Evening all!

I've got a bit of a question regarding how brake/hydraulic unions seal. I hope this is the right section for this, apologies if it is not!

Anyway, If I take my Sierra rear caliper and Goodridge braided hose as an example, I'm wondering what part of the union (that screws into the caliper) does the sealing to stop hydraulic fluid leaking everywhere. Is it:

a: the copper washer that is pinched between the surface of the caliper and the union when tightened up
b: the threaded section of the union and caliper
c: The concave section at the bottom of the threaded hole that the union screws into (the union has a convex bit that looks to be the same taper angle)
or d: all of the above?

My gut feeling is that it option c that does the sealing, but if that is the case, why the copper washer? Does anyone elses brakes use a copper washer?

AS you can probably guess, I'm trying to expand my knowledge of why things are this evening!

Many thanks in advance!
Andy

If its a banjo connection (ie looks like a bolt with a hole through the neck of it and another down the centre the length of the threaded part) then its the copper washer but there should be one either side of the hose conection i think.

Sorry, I should have pointed out, it isn't a banjo type fitting, it is more of a union fitting. The pipe exits the union perpendicular to the surface of the caliper.

Cheers
Andy

OK would say its the copper washer especially if its a parrallel thread but if the pipes tight and the washer is still slack then perhaps someone's been at it before.

If the thread on the hose is longer than the depth of the threaded hole in your caliper and the caliper as you say as a taper at the bottom of the thread to correspond to the taper on hose than this would normally make the seal ie like the way a bleed nipple seals. If the threaded part of the hose is shorter than the threaded hole in the caliper then it is normally sealed by the copper washer. Hope this makes sense .

In plumbing union terms (Iron fittings) it is C, usually made off brass like a large valve seat that seals the water in over as large an area as possible I think thats why it is at the chosen angle.

The same as olives in compression fittings, if they leak you put PTFE (of cause!) or jointing paste on the male and female part of this concave/seat arrangement to get them to seal.

Hope this helps and is releven't I'm sure there's people more experienced than me who can explain this.

Well, I tried fitting the flexi hoses and unions last night, and with the copper washer in place, and the union screwed down hand tight, it just gripped the washer. Only just mind, in that the washer could be moved about by finger pressure.

Without the washer, the union tightened down to leave about 1mm between the surface of the caliper and the union.

So, I'm going to try leaving the copper washer off, as i think the seal is going to be made on the concave surface of the caliper, at the bottom of the threaded hole.

Does anyone know if the standard flexible hoses on sierras have copper washers fitted?

Cheers folks!
Andy

You should leave the washer in. When you tighten it finger tight thats the seats touching. When you tighten it with a spanner it will grip the washer and bed the pipe onto the caliper seating properly.

Thats the way i understand it anyway. I think you will find that the concave seat does most of the sealing. Then the copper washer completely seals it off.

David

iam no expert so dont take this as gospel. On mine it is the tapers that form the seal on front calipers.

I had a problem with the Tee piece at the back end. Copper pipe to the Tee then flexis from each end to the drums. The flexis screwed in such that they bottomed out on the end face of the Tee. I was informed this is wrong and will cause leak. The fix was to remove small amount of material from the either side of the brass Tee so that the tapers lock down first. After completing it it certainly looks like a correct solution. No brake fluid in yet so i cant conclude, other than to say it is how the kit manufacturer do it and they have never had a problem as a result.

As before this is for std unions, NOT banjo's. I would never recommend touching banjo connection faces as they must be machined parallel.