1973 Front Caliper leak after full rebuild that I can't understand. Could it be a right fork seal leak going down onto the right side of rotor?

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DennisMo

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I fully rebuilt the caliper with stainless pistons and new seals and a week or two after, the right side of rotor was wet and dirty.
After cleaning after each ride, I pulled the caliber outer piston thinking I would find I had somehow twisted it or nicked it on install.
But it looks perfect.
But I can't see any fork fluid dripping down.

Has anyone had right hand side fork seal failure which dripped onto right side of rotor??

Thanks

Dennis
 
DennisMo said:
I fully rebuilt the caliper with stainless pistons and new seals and a week or two after, the right side of rotor was wet and dirty.
After cleaning after each ride, I pulled the caliber outer piston thinking I would find I had somehow twisted it or nicked it on install.
But it looks perfect.
But I can't see any fork fluid dripping down.

Has anyone had right hand side fork seal failure which dripped onto right side of rotor??

Thanks

Dennis
Click to expand...
I had drip from my master cylinder ( torn boot ) that showed up on the rotor.
 
Discerning the difference between brake fluid and fork oil should be obvious.
Dirty, fluid covered rotor indicates pads not engaging.
Take down the caliper and find the problem.
 
Last edited:
I have a rebuild kit coming and will put new seal in it. I am also going to tie a cloth around the fork just under the fork seal so when I rider it I can check it after
ride to see if it is wet.
Thanks to all!
Dennis
 
You should be able to see fork oil trail from anywhere its leaking from, maybe throw a bit of talcum powder on the places you think the leak is coming from will tell you where its leaking.
 
It's quite strange as I have never had a rebuilt caliper leak if new seals and pistons installed. The leak coats the right side of the rotor. But just to be sure, I will pull out the left side caliper piston and put a new seal in it too.
 
Make sure the seal grooves are clean and good surface finish. No scratches from removing old seals. Graham
 
DennisMo said:
Has anyone had right hand side fork seal failure which dripped onto right side of rotor??
Click to expand...

Tie a thin strip of cloth around the folk leg to check if it is getting wet from oil, It might also show a stain from the color of the oil from the forks to tip you off to a leak.

You can also put a rope around the brake lever ( like you have applied the brakes) to put pressure on the brakes overnight and see if the lever stays firm and if brake fluid is dripping out.

If you feel it is brake fluid , You will have to carefully inspect the pistons for defects or burrs and put new seals in after carefully inspecting the grooves and parts. Some pistons don't have much of a bevel/ chamfer on the pistons, so it doesn't go in as easily as it should.
 
A previous owner had replaced the mudguard retaining studs with bolts. A sensible modification, apart from the fact that the bolts must have been a tad too long and one had broken into the slider causing an oil leak. That took me quite some time to find!
I went back to studs with sealer on the offending hole.
 
Do a finger taste test on the fluid, you soon find out if its oil or brake fluid, just a small taste on the tip of your tongue.
 
A leak at the hose connection to the caliper or a dodgy bleed nipple are possibilities.
Since the caliper has just been overhauled this is more likely than a fork leak, surely?

Clean the whole area, pull hard on the brake lever and watch for fluid welling up around the threads.
Ask me how I know ;)
 
DennisMo said:
I fully rebuilt the caliper with stainless pistons and new seals and a week or two after, the right side of rotor was wet and dirty.
After cleaning after each ride, I pulled the caliber outer piston thinking I would find I had somehow twisted it or nicked it on install.
But it looks perfect.
But I can't see any fork fluid dripping down.

Has anyone had right hand side fork seal failure which dripped onto right side of rotor??

Thanks

Dennis
Click to expand...
Check the piston seal is the correct size.

A number of years ago I had a new seal from AN that was slightly too narrow for the caliper groove and leaked immediately after fitting.

It would have cost too much to post it back to them, so I re-fitted the original seal and all was good.
 
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