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Brakes.
Drums. Anybody got any good tips for the current linings to use, and best method of set-up? Parts for these Brakes are available from ( a few specialised suppliers ).
Callipers. Despite the fact that most of us don’t use the maximum braking power available on our bikes, many of us, unless originality is an issue, look for a better brake set-up: better callipers, better master cylinder, braided lines, or at least better pads. At first it was replacement of the big four-leading shoe drum with the RD disc, then Lockheed callipers were all the rage…now there are those (of which I am one) who are reverting to the original little black Yamaha callipers.
It should be noted that the alloy version of this calliper, as fitted to TZ250/350 F/G, etc, and the similar-looking calliper of the early RD250/350 series bikes are, as far as matters, interchangeable. Mounting holes and after-market pad size are the same (Yamaha TZ pads are available, though not cheap). Note, though, that the rear callipers are different to the front – different thread for the hydraulic line, and a little lug to hold the hydraulic line is cast into to the rear calliper. By the way, the alloy version is much lighter, but flexible (not helpful) – hold one that is set-up to use in your hand with a block between the pads and squeeze the handle-bar lever – feel the calliper expand in your hand! Note that Yamaha went back to the 1974-style calliper for the front of the 1981 TZ250H, and used it for a while after that.
Anyway…there are cosmetic differences between the black RD and TZ callipers, but that’s not important right now. What is important is that these callipers actually work quite well; especially if you consider that a brake that has far more ‘feel’ and that allows you to use more of the available braking effort predictably is better than a brake with more pad area/better name, etc, but gives you no feedback. That is the case, for example between the Yamaha calliper and say, a Lockheed, where a stock master cylinder is used. See the performance section for a look at how to get the most feel from the brakes by considering the master cylinder/calliper relationship.
So…the short answer is that the original black callipers are worth using, as they work well, they fit the standard forks, they are rebuildable (kits are available from Yamaha) and good pads are available for them. Great brakes on my 350F with a single disc, braided lines, and SBS 504HF ceramic pads – these are just the street/sport version too! The recommended applications are TZ250/RD250, etc. They do not appear to be too hard on the disc, either. There is also an SBS race pad for the same calliper – SBS 504RQ3 ‘Carbontech’. We have some, but have yet to try them.
Since we rebuilt the 750B we have used the SBS 504HF in standard Yamaha callipers. While the brakes can’t compete with those fitted to current-model (as at 2001) Aprilia Mille and Ducati 748R (I tried – beat the Aprilia once!), they are great – good feel, no noticeable fade and quite long-lasting. Recommended.
Lockheed. There are various versions of this popular calliper, in magnesium and aluminium alloys, with a greater or lesser amount of finning. Ferodo CP901 Brake Pads #FDB-342CP apparently fit as do, according to accounts, Mini Cooper S (not just straight Mini Cooper – there is a difference) M64 pads, though the wear rate was quite high – this was 20+ years ago! Look cool, common fitment, though you have to fiddle about with mounting adapters and make sure the master cylinder ratio will work for you. See Performance section on how to solve this. Rebuild kits, including pistons, are available. ( from a few specialised suppliers ). There is also a problem with fitting the Lockheed to the TZ – the inside of the calliper can touch the spokes on wire wheels.
Discs. Brake technology has come a long way since these bikes were built, though we may be constrained by class rules preventing floating discs and 4 or more piston callipers when racing old TZ’s these days. Kevin Cameron’s ‘Sportbike Performance Handbook’ (see the ‘Reviews’ section) has a very well explained small section on why the modern brakes are better. Essentially, it’s a function of the traction available at the front tyre, and thereby the amount of brake that can be used before the wheel locks. More braking = more heat. More heat results in these older rigidly-mounted discs ‘coning’ with differential expansion rates near the edge of the disc, caused by the old-style ‘wide’ (measured from the centre of the disc out) pads. Have a look at a modern ‘rectangular’ pad and see what I mean.
What to do? If you can’t use a floating disc (which will minimise the coning) slotting the disc is one answer. This brings other problems, such as high pad wear rate and excessive heat, causing fluid boiling problems. Using a second disc, thereby spreading the heat over two discs is another solution, though is heavier and may require a different master cylinder. Using a bigger or thicker disc may help, as might a disc of different material. Or just brake less hard!
Front Disc Wear. The standard TZ item is only about 5mm. The equivalent street disc (XS650, etc), still 11 inches diameter, is 7mm. These can be thinned down if required, or used as a thicker replacement that is cosmetically the same as original. Measure the run-out and thickness of old discs. Not sure what the Yamaha limits are, though Cameron recommends no more than 0.004” run-out, or the lever will ‘pulse’. New discs (still in stainless steel, identical to original) are available from ( a few specialised suppliers ).
Rear Discs. Where fitted, they are handy for hill starts.
Thanks Kerry Wilton for this excellent article.
A link to an interesting page about master cylinder ratios: http://www.vintagebrake.com/mastercylinder.htm
04/27/09 08:27 PM +1100
This website © Greg Bennett 2002.
