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leaking union


Gadgetman
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I've put new type 16 calipers on with new pipes. one caliper leaks slightly (just damp) where the brake pipe screws in. I've replaced the pipe and cleaned out the hole in the caliper but the new pipe leaks also.

It looks like there are still machining / judder marks on the mating face in the caliper....is there a re-facing tool to cut a smooth face 

is there a seal / o ring you can get to put in the caliper female thread to help seal it?

I see frosts sell a brake pipe thread sealant but I'm reluctant to use that.

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Any seal in the caliper should be down inside where the flare seats and the brake pipe end doesn't usually screw in so far that it has to mate with the caliper edge. Is it leaking out around the pipe where it enters the pipe end?  I'm wondering, have you used the correct pipe and pipe end? I know there are both metric and imperial and mixing won't be as good a seal as a matched set; similarly, what flare did you use? 

Just pondering the causes and options out loud... but I've never liked using any kind of seal on the braking system, it should be fluid-tight by itself.

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29 minutes ago, Colin Lindsay said:

Any seal in the caliper should be down inside where the flare seats and the brake pipe end doesn't usually screw in so far that it has to mate with the caliper edge. Is it leaking out around the pipe where it enters the pipe end?  I'm wondering, have you used the correct pipe and pipe end? I know there are both metric and imperial and mixing won't be as good a seal as a matched set; similarly, what flare did you use? 

Just pondering the causes and options out loud... but I've never liked using any kind of seal on the braking system, it should be fluid-tight by itself.

Colin, it’s leaking around the tread, see attached picture 

the caliper is imperial as is the pipe end 

it must seat onto the bottom of the caliper female orifice / threaded hole otherwise it won’t seal at all 

DAD117A7-93EA-40C5-A71D-A6EA8A60C4B1.jpeg

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The seal is formed between the tapered bottom of the hole in the caliper and the bell flare of the pipe end. The former is made by a standard drill, the latter by a flaring tool. It's much easier to get the latter wrong, but you say you've fitted a new pipe?

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a word on hydraulic sealant

in production we used loctite hydraulic seal on certain fittings its very permanent ,wont fail, and does the job if needed , that was 20 yrs ago it worked then 

taking apart was not easy , needs a spit ring spanner or you round off the hex .

Pete

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46 minutes ago, NonMember said:

The seal is formed between the tapered bottom of the hole in the caliper and the bell flare of the pipe end. The former is made by a standard drill, the latter by a flaring tool. It's much easier to get the latter wrong, but you say you've fitted a new pipe?

Sounds like the seat face in the caliper could be smoothed off with a suitably sized drill then? Have to be careful not to damage the thread though...

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Inspect the flare when you remove it, and see if there's any deformation caused by tightening - this will give an indication of what's down the hole causing the leak. Those look like Kunifer pipes? Copper being softer will compress more and give a better seal - might be worth a try?

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13 hours ago, Gadgetman said:

I've put new type 16 calipers

Good luck with them......  If you find they apparently won't fully bleed...... that isn't the problem.  The seals pull the pistons back too much.  You can overcome this by removing the pads and carefully pumping the pistons out a bit.  Then lever the pistons back in until you can JUST squeeze the pads back in.  That should give a you a pedal.  Until the pads wear down and calipers fail to self adjust.......  Hopefully you'll be luckier than we were - anyone want a couple of door-stops!

Nick

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Looks like the culprit is a poorly machined counterbore face.... Judder marks causing the joint not to seal! It leaves the judder impression on the pipe end!

I’ve tried  a pipe made from copper to no joy so now I’ve tried loctite 592 thread sealant as a last resort otherwise the caliper is going back to Moss!

 

C637624D-A1F3-405A-9A8E-40D7C1A21334.jpeg

C09C0282-18BD-4D05-95C7-71B79C19C419.jpeg

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It's brakes don't mess around with them send the caliper back as "not fit for purpose"! the seal must be on the flare NOT the threads, anyway if the flare leaks & you seal the threads the weak link so to speak will be the back of the flare and up the pipe/union inner barrel.

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i agree send it back 

the thread sealants including 592 and 542 are for sealing hydraulic threads not the seating , it will solidify with no air and seal up leaks but really for threaded fittings

rather than seatings like flares ,

 it was  used on truck production for troublesome fittings on some odd french  air/ hydraulic actuators , but i cant remember what the pipe fitting was but once it set , quite a pig to remove the fittings 

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