Jag rear radius rod mounting point question

[Ted Brown]

Ted, what mode of failure are you anticipating with my set-up?

Hi Lee, Please do not take me wrong, I love your ride, I just do not want to see you hurt it at a very unfortunate/embarrassing time, like I have seen other's do... The extra width of the complete assembly with the wide tires presents a huge amount of leverage to that whole "close mounted" center section that is trying to hold/keep the tires from driving forward, one side or the other, which ever gets a hold of the ground the hardest... and then breaks either the center plate mount off the frame, or the bolts that hold the third member, then all hell breaks loose... Drive safe

 

[GAB]

So what is the stock coil strength and what did you use in yours? I have been thinking of taking the coils to a spring shop to see if they can lighten them up, but I do not know what weight they need to be!

Here is what I posted on the NTBA tech pages on determining spring rate:

Here is a method of checking spring rates yourself. You just need a bathroom scale, a scale (ruler), a couple of pieces of bar stock, and the biggie, an H-Frame press. If you have the rest of it, it probably wouldn't be too hard to find someone to let you use their press for a few minutes. I don't know that the bottom plate is entirely necessary. On these old scales, it seemed that the platen wanted to deflect in the center more than I liked so I put the piece on there. The bar on the top serves as a place to apply pressure and also as a pointer for reading the scale. Assemble the items as shown and use the adjuster to zero the scale. Bring the ram down until it just touches the bar on the top and the scale has not began to register. Read the scale for a dimension and then apply force to the spring with the ram. If the spring is light enough, you can travel it a full inch and get a direct reading. In other words, when you stop the ram at an even one inch of travel, the scale will read directly what the spring rate is. If it says 187, then you have a 187 lbs. per inch spring rate. What you have to watch out for is when the spring rate exceeds the scales capacity. That is what is shown in the photo. That is a spring off of a Harley and in the photo the reading is just about 147 lbs. What I had to do here is just travel the ram 1/2" since the scale is only a 250 lb. capacity. If I had of gone the full inch, I would have broke the scale. Since spring rates are lineal, it follows that the spring rate for this spring is 294 lbs. per inch. (2 x 147)

 

[Lee_in_KC]

Hi Lee, Please do not take me wrong, I love your ride, I just do not want to see you hurt it at a very unfortunate/embarrassing time...

No worries, Ted. I appreciate your concern and respect your experience. I'll be sure to check my set-up regularly for signs of stress. I don't get on it very often, so hopefully I'm not pushing the limits of this particular design.

 

[Keeper]

okay an update and some questions. I finally mounted the rear spring perches, I do not know why but I was nervous about mounting them. Its done and I took Ted's advise from a while ago about mounting the tops of the springs closer together to soften the stock ride. The CCR plans call for 27.5 inches center to center, I mounted mine at 25.5 I will see how this works, and can always change it later.

Now to my questions. I have two options in my head for attaching the rear radius rods to the cross member.

Option 1 - this would involve me making a plate that attaches to the bottom of the trans mount and it would hold the attachment points. This is the hardest of the two, but gives me a more level radius rod.

and

Option 2: - this involves making a small bracket to hang from the cross member itself. Much easier as all I need to do is cut and drill some square tube

and

So which would be better? Both have plenty of clearance to the frame. One easy, one a little more involved. hmmmm

 

[Ted Brown]

The leverage can be super great at the radius rod mounting points, I would weld mounts to the cross member (at the correct pivot point, same as the inner lower rear end bars) as the trans mount is bolted in and not that much good for that kind of leverage, made to hold the trans up mostly...

 

[fluidfloyd]

Now to my questions. I have two options in my head for attaching the rear radius rods to the cross member.

Keeper....

Either way will be fine. There will be very little leverage or torque reaction on thse radius arms. All the axle torque will be through the center diff case and chassis mounting points. Very little reaction at the wheels/hub assembly. Radius arms in an IRS see thrust loads from acceleration. They just drive the car forward. Even brake reaction is taken through the center diff on cars with inboard brakes. This is not to be taken as a don't mount if correctly. Put everything in double shear and tie it into your trans mount with good welds and gussets if needed. Hope this will be helpful to you.

Good luck and have fun!

George

 

[Keeper]

Thanks for the input. I was leaning toward the lower one, but the more I looked at it, the less I trusted it.

Upper mount welded to the cross member it is.

 

[Old Rotor Flap]

George,

Regarding your drawing "Wishbone and Mounts", what is the bent sheet metal plate closest to item 20? I don't see that it does anything we're interested in, I'm just curious.

By the way, I just read the note where you had drawn your setup on a board with pen and ink....... Before CAD. I'm impressed.

 

[leg show T]

The rear radius rods or traction bars, as I call them, are just that. I'm having a hard time understanding?! We have a professional chassi builder who gives away free


advice. The longer the traction arm the better. THINK ABOUT IT, IT'S LEVERAGE! The plate can be welded to the bottom of the frame going as far forward as to meet with the front

rods, in my case, 4 - bar suspension. Anyway, for what it's worth, I would listen to the guy who built chassis for a living. Although, I like hearing what

everyone has to say. And 13 is unlucky! Black cat thing. @bobnunes

 

[Old Rotor Flap]

Admittedly, I haven't thought this through..... so, I was thinking - something I can do occasionally that doesn't require much physical output.

Do you remember the rear wish bone design on early Fords? The wish bone incorporated two mounting points at the rear axle, one fore and one aft of the axle housing and then the rubber mounted ball at the front of the torque tube. The two point solid mounting at the axle housing on either side cured any notions of twist as those 85 HP flatties lit the candles coming off the line.

So... would it be worthy of consideration to adapt that design to the radius rods of the Jag lower control arm to resist twisting? I could envision rubber or urethane mounts rather than solid mounts at the control arm. There is a boss on the aft side of that arm that would have to be drilled and tapped for such a mount and of course the radius rods would have a connection between the two mounts sweeping under the control arm tube.

 

[fluidfloyd]

Admittedly, I haven't thought this through..... so, I was thinking - something I can do occasionally that doesn't require much physical output.

Do you remember the rear wish bone design on early Fords? The wish bone incorporated two mounting points at the rear axle, one fore and one aft of the axle housing and then the rubber mounted ball at the front of the torque tube. The two point solid mounting at the axle housing on either side cured any notions of twist as those 85 HP flatties lit the candles coming off the line.

So... would it be worthy of consideration to adapt that design to the radius rods of the Jag lower control arm to resist twisting? I could envision rubber or urethane mounts rather than solid mounts at the control arm. There is a boss on the aft side of that arm that would have to be drilled and tapped for such a mount and of course the radius rods would have a connection between the two mounts sweeping under the control arm tube.

Old Rotor Flap,

The Ford design was in fact a long traction device that counter acted axle torque. Now you being a Rotor Head I'm sure you have experienced the same effects through tail rotor torque. Opposite reactions! In a 60 HP Ford of the day the axle torque was nil. Henry joined the two arms to a single piviot point so the chassis could lean in turns, bad roads and such without binding and twisting the frame rails. In todays power range the actions and reactions are the same but the numbers are a bit higher. In a conventional axle housing design (Ford 9", 12 bolt etc) driveline torque is fed into the pinion gear of the differential and turns the ring gears and axle shafts. The tires drive forward and the housing tries to rotate the opposite direction with an equal amount of housing/axle torque. The more power the more pinion or housing rotation. That's where long radius rods, traction/ladder bars, 4 links, 3 links, torque arms and leaf springs come into play. They all resist torque. Depending on the choice, their length and design, the car can be made to do pretty much anything you want. In the old days of drag racing the guys jacked up the nose to transfer weight and ran short latter bars or leaf springs with slapper bars on relative narrow tires. Today they run highly adjustable 4 links with about 52-53% weight on the front end. But now back to the IRS problem. The differential case sees all the axle torque. As there are no axle tubes there is nothing to rotate or load the chassis. The diff case puts all the torque into the mounting brackes and the chassis become a long torque arm or ladder bar. As the tires rotate forward they deliver forward thrust thought the radius arms and helps drive the car forward. The Jag design is designed to piviot at the front arm bushing on an intersecting point with a line drawn through both lower in board control arm pivots. This forms an imaginary triangle causing the outer wheel assembly to swing upwards along these three points. Look at GAB (George Barnes) drawings and you will see how this works. The C2 & C4 Corvettes use a straight forward mounted trailing arm that locates the outter wheel assembly. It to delivers all driveline/axle torque through the diff case. With high horsepower engines it is hard to make IRS designs work well in drag raing applications. It can be done but it's tough. I hope this clarifies my earlier post and I hope it doesn't cloud the discussion even further. One just needs to really look at the OEM layout and copy that geometry.

Onew other thing, I to am an old Rotor Head. We called them Hueys.

George

 

[Old Rotor Flap]

Howdy George (Fliudfloyd)

Those Hueys with 1350 HP (look at the 412's) - the heavy haulers are very intimidating. However, nothing telegraphs the arrival of a Huey more than the whopity-whop or "Bell Shuffle" of a Huey. Congrats for surviving the ground fire. I had a pal who was shot down six times with no serious injuries among any of the crews . All that noise is what happens with two very long and large chorded blades at relatively low RPM.

I loved the Loaches - the OH-6's. I really like the MD 500F with the 450 HP Allison 250 series vs. the old 318 Hp jobs. They're very amble, quick and responsive. Sure, a tad under-armed back then, but a very sexy design. Freshie back seaters would bump their heads on the trans drive shaft housing. Hey boy! that's why you have a bucket (helmet)!

While Gerry (UK)* might cringe, I'll draw up - one of these days - my idea of Jag radius in SolidWorks and look at the FEA to see if i'm even on the right page.

In the meantime, I need to spend more time on my project and less time speckulating about abstracts.


*Gerry buddy, I am hooked on CAD/CAM ...... It's SBE...... So Bloody Easy..... LOL

 

[Keeper]

*Gerry buddy, I am hooked on CAD/CAM ...... It's SBE...... So Bloody Easy..... LOL

(Off topic) For those that are interested I have been hosting files for some folks on the HAMB, mostly CAD and solidworks files, There is a small block chevy, a blown hemi, banjo rear, and some others.

http://netquickposse.org/hamb/

They are all in there and anyone is welcome to them.

(On topic)

I should have the mounts sorted out this weekend. I will post a photo spread once everything is attached.

 

[Ted Brown]

Just a short note; if the third member (AND SPRINGS) was mounted in rubber like stock, now you would use a heavy duty set of radius rods, the look of your choice, and they mount on the frame as a normal straight axle rear would be mounted, except the mounting point at the Jag, would be the same place as stock (in the stock rubber bushing)... so simple it is crazy...

 

[Keeper]

Just to clarify any confusion. Here is where things sit for mounting. I used the CCR plans for the spring and center mounts, with the help of Ron (youngster) making the mounting plate and the tabs for the inner mounts.

Inner mounts:

Spring perches:

Center Mount:

 

[Keeper]

Okay as it so often seems to do, things change. I was considering going with an upper mount, but I decided to give the lower ones a shot, as this way if I change to the uppers, I do not need to buy/bend more tube, I can just shorten the ones I have.

Anyway here is what I came up with, it still needs a bit of polish and clean up but it should do the trick. I was thinking that the bolt on might not be able to handle it, but then I realized I have 4, 5/8 grade 8 bolts holding this thing on. Don't think its going anywhere.

With this version I built a 1/4 plate and welded it to the bottom of the existing mount. I am thinking I might just make a new longer 3/8 plate mount and remake the mount as this one looks a bit chunky.

The pics.

So what do you all think?