PTFE good for Banjo bolt seal?

[knowlittle]

Copper crush washer (3/8" or 10 mm ID) could not seal the brake line-to-caliper joint at the specified torque. Upon close examination, I found a pit on the caliper sealing surface. Of 6 or 7 concentric ridges, 3 outer ridges were compromised by corrosion. I raised the torque from 25 to 35 ft-lb and the joint seems to hold for now. I searched internet for alternate sealing materials (in the washer form): aluminum, Dowty seal (steel washer with rubber in the middle), and PTFE. I can make PTFE washer to the size with punches. I am sure PTFE will crush more than copper. Brake fluid stays below 200 C. So PTFE seems to be a good fit. What do the experts think? Or just replace the caliper?
Thank you.

 

[swall]

PTFE tends to creep. Not a good choice for a banjo bolt seal.

 

[Tmoose]

Is the caliper sealing surface made by "spot facing" or milling a large exposed surface?

If the caliper is otherwise in good working order, I'd focus my efforts on restoring the washer sealing surface by careful flat filing with a fine mill file, after plugging the hole leading to the caliper's innards. I would not expect defects in the outer 50% of the surface to leak using a new dead soft washer unless those ridges were quite severe.

 

[knowlittle]

Thank you for the replies.
The sealing surface is about 1" diameter. Only this area is machined (slightly recessed) and has concentric ridges. It will be difficult to resurface the area. I am more inclined to have an alternate crush seal. If PTFE creeps much, what about glass filled PTFE? Or I can buy a bonded seal (dowty seal). Or I can anneal copper washer with propane torch. Either would be easier than resurfacing.

 

[TugboatEng]

If you want a resilient seal look into replacing the banjo washer with a Dowty washer with an EPDM seal.

 

[Screwman1]

PTFE is not a good compression material for sealing- too much creep. I would go back and try to rework the sealing surface like Moose suggested. Just plunge an end mill onto it and your good to go. Otherwise, get some new copper or aluminum washers and try those. Don't reuse, they work harden during installation. No plastics- never ever.

 

[SwinnyGG]

Did you re-use the copper crush washers? If so, that's your problem.

 

[knowlittle]

I don't have a shop. Buying a new caliper would be more practical than milling the surface. No, I did not use the old copper washer. I know about work hardening of copper. I will anneal anotgher copper washer with a torch. IF this doesn't hold, I will use Dowty or aluminum. Thank you.

 

[TugboatEng]

If you go the Dowty route it's imperative that you get the correct elastomer for the seal. Brake fluid isn't friendly with many types of rubber. Dowty washers are almost always nitrile or Viton rubber which are not compatible with brake fluid. They are available in EPDM but you're going to have to special order which means minimum purchase quantities.

 

[Tmoose]

1 - 25 ft-lbs // may // have been kind of low, generically speaking.

http://www.hoseandfittings.com/banjo-torque/

2 - It might take surprisingly little manual refinishing to lower the high spots off the concentric ridges without removing them entirely, and get the copper washer to seal at the lower torque.

3. A quick scan of This Info from Dowty seems to say 3/8" has a burst pressure of 1470 psi. Much too low for brake service.

http://www.potterassoc.com/pdf/bonded_seal_information_and_sizing_chart.pdf

 

[DAVIDSTECKER]

Just a thought to recondition the surface.
Take something like an old fashion hand valve lapping tool and some self sticking sand paper with a stiff card board backing and try to bring the surface back.
The valve lapping tool had a flexible end that will stay flat on the surface even though the handle is going to wiggle.