Yamaha TRX850 Enthusiasts Forum

Hi all, I recently rebuilt the Brembos on the front of my bike and had a hell of a time trying to bleed the system back up. Ever since it has changed from a solid lever to a squidgy one and on two occasions left me with no front brake at all - this was something of an inconvenience when I was 70 miles from the hotel in Germany and had to make my way back. The engine braking allowed me to impress everyone with my apparent skills but I digress..

While I was bleeding it I noticed there was a lot of black stuff appearing in the reservoir - at the time I thought this might be crap that had somehow managed to stay in the caliper and was working its way up to the top, but that's a very long and difficult journey. I now understand it's much more likely to be bits of the seals inside the master cylinder! This leaves me with a few questions..

1) Are these M/Cs worth rebuilding? A bloke on the same trip is a long time Yam fan and reckons these Nissins have a wonderful habit of scoring their bore, making them useless. I believe him (I'll believe anything bad about these things after what happened) but can't find much info on it. Anyone know anything?

2) Are the rebuild kits any good?

3) Should I just forget about it and use the opportunity to track down a 5/8 radial master cylinder? Are they really that much better? Anyone know of a popular model that has such a cylinder on it? Perhaps, even, should I go a little smaller - When properly bled the lever can have very little travel on it and lots of initial bite. Anyone played around with the Brembo caliper setup like this?

Thanks for any help at all!

I have 2006 silver spots on a 14 mm trx master cylinder. The lever feels quite hard and lack of feel. I intend to buy a brand new 2006 master cylinder which actually is a Brembo design. Those levers have good feel and after so many years I feel I d rather just renew an important component such as this.
What calipers do u have?

I have a '95 Japanese 4NX model with Brembo calipers, the same as fitted to Ducatis and other such exotica. I actually really like them and have no plans to replace them with spots of any colour, if I could just get the whole front brake system to work properly I'll be happy! As it goes Ducati also went with 5/8 so maybe it is the correct choice, but it's not a popular size for radials to be in..

When my OEM m/c got a bit sad I pulled it down to find the bore scored. No good spending good money on bad so I just bit the bullet and bought a Brembo radial m/c.
I have run the Brembo radial m/c with both R1 blue spots and the Japanese spec Brembo calipers.
Absolutely sensational either way.
Not cheap, but money spent on great brakes is money well spent.

Aha thankyou sir for your input, it is exactly what I expected to hear. What size cylinder did you try for the Brembos and what would you recommend?

I run the 19/20 m/c. You can also run the 19/18 m/c.

The 19/20 will give you a firmer lever feel. You get greater brake pressure from less lever movement, but more force is required to pull the lever.

The 19/18 will give a softer lever feel. For the same brake pressure you have to pull the lever further, but less force is required to move the lever, and you get more feel and modulation.

As with all these things there is a lot of personal preference involved.
Brembo often say 19/20 for street and 19/18 for track as it enhances trail braking feel. But again this is open to personal preference, riding style and opinion.

If you want the best of both worlds spend a few extra bucks and buy the RCS unit. You get the same 19mm bore but can switch between the 18 or 20 ratio as you wish.

Don't forget to get yourself a brake switch.

19mm is massive, with braided lines I was hoping for a bit of squishing - I'm not really a fan of a solid lever.

I was more expecting you to say 14mm or stick with 16, but if 19 works then that's fine. Being a tight git I won't be buying anything new or trick, just something from a 2-3 year old crashed bike. This has caught my eye but I can't be sure what size it is (will have to ask), but I thought I should find out what I want before annoying ebay sellers

The Brembo 19mm bore m/c works in either the 18 or 20 ratio. As for other manufacturers bore sizes and ratios you'd have to check.
If you want to go cheaper I think some use a radial m/c of later model R6 or R1. Someone who has gone down that road may chime in with what suits.

FWIW, I rebuilt my old M/C with no ill effects. A/M rebuild kit off eBay, worked fine until I upgraded to R1 Radial M/C & Golsdpots

Rebuild kit was about $30 IIRC...

Edit: Oh, & do a reverse bleed, inject the brake fluid into the calipers & up the lines to the M/C, instant brake pressure, then a quick bleed & you're done.

M.V, did you check the bore for scoring or just replace the bits and lap it back together? How far gone was the cylinder before you decided to rebuild it? I have a sneaking suspicion I may have left mine too late and have ruined it.

Some reading up on the subject shows that the Brembo cylinders fitted to mid-00's R1s and many R6s are 16mm which is just perfect, unless you can get away with larger diameter with radial? Come on people, post your experiences!

I did check it, couldn't see any major damage... More a piece of mind rebuild than fixing a problem. They are easy to strip down & rebuild, it's worth having a look I think.

You can use any M/C with any calipers really, but there's no gaurentee they'll work as desired! This is a good read: http://www.vintagebrake.com/mastercylinder.htm

That is interesting, calculations show I either end up with a ratio of 32:1 (squidgy, lots of feel) with 16mm or 22.7:1 (hard, lacking feedback) with 19mm. My personal preference is for some squish so 16mm it is!

EDIT: Given the extra feel of radial master cylinders though, might 19mm actually be the better choice? Sod it I'll have whatever I can find

In the interest of trying to save money I have dismantled the old m/c to see what was going on. Certainly the seals were perishing, but there is also some mild/shallow scoring to the bore:



Hopefully you can just make out the marks running along the top of the picture. They are minor and not sharp, you'd probably have difficulty noticing them with a fingernail. Is this too far gone? There are a couple of tasty 11/16 radial units on ebay that are exactly what I should need according to the link given above..

Today a tasty looking 11/16 radial Nissin master cylinder from a ZX10-R arrived in the post, a quick bleed and it works an absolute treat compared to the original unit. It seems surprisingly squishy though, I can just about pull it back to the bar - I take it this is not normal? I have bled the system at both calipers and from the nipple on the top of the M/C (a fantastic idea) and can get no more bubbles, and the initial bite and braking power is very good, but it don't half squish if you force it to!

Would it be worth my time to blow fluid through it from the bottom? Should it be as solid as the old type?

It is better to reverse bleed and then normal bleed. Not only is it quicker but also releases
trapped air bubbles upward so there is no remainder of air what so ever.