F.A.Q.'s
Wheels & Axles
Q: I've been told my trailer has "Split-Rims", and the
tire dealer won't replace my tires on them. What are these split-rims?
A: Split rims are used to describe a style of wheel popular
up until the early 1960's. The wheel consisted of a 2 part ring on the
outside rim of the wheel. This was to allow easy replacement of the tire
and inner-tube. The only catch was that if the ring was not seated correctly,
as the tire was inflated it could fly-off with explosive force, injuring
the person standing over the wheel. There are special cages to inflate
such wheels, but most shops just have a blanket policy of no split-rims.
The fix is to replace the rims with new 6 lug 6x15 conventional wheels.
Dexter Axle makes one available
in a appropriate black finish with matching moon style hubcap.
Q: My Airstream doesn't have any hubcaps. Where can I get some?
A: Depends on your year trailer. If it still had the
split-rims wheels, the moon style hubcap has spring-clip that slipped
inside the wheel center - these are no longer available and are hard to
find. If you have conventional wheels, the style up to 1971 was a baby
moon style of hubcap. 15" wheels use a 10 1/4" ID and 14"
wheels use a 9 1/8" ID style. You can find them at any utility trailer
dealer, Dexter dealer as noted above, or on eBay.
Q: I'm not sure of what size tire to get for my trailer, as it
seems the original sized tires are not readily available. What should
I do?
A: Best bet is to get the trailer to a dealer, provide
them with as much information as you can, and let them match, mount and
then install the tires. That way if there is an issue, they are responsible
for making the tire fit. Generally, the tire used on the older trailers
were 7.00 x 15 LT (Light Truck) bias ply tires of the era. Some exceptions
are the small 15 to 18 foot trailers, which used a 6.70 x 15 LT tire,
as were some early tandem axle trailers.
ST type (special trailer) tires weren't available back then - the same
with radial tires. The ST has a stiffer sidewall than a passenger car
radial and has UV inhibitors in it - not really an issue if you use the
trailer at least 6 times a year to release the friction activated inhibitors,
and protect the tires from the sun while in storage. Radials were used,
usually the 225SR15 size once they came out in the '70's. You can retrofit
radials in some cases where clearance is not an issue, but it is recommended
to use the ST type, as the average radial sidewall flexes too much when
used on a trailer.
Q: What style are these axles on my trailer?
A: Until 1962, axles used on airstreams varied greatly,
from the cast cross member leaf-spring “Model A” type axles
of the ‘40’s and early ‘50’s, to the heavy duty
leaf-spring tubular type specialized trailer axles of the mid and late
‘50’s, usually by Hadco. In 1961 Airstream introduced their
own unique suspension assemblies which were called Dura-Torque. Later,
the suspension manufacturing unit was sold along with the design and rights.
It became Henschen Mfg, and is located in an old building several blocks
from Airstream in Jackson Center.
This new design was a square tube (axle) with a smaller square steel shank
with two 90 degree angles (suspension arm) inserted into the larger tube.
Cushion and support is provided by four approximately 12" long round
rubber rods of approximately 1/2" diameter inserted between the flat
side of the suspension arm and the corners of the square axle tube. The
rods are temporarily placed in a super cooling freezer beside the work
station, using liquid nitrogen to shrink the rubber rods. The rods are
quickly removed from the freezer, placed by a gloved hand against the
suspension arm, and the arm with rods are shoved into the axle tube. The
weight ratings of the Henschen Dura-Torque axles are determined by the
diameter and hardness of the rubber rods. To this durable but smooth riding
system, conventional shock absorbers are then added for additional ride
dampening.
Q: Do these Dura-torques wear out?
A: High-mileage trailers, or those left out in the elements
can suffer from deterioration of the rubber rods. There isn’t any
hard and fast rules. There are early ‘60’s trailers with plenty
of spring left, and 1970’s trailers that are shot. When the spring
goes from these axles, going over bumps and pot-holes can result in the
torsion arm coming up and hitting the stop there to prevent the wheel
from contacting the wheel-well or the rubber rods from being displaced.
This jolt and not only shake up your packing, but can weaken the frame
and trailer structure and skin joints.
Q: How can you tell if the Dura-torque axle is worn-out?
A: This is going to vary depending on who you talk to.
A good rule of thumb is that the trailing torsion arm shouldn’t
be angled upwards when the trailer is fully loaded, no more than 5 degrees.
A good second opinion verification is to put masking tape or sealant on
the up stop. If the stop gets hit during routine travel, you will be able
to tell, and your axle is a candidate for replacement.
Q: If I have to repair/replace my Dura-torque axle, what are my
options?
A: Henschen no longer repairs the older Dura-Torque axles,
replacement is the only solution. Airstream dealers and Inland
RV in Corona, CA are the only sources to replace your axle or can
ship one to you. For experienced restorers, you can spec out a new axle
direct from Henschen, but you cannot order, say “an axle for a 1968
Safari”.
Q: What about the older leaf spring axles?
A: Here you have many more choices. The axle components
can be replaced or repaired using conventional auto/trailer parts, such
as leaf springs, brake drums and brake parts, shocks, hubs, bearings and
wheels. If an axle is too far gone (rusted or broke) a new Dexter or Hadco
axle can be attached, or a new Henschen Dura-torque axle can be retrofitted
(see above).
Q: The small 13 inch wheels on my Bambi are not split-rims, but
the hub caps are no longer available, what can I do?
A: These wheels were actually low cost 4-lug Ford Mustang/Falcon
wheels of the era. Replacements are usually made using Dexter wheels and
moon hub caps just like the bigger trailers. As an option, you can usually
go up to 14” wheels and use P185/75R14 tires and have just enough
wheel-well clearance.
Q: What if can't find parts for my small Bambi axle?
A: Replace the axle with one from Dexter. The old axles
have a 10" brake drum with 4 bolts. That pattern is no longer available.
Use the 10" drum with 5 bolts and get the new Dexter matching wheels
and Moon hubcaps. The new axle actually fits the frame better than the
old one. Installation only requires that new holes be drilled in the frame
rail. The new install is actually cleaner than the old one.
Q: What is a Pipe Frame” Airstream?
A: "Pipe frame" Airstream trailers were built
from 1947 to 1950, and usually have both or one end rounded with a single
wide oval window on that rounded end. Travel trailers back then were built
very light with few appliances and furnishings, so their frame could be
relatively lightweight. The pipe frame was strengthened slightly in 1949
by adding another 3' section of pipe inside the front most 3 feet near
the hitch. But the frame soon became insufficient for the added weight
of larger trailers with more stuff installed and loaded inside.
The "pipe frame" was also called a "Centerpole" by
Airstream. The frame is like a fish skeleton: a longitudinal center rib
with outriggers to both sides. The outriggers are not all that strong
and cannot take too much weight being placed on them, other than above
the wheels, which has some additional framing to attach the axle. You
will typically see the appliances mounted in the center of trailers, usually
above or just forward of the wheels, as that is best for weight distribution.
If the small brackets that secure them to the centerpole become detached,
you can (it has been done!) pull the centerpole right out the front of
the trailer.
The first ladder frame Airstream with a "A" frame up front appeared
in mid 1949. It was the 24' "Unlimited", soon to be renamed
the "Cruiser." By late 1950, all new Airstream trailers were
built using the ladder frame.
The pipe frames are still OK if not rusted inside the tube, the outriggers
have not become detached, if the trailer is kept light and not overloaded,
and if you avoid using weight equalizing bars.
Q: My leaf-spring axle has hydraulic brakes, can these still be
used?
A: More than likely the axle was made by Hadco
Engineering, a supplier to Airstream in the 1950's. You can either
maintain the brakes as hydraulic, which requires special mods to the tow
vehicle, or you can convert them to electrical operation. Both hydraulic
and electrical components are still available from Hadco.
Q: What is "rear end sag" or droop?
A: It is a chassis to shell separation on longer Airstreams,
usually Ambassadors and Sovereigns prior to 1982. It was caused by the
installation of gray (1973+) and black water tanks, along with the battery
and weight of the bathroom fixtures in the back end of these long trailers.
This combined weight, especially when the trailer was towed with the tanks
left full, caused the shell to separate from the frame in the back from
all the dynamic flexing, and ultimately bent the frame just aft of the
wheel wells.
The fix is to install Airstream bulletin #29. It consists of two perforated
plates, notched and pre-drilled to fit over the axles on both sides. You
need to go through an Airstream dealer or authorized repair service to
have the work done. If the shell is detached from the frame or the frame
is bent, that will have to be corrected also. The bulletin is in the VAC
Online Library if you wish to see if the mod has been done to your trailer.
Ways to recognize the condition is to stand on the bumper and see if the
frame moves and the shell doesn't. Other sure signs are loose interior
partitions and cabinets, or a 45 deg bulge in the side of the skin just
aft of the wheels.
Q: What is the best way to replace the old worn electric brake
parts? How often do I need to grease the wheel bearings?
A: Use a loaded backing plate, replacing the entire brake
assy at each wheel. It consists of the magnet, brake shoes, springs, etc.
mounted on the "backing plate". There are several advantages
to loaded backing plates. Often the cost of the individual components
meets or exceed the cost of the complete unit. The process for replacement
is: undo the 5 (or 4) bolts and two wires. Reinstall, connect wires, which
do not need to be connected in any certain way, reinstall hub/drum and
adjust. You're done. You will now have all new springs, brake shoes and
a current style magnet.
It also makes sense to repack the wheel bearings at the same time. A tip
for removing the grease seal. Pry off the dust cap, cut and remove the
cotter pin, remove the castle nut and washer, remove the outer bearing,
replace the washer and nut, pull the hub/drum toward you allowing the
washer to bear against the inner bearing, pulling with a sharp movement
nearly always dislodges the inner bearing and seal with no damage to the
bearing. Pack the bearings per this Champion
article.
Another area that you need to be aware of are the different grease seals
available. Many RV outlets have a simple single lip seal that will fit
in Airstream axles. Airstream does not use nor do they recommend the use
of single lip seals. Their recommendation is to use double lip seals only.
They may be a little harder to find is a small price to pay for the added
security.
The original P/N was a National 291148 felt seal and 292100 in the ‘60s
Henschen axle. The 292100’s are available from OasisRV.
The TCM 21325TB is a good substitute for the 291148. It is a double lip
seal, also.
Q: What shocks should I use?
A: Except for later model tandem axles, conventional
heavy-duty auto and light truck shocks are correct. Take a shock to an
auto parts store so they can match the ends, stroke & length.
With the big body style change in 1969, Airstream changed to a horizontal
mounted (trailing arm) shock absorber configuration. They can also be
found on some later '60's dual axles.
What makes the new shock special is: "The shock used in the horizontal
mount is a specialty shock built for Airstream by Gabriel. The difference
is a bladder is used to hold the oil on the piston. The typical design
of shocks would allow the oil to pool away from the piston leading to
premature failure." This shock is the one you need to get from Airstream
dealers. While a conventional shock can be made to fit, you can see it
may eventually fail.
