FYI,
I had no problem threading the grease gun into the brake line inlet on the
caliper and only screwed it in far enough to get the job done. I'm
confident that there was no damage done. After freeing the stuck piston, I
blew compressed air through the same inlet to force the majority of the
grease into the chambers where most of it fell out onto a rag I had on the
garage floor. I wiped out the rest, sprayed the caliber with brake cleaner
to REALLY dissolve any remaining grease, and then shortly thereafter,
flushed the calipers with denatured alcohol. Actually, I let the calipers
soak in a tub of the stuff for a few hours. Then, I used compressed air
once more to blow out the denatured alcohol and the calipers are airing out
for a week until my new pistons arrive. I decided to throw out the old
ones.
Unless I screwed up somewhere along the line, I consider the mission a
success, so far. I'm sure someone will let me know if I blew it or not. As
soon as my DOT 5 arrives, I'm going to clean the calipers further with that
stuff, then insert all new rubber seals. I just rebuilt my MC today with
new rubber. New hoses are in the offing as well. I'm ready for DOT 5.
I've owned this car since January 4th and I can't wait to take it for a
drive!
Best wishes,
Jeff
http://www.ohms.com/spitfire/spitfire.shtml
----- Original Message -----
From: Karl Vacek <KVacek@Ameritech.net>
To: TR Listserv <triumphs@autox.team.net>; <peterz@merak.com>
Sent: Tuesday, January 11, 2000 10:19 AM
Subject: RE: Removing stuck caliper pistons the safe and effective way
>
> > 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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