View Full Version : Another new guy from Texas - front axle

12-04-2007, 05:08 PM
Hi ya'll ! My name is Randy and I am new to the forum. I live just outside of Houston. I am seriously looking at a 27 kit from Spirit. They seem like really nice people and I like the look and contents of their kits. I have a question. Is everyone running a tube front axle ? From the info I have read all these kits use hairpins/radius rods with tube axles. All the "hot rod" builders(Posies,etc.) say that this is a no-no. They say that tube axles are ok with a 4-link set-up. If you are using hairpins (single point attached to the frame) then you must use an I-beam axle. They say that the I-beam will flex and the tube type doesn't. The problem is that if the tube axle doesn't flex then it may eventually break the hairpin/radius rod or rip it out of the frame. Has anyone had any problems ? Any suggestions ? Help !

12-04-2007, 05:40 PM
This is the first I have ever heard of anything like this. I have built several buckets and never had a problem. Maybe its the way Posies mounts there radius rod mounts?

Oh and welcome to the forum and you won't be sorry you bought a kit from Spirit.

12-04-2007, 06:40 PM
I've not heard about the tube axle problem but I have heard it said that you should not weld a spring behind bracket to an I beam axle. That may be true but I have never heard of a problem because of it.

12-04-2007, 10:34 PM
All I know is that thousands of cars have used the tube axle for a crap load of years. I think it's more of a personal preference. If there is a difference in ride or handling, it can't be that much. Bottomline is that either way, it's a design that is almost a hundred years old. These cars will never ride like a Lexus.

12-05-2007, 05:58 PM
the tube axle mounted with radius rods is stiffer and kinda works like a sway bar for the car.
the i-beam does flex more and twist with the suspension, built for the roads of the '20s

12-07-2007, 05:16 PM
Because the radius rods only mount with one point on the frame the axle and radius rods in effect act like a sway bar. If you raise up on one side of the radius rod the other side radius rod has to raise also.
When you have a four bar it has two mounting points so it can raise and lower on one side without effecting the other side.
Thats the reason Ford ran the radius rods for the front and the rear to the center of the car ,so it would just pivot. Hot Rodders needed to lower the cars and keep clearence for oil pans ect.
If you are pulling in a parking lot or going over some obstacle you put some strain on the other side radius rod. Will it break? Probably not, depending how strong the components are and how rough you drive it.
How heavy the car is will be a factor.
This same thing happens with the rear axle also.
In my opinion, you are not going to have any trouble with a radius rod and tube axle ,particularly if its a lite weight car.
But a four bar( link) will probably ride better ,and cost more.
best of luck.

bucket nut
12-07-2007, 08:20 PM
I agree with the last 2 posts. You won't have any problems.

12-08-2007, 09:54 PM
as has been said, it is in the twist. tube axles don't and i beams do. the real problem is actually, in the fact, the caster centerline of the king pin and axle rises in an arc as the axle goes up and down from the road surface. this causes the drag link to move forward and back and in turn, it jerks the wheel out of your hand. this is what is called bump steer. as i have built about 8 t's and alot of other axle cars, i can tell you, some will be bad and some won't. the four bar type will remove alot of the bump steer but not all. if they are to short for instance. i do know if the radius rod type locators are long enough to reach the center of the car for the front and back, they will have less bump steer also. four bar or radius rods i haven't ever seen either brake from this geometry, but i have seen brakes do to poor welding. choose either way and you won't have a problem. just my 2 cents, can i get some change?

01-10-2008, 12:02 PM
Thanks guys ! I just want to try to do it right the first time !

01-21-2008, 04:12 AM
From my understanding, a tube axle is much stronger that the I-Beam. Because the radius rods move in an arc, when the axle raised on one side and the other drops, the axle actually twists. Because the tube axle doesn't have the flex, this causes a twisting stress on the axle, rods and frame, usually the chassis simply picks up the wheel. A hairpin rod has more inherent flex in their design so are marginally better because at the point they start to bind, they will allow more movement (also dependant on design... braced ones will not flex as much so becomes a moot point. So ideally with a tube axle you'd use a 4-link setup to eliminate any twisting of the axle. You want to use a panhard bar if you are doing a cross steer setup to counter the left/right forces of the steering link.

Keep in mind, the more the suspension travel, the more all this comes into play, the less the travel, the less stress (twisting or binding) will occur with any of these...