From: emory!STDVAX.GSFC.NASA.GOV!OADDAB (DIRK BROER)
Subject: Car Trailers
Date: Mon, 02 May 94 21:22:12 GMT
In the Drag Racing list there has been some discussion on car trailers.
I was wondering does anyone have a source for top quality parts and
perhaps even design of a car trailer.
I could grab axles and suspension from a FWD mini-van and perhaps lengthen
them (the axles). But I also know that a proper design is needed to keep
the average load from swaying the trailer. Short of finding a trailer that
I like and taking measurements where can I look for info?
Hey, I know its a little off subject - but you have to haul those project
cars around somehow...
[Being deep in the process of building two trailers right now and having
built several others in the past, I can comment. Getting the rear axle
of a FWD car or van is possible but you end up paying yourself oh, about
10 cents an hour while you work to adapt it. By far the cheapest place
to get axles and other trailer hardware is Northern Hydraulics (800
533 5545.) I have a store about a mile away so they are real handy
but they also do mail order. When I had to look elsewhere for an axle
that northern was out of, everyone told me to just wait on them to restock
because no one else can compete with them and their chinese manufacturing
sources. They also sell a book on trailer design.
In general, the industry has settled in on two classes of axles - 2000 lb
and 3500 lb. The springs hubs, brakes and bearings are standardized
to these classes. Northern sells straight, dropped and sprung axles
in each capacity.
The BBQ smoker trailer I'm just finishing up weighs about 1500 lbs loaded.
Here's a rundown on what I used.
3500 lb axle 62.99
2000 lb leaf springs 32.99 set
3500 lb shackle kit 13.99
3500 lb u-bolt spring kit 9.99
3500 lb 5 bolt hubs 47.99
B78-13 tires and wheels 65.00 ea
Fenders 19.99 ea
Lighting kit 34.00
Tongue jack 29.99
I constructed the trailer frame, as I usually do, from 2" X 3" X 0.120"
(thinwall) rectangular steel tubing. This stuff is very strong, easy
to cut and weld and looks REAL good when painted. I used 3 20' sticks
of this stuff on my BBQ trailer and it cost $128 from a very high priced
but handy local steel distributor. Figure about 2/3 that from a large
distributor (Atlanta Steel recommended for Atl area people). I decked it
with 11 ga diamond plate, the lightest commonly available in stock.
This stuff weighs 200 lbs a 4X8' sheet. To give you an idea of how
strong a trailer can be, I have a flatbed trailer I built from a mobile
home axle over 10 years ago. I once used it to haul an 8000 lb lead
radiation shield. First time those mobile home springs had ever flexed :-)
but the trailer didn't. I do all my welding with a DC arc welder and
7018 rods. I highly recommend MIG for this but I don't have one (sob!)
7018 is a low hydrogen rod which is very strong and welds well in
all directions but must be baked to remove any trapped moisture prior
In terms of design, I roll my own, just using the basics of good
chassis design - triangulation and gusseting at the stress points.
In terms of balance, the rule of thumb is that about 10% of the load
weight should be on the tongue. That is, for a 3000 lb trailer, put
about 300 lbs on the tongue. How to do that, you say? I do it
the old fashioned way - by hand. I fabricate the frame of the
trailer, lay it on the floor with 1" steel dowels under each side and then
load the trailer with what I expect to haul. I then roll the frame back
and forth on the dowels until my bathroom scales show the right
amount of tongue weight. I mark that point on the frame and then place the
axle(s) under it. Works every time.
For a car trailer, you'll want brakes and tandem axles. Northern has
both. The tandem axle shackle kit costs $36.99 plus the above cost for each
of the springs. Brake kits cost about $99 per wheel.
For brakes you have two choices - electric or inertial surge. The electric
system requires the tow vehicle be equipped with a controller. A good
controller will set you back $100. The surge brake system uses a hydraulic
master cylinder mounted in the hitch such that the inertia of the trailer
actuates it. Hydraulic brakes on the axles do the braking. Both have
advantages and disadvantages. The electric brakes cost more and require
the tow vehicle be wired for the controller. But they allow you to
actuate them manually which is the only reliable way of quenching
severe sway. The surge brake system works with any tow vehicle, is self-
contained, is IMHO more reliable and does not need external power.
The hitch contains a breakaway trip that when actuated, fires a spring that
locks the trailer brakes. This too, requires no external power unlike
electric brakes which must have a breakaway switch and battery.
There seems to be some controversy about surge brakes. "Circle Track"
magazine did a series on towing awhile back in which they quoted some
official saying that surge brakes have been outlawed by the feds.
The problem is, I can't find anyone who agrees with this. I've called
Ga-DOT AND have stopped at a "chickencoop" to see what the actual
enforcement peckerheads look for and write tickets against. None of
them have heard of any ban. I'm installing surge brakes on my
BBQ serving trailer. I recommend anyone else doing this call their
state DOT and make sure there are no local rules against them.
The rules enforced here are that surge brakes may be used on any
trailer of 3500 lbs Gross weight and on boats to 10,000 lbs Gross.
A heavy full-sized stock car and trailer may bump up against this
limit. One thing you can do (and I'm doing on my trailer) is install
surge brakes on one axle and electrics on the other. That gives
me the reliable braking of the surge brake system plus the
unquestioned legality of electric brakes plus the ability to activate
them from the cab in the event I ever get into a sway situation.
Finally, a word about mobile home axles. These are wonderful creations.
Huge hubs, spindles, bearings and brakes. Gobs of load capacity. BUT.
The first problem is it must be cut down for trailer use. I cut my own
but I don't recommend that for anyone who doesn't have a TIG welder and
the ability to re-heat treat it. Will cost you about $50 to have it done.
The big potential problem is that I hear from a wide variety of sources
that these axles either have been or are about to be outlawed for other
uses. I took my flatbed trailer down to the Ga Hwy Patrol and had it
inspected and an approval sticker affixed and they had no problems.
I'd certainly check around before using one today. The other problem is
the wheels are real hard to get centered on the hub because of the way
they are clamped. It can be done but it is a pain in the ass.
Subject: Re: brake controller question
From: firstname.lastname@example.org (John De Armond)
Date: Wed, 18 May 94 04:19:34 GMT
email@example.com (Dave Schrader) writes:
>I just got an bumper hitch camper with electric brakes, and would
>appreciate some advice/do's/don'ts about how to adjust the brake
>controller etc. Is it desirable to have the trailer brakes do more or
>less of the braking than the tow vehicle etc.
From another post, "how long is that string, anyway?" :-)
In short, it depends.
First off, there are a bunch of controllers. The ones I know of include:
* Hydraulic actuated - taps into the vehicle brake system, applies
trailer brakes proportional to vehicle brakes.
* Static application - applies a fixed current to the trailer brakes
whenever the brake lights are on. Typically used where the need
for trailer brakes is marginal and/or the load seldom changes.
* Ramp controller - Triggered by the vehicle brakes, starts with a
gentle current, ramps up with time. I can't see the utility of
this but they are sold.
* Inertial - applies trailer brake proportional to the deceleration of
the vehicle. Typically measures the deceleration by means of a built-
in magnetic pendulum in proximity to a linear hall effect sensor.
Probably the best compromise between ease of installation and
effectiveness. Major problem is that it is thrown off by
inclines and by changes in attitude of the tow vehicle, such as
from charging air shocks or adding load.
* surge brake - tongue of the trailer containes a hydraulic master
cylinder which feeds hydraulic brake cylinders. The force
of the trailer pressing on the tongue actuates the brake and
tends to keep the force on the tongue constant, applying
whatever braking is required to do so.
I have the inertial type and another trailer with surge braking.
I like surge braking because it works with any vehicle and is very
simple and requires no outside power.
On the inertial controller, I adjust it so that the vehicle feels about
the same when braking without the trailer as with it. I'm not sure if
that's the "standard" way but that's what I like. At the minimum,
it should apply sufficient braking to dampen out any tendencies to
fishtail. It is also equally important to be able to maually apply
sufficient braking via the manual actuation control, to damp
any sway or fishtailing that may start while underway.
John De Armond, WD4OQC, Marietta, GA firstname.lastname@example.org
Performance Engineering Magazine. Email to me published at my sole discretion
You know your country is dying when you have to make a distinction between
what is moral and ethical and what is legal.