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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering> rack on a tube axle
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Topic Review (Newest First)
09-14-2007 05:47 PM
LiftFlat I saw the mention of unsprung weight, but I don't think 10 lbs is going to affect much...I've heard that "unsprung" weight shuold be multipplied by 4, etc, but I've never noticed a difference in ride quality from running Aluminum skinnies to the track for racing or wide steel/mags for racing on I-beam axles...besides, I'm betting his tube axles weighs a lot less than the I-beam he had...even with a rack on it? If not, it's neglibale IMO.

I also think he's fine with a greasable slip joint, as long and it's not "sealed tight", so air and grease have a place to escae under pressure...heck, my Peterbuilt has a similar thing (although it's spline with seals on the end) and my slip joint moves an easy 1.5 inches in daily use.

Just my thoughts.
09-14-2007 05:24 PM
ajbcc2
rack on a tube axle

i am concerned about safety too.. i think that the rack was designed to pull on steering arms and take the vibration from them...with my setup the whole unit will move and there would be less shock at the inner tie rod ends.(because the whole unit moves with the axle and not the center section tied to the frame) True the whole unit will be moving but it will be cushioned somewhat by the tires and the suspension too.. if I thought that I was putting this equipment out of its range of operation then I would can it for sure...I saw at the summer nationals in worcester,ma a few yrs back, a coupe with this same setup and the owner claimed no problems.. as far as ugly..I think it is actually a cleaner look than a vega or mustang box hanging off of the frame..but then to each his own...a panhard may still be needed as the axle will still try to rock sideways on the shackles(side pressure while cornering),though not from the steering pulling or pushing on it...but if a sway bar is mounted then that may hold it some too aside from sway control.
the grease compression(brg removal works because it is confined in an area with no room to trave)l...with the extraction of the shaft the 1/2 inch this would not allow the shock transfer..still i would think that a thin coating might be better than the origional idea of filling and inserting...as retracting a shaft from filled tube wont allow air to enter down the shaft to the bottom...thanks for the thoughts on that
09-14-2007 12:18 PM
Youngster
re: rack on a tube axle

If you go with this setup, use lithium grease and don't forget to drill the vent hole or the air in the tube will just push the grease out. I am still concerned about the safety issue. Why wouldn't you run a Vega steering box? This might just be one of those times when it is better and safer to follow the crowd.

Youngster
09-14-2007 10:49 AM
Chopt 48 There is a guy who runs a rack hanging off the back of the axle on a sky high jacked up 37/39 Chev Coupe here in the Pacific North West. I used to see him at rod trots all the time. I didn't like the looks of it because it looks like a big scab hanging on the axle. I don't know what he ran for a steering column but he did drive the car for years with that setup and may still be running it.

Personally I don't like the looks of it (too cluttered) I am not sure how the rack takes the vibration of riding on the axle instead of the frame and some of the steering column setups to make it work may be suspect as far as safety goes. If it was a good idea to hang a rack on an axle some major rod suspension mfg would have had a kit out long ago.



Advantages may be that you wouldn't have to run a panhard rod and you may solve a clearance problem with that huge engine filling normal usable spaces for a conventional steering box.

If you can stand people pointing it out and questioning your wisdom for hanging it on the axle head on because it will for sure strike up a lot of conversations at rod trots.
09-13-2007 07:31 PM
ajbcc2
rack on a tube axle

yes..when i said fille the tube with grease..i was thinking that the shaft would displace it causing complete coverage.then with the withdrawal of it the 1/2 inch would allow air to be compressed as it worked in and out..this "air" secton would not allow the grease to transfer shock up the shaft..at least that was the theory.. all things considered it may be just the ticket to just coat the shaft then slide it into the tubing....less chance of the "grease shock transfer"..
09-12-2007 07:44 PM
Youngster
re: rack on a tube axle

I think I understand what you are doing. If you are just using the grease to lube the D shaft, that's one thing, but if you want to use the tube it siding into as a reservoir, that's another thing. Have you ever heard about using grease to remove a crankshaft pilot bearing? First you put grease in the bearing and then using a shaft the same size as the hole in the bearing, hit it with a hammer and the bearing pops right out. The reason this works is because the grease is not compressible. I'm thinking you would find the same thing happening here. If you are just lubing the shaft and the tube, then drill a small hole in the tube to vent the trapped air, otherwise you'll end up pushing the grease out when the shaft compress'.Hope this helps.

Youngster
09-12-2007 06:35 PM
ajbcc2
rack on a tube axle

well with the double d shaft retracted there would be a gap so a solid material transfer i dont beleive would be a problem. In fact i would think that the grease being a very pliable substance would have a dampning effect. Any up and down travel of the joint would be absorbed by the next universal joint further down the steering shaft. i dont see how movement would transfer up to the wheel as you say..explain? The whole point of the grease was to minimize any wear that may take place between the two mating parts. I suppose for insurance, i could put an inline vibration minimizer coupling.
As the suspension works, the steering shaft wiil lengthen and retract a tiny amount hence the slip joint. There might be a slight bump steer effect as one side of the axle goes up with the spring mount being a pivot point ,the joint will be moving in an arc which would have a slight turning effect on the shaft. I think it would be small.
I understand the added weight thing but i cant see adding the weight of the relatively light rack any difference than say going from a small tire on a mag wheel to a slightly larger one on a steely.even if it (the rack)were more by a few pounds it would still be minimum. The car wont have sportscar handling..they didnt when they were new...the straight axle is an old outdated setup which has its limits...(which is why that mustang frontend is so popular ,it fits and improves handling and ride) as long as it is safe for normal driving i will be happy...
i plan on a panhard or maybe a torsion/sway bar in front and /or back. ...and mounting the rack to the frame would induce ,(i beleive) more bump steer potential due to the pivot/arc geometry differences.
09-12-2007 05:29 PM
Youngster
re: rack on a tube axle

I just reread your posting. You might want to rethink filling the tube with grease. The grease in the tube would be non-compressible. Any movement would go through the whole assembly right up to the steering wheel. Even with out the grease, with nothing but air in the tube, there is still going to be a lot of movement and stress on your brackets. I hate to say this, but about the only thing I can think of would be to use a flexible shaft like those used on the Pinto's. With a torquey big block, that could be real trouble too.

I'm sorry, I don't mean to rain on your parade. I just want to present another point of view.

Youngster
09-12-2007 05:09 PM
Youngster
re: rack on a tube axle

Deuce is right ...unsprung weight is something that should be minimized as much as possible. It really has a negative effect on handling. Any handling issues get worse when you add more weight before the spring. Just curious, what was your reason for not mounting the rack on the frame? Are you going to run a panhard bar?

Youngster
09-11-2007 08:06 PM
Deuce If it suites YOU ... OK

But the added weight of the rack on the axle ... adds unsprung weight ... something most rodders try to avoid ...

Deuce
09-11-2007 07:49 PM
ajbcc2
rack on a tube axle

On my 34 ford coupe frame with a 69 Lincoln 460, a Dodge omni manual rack was fitted and placed so that the ends were a straight shot at the steering arm ends. the slip joint was easily made by welding double D tubing to the shaft exiting the universal on the rack. Then a double D shaft will slip into the tubing and be overlapped by about 5". this tubing and shaft was used from a set up that had the plastic injected into the tubing to creat a collapsable shaft in case of an accident. What i did was removed the plastic so that the tubing would slide. the tubing will be filled with grease then the shaft inserted all the way in then withdrawn about 1/2"(to compensate for any suspension travel and length change. Brackets were made from 3/16 sheet with (under the main mount) a 3/8" pc cut to fit inside the bracket welded solidly to the axle to prevent any side to side flex. Then it was drilled and tapped for 3/8 bolts. Front veiw pic shows a relatively clean look with this setup and the 2" dropped stock crossmember...any additional unsprung weight will be, i beleive negligible...ps new boots and ends are on order

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