> I have just one comment about this -- it is based on my (possibly
incorrect)
> assumption that a standard "US made" grease gun uses a 1/8NPT fitting on
the
> end. If anyone (Karl specifically) can point me at a brake line fitting
(on
> any reasonably modern car for that matter, not just british) with NPT
> threads, I'd sure like to see it. <snip>
Well, technically you're right - the threads ARE different. However, the
TR's (up till later 6'd which AFAIK used metric threaded brake hoses) used
1/8 British Straight Pipe (BSP) with a thread count of 28 threads per inch
(TPI), while the 1/8 National Pipe Tapered (NPT) threads on a grease gun are
27 TPI. However, the outside diameter (OD) of the BSP (brake hose) threads
is about .370" while the NPT threads (grease gun) get as big as about .390"
(roughly). The BSP threads are straight, while the tapered (grease gun)
threads taper. The BSP threads go WAY into the grease gun before anything
engages - only a thread or two even engage, right at the bottom. You're not
holding any great force here, because the diameter of the hole is so small.
Practically, a pretty big difference in thread counts would likely work fine
without any significant damage, and I've never seen a thread marked in any
way. I do this fairly often. Maybe my grease gun is now a hybrid
BSP/metric/NPT at the bottom of the threads !!
Seriously, though, with an engagement of just over 2 threads (about .050") ,
you're talking about an interference of only .003", which is easily taken up
by the threads not bottoming all the way - there's not likely to be much
damage. And, since you're doing the brakes, you're NOT going to use that
old brake hose anyway, are you?? It's all full of grease!!
If all this still leaves you apprehensive, you could either get a custom
hose or adapter made up for the purpose, or make one yourself by re-cutting
BSP threads on a flexible grease-gun hose, or take an old brake hose and cut
USS NPT threads on one end.
BTW - I should have mentioned that you could actually fill your grease gun
with any fluid instead of grease for this purpose - but I'm lazy and just
use whatever is in the grease gun, usually the expensive synthetic stuff.
I also should have mentioned that if you DO use grease or anything other
than brake fluid, you MUST flush everything out thoroughly. If you put
anything other than brake fluid through a brake hose, it'd be best not to
re-use it. Oil and grease attack many types of rubber, and could cause a
failure at a later date. Remember many years ago, when we had to use only
Lockheed or Girling-approved fluids as appropriate in LBC's because of the
difference in compounds? Fortunately, the newer hydraulic rebuild kits have
different material and tolerate the commonly-available DOT fluids. However,
oil is still not good for any of this rubber, and it'd be best not to take a
chance. I assumed that everyone knew this applies to taking an old assembly
apart, and that nobody was re-using any rubber parts in their brake systems
anyway.
Karl Vacek
'66 TR4A - IRS
'64 Amphicar
'16 Ford T Touring
'46 Piper J-3 Cub
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