SEALS/CRUSH WASHERS FOR STRAIGHT THREAD
With NPT threads, simply apply Teflon sealing tape or compound. However, when using an AN adapter that features straight thread at one end, you need a sealing washer. Depending on the applications, you'll need either an O-ring or a crush washer. O-rings are available in both Buna N synthetic rubber and in Viton. Buna is compatible with most fuels, hydraulic fluids and lubricants up to about 275 degrees F. Viton is preferred for synthetic lubricants, oxygen-bearing fuels and additives and non-ether-based brake fluids. Viton also offers better scuff resistance, longer service life and offers a higher operating temperature range of about 400 degrees F. Crush washers do exactly that....they crush under compression, providing the needed seal between two flat surfaces, where there is no groove relief to accept an O-ring. Crush washers are commonly available in aluminum and copper. Banjo fittings, for example (as used on brake line connections to calipers) require two crush washers...one between the banjo fitting and the caliper, and one between the banjo fitting and banjo bolt head. Crush washers MUST match the inside diameter of the adapter. Whether you're dealing with aluminum or copper, it is highly recommended to never re-use old crush washers. Always replace with new, since once they're crushed, they don't "spring back" to their original thickness, and the "fingerprint" will have mirrored the parent surface of the original installation, and might not seal against a different surface. Crush washers are generally available in hole diameters including 3/8", 1/2", 10mm, 12mm, 7/16" and 9/16". Another...and better approach to sealing banjo assemblies are aluminum washers with built-in rubber O-rings. This approach offers the best of both worlds...the strength and crush of aluminum, plus an O-ring that expands to provide a superior seal. This type of sealing washer is available in two basic formats (one is of American design and the other was born in England). The American design, called the Stat-O-Seal, features a synthetic rubber O-ring captured (mechanically locked) inside the I.D. of an aluminum washer. This is a great choice to seal anything that normally would use an aluminum or copper crush washer. The English-origin version is called the Dowty seal, which is similar to the Stat-O-Seal, but the O.D. is smaller and the washer is thicker. Either works well, but the Stat-O-Seal is more readily available. As an example of the superior sealing offered by a Stat-O-Seal, I recently reconfigured the front brakes of a 1973 Duster (fitted with a non-original 426 Hemi) to disc brakes. The owner wanted an "OE" look, so I chose single-piston cast iron calipers from a well-known caliper remanufacturer. I initially installed copper crush washers at the banjo fittings, but could not achieve a seal (constant wetness). I tried different-thickness copper crush washers, and even tried aluminum crush washers, but to no avail. Further inspection showed that the sealing seats on the calipers (where the crush washer was position between the caliper seat and the banjo fitting) were never re-faced after the caliper bodies were blasted during cleanup. The sealing seat surface was irregular (not milled). I exchanged the calipers for replacements, but got the same pitiful results. Finally, I replaced the crush washers with Stat-O-Seals. Guess what? Instant perfect seal. No leaks, no more cussing and no more re-bleeding.
Dowty seals. These sealing washers are of British origin. They feature a smaller-O.D. and a thicker cross-section than Stat-O-Seals, but essentially work the same way, with an O-ring inside an aluminum housing. While we're on the subject of sealing fluid, here's something many people aren't aware of: If you have a damaged AN 37-degree sealing surface (hose end of adapter) that may have been caused by galling when assembled dirty, etc., you can make a quick and easy field-fix without the need to replace the hose end or adapter. Aluminum conical seals are available in all AN sizes. This is simply a small, shallow conical "cup" that matches male and female seat angles. Simply push the conical seal over the male cone and reassemble the hose end to the adapter in the normal manner.
Conical seals offer a quick field-fix for damaged 37-degree AN hose end-to-adapter connections.
HOW TO ASSEMBLE -AN HOSES
NOTE: -3 and -4 sizes are relatively small in diameter. Especially for brake hose applications, these are very difficult to assemble by hand and often require crimped hose ends. For brake lines, or high-pressure hydraulic clutch hoses, don't try to make your own. Buy brake hoses or clutch hoses already assembled in the lengths you need. The following instructions apply only to stainless steel braided hose and appropriate hose ends. Crimp-type hose ends require special crimping dies, available from the hose maker. Dedicated hydraulic crimping machines are also available and come in handy, especially if you plan to assemble a bunch. Slip-on hoses and barbed nipples are self-explanatory. Simply "slip" the hose over the barbed nipple. Be aware that this isn't as easy as it sounds, since the fit will be very tight. Eat your Wheaties before tackling slip-ons.
CUTTING STAINLESS BRAIDED HOSE
When you buy a length of -AN stainless-steel braided hose and plan to cut pieces to desired length and make your own assemblies, you first need to know how to properly cut the hose. Yes, you can use a hacksaw, but frankly, that method stinks. It's difficult to obtain a square cut. To do so, you need to use a special hardened blade, and chances are very high that you'll end up with frayed wire ends that you'll then need to snip off with wire cutters (by the way, snipping this hard stainless wire braid isn't as easy as it may seem). If you secure the hose in a vise to make your cut, you'll have a tendency to smash the hose out of round, which will only aggravate the problem. The best method is to use an abrasive "chop saw." First, wrap the area to be cut with electrical tape or a quality bodyshop masking tape (wrap the hose tightly). Mark your intended cut on the tape, carefully cinch the hose in the saw's vise without distorting it, and let the abrasive wheel slice through. Don't apply a bunch of pressure on the saw arm. Light to moderate pressure works best. Once the cut is made, remove the tape and thoroughly rinse the hose out using compressed air to remove all wire and rubber particles. This is important! Make sure the hose is clean inside. Naturally, you must always wear eye protection when cutting hose, when trimming stainless braid or when blowing hose clean.
This is exactly what you don't want. This is what happens when someone tries to cut stainless-steel braided hose with a dull hacksaw, with "snips" or by cutting the hose without wrapping the cut area with tape. This cut is useless. Don't even attempt to install a sloppy hose like this onto a hose end. If you start to snip the frayed ends with metal snips, you'll just end up making more of a mess. If you have a cut like this, simply start over.
This hose was cut on the abrasive wheel chop saw. Once the cut is made, be sure to blow the hose out with compressed air to remove bits of rubber and braid. We lightly secured this hose in a vise only for the photo.
If you plan to assemble -AN hose ends, buy a pair of these soft aluminum vise jaws. You can secure aluminum hose ends or adapters in these jaws without damaging the material. If you keep the jaws clean, you can also eliminate surface scratches on the anodized pieces. The jaws feature female V-cuts that accept the hex of the hose end or adapter, in either horizontal or vertical planes, as you wish.
Here we insert a stainless-steel braided hose into a hose end collar. There are many ways to go about this. Often, I simply screw the hose end collar onto the hose by hand. We're simply showing the collar in a vise for illustration. However you approach this, be careful of the braids at the cut end. If you're going to draw blood, this is when it's gonna happen.
Check to make sure that the hose is fully seated in the hose end socket. Don't push the hose into the threaded area If the hose (and its stainless-steel braid) enters the threads, they can jam between the male and female threads when the hose end is assembled.
The section of the hose end that features the metal sleeve threads into the hose end's socket. Apply a bit of lube to the sleeve and to the threads to aid assembly and to prevent galling. A light lubricant such as WD-40 or lithium grease works fine.
A 45-degree hose end shown here before being fully tightened. The hose end's socket (attached to the hose) can be secured in an aluminum vise jaw, while the hex on the hose end's threaded collar is tightened. Note that some hose ends are designed to rotate, while others are designed to retain a fixed position once tightened. If the hose end is not designed for rotation after it's assembled, make sure that the angle aligns with your intended fitting once installed.
Once the hose end collar is installed, I like to place a piece of tape on the hose, flush to the base of the collar. This provides a visual reference so you will still be able to tell if the hose begins to pull out of the collar during the rest of the hose end assembly.
Insert the hose end's tube into the collar, being careful to center the nipple to the hose I.D. If you try to insert the nipple off-center, you can force the nipple edge into the hose rubber, damaging the hose. Take your time. You'll be able to feel the nipple entering the hose.
Continue to tighten the socket/tube into the collar, using moderate pressure. Do not overtighten! Remember: These are aluminum parts. Also, as you tighten, the nipple seals into the hose I.D., creating a leak-proof connection. Note: it's a good idea to apply a bit of a push of the hose towards the collar during tightening just to make sure the hose isn't pushed out of the collar. Again, observe your reference tape.
Blow with compressed air again. Once a hose is fully assembled, I like to run hot soapy water through it, followed by compressed air, followed by air-drying. Do everything you can to make sure the hose is clean inside. I know plenty of guys who gripe about clogged carburetor jets or stuck needles and seats when it's their own fault because they didn't take the time to inspect and clean new hose assemblies before installing them.
Hose end fully installed onto a braided hose. Note that the reference tape only moved about 0.020", which is fine. Using the tape helps. If the hose walked out noticeably, the hose end socket/nipple must be removed, the hose repositioned and re-assembled.