Front master cylinder replacement

[ajh]

Hi

Im new to the forum having purchased a 1984 gs550e at the weekend. I have 3 other 70/80s Yamaha 2 strokes but suddenly had an 'itch to scratch' in terms of getting a GS as I had one back in the day! So now the work begins and the immediate problem is brakes

Previous owner has fitted some sort of after market chinese m/c but it doesnt work very well, lever runs out of travel. No air in the system so can only assume the M/C is no good or wrong size

I have twin disk so assume I need a 5/8 master cylinder, can someone make a recomendation of an aftermarket m/c that will connect to standard banjo fittings? I saw someone here uses EX650 m/c, do they connect to standard banjo fittings on a GS?

Thanks in advance

[Rich82GS750TZ]

Just be careful with your banjo bolts when mixing brands. Suzuki, at the time, used a 10mm x 1.00 thread pitch. Other Japanese manufacturers were and still are 10 x 1.25. Suzuki changed to 1.25 later, not sure exactly when. Just be sure you know what you got before you start threading bolts into MCs and calipers.

[Grimly]

My personal recommendation for the twin disc setup on most 80s GSs is the Honda Deauville (NTV700, iirc) m/c. Adjustable span, the right bore 5/8" and nice action. It's only a problem if you're more fussed about originality than function, and as you've found, the cheap ones are rubbish.
As the Deauville m/c is made by Nissin, a decent Japanese maker of brake systems, I've got no qualms using them.

[hillsy]

If you want to stay with Suzuki - Bandit 600/1200 will work and the angle of the reservoir will also work nicely.

[ajh]

Thanks all, that gives me some options

[Nessism]

If the caliper pistons are binding up it will result in the brake lever feeling soft. If you haven't already done so you might want to remove the caliper pistons, remove the seals, and then clean out any accumulation of grunge. Replace the brake lines too. Then if the hand lever feels mushy when the system is properly bled, pump up the lever best you can and tie the lever back against the bar for several hours. This will keep pressure in the system and allow the caliper pistons to move closer to the disc. You may have to do it a couple of times but if the pistons are moving freely the problem should go away. Of course, this assumes the master is okay. Master cylinders in of themselves are very simple devices and rarely fail unless there is corrosion in play.

[ajh]

Thanks all, that gives me some options

Thanks. My calipers are free and working and theres no air in the system. The brakes work fine to a point but theres too much travel in the lever to get full braking. Its a new unbranded M/C so Ive no idea what it is but Im guessing its the wrong size and needs more travel to achieve the force needed for hard braking. I tried some 'shims' between the piston and lever to reduce travel and I think this proved it was wrong because I could then get full braking but brakes were then binding a bit all the time

[Grimly]

Thanks. My calipers are free and working and theres no air in the system. The brakes work fine to a point but theres too much travel in the lever to get full braking. Its a new unbranded M/C so Ive no idea what it is but Im guessing its the wrong size and needs more travel to achieve the force needed for hard braking. I tried some 'shims' between the piston and lever to reduce travel and I think this proved it was wrong because I could then get full braking but brakes were then binding a bit all the time

Yeah, I went through this exact thing with my XS. After refurbing the OEM calipers I thought I'd try a 14mm master cylinder.
Whooo....eeee - could stop on a dime/pebble/quarter/sixpence (choose your metaphor) but the lever came back too far for comfort.
I ended up fitting the Deauville 5/8" m/c as it was still a size down from the Yamaha m/c (11/16" or 17.4mm) and gave excellent results.

[ajh]

Yeah, I went through this exact thing with my XS. After refurbing the OEM calipers I thought I'd try a 14mm master cylinder.
Whooo....eeee - could stop on a dime/pebble/quarter/sixpence (choose your metaphor) but the lever came back too far for comfort.
I ended up fitting the Deauville 5/8" m/c as it was still a size down from the Yamaha m/c (11/16" or 17.4mm) and gave excellent results.

thanks for that!

[limeex2]

Most used master cyl's have had poor service and the bores get wore outand are not worth rebuilding. Get a fairly modern, less than 5 year old m/c with low miles or get a new one from Z1. Smaller bore sizes (1/2")tend to have a better feel. Went through this with my ZRX. Naked bikes have fairly flat bars so they tend to fit/look a little more normal. Calipers have to be perfectly clean, no corrosion in seal area, seals greased properly and new OEM seals only. GS's with modern, well working brakes are an amazing improvement.

[salty_monk]

I've used EX650 ones for years. Work great...

[tas850g]

If you’re still looking for options. I put my 2004 SV650N MC on my ‘79 850. The N model incorporates the mirror attachment if that makes sense. Not sure if your bike uses the remote reservoir or not. If it does then the Sv S model would work.

[ajh]

So got myself a used Bandit M/C with adjustable lever and it works great. Thanks for the help all!

Quick question, I found the bleed nipples on my calipers have been butchered, can anyone tell me the threadsize of the bleed nipples to buy new? (Save me having to take one out and have to rebleed brakes )

thanks