Subframe is OUT

Ok. Sounds Good.

This is actually quite fun, as I’ve never done such a big restore section at once. I’ve been taking lots of photos and notes and drawings as I disassemble, and marking things in boxes and baggies. Nice to take my time, currently cleaning, treating, and Por15 parts that connect to subframe. I probably won’t be ready to reassemble until March which is why my notes will be handy!

3 Likes

The bushings of choice are irrelevant. The lower control arms need to able to rotate freely as Aristides says. Even if we were to put tightening aside after being fully loaded. The control arms need to be able to rotate for the sake of reconnecting the hub assembly to the upper and lower control arms.
If you’ve ever desired having a fatter front sway bar now’s the time to upgrade. Likewise, this is probably the only time that you will ever have to install new subframe mounts.

Yes, I just realized how simple it would be to replace with subframe out, great idea. Is the 1" AddCo the only one available for our cars? Does it need/come with stronger end link post? Can rubber still be used on end link bushings?

Just checked my current sway bar, it is 7/8". So i dont really see the help going up to 1".

And yes, I bought OEM subframe mounts, all four. Also OEM engine mounts.

IIRC, the XJ6 has a thinner front bar, the one on the XJ-S and XJ12 is thicker, and the Addco is thicker yet. Not sure there are other options, but I would think the Addco is plenty for anything short of autocross.

My usual recommendation for anti-roll bars is to use either poly or rubber on the inner bushings depending on what I’m looking for in stiffness, and rubber on the end link bushings. If you use poly on the inners, you’ve gotta be careful what you lube them with. It needs to be a red grease, and you may need to re-lube them occasionally if driving through puddles or whatnot rinses the grease out. You’ll know if they start squeaking.

Stiffness of a torsional element is related to the thickness to the 4th power IIRC. That means a 1" is a lot stiffer than a 7/8". In fact, it’s probably so stiff that the compliance will be in the rubber bushings and the tires rather than in the anti-roll bar.

1 Like

There was another post just recently from a guy that wanted to locate a larger bar because Addco is suffering from the same supply chain issues as everyone else is. I think he mentioned something about late February, March, but who really know. At any rate I suggested he should try Andrew over at Jaguar Specialties and he indicated that Andrew had some in stock.

Not to mention that changing one end of the cars anti-roll bars isn’t an action that exists in a vacuum: you change that, and you change a whole host of other handling dynamics of the car, many of which are not desirable.

When I had my 4.0 subframe out I upgraded the bar to the one from my parts car (coupe), but I also added a the Jaguar rear bar as well. We’ll see how that goes once the car hits the ground.

The rule of thumb is that uprating the anti-roll bar on one end makes that end handle slightly worse and the other end handle a lot better.

“How it handles” is arguably more a function of personal preference rather than actual lap times. In fact, some have argued that lap times are optimized by taking those bars out to reduce the weight, and just drive accordingly. I hate the way the car feels like that, though. My own preference on the XJ-S was to leave the 7/8" front bar alone and to add the OEM rear bar which is an amazingly skinny thing, something like 9/16". It made a lot of difference, though, giving the car the right “balance” for me.

Then they are dead wrong: the subtraction of the weight of the ARBs wouldn’t amount to a tinker’s dam, wrt to performance.

You are correct, somewhat, that the addition/subtraction of any given element at one end of the car will demonstrably affect its performance in either a negative or positive manner.

I will find my article from Datsun Conpetition that sums up the issue of this in a very succinct and clear manner.

https://forums.jag-lovers.com/t/datsun-handling-article/406325?u=wiggles

Well, that certainly puts the onus squarely on the drivers ability to handle the car. It seems clear to me that Sunday drivers will have little use for this type of upgrade, which would also include any type of poly bushings, etc… That being said, it makes me believe that I am really going to enjoy every upgrade that I’ve implemented.

Not to belabor the point, but at the end of the day suspension upgrades are really only as good as the tires on the car. As the old cliche goes that’s where the rubber meets the road.

1 Like

WRT the ‘D’ bushes, when I acquired my S11 XJ6 the car had been fitted with red poly bushes of some sort. They came out resembling rubble, they had completely disintegrated.

I put the Addco bars front and rear on my 87, along with the Simply Performance Eibach springs and Gaz shocks. Used stock bushings on the lower front control arms, with polyurethane on the uppers. On the rear I used stock large bushings on the trailing arms in the XJRS orientation, and polyurethane on the rear of the trailing arms. Used polyurethane steering rack bushings. I set it up to XJRS alignment specs. Handles very well, far less body roll than stock, still a comfortable ride. I still need to slightly stiffen the shocks, maybe a click or two from full soft, but they don’t need much. I’m using a set of XK8 wheels with appropriate tires. Very pleased with the transformation.

As Kirby said, roll stiffness goes up by the 4th power of the diameter of a sway bar. That 1/8" is a dramatic change. That’s why some cars use hollow sway bars for weight savings as the material in the center of the bar contributes little to the roll stiffness.

1 Like

Absatootly!

It takes a high level of driver competency, and very defined practice on a given course to fully explore the handling envelope of any given car.

The indiscriminate tossing-on of any given suspension component on a street car is virtually always a complete guessing game, and often time doesn’t necessarily improve what the factory designed.

2 Likes

Welllllllll…not exactly.

Case: take almost any given older car: replace the “perfectly adequate” bias-ply tires with decent radials–and I’m comparing contemporaneous tires–and the handling will be likely improved. Adjust the suspension to the characteristics of any given tire, in the context of improving ultimate road holding can be done, but as in almost all such modifications, adjusting those parameters will almost always alter the “center of the envelope” handling.

Suspension design can, and does, affect how any given tire interacts with the road, in dynamic conditions.

1 Like

When I removed and replaced the rear subframe/ suspension cage from my E.type I did it on my own, not exactly the same job you face but a very similar procedure. I removed the crutch from my small trolley jack and replaced it with a 15" long piece of inch and a half thick plank which I bolted through the hole in the jack where the crutch should sit. The suspension cage was fastened to the plank using thick strong Zip ties. It made everything very stable and balanced and the whole job was much easier.

2 Likes

The hypothesis there is a car that understeers at 7/10 but is neutral at 10/10. That seems to me to be neither likely or common. In fact, just about the only way to get there would involve aerodynamics, would it not? Something that generates a lot of downforce at speed? Because in my experience any car that understeers at 7/10 understeers at 10/10.

Read more…

For example, assume that a car that understeers at .7G lateral acceleration and becomes neutral when 1.0G is reached. Also imagine that the gap between .7G and 1.0G can be bridged by some suitable driving techniques. A driver who is capable of pushing the car at no greater level than .7G might want to eliminate the .7G understeer, and in the process eliminates the car’s capability of generating the very desirable 1.0G neutral characteristic.

I can guarantee you, from personal experience, that “suitable driving techniques” do indeed exist to bridge that gap.

Good suggestions Casso. You have to get a bit creative to handle the front and back suspensions on your own - hence my post advising to remove and fit discs/hubs and calipers for the front assmebly while on the car. For the rear, I remove the spring units and replace with two pieces of timber of such a length so the whole unit sits flat on a board attached to the jack.
I can have the rear unit out and back in in a day with no help other than my wife to bleed the brakes.

Left spring is OUT. Boy, the four stud method takes FoReVeR. Slow and safe. I only had enough energy to remove upper control arm. See my two safety chains? I tied spring to lower control arm for piece of mind.
May take a day off.

PS i am renting Jag tool for reassembly.

3 Likes