TECH...well sorta... JAG IFS into mid fifties F100

4T6Ford,
You seem well versed. When looking (and measuring) the jag front (and referencing the above diagram), B is higher than A: 2" higher over 7.5" run. Calculations put this on an incline of approximately 15 degrees. F is also higher than E: 2 inches higher over a run of 11.5 inches - calculating out to approximately 13 degrees. From C to D also higher: 2 inches over approx. 12 inch run, calculating to 9.5 degrees. Please remember, these are approximations. Regardless, the instant center would never meet towards the center of the vehicle - in fact would only meet outboard of the spindle.

Am I looking at this right? It made perfect sense when I looked at that diagram for about 5 minutes until I started measuring. If this is right, then what I'd need to do is calculate rack height to allow the E/F line to intersect at the point where AB and CD intersect, correct?

 

The bottom spring plate is bolted on, so in essence you "could" space the plate. However, that opens another can of worms as it would effectively change the pre-load and spring rate...not certain how much, not a spring engineer!

We're really happy with using the rubber mounting on the '51 - no vibration, etc.

 

flamed34, I understand where you are coming from. My thoughts are this, the Chaps (they were english remeber !) at Jaguar would spent plenty developing that front end/geometry setup so I would be setting it up as per their settings. With your narrowed front end , as long as you have made no other changes (bar the narrowing) set the rack back at the stock hieght (this is pressuming you havn't taken a big lot out of the width?) and as long as you can still line up points B , F and D as shown in the diagram when you fit the narrowed rack you will be fine .

.

 

I've just read your post above again , The front end you are looking at/measuring is "unloaded" the diagram shows the suspension effectively "loaded" . If you were to remove the springs from your front end and sit it in the "loaded position" i.e. line up points C and D on a level plane you will find the other measurements will fall into place .




.

 

Shimming the spring plate will not change the rate or the preload (appreciably).

The only way to change the rate is to change either the dia of the wire, the number of active coils, the diameter of the coils, or the material the wire is made from.

When you cut a spring to reduce its height, you are stiffening the rate in the process.

The preload is determined by how much weight is on the spring, and that won't change by shimming the bottom plate.

What that changes is the relationship of the bottom of the spring to the lower ball joint in Z height. The motion ratio won't change appreciably, so the preload and wheel rate will remain constant, the lower ball joint will just be raised in relation to the spring bottom.

If you want to maintain the stock ride of the IFS (assuming the new vehicle is of similar weight and mass placement), this is how you should lower it (or buy new springs of the right length and the same rate).

Cutting coils to set the ride height is going to stiffen the spring rate and make the ride more harsh. It will also reduce the amount of bump compression available before coil bind.

 

So you're saying that shimming the lower spring plate will not effect the ride quality and cause any alignment and/or steering issues? I tried searching for theads on it and can't find anything. How far can you space it?

 

If I recall correctly, the washers are 1/8 " thick each and each washer removed lowers the suspension by 1/4". I had 4 on each side that I removed which dropped 1 inch at the suspension and just a little more at the bumper. I have not, but you can space the bottom spring plate down perhaps 1/2" which should lower the suspension another inch. I can't remember who had a picture of a rod that spaced down the lower plate. It was spaced down with tube spacers and longer bolts. If it was me, I would be more comfortable with machining a solid spacer. It may have been one of the Oz rodders.

 

Is your lower control arms sitting approx. horixontal when you look at them from the front, as at this point I assume they're not, with the standard springs basically forcing the front end to sit at its extreme up position (on its upper bump stop).

Step back and look at the big picture for a second, the great things about Jag front ends is their relative compact nature, ease of fitment/adaption, suspension geometry, quality brakes, cost effective, and well sized for adapting to vehicles most rodders/customisers play with.
Their reputation about offering good handling and ride comfort from the front end is justified, however, when you fit a front end from a Jag into a vehicle that has a different static load over the front end you need to adjust the spring rate to suit (ie either get some custom springs made to suit your vehicle, or experiment with other springs that are a similar size but with a reduced spring rate, as the Jag ones are heavy duty and basically way to stiff).

Until you find a spring to suit your equation, you can't expect a spring that suits a Jag to automatically suit your combination, as their spring rate is very high, hence it will sit high, and the ride quality will shake you to bits.

Anyhow here's a link, to a heap of other useful links with different fitments and details that I think you will find useful.

http://www.ozrodders.com/forum/viewtopic.php?f=2&t=23839

Cheers,

Drewfus

 

When I mocked it up in the picture above, the Jag crossmember is just loosely touching the frame in the rear. I put the bolts in from the top of the rubber mounts as seen in earlier pics. This spaced the rubber mount about 1/4" from the frame. I plan on having it sit flush against the frame rail so there is a tiny bit of drop to be had there. I'll reinforce the inside of the frame in that area. But with it sitting there in the picture above, the lower A arms are angled down and the upper is resting on the upper bump stops. This is why I am assuming a lot more drop as the suspension rests down to it's neutral position. Am I still wrong for thinking this?

 

Hi
I have spent the last couple of days working on front shock mounts and have something made up. 1/8 plate two pieces and gussets. Some more work and it is done mounted them to the cross member. just updated the blog so it is there. some day When the kids are home I will learn how to post pictures here, Sorry.
Thomas
1948fordpickup.blogspot.com

 

It will not change any of the ride qualities, because you're not changing the spring constants.

You will be altering the link angles though, so you'll need to check your alignment and camber curves to make sure you're not way out in left field.

But if you're not going down too much, that shouldn't be too big an issue.

As for how much you can shim, I have no idea.

The springs not changing is a physics thing, I don't need to know the exact dimensions of the Jag IFS to know what will happen there, the how far down can you space it is a Jag IFS specific thing, and I don't know enough about the parts specifically to give you a safe figure.

Gonna have to defer to someone with more intimate knowledge of the parts on that score.

Generally speaking, you are better off to use big plates with a hole through the center for the spring to pass through for the spacers than you are to build little standoffs.

The plates let the bolt stay in tension and shear only, which the little standoffs will turn shear loads into bending loads, and threaded fasteners really don't like being loaded in bending.

How far are you wanting to go down from where you are now?

If you can't get anyone with the info you need, take some good measurements on the spring mount and get the weight it's supporting, and I'll run the numbers for you.

 

The mounting of the front end looks like it will be easy as, so all good there, however, as per your above description, your suspension is effectively jacked all the way up due to the factory spring having a 'spring rate' higher than what you need. you can space the spring locator plate down, however, as previously mentioned, we expect that you will require a much softer spring to suit your situation.

Best option at the moment is to remove the springs, and set the front end with lower control arm to be about horizontal as this will effectively be it's 'neutral position'. Compare this with some of the front view photo's in the provided links as a comparison, in particular, compare the gap of that upper bumpstop with those in the threads.

doing this should show you the expected 'ride height' (assuming you mount it as described), and then you can measure the coil sizes, and the desired compressed length. If you make a temporary rigid spacer to maintain that height until you can either fit the engine/box in place, which will then allow you to measure the expected front end mass via a load cell. You can then forward this info to a spring manufacturer who will be able to make a custom spring for your fitment, or at least offer you some dimensions so that you can find an existing spring that will compliment your needs.

Cheers,

Drewfus

 

The International K3 weighed in from the factory at 3789lbs. I'm expecting it to be maybe a bit heavier when I'm done. The Jag is around 4000lbs. Is that really too far off for some 14-15 year old springs? I'm hoping I can get away with keeping the stock springs.

 

Yeah, that's close enough.

If anything, the truck will have a higher front weight percentage than the Jag did, so you should be OK.

 

Have you checked with any of the aftermarket racing spring manufactures, like AFCO? They might have something that is a drop in, so to speak.

 

Stock Jag springs ride fine....



and sit right...

.

 

Damn thats sweeeeet!

 

As I previously indicated I have been thinking that my springs, which came off an early series Jag were a bit on the soft side. Looking at earlier pix shortly after I installed the crossmember, the upper wishbone was hard against the upper bump stops. When I look today (2 years later) the gap at the upper bump stops is about 1 ". I have not driven the truck yet so the jury is still out. I am going to drive it before I do any spring changes. I know that Holmsey also thought that his original springs were too stiff and had softer custom springs made. IIRC he went back to the original springs on his 55 F100.
I have tried unsuccessfuly to research the different original spring rates.

 

I'm just not gonna worry about it for now. I have my frame level with 1 degree of rake in the back. Have the wheels centered in my fender wells and the position of the Jag crossmember marked on the frame. I just used a long level layed acroos the frame rails touching the upper arms. I will pull the grille and fenders back off so I can TRY to level and position the crossmember. I'm gonna post up some pics. Nobody has yet been able to exactly describe the proper way to level the crossmember. In other words, where do I place my level? I used the motor mount pads on the crossmember as they are nice and flat. But are they level relative to the suspension? I want to be sure I'm leveling the crossmember from the right spots.

As far as the springs go, I'm leaving them as is for now. No need to even worry about it when the truck is so far off. If I get the brackets made and the crossmember installed.... get the motor mounts, transmission mount made, and motor/trans mocked up.... front clip back on..... if the front suspension is still sitting on the bumpstops, then I will worry about it.

 

The above portion of my previous post explains the process. Place the level fore and aft in the center of your crossmember and on top of it.

 

I got my chassis sitting at ride height and rake.
Then levelled the crossmember bottom with a level.
I figured the engine mount plates were more than
likely laying back a degree or two from level.
That seemed to be the case with mine.

 

Here's where I'm at. I had some 1/4" steel plate, well the bumper that used to be mounted to the truck did, so I cut all the pieces out of that. Actually I had my buddy cut it up. Some stout 3/8" steel as well. At least I'm recycling the bumper back into the truck ; )



Still need to grind/shape it some more to get it how I like, but this is the basic idea.

 

The rear rubber mounts will bolt up to the center of the frame rails. I still need to decide on how I'm gonna come off the bottom of the plate to mount up to the front Jag Donut.
I'm tossing up the idea of just some tabs out of the 3/8" plate with a gusset between the two in the front/boxing the front of the tabs. It would simply be welded and fixed in place.
Or something like this that could be bolted to the bottom of the plate. Then I'd have the ability to shim the front and rear mounts to adjust the caster of the crossmember.

 

As far as I remember, the bottom flat surface of the Jag crossmember should be level at ride height. First you need to know the ride height - see below.

Get yourself a short spirit level. Check how far off level the imaginary line between the centre of the lower inner pivot pin and the centre of the lower ball joint is. I'd be guessing 4 to 5 inches. That number is how far down the suspension needs to come when the truck is finished. Ride height will also be affected by the size tyre you run, so you need to account for this before setting your caster.

When the truck is up to full finished weight you can have springs made to suit that will set it at this nominal ride height. Or you can cut the springs to suit. Your truck is heavy enough that I garantee the ride won't be harsh with cut springs.

 

Stock XJ6 ride height is 160mm from ground to underside of crossmember.
This is the loaded height so take that into account when fitting crossmember.

Cheers

Clive

 

I'm limited on tools and funds($).
Frame is sitting level with 1 degree of rake towards the rear.
Jag Xmember is level front to back, side to side and is snug against the rear mounts & frame rails. As the frame sits now, the running boards slightly rise towards the rear. This is how I want it. I plan on running 15 x 8 wheels in the front and 15 x 10 in the rear. Same height, just a bit wider tires in the rear. I plan on adjusting the rear height to keep the slight 1 degree rake. What am I missing here? Shouldn't that keep the same rake on the truck?
This is yet another reason I'm thinking of having the front mounts bolt on. They could easily be shortened or shimmed out to adjust. This way I can get the chassis rolling and keep going forward. When the truck is fully mocked up, sitting at ride height with new wheels and tires, I can then adjust the front and rear mounts on the Jag IFS to level it out. if this is crazy talk, feel free to tell me and explain why this is the wrong way to do this.

 

Your plan sounds pretty good.

If you want the suspension to work at its best, then the bottom of the crossmember should be 160mm off the ground when fully laden with the original Jag wheels and tyres. This is how its set up in a Jag. You wont be able to get this right until the car is nearly finished, SO until then you can just leave the wheels off the front and set it up on stands or blocks to get that 160mm ground clearance. When the front is set like that you can then adjust the back to get the rake that you want, and then bolt or weld your mounts to the chassis and it should all be sweet.
After that you just build the truck as you choose, but leave setting the ride height until last, because it will be affected by what you do or don't fit (weight wise). And its pretty easy to change springs anyway.

 

what you are doing all appears sound to me, make sure you use the slip in the lower steering shaft from the donor Jaguar . It is there to take up some of the movement created by having the sub frame on rubber mounts.


.

 

Got it. Just had it off out of the way. Thanks for the advice gentleman. I'm just gonna make some temporary hangers to bolt to the front. I can make new ones to fit proper when the truck is almost done being mocked up with all its bits and pieces in place.

 

i have some ?'s, now im using the stock jag shocks. when making the shock mounts, should i leave the suspension hang or sitting with atleast motor/trans weight? how far should the shock be depressed to figure out the top of my mount position? 1/4, 2/3 1/2 pushing down from the shock being extended out of its full stroke.