Brake master cylinder required

[Kickstart]

Hi

My TZR250 has very dead feeling brakes. Think the problem is down to a mismatch in master cylinder and caliper (although it is all original other than a braided line).

As a quick try I used a master cylinder from an Aprilia AF1 Sintesi on there (12mm bore rather than 14mm bore). With this the brakes are far nicer to use and you do not need a vice like grip to get something close to the same performance as the rear caliper manages (let alone something exceeding it).

However I would prefer a master cylinder than looks as close to the original as possible.

Anyone know of any mid 1980s Yamaha master cylinders (square shaped) with a 12mm bore?

All the best

Keith
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[steo]

I thought you might have favoured the bigger bore master cylinder for better braking pressure with an adjustment on the lever? Just had a look at my old RD350LC it's pretty close to what you're looking for. Unfortunately I can't take it off to measure bore dimensions without losing fluids but it's rectangular in shape & also has a screw on the lever you can adjust to your radius so you don't need to be Hulk Hogan to use it.

[Kickstart]

Hi

Larger bore means way more lever pressure and a dead feel, and I would far rather have more lever travel than no feel. As it is at the moment (14mm bore) you may as well be pulling against a block of concrete for all the feel it has (it is FAR better with the 12mm bore master cylinder from the Aprilia).

Unfortunatly the screw barely changes the radius but just brings the lever far closer to the bar.

Could be the RD has the same master cylinder (or even a larger bore given that it has twin calipers, although only twin piston calipers) as it is from about the same date.

Original master cylinder can be seen here

Stock lever master cylinder to piston ratio on the TZR is about 23.5 (ie, area of caliper pistons to area of master cylinder piston), which is probably borderline for having any feel. However it also has "worse" ratio for lever movement to piston movement than other bikes I measured. Checked it, the Bimota (Brembo m/c from an Aprilia Mille) and the 1200 Bandit. While all 3 had about the same distance from my fingers to the levers pivot point, with the TZR the distance from the pivot point to the master cylinder piston was a fair bit greater (28mm compared to 24mm).

Cheers for the suggestion.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[steo]

Good picture, looks quite similar to the LC. The master cylinder you want to source would also need to shaped so it also fits around the half bar set-up of the TZR & not get snagged where it clamps onto the forklegs. A lot of the early yammy stuff all had ordinary handlebars.

[Kickstart]

Hi

Think I would probably be OK with most. There is a fair amount of room as the "clamp" section barely sticks out further than the tubular bar (certainly less than most pseudo clipons).

The common one that looks closest so far is from a late DT125, although on that the brake hose connects to the front of the master cylinder.

Of some concern is the angle it mounts at.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing