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Old December 19th, 2007, 10:49 AM   #1
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Location: Santa Rosa, Ca.
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Default Split Tube Axle How To
Re:: The way to use a tube axle with split wishbones or hairpins   

I thought I'd try to do a little How to article on the split tube axle that I built for the FLAT 4RD project. Wish me luck here goes.

Independent Tube Axle

When the first person removed the stock four cylinder or flathead V8, engine and transmission, from his early Ford to replace it with something a little more powerful, he found that it became necessary to split the wishbones on the front end to clear the more modern transmission. The early ford front end was a marvelous design due to its triangular geometry. The single pivot point of the wishbone, enabled the front axle to move unimpeded. The first hot rodders found that it was necessary to split the wishbone and remount the ends at the frame rails so that the often much larger transmissions could be mounted between the frame rails. When they did this they had inadvertently created a problem that would continue to haunt hot rodders for years to come. When the wishbones are remounted in this way, they become part of an anti-roll bar or stabilizer bar with the axle itself becoming the torsion bar. The early I beam axles would perform fairly well as a torsion bar because they would flex with few problems but this design would put a lot of additional stress on mounting points and the frame rails themselves. When these guys started to use the much stronger 36 Ford tube axle they found that the problems became even greater. Then when the reproduction tube axles started to appear on the scene it became apparent that something had to be done to eliminate these problems. Eventually someone came up with the four bar design which allowed the front axle complete mobility with a rigid tube front axle.
Recently, there has been a renewed interest in old style hot rods that are built as closely to the originals as possible and the builders are finding that some of the old time problems have also returned. Whether we use an original split wishbone or manufactured hairpins there is a definite compromise when it comes to trouble free use and, the ride quality, is diminished significantly, over a four bar front-end.
There have been many attempts to deal with this problem such as a twin “I” beam axle like Ford uses on their pickup trucks but that design adds additional weight and creates a few undesirable geometry traits in itself. I will attempt to show you the way I’ve addressed this problem while working on my latest creation. It is not an old school project but I refer to it as a new old school rod. I’ve tried to keep as much of the classic hot rod touches and overall appearance as possible but have brought the whole thing into today’s world incorporating 4 wheel disc brakes, muti-link independent rear suspension, and all of the other safety features that are in the rest of the cars that I build.
I used a tube axle that I purchased from Speedway Motors because of the design of the axle. The center section of the axle is perfectly straight apposed to the gentle curve of the super bell and other after market axles. This allows me to cut the axle in half and machine an axle and bushing setup that will let the tube axle twist with out creating a bind at the frame rails.
First I machined shoulder bushings from bronze that will be pressed into the axle halves 3 ˝” on each side. I have also machined an axle made from 1” solid stainless steel shaft material. The ends of the stainless shaft have been turned down and threaded to 5/8” fine threads. I have also machined Stainless washers to act as a thrust washer between the bronze bushings and at the ends of the stepped axle between the bushings and the nylock nuts that hold the complete assembly together. When the nuts are tightened, there is only .0005” clearance in the whole bushing pack to insure a very tight fit. The bushings were then pressed into the tube axle ends and held in place with four 3/8” flathead screws in each bushing. It was also necessary to install a grease Zerk in each bushing so that lubrication can be maintained.
After reassembly of the front axle it was installed on the chassis and as you can see it has the unimpeded movement of a rock crawler with only the tell-tale signs of the bronze shoulder bushing at the center.
With this design, the front-end still has the un-sprung weight of a tube axle to deal with, which doesn’t ride as smoothly as an independent suspension, at least it does not allow the transfer of an uneven road surface transmitted to frame rails and ultimately to the seat of your pants.

Here is the axle cut in half in preparation for the bearing

The bushings are made from Bearing bronze on the lathe.

The bearing halves are secured to the axle with 5/16" N.F. flat head machine screws.

All of the parts are machined and ready to assemble. The inner axle is made from 1" diameter stainless steel. the ends are turned down and threaded to 5/8" N.F. threads. Heavy thrust washers are also made from stainless steel.

Here is the inner bearing assembly assembled.

And another picture with the bearing assembly installed in the axle.

Another view ready to bolt up to the hair pins.

This shows just how much flexibility the front end has now that the axle can twist.

Try that with your beam axle.
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