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I'm starting to gather all the pieces to complete my front and rear subframe out refresh and I am planning on replacing every wear component in the suspension while I'm in there. With that, I recently watched Harry's Garage video on his newly restored series 2 coupe and have begun looking into how to make my XJ handle a little bit better. Adding a sway bar from an XJR would help, but I began digging into if there were any other suspension options beyond Bilstein B6s.
As it turns out, the same company (Simply Performance) that provided Harry's series 2 suspension kit offers an X300 kit with new uprated springs and adjustable dampers. That being said, obviously standard X300 front springs can't handle the weight of the V12. However, I spoke with Ben at Simply Performance and when developing the X300 fast road kit, they gathered data on XJ12 front spring rates and would be able to produce springs for an X305 specific fast road kit.
With that, would anyone be interested in a Fast Road suspension kit for your XJ12s? To be clear these kits don't appear to affect the ride quality too negatively (my primary concern here) and spring packers could be utilized to maintain the stock ride height.
Here's the link to Simply Performance's website for you to take a gander. I would link the eBay listing to the kit, but it seems like any post with an ad gets immediately deleted....
Also, here's the link to Harry's video immediately after he installed the suspension but before the full resto:
I met the simply peformance guys in the UK at the retropower event at Stoneleigh before the pandemic. They are great and particularly good for manual box conversions. I am doing a xj coupe gradually, and king springs from Australia seem to be the way to go to get the nose down. Like Harry I like them very original looking but I don't think he strengthened the very flimsy shell enough while they were doing bodywork.
Anyway x300 - I've used all the street powerflex products on my front end rebuild and will probably use their stuff for the rear end when I do it. They gave me 10% off when I ordered all the front end parts. The front x305 swaybar is 25mm so I don't think you'd gain much with an XJR one but I may be wrong there, not sure about the rear one . The x300 springs seem ok to me - the oil line and lower radiator hose are already perilously low for a 100mph + tourer imo wouldn't want it any lower.
(I've zip tied my oil line up high away from road debris)
Haven't really considered the rear rebuild yet but assuming Bilsteins and the powerflex bushings will suffice.I'm going for silky smooth very fast rather than harsher autocross feel though....the rear springs seem pretty good on mine...
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(That's the lower radiator hose version with heater which I'm using as a coolant drain point in second picture)
// Adding to this post - once i'm driving my car with poly bushings I'll report back on how much 'sport' stiffness needs to be added - I've heard they are much snoother without a knackered undercarriage
Last edited by olivermarks; 06-29-2022 at 06:47 PM.
You do remember that the Powerflex front lower A-arm bushings don't fit any of the XJ40 or X300 cars, right? Their bushing diameter is about 8mm too small. I explained that to them but we thought it was because my car has the newer A-arms. Truth is all these front A-arms have the same diameter hole.
Apparently I was the first guy to ever buy those because they had no knowledge of the problem. Or maybe a new production batch got screwed up. Anyhow, they gave me a half-refund for one front lower bushing, and I am in the market for some that fit without the need for a press.
Just adding when I degreased and painted the 25mm front sway bar on mine it had wrecking yard green pen markings on it, so maybe the PO swapped out a weaker OEM swaybar?
Just to clarify, I meant to say REAR sway bar! Front sways (As far as my manuals have told me) are identical. XJ6s, XJ8s, and XJ12s, did not receive a rear bar in the US market. XJRs on the other hand did. Retrofitting that alone should help with alot of the body roll I was referencing.
I'd like to hear the report back on the powerflex bushings! I have experience with them in Volvo P2s and got ALOT of extra vibration and harshness. I'm doing them again in my XC70 build here soon, but thats lowered on coilovers with the thickest available sways so it suits the character of the car. NVH is priority #1 in my XJ12 "recommissioning" so I was just going to buy a slew of brand new OEM bushings for when I drop the front and rear sub frames. If they don't too negatively affect the refinement of the car, I'd strongly consider getting them as the Jaguar stuff is quite pricy for how quickly it tends to wear out.
Number one in this diagram, understood. I've been looking but haven't found one yet. I haven't started on my rear, will report back on driving with the new front end hopefully next week, have to put all the cooling stuff back in place above the shock mounts etc and make sure it doesn't leak first, fresh power steering fluid etc
There's a 98 xjr in a local wrecking yard I'll be visiting next week. It looks like the X308 rear sway bar car will work on our x305s if it was fitted and is still there? Anyone raided one of these x308 xjr's for these parts?
What else should I grab - I'm assuming the 2 stabilizer bar drop links and the modified wishbone tie as well as the sway bar?
I need some trim pieces as well ...assuming it hasn't been picked clean
Useful tech details about Lee Evernden's XJR6 mods including a lot of suspension info.
Question - do I need to get the triangulated rear brace bar off the x305 I am visiting in the wrecking yard next week, and if so any handy tips on how to do that in the dirt? They look like the same part as on the x305's so do I already have that? The Ultra Racing AR20-293 rear ARB mentioned below looks like a good rear stabilizer option with the custom rose joint drop links also mentioned
06-28-2022, 04:47 PM
Gauging Interest: Fast Road Suspension
Powerflex
