I really should have made everything into a single build thread a couple of years ago when I started this, but I didn't see it going this long or having this much to say (or, this much to worry about).

For those keeping up so far, I am converting the suspension on a 1989 XJS V12 coupe to something more modern, which basically involved the use of Bilstein and KYB strut components and custom wheels and tires (along with changing out the transmission and shifter, but that's another story). We settled on 17x8 custom-built CCW wheels and Firestone Firehawk Indy 500 tires in 235/50-17. If this sounds familiar, it is a carbon copy of Bernard Embden's setup on his car. I also copied the offsets he used. The only difference was I used CCW as my wheel manufacturer and he used Ronal.

First, we ran into serious snags with the actual wheels, but CCW has made an effort to fix that (issues with the valve stems). I just got the last one repaired today, and we fit it to the car this afternoon to check clearances.

And all hell broke loose.

Either the tire store mis-marked the tire we tried to fit (a rear tire), or my car is going to have serious clearance issues with the tire. The wheels do not come close to fitting inside the lip of the rear wheel wells. When the car is sitting still, this isn't an issue, as the tires are below the level of the lip. But if you have someone push down on the rear bumper (mimicking a heavy load in the trunk), the body of the car will touch the tire. And when I say it's not close, I don't mean we're rubbing a centimeter here or there, I mean we've got half a tread block (there are three main blocks on a Firehawk Indy) impacting the wheel well on the outside at full load.

The one thing that has to happen here is, we have to use these wheels and tires. I've got too much invested in them right now to have them remade at my cost (about $4,000 just for the wheels). The second issue is we don't know whether we're impacting because the wheels are that far out of spec, or if the springs are just too tired to hold the car up. If that's the case, then I have another problem: The only place I can find springs for this car are from JagBits, and I've dug up 2-3 threads already talking about how their cars sat too low in the rear after using those springs, which is a problem I absolutely cannot afford to have at the moment.

I managed to find four rear ride height shims and purchase them, but they're not on the car yet and I'm not sure by themselves they're going to fix the problem. I would like a stiffer rear spring anyway (and will be forced into it if we can't keep the body of the car off the wheels), but I don't know where to find one.

Presuming the wheels didn't get switched at the tire store and I was trying to put a front on the rear, I'm going to need springs and/or recommendations on how to lift the front a bit. Most of the threads on this are from 2015 and back, so can anyone provide some more modern advice?

Jess

 

If all else fails why not put a half inch of steel between your suspension mounts and weld it in for a 'body lift' ? Or try https://simplyperformance.com/what-are-we-breaking. Or Jaguar Upgrades, Servicing - XjRestorations to see about custom sized shims or longer springs etc?

You say your changing the suspension so...not sure how much of that would still be OEM but the guys there can probably find you something.

 

Why are you concerned about having mixed up the front and rear wheels? Do your front and rear wheels have different offsets?

I've got 17-inch wheels on my car with 235/45 R17 tyres (smaller diameter than stock) and they fit fine. I couldn't tell you what the wheel offset is. Maybe I could find it written somewhere if I took a wheel off.

 

Yes, the fronts and rears have different offsets. It's only an 8mm difference but here's what I was trying to copy: Rim and Tire upgrade Decision

Further, here's Ben's car (scroll down again) on the ground with sort of the same clearance issues I was having, except he notes that the swingarm suspension allows the wheels to get up inside the fenders. I'm hopeful that mine will do the same while driving but I'm not optimistic after seeing the initial fit. More importantly, I do a lot of travel in my car and load the trunk when I do, and I fear a heavy load will push the body down onto the tire as was happening tonight: Installing 17 Rims and Tires

Jess

 

One of the workarounds is to source a lift kit from a 4x4 supplier and do just that. I'm hoping to avoid this but if I must do it, I will do it.

I've looked into XJ Restorations' offerings before; with new shocks/struts all the way around and a new poly bushing kit just installed, the only part of that kit I need are the springs. I'd love to run Eibachs but they're marked as a lowering spring and I definitely don't need to drop it any lower than it already is. I'd like to find something at factory ride height in the rear, but stiffer.

Jess

 

It may be too stiff, but you might look at the shocks and springs for the Daimler DS420. It's about 2,000lbs heavier than an XJS, so would be a stiffer spring. No idea if its taller.

 

Jacking up the ride height will ruin the cornering ability of the chassis. It sounds more like the offset is incorrect on the new wheels, or the tyres are just too big - whatever spec is printed on their sidewalls. Fixing the actual cause of the problem is the only safe way to go, just treating the symptoms by arbitrary add-ons is not a good plan.

 

Get the right wheels. You simply need an 8 or 9 inch wide wheel witjh a 35 to 45 mm offset. All this talk about jacking up the rear of the car will make the car look goofy and make it handle loose and more prone to a spin. If you need a more clearance at the fender lip...then the lip can be rolled. 3/8's is typical. The tool is about 75$ on Amazon.

 

Hmm. Custom ordered springs ($$$$) or Bolt / snap-on stiffeners maybe? I've considered them but havn't bothered to measure the coils and find the right part yet. I also went full poly on my car like the XJ kit except...lower front bushings? I think those need to be OEM which is what my Jag mechanic and the forum said, all poly but be warned it will begin to tear the radius arms out over time, and then you'll have to do some welding.

 

Great Idea.

 

Lol. Can't imagine what Sir William Lyons would say about that abomination.

 

What is confusing to me is this setup worked for another user. Same offsets, same tire sizes. Thanks for the lead on the fender roller, though.

We're going to get new springs (and use the factory shock shims I found from Everyday XJ) and hope that fixes the problem. Right now dropping another $4,000 on wheels is not an option I can consider. I would doubt four tires from a reputable label like Firestone are mis-sized.

Jess

 

I found an ad for those on the SNG Barratt site. They are identical to what SNG Barratt is offering for the XJS of the same age, part number is identical. They are the Eibachs, meaning they will actually lower the car 25mm.

I wonder if that's what JagBits also offers.

Jess

 

I just bought a set rear springs from Welsh Enterprises.

https://www.welshent.com/Jaguar-Rear...-4-P27303.aspx

I will be installing them this weekend and will report back.

 

I installed one side this evening. The car now rides about 1/2 inch higher than the side with the old springs. The old springs seems fairly worn — when pressing down on the rear end the car would wallow quite a bit — so your results may vary.

 

I think those are the part numbers for the convertible, which from reading other posts are a softer overall rate than the coupe components. The coupe part number starts with a "3" and they're about 2x-3x as expensive as those.

I ordered the set from JagBits today as they're advertising the same manufacturer as the OEM units for the coupe. Eibachs would be preferable to me personally but I'm skittish of the advertised ride height drop from them. Eibach used to make a kit for my other car of choice (Chrysler Conquest/Mitsubishi Starion) and while Eibach-equipped StarQuests handled very well, those cars REALLY sat low and rode roughly.

I would kill to have the company ST (Suspension Techniques) make springs and Tokico to make Blue-series shocks/struts for this car. I'd never buy anything else.

Jess

 

Interesting. In the Jaguar parts book the numbers for the limo are unique to it. Shocks are C29163 and springs are C29164.

 

The reality of springs is that Jaguar no longer have data or records of the original sizes and spring rates for any of the springs used on the XJS! I had this confirmed to me by Jaguar Heritage. Furthermore, over the years springs were rationalised and minor differences in spring rates and lengths were ignored and one type used where originally there had been differences.
There is one specialist company in the UK who have got details of the original spring rates and part numbers; but even they have identical part numbers listed for (eg) Jaguar XJS V12 HE front springs and certain saloon models. i got a set of fronts made by them to my own ride-height (ie spring length) spec, and they are absolutely superb, and all things considered not at all unreasonably priced.
My own view is that the best thing to do, unless you want the full XJ Restorations spring/shocker kit - which for many is too hard for proper "Jaguarness" - is to buy springs from Berkshire Jaguar in the UK and use adjustable rate shocks. For the rears the same, but use adjustable rate and adjustable platform shocks.
That way the ride height and stiffness can be easily tuned to the exact likes of the driver.