Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: AndyD on April 21, 2021, 05:02:27 PM
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Finally getting back to doing some work on the bikes after a seemingly endless series of diversions.
On the recently fitted (new pattern) brake caliper I've got a slow weep from both the bleed nipple and the screw connector into the caliper for the brake line.
Don't want to tighten any further so guess I'll drain, remove and refit so I wondered if there is something people recommend for these threads to help seal the joints?
Cheers,
Andy
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PTFE tape cured a weeping bleed nipple for me.
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+1 on the PTFE tape. Use it on the bleed nipple as well. It prevents it seizing
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PTFE tape can degrade with some types of oils, better of with loctite 542 hydraulic seal, (google it) it is proof against most things except extreme heat, it was 1st choice on industrial hyd. systems
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Many brake hose manufacturers e.g Hel, Goodrich use PTFE inner liners for their hoses. So personally, I wouldn’t be too concerned about degradation.
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The bleednipple shouldn't seal on the threads but on the point in the bottom of the hole.
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Sounds like flares and seats are not quite right to me
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A few months ago I replaced the complete front brake system, top to bottom. Just to be doubly sure, I checked with my vehicle engineer/MOT tester neighbour, and he informed me that all brake components should be assembled dry and without any sealants whatsoever. If there is a leak, it's either mating faces not clean, not tight enough, or incorrectly seating. Bone dry joints without any sealants are the only acceptable condition.
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No tape should be used on brake systems plumbers ptfe tape isnt isnt oil/petro/gas l resistant. There are different types of Teflon tape for different types of applications.
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I would use the Yellow PTFE tape as per gas fittings not expensive from a builders merchants etc.
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Use of PTFE tape on domestic gas fittings - OK. Max pressure of domestic gas is 60PSI
Use of PTFE tape on domestic mains water - OK. Max pressure of domestic water is 80PSI
Use of PTFE tape or any other sealant on hydraulic vehicle brakes is a no-no! All fittings must be assembled dry. The 'lock-up' pressure in a non-servo assisted brake pipe is approx. 900-1000PSI. The metal brake pipes have to be manufactured to withstand a test pressure of 5000PSI. Leave the PTFE tape in the drawer in the cupboard with the plumbers fittings.
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I agree that hydraulic systems are best built dry of sealants etc., But having spent my working life on control systems and industrial hydraulics operating up to 12,000 psi, loctite sealants were often used, industrial breakdowns costs were to be avoided if at all possible
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As far as im concerned fix the problem not the symptom
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Thanks everyone,
Interesting range of views and I guess no 100% simple answer.
I haven't had any brakes in the past with the screw-in flared type connector, always had banjo bolts and washers so I wasn't sure if there was something I missed at assembly.
The bleed nipple weep seems to have stopped with a tiny extra tweak tighter - I'm just nervous of overtightening and thought I'd seen various mentions of PTFE tape on these on the forum.
Weep from the main hose is still there and I don't want to risk tightening further so I think I'll drain the brake and take the hose off - give it a good clean along with the caliper inlet and see if that cures it.
Thanks again,
Andy
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Use of PTFE tape on domestic gas fittings - OK. Max pressure of domestic gas is 60PSI
Use of PTFE tape on domestic mains water - OK. Max pressure of domestic water is 80PSI
Use of PTFE tape or any other sealant on hydraulic vehicle brakes is a no-no! All fittings must be assembled dry. The 'lock-up' pressure in a non-servo assisted brake pipe is approx. 900-1000PSI. The metal brake pipes have to be manufactured to withstand a test pressure of 5000PSI. Leave the PTFE tape in the drawer in the cupboard with the plumbers fittings.
My understanding of most brake fittings is that the convex & double convex type fittings rely on compressing the end of a brake fitting into the mating surface so no sealant or tap should be used. New steel pipes that have not been fitted perviously will in some cases require some extra pressure from the fitting to meet up with the mating surface to form a new seal. So I agree with you.
I've used PTFE tape on taper threads such as a plug. My belief is that in these circumstances the PTFE tape film acts like a thread blocker/locker so the comparison between say water pressure & brake pressure might not apply. I've not used on a bike but on my various cars I have used the Kunifer (Copper based) type brake pipes as they are easier to form- I find they do not require the same pressure to tighten a union even with new pipes compared to all steel ones. Interestingly MB only supply new all steel type brake pipes as authorised fittments to the dealer workshops.
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Use a proper brake pipe nut spanner(full six sided hex with a slot to clear pipe) and tighten the nut more, you need to "bed" the flares together
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Thanks again,
Brian - I hadn't come across a brake line spanner before so had a google and one on order now - hopefully that'll allow proper tightening of the fixings.
Cheers,
Andy
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Bryan,
Flare spanner did the job - thanks for recommending that as I wasn't familiar with these.
Tightened the bleed nipple a bit more and that stopped the leak there as well so looks good to go now.
And always good to have another shiny tool in the drawer!
Cheers,
Andy
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Andy, just remember in years to come that you need to warm the caliper with a plumbers type torch before trying to undo the bleed nipple
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Thanks Bryan, will do.
Also I've got another old caliper with a damaged bleed nipple I'm looking to sort.
The nipple has been broken at the top but has a reasonable bit still sticking out to get hold of.
It's been soaking in penetrating oil for a while and I wondered whether sticking the caliper in the oven for a while would help to free the nipple before trying to loosen it - what do you think?
Cheers,
Andy
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Use a blowtorch or buy a repair kit from me, drill and tap 1/8 npt screw in the kit adaptor and use the bleed nipple into the adaptor. Look up NAPA bleeder repair kit