Bothering at my TDR250

[cheb]

Recap: It looks like this:





Today I've been changing the rear brake master cylinder. I dislike remote reservoirs and a CRF m/c has the same pitched mounting holes.



To be replaced with this:

[cheb]

They are substantially different bore sizes, 14mm and 3/8", but rear brake feel is only a concept for me when wearing MX type boots. The caliper may be swapped too, I'll need to sort a mount for it first. And before I do that I need to do the swinging arm.

The 200g+ weight saving isn't to be sniffed at either.

[Potter]

Mine is currently tucked away as well, it's running and MOT'd but unlikely to be used this year, again.

[cheb]

I was hoping to be back on the road this year, we'll see. I'll try not to fix it until it's broken.

[cheb]

I've come to a decision on the swinging arm. It's not the original part, it's from a 3MA4 TZR250, and has been modified but cutting the pivot tube down. On the wrong side and the chain was hitting it. That's been repaired, offset sprockets have been fitted and I'll fix some stainless plate to protect it. There's also oddness going with the needle bearings, spacers and covers. I'd like to see an original set up before I do any more. I thought about offsetting to the other side but that's a lot of work for a small amount of gain, maybe one day.

It's black painted alloy and it needs the paint removing so here goes: viewtopic.php?f=26&t=251

[A_morti]

They are substantially different bore sizes, 14mm and 3/8", but rear brake feel is only a concept for me when wearing MX type boots. The caliper may be swapped too, I'll need to sort a mount for it first. And before I do that I need to do the swinging arm.

The 200g+ weight saving isn't to be sniffed at either.

The caliper you have has a 38mm pair of pistons.
3/8" is probably going to leave you with so much lever throw, then a really strong but smushy brake.

Suggest the common brembo caliper with 32mm pistons should be a better match. That's the unpopular one that plenty of folk took off sports bikes as it didn't work. Also has alloy pistons, so a few more grams saved.

[cheb]

Thanks, I'll look into that.

[bob_summers]

*Approves of this thread*

[cheb]

They are substantially different bore sizes, 14mm and 3/8", but rear brake feel is only a concept for me when wearing MX type boots. The caliper may be swapped too, I'll need to sort a mount for it first. And before I do that I need to do the swinging arm.

The 200g+ weight saving isn't to be sniffed at either.

The caliper you have has a 38mm pair of pistons.
3/8" is probably going to leave you with so much lever throw, then a really strong but smushy brake.

Suggest the common brembo caliper with 32mm pistons should be a better match. That's the unpopular one that plenty of folk took off sports bikes as it didn't work. Also has alloy pistons, so a few more grams saved.

Boing. I might have spent a bit too long trying to get the last bubbles air of this caliper as it felt really squishy

As I'm a lazy git, any suggestions as to which bikes a suitable caliper might have come off. I presume it'll need to be an opposed piston caliper, or I'll have to modify or make a suitable bracket for the slider pins.


I fitted the rebuilt oil pump. Revel in it's shininess:



Next is buying some new oil supply and delivery hose. And then onto the headlight and instruments.

[cheb]

Ducati 748/916 has a 32mm piston rear caliper. Part number P05

[Le_Fromage_Grande]

If you're using the Sumitomo twin piston caliper fitted to most Yams of that era, they all use the same master cylinder, FZ750, FZR400 and YPVS350, all of my bikes have the same rear master cylinder, you can get pattern ones off eBay for about £15, they work okay.

It is a total arse to bleed though, I have to in the end and bought a complete rear brake set up of Dennis Trollope Racing, it came complete with 1985 brake fluid, which is still in there.

[cheb]

I've fitted an MC from a Honda CRF. It's got an integral reservoir and therefore looks prettier, and is also lighter.

[Potter]

For brakes, there is a calculation that is based on master cylinder piston size vs caliper piston size.

Can't remember on the back, but for the front a single disk (four pot caliper) should be around 14:1 to 12:1.
I made some notes a few years ago and according to those the optimum would be 13mm MC bore which on a standard TDR caliper would give 12.4:1
*But don't rely solely on that, I can't even read my own notes properly.

A rough guide would simply be Pi x R^2, multiplied by the bore ^2.
If you feel like being nerdy the calculation is (((Pi x R^2) + (Pi x R^2))x n) / (Pi x R^2).

I can't remember now but on the front I think I put a 12mm YZF125 master cylinder on mine and it had so much power that I warped the old disk and had to get a new one. I put the old standard 14mm one back on but it felt a bit wooden in comparison.

I don't really use the back brake so I didn't put much effort into it and I can't remember, I'm 99% sure it's just standard and it worked well enough to lock the rear up at will.

[cheb]

Morti knows about these things. He suggested a caliper with 33mm piston up there and that's good enough for me.

Ebay will be scoured, the cheaper end first of course.

[Potter]

Morti knows about these things. He suggested a caliper with 33mm piston up there and that's good enough for me.

I've always found it a lot easier to use the standard caliper (because Yamaha designed it to fit properly) and change the MC because they're mostly a generic fit on the bars for most bikes.
I think I paid a tenner for mine on ebay.

[cheb]

This is a rear caliper, and will be operated by a chimp wearing motocross boots. Front brakes are taken a bit more seriously.

I don't for a second think I can improve on Yamaha's design, but I like tinkering. I'm also under no illusion about the financing, hobbies have to be paid for.

[Potter]

This is a rear caliper, and will be operated by a chimp wearing motocross boots. Front brakes are taken a bit more seriously.

I don't for a second think I can improve on Yamaha's design, but I like tinkering. I'm also under no illusion about the financing, hobbies have to be paid for.

The standard rear caliper is very good and the MC is shared across numerous Yamaha models so it's easy to find a cheap one - although I've just noticed you said you're changing it to do away with the remote res, so ignore me.

[cheb]

That's £15 worth of caliper on it's way to me. As well as a longer sidestand and another gear lever.

[A_morti]

@Harry it's easy to say Yamaha know what they're doing, and that may apply on modern superbikes, but my 600 divvy front brake was wooden until I put a smaller master on it. TBF, the rear brake was always spot on.

It's not quite as easy as 12:1 or what have you on rear brakes, because the pedal's leverage ratio can have a big influence too.

@cheb I reckon it'll be fine with the new smaller piston caliper. Fingers crossed!

[Potter]

@Harry it's easy to say Yamaha know what they're doing, and that may apply on modern superbikes, but my 600 divvy front brake was wooden until I put a smaller master on it. TBF, the rear brake was always spot on.

It's not quite as easy as 12:1 or what have you on rear brakes, because the pedal's leverage ratio can have a big influence too.

@cheb I reckon it'll be fine with the new smaller piston caliper. Fingers crossed!

You might already know this, but you can work the whole lot out on a piece of paper with some fairly simple maths before you do anything, including levers if you want to start changing those as well.
Ordering parts from ebay and keeping your fingers crossed just sounds unnecessarily expensive.

Anyway, I'll say no more, crack on and keep the updates coming.