So Close!...
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@Calum
I’m such a martyr
…I can’t believe the input shaft needle/roller bearing turned up today already! I just wish we had better weather. Cleaning up the casings & gubbins is bad enough, but trying to build anything on a windy day is a nightmare. Crap flying everywhere! Actually, I wish I had a workshop, or a shed even
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@SpookDog They do come apart, and the O-ring and circlip are less than £1 genuine from Fowlers. The trouble is DOT brake fluid doesn't contain a corrosion inhibitor, meaning crustyness builds up around the O-ring and where the plastic elbow fits in to the m/cyl (it's worth replacing this as well). They're always difficult to remove so you have to be gentle if you want to save the elbow, and expect where the O-ring fits to look like an STD clinic once you get it apart. The holes for the fluid to keep the m/cyl piston fed are like pin holes so make sure they're clear. This is why one-piece front master cylinders get all scabby around the cap over time.
I just bought a used mountain bike to restore which had Avid disc brakes (DOT4 fluid) and these are in the same state, whereas Shimano brakes use mineral oil fluid (same chemical base as baby oil) and you can run them for years without the pistons seizing or corrosion building up. In fact one of the YouTube MTB channels fitted a brand new set of Shimano brakes to a test bike, left the front alone and re-bled the rear with baby oil, ran them for a year, then stripped them and measured every component. They reported no difference in brake performance or component wear between the front and rear brakes. You can't run mineral oil fluid in a DOT fluid brake though, otherwise I'd have changed all my DTR brakes over!
https://www.youtube.com/watch?v=63VIuPiX3CA
I also like to replace the tube between the m/cyl and reservoir when doing these as they often get overlooked and the stock tube swells up over time. This is no longer available from Yamaha and as DOT brake fluid is a solvent, you can't just use any old length of fuel line etc. I used Tygon 2375 tube off eBay:
https://www.ebay.co.uk/itm/121518690884
I've always found the Yambits master cylinder kit to be good for the rear on the DTR, and they also sell the round rubber membrane which fits in the rear reservoir.
If you want to rebuild your rear caliper though, I'd go with a genuine piston and seal kit. The eBay ones are cheaper but the fluid seal has a slightly smaller cross-section which allows fluid to leak past it! I fitted a set to a sub-6000 mile French import with calipers in good condition even before I stripped and cleaned them and noticed a dribble of fluid on the pad backplate during bleeding. Wiped it off and it came back several times, so to get me out of a jam (summer evening) I refitted the old OEM seals which cured it. Bought a genuine set shortly afterwards and had no more issues. And the piston DOES fit into the caliper with the closed end facing outwards like in the Haynes/Yamaha parts schematic; it's the same rear brake as the '88 YZ125 and this is to stop the inside of the piston filling with mud.
I feel like I've gone full Hermione Grainger writing this but for something which looks simple, the DTR rear brake is one of the biggest PITA jobs I've ever had to do. Once it's right though it works very well.
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Do you know of a good place to get the elbow? Only one that I’ve found is in France…
I found bleeding the front brake in to be the biggest PitA!
…Are you 100% about the orientation of the piston? I questioned it the first time I did them and wasn’t sure. Everyone told me it was ‘base in’ IIRC?…
PS: Does anyone have any decent tips on bleeding in the front brakes? I’ve got a cheap vacuum pump that I’ve been using, but I still don’t think it’s right…
I’ve even thought of laying the bike down on it’s side! It’s just getting the reservoir level! … -
@SpookDog I think every time I bought one of those elbows I just got it from Fowlers. Also try cmsnl.com in Holland though.
All the schematics I've seen have the rear piston with the closed end facing outwards towards the pads, there was a discussion on one of the FB groups the other day and someone noticed the open end of the OEM piston is bevelled slightly, presumably to lessen the chance of catching the seals during installation. It is unusual but Yamaha have gone out of their way to show the closed end of the piston facing outwards, and the mud issue is the only reason I can think of.
Yes bleeding the front brake is difficult. I've had some success back-bleeding from the bleed nipple upwards using a syringe (keep an eye on the reservoir level) which just leaves you with a little bit of air behind the caliper piston above where the fluid enters the caliper and this can just be bled out conventionally (i.e from the m/cyl downwards) last thing.
And vacuum pumps yes, I've never tried one but Jennies Garage on YouTube used a pump from one of those hand soap dispensers to do the rear brake on a Kawasaki KLR250-looking thing:
https://www.youtube.com/watch?v=x1ddFwEkn3E&t=522s
Get a MX bike stand to get the res level, it makes everything easier like doing the chain, gearbox oil etc. Or make one out of wood, it only needs to be a plywood box with a bit of carpet etc. on the top to protect the frame underneath.
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Cheers bud! The vacuum pump kit has a few different fittings. One of them is a rubber do-da that looks like it’ll allow you to suck fluid up into the reservoir while feeding it via the bleed niple. Only problem is getting it airtight. Making sure the tubing is tight, also no sucking air past the threads! (Red rubber grease on them I recon)…
I’ve never known another bike that won’t push the air down & out like the Dtr! I think air contamination is the biggest problem with ‘Dtr poor front brake syndrome’ . The rear brake is fine once bled, locks up easily if you’re so inclined
…Another question! Does everyone else suffer from ‘headlight dim’ as much as me?! Every time that the brake lights go on, or indicators, or even the horn! The lights dim badly! I don’t understand why battery powered ancileries should affect them the way it does…
I’m running a 6Ah fully charged gel battery as well! If it’s normal with all the early (1988~96) bikes then fair enough. It just doesn’t seem right though. I’ve had scoots with 6V electrics that never did this!…I read somewhere that you can rewind the lighting coil to produce different amps, volts, ect by using finer wire?…
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PS: I found the master cylinder plastic outlet on Fowlers, cheers bud! I broke the one on my 14mm replacement. It was as clean as a whores whistle inside though! It has a black plastic/paint coating on the whole inside that looks like it inhibits corrosion and is super slippery to help the piston rubbers. I’ll show some pics when I can…
Pics!…
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@SpookDog No worries
That 14mm m/cyl does look clean inside so I guess it is some kind of anti-corrosion coating.
All the early DTRs I've owned have dimmed the lights like that when the brake light, horn, indicators are used, it's never done any harm even when running a 100/80W bulb so I think it's normal. Here's a pic of the 3NC wiring diagram, as you can see the AC side (headlight/taillight/side light/instrument illumination) and the DC side (everything else) share a common earth. Not only that but the yellow/red (main feed from the stator to the lights) also branches off into the regulator/rectifier where it comes out as DC (red wire) to charge the battery. So I suppose when you operate a DC ancillary, the battery voltage drops under load meaning it pulls a bigger share of the current ultimately from the stator via the yellow/red and white wires, which causes a volt drop across the lights?
This is only a guess really as electrics have never been my strong suit; any auto electricians on here I'll bow to their superior knowledge. IIRC the DTR stator has a source coil (powers the CDI unit, not the same as the pulse coil outside the flywheel which sends it a signal every crank revolution), lighting coil and a charging coil so in theory the charging and lights shouldn't interfere with one another but if that's the case, why does the yellow/red wire also go through the reg/rect? It doesn't have any other purpose apart from powering the AC lights. And it's a very unusual system generally, normally dirt bikes have AC lighting so they don't need a heavy battery and road bikes power everything from the DC reg/rect output so combining them like that is strange. Personally I like it as you can run high wattage headlight bulbs in the stock light without flattening the battery which you can't do even on some bigger bikes.
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@HOTSHOT-III
That is pretty much what I thought. I wonder if a diode somewhere would stop it happening. It can get quite hairy on dark night when your beam brightness halves!….Yeah charging, lighting & ignition coils…
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Interesting to see a diagram with the power valve servo on it!…
One thing I’ve never been able to find on any wiring diagram is the two relay type boxes that I have under my seat. I imagine that they are both to do with the side stand switch ~ ignition cut-out. I’m kinda scared to touch them! I don’t have a side stand switch fitted on my bike (deleted by previous) and I don’t have a clutch switch either (electric start only?) so I’ve never been able to work out what they both do…
On bikes with the side stand switch connected, can you start the engine with the stand down or not? Or does the cutout ‘activate’ when a gear is selected (neutral switch is diss-engaged)?…
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Just drilled and threaded a broken stud on the replacement casing I got (the one that tried to cut off my middle finger removing the barrel base studs!) and have since discovered that two of the threads around the crank , that join the casings are stripped! I thought it was just old silicunt sealant in them, but it turns out that you can get these plastic inserts that are kinda like rawplugs!…
OMFDaze!
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@SpookDog What do you mean again?
It's only changed the once in the entire time I've hosted it.
I bumped the software from 2.X.X to 3.X.X (it's been on 2.X.X for many years).
Along with the software bump I have swapped out the theme, this seemed a bit more mobile friendly.
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Yeah, ideally you'd clear your computers cache settings as it does try to be clever and preserve the last theme from a specific software version. This causes problems where by the code has changed, but your browser has cached certain parts of the website, resulting in a conflict of information. It should fix itself when the cache expires.
The main thing is we've moved to Bootstrap 5 now.
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@Calum , since the format changed I've not been receiving notifications about unread posts/reactions to replies etc. Is there something I can change on my PC to sort this? Still running Windows 7 so as you can imagine I'm sat here jumping on my stove pipe hat like an irate Victorian railway engineer.
damn, that's annoying.