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Discussion Starter · #1 ·
ok, so... the bike has had little use over the last 10yrs, iv got it running good now but the front brakes are pissing me off... they lock on but one caliper wont release, here's what I have done so far
CX500TC
new caliper kits
new master kit
eased and greased all pivots and mechanics related to the caliper
new fluid...
BUT still with front wheel of the ground it spins pull the brakes on and it stops spinning, do this several times and the wheel binds up more and more... to the point where I have to crack the bleed nipple to release the pressure... WHATS with this its got me buggered???
 

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Crack a bleed nipple to let the hydraulic pressure off.

If they spin now the problem is hydraulic and may be a blocked MC pressure return.

If it doesn't release the issue is mechanical.

Another possibility here on the hydraulic side is that the rubber brake line is breaking up internally and small pieces of the rubberised lining can begin to act like valves.
 

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There are two holes in the bottom of the master cylinder. The larger allows fluid to go from the reservoir to the hydraulic pressure area.

The small one allows the pressure applied to the braking system when the lever is squeezed to bleed back when the lever is released. If it is blocked the brakes will remain on.

The drilling is very small and blocks easily and is a common issue.

It can be cleared with a small probe. Something around the size of fuse wire.
 

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As i recall the tiny return port (hole) is in the bottom of a dimple and when clogged can be difficult to see the actual tiny hole.
 
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swap your brake lines for modern , braided lines. Those old rubber ones are 40 years old now , and likely shredding internally
 

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1982 Honda CX500Turbo, 1983 Honda CX650Turbo, 1974 Norton 850 Commando, 2012 Triumph Tiger Explorer
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The caliper pistons are not returning, it could be the MC return hole being clogged as others have mentioned, but also the caliper piston bores may be corroded if moisture had contaminated the brake fluid while the motorcycle was stored.
 

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The caliper pistons are not returning, it could be the MC return hole being clogged as others have mentioned, but also the caliper piston bores may be corroded if moisture had contaminated the brake fluid while the motorcycle was stored.
According to the first post in this thread, new caliper kits were fitted. Your point is valid if the OP did not make sure that the seal groove was clean and free of debris and corrosion. If not, then the new seal would be pushing on the piston preventing its return.
 

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Discussion Starter · #9 ·
Yip new kits in the calipers and I cleaned all parts well... Pistons move fully and freely all the way in and out... HOWEVER... All four will only go in so far on their own ie: can fit one caliper over disc but not the other Unless... Bleed is cracked.
Lines are braided so have been replaced at some stage.
209095

I'm thinking... I missed the return hole in the MC, so tomorrow I'll take the bastard off again and do a better job... Not looking forward to beading the MC it took forever last time.
 

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Discussion Starter · #10 ·
Re above photo... Hole on right is the feed into the lines... So is that the return to its left???
Looks odd
 

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1982 Honda CX500Turbo, 1983 Honda CX650Turbo, 1974 Norton 850 Commando, 2012 Triumph Tiger Explorer
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According to the first post in this thread, new caliper kits were fitted. Your point is valid if the OP did not make sure that the seal groove was clean and free of debris and corrosion. If not, then the new seal would be pushing on the piston preventing its return.
Correct, I have rebuilt several of these calipers and the seal grooves usually need a careful cleaning to remove muck-gunk and corrosion.
 

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Yes, the tiny return hole can be difficult to even find when crudded over. Nice picture of it.
 

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1981 CX500D, 1976 RD400C, 1972 H2 750
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Never pull off road in to the grass if brakes are binding lol 😜 wheel locks and you're sitting there on ground wondering wtf 😂
 
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