd useable secondhand part that was missing and I’m on the road to rebuild.

But I need help, I’ve heard that before from one or two of yous. It’s the suspension bushes, predominantly on the linkages. What are the part numbers and where can I get them?

Cheers

[Sister Sledge]

[Ste]

Part numbers: https://www.bike-parts-honda.com/honda-motorcycle/125-MOTO/CB/1982/CB125TDC/Frame/2/667

[Ste]

More parts: https://www.davidsilverspares.co.uk/CB125TDC-SUPER-DREAM-1982/

I'd probably be lazy and email them to find the parts you're after.

[Martin125tdc]

Hi Ste and Sister Sledge.

I have the swing arm bushes and the upper composite rubber bush on the main linkage. I don’t have the parts and I cannot find the part number for the lower bush on the bigger linkage (bigger wishbone) and the part number on the lower smaller linkage.
I’ve ordered most parts from David Silver but they said Honda don’t list these parts.

Hopefully someone can give direction from where to get these or if the swinging arm bushes that connects to the linkage can be used

[Teflon-Mike]

CMSL:- https://www.cmsnl.com/honda-cb125td-superdream-1982-c-england_model18943/partslist/F__2300.html#.XFl8P1X7TX4

Have fun!

https://images.cmsnl.com/img/partslists/honda-cb125td-superdream-1982-c-england-rear-cushion_big00028366f__2300_06d0.gif
____________________
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?'

[Martin125tdc]

Hi Teflon-Mike
I’ve really enjoyed your post and comments on other threads, your views are partially a bit of my reasoning to keep it original.
Thanks for the schematic diagram, I already sleep with this and it’s causing me nightmares. I have the collars items 10 + 8, but it’s the fibrous plastic bushes, these are tough to source.

Regards

[Fisty]

[redeem ouzzer]

Someone tell Teffers a 125LC or similar can run rings around even a “full power” 125 pooper dream while having similar engine life but cheaper rebuilds. I bet I can here the autistic screeching from here...
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Be a REAL MAN!

[ZebraDriver]

Tef touched on it, but have you run this possible modification past your insurance company? I can see them throwing the dice again to work out a new premium (and I can guarantee that it won't be downwards....). If they do want to cover it then they may insist on engineers reports etc.

[Fisty]