revtothelimit - motorbike forum

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:

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.

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.

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

cheb wrote: Sun Mar 29, 2020 12:05 pm 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.

Thanks, I'll look into that.

*Approves of this thread*

A_morti wrote: Sun May 31, 2020 10:22 am

cheb wrote: Sun Mar 29, 2020 12:05 pm 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.

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

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.

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

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.

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.

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

@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!

I've finally ordered some oil delivery pipe. It's best not to rush these things.

cheb wrote: Fri Mar 26, 2021 9:14 am I've finally ordered some oil delivery pipe. It's best not to rush these things.

LOL some of you fellas confuse me... if something needs doing it needs doing.... not in a month, a year... that day... or sooner

For the last however long, pre lockdown for sure, my workshop has been filled with other people's stuff*. Bikes are a hobby so I've had to get other important jobs done first. Having the spares ready to go is merely frustrating.

I also had to decide on which hose to buy. Buying hose online can be frustrating IME, what you get frequently isn't what was pictured nor described, fuel hose especially, I try to buy that in person when I'm on the big island.

*The shed and one of the spare rooms still is.

weeksy wrote: Fri Mar 26, 2021 9:24 am

cheb wrote: Fri Mar 26, 2021 9:14 am I've finally ordered some oil delivery pipe. It's best not to rush these things.

LOL some of you fellas confuse me... if something needs doing it needs doing.... not in a month, a year... that day... or sooner

You need to grasp the old git fiddling with things mentality, there's no need to rush.

I've not even started the DT200R I bought last year.

FFS.