IFS Same Between XJ6 and XJ12

Hi Everyone,

Question…Some time back I bought a 71 XJ6 that is missing engine and tranny with the thought of putting in a V12 with manual tranny, is the IFS assembly the same between the 6 and 12 cars? I have a line on a possible V12 and I’m wondering if I should grab the IFS if it hasn’t already been parted out.

Jeff H.

I’d assume the same except for heavier springs due to the extra weight of the 12 vs the 6

I think the rotors on the 73 v12 were vented.

Heavier ARB as well.

This is a long story, so please bear with me. My S1 V12 suffered an accident, and believing the the front beam to be damaged, I replaced it with one from an S1 XJ6, swapping the front hubs and road springs. After a wheel alignment, the car used to “saw” at the steering when rounding sweeping corners and chopped out the inner treads of the tyres in quick ( 200 miles) order. I never actually resolved the issue, but I think there may be a difference with the lower wishbones to accomodate the difference in width of the vented discs, given the front track is the same between both cars. I’ve never compared part numbers , but someone here probably has access to that information. The upper wishbones were the same so something had to be changed to keep the geometry the same.

1 Like

Further info, if you intend swapping out the entire unit, a road spring change should be all that is required.

1 Like

Thanks everyone for chiming in with information. Much thanks. Interested though that no one mentioned the engine mounts? Are they the same for the 6 and 12?

Jeff H

Can’t see why they wouldn’t be the same but if the ifs you have is the early version with the non vented discs, three pot brakes and thinner stub axles try to get the V12 on the ifs and with the stronger springs and rollbar.
Kevins car sounds like it should have had more toe out regardless of specs? But the 12 is only 60 kilos heavier than the 6 is it not.
Very early XJs apparently did have a narrower spot in the engine bay but I don’t know where exactly, maybe the air filter area and I believe it can still fit in.

If you are talking the Metalastic ones, I think they are. If ones on engine block, different.

It certainly felt like an alignment problem, but it was done by a reputable firm, so I assumed it was a geometry conflict with components.

If the firm could get the settings to specs, Kevin - nothing in the suspension components could be seriously wrong…

…and with correct settings; the car should not behave like you describe. One question; did the check the rear suspension geometry as well? A general suspect would be play in some joinery, which the firm should also detect - and utter some reluctance on performing adjustments…

xj6 85 Sov Europe (UK/NZ)

Professional shops make mistakes too - last time I had a car aligned the steering wheel pointed to half past ten and I‘m almost sure the toe was out a little. But what I‘m thinking is that the toe was off even though it was to spec.

My Mercedes has had some bump steer, pulled in towards full lock and wore the outside of the tyres, one and a quarter turns per side and it feels a lot better now so a little goes a long way.

Car was behaving fine prior to swapping out beam. Had been in a front end smack, and after repair, looked like it was down on one side so I swapped it out and had the alignment done. Life got in the way and I never drove the car again. Sold it about 17 years later.

No experience directly on point.


  1. The alignment was poorly done.
  2. Added weight of the v12 caused excess camber. Matches excessive wear on inner tread.
    ! more likely Fast tread wear, odd steering…


When my 83 XJ wuzza six was still DOHC powered, it had a low front stance. I kind liked it.
The Lt1 that replaced the 6 was a lot lighter. the nose arose!!! I forget the ride height measure.
But, the car’s nose arose a bit. Now, right on spec!!! OK here, looks great.

I don’t think so, as car tracked perfectly in a straight line, alignment by eye looked ok and I used the V12 road springs, so weight would not have been an issue. The only bits I used that were 6 not 12 were the beam and lower wishbones, all other bits were swapped over from the 12. The definitive way to tell would be to compare part numbers for the lower wishbones; I’ve never been able to find them. Thorley states" Also the lower wishbones were altered to compensate for the effective offset of the ventilated front disc. It is therefore not possible to fit a ventilated front disc assembly to a standard XJ6 upright"

Yes, I think that’s right. But the lower control arms (wishbones; C27761), I think, are the same for S1 XJ6 and XJ12 (and maybe some S2 XJ6). These are the same part left or right. Sometime in late S2 or start of S3 production they changed to separate left and right lower wishbones so as to offset the ball joint to allow more caster. But I think the later and earlier wishbones can be swapped. But the late uprights are different–provision for vented rotors (different than the early V12 and S3 E-type) and beefier wheel bearings. IMHO from foggy memory; Doug Dwyer is the expert.

My C class ran straight at any speed but the slight bump steer and funny steering (heavier and pulling in instead of straightening at full lock) gave it away. That is probably owed to the peculiar suspension geometry but it did track straight and the steering wheel was perfect. As if the 4 new arms were all a hair longer (that’s what must have happened. Tie rods are old).

Anyways something like that can be dialed out with some patience; at least I think it can be. The later A arms are different, I heard that too. Probably worth getting the V12 parts if possible.

Well and good, Kevin, but later 6s had ventilated discs as well - so ‘standard’ is somewhat misleading…?

However, geometry is geometry, and if the shop got the alignment right; the slight difference in wishbone lengths would be immaterial to car behavior…

xj6 85 Sov Europe (UK/NZ)

IIRC it would be the other way around, the upper arms are shorter than the lower ones and this would result in more negative camber as the suspension lifts.
It would also alter toe, giving more toe-out.

True Frank. Unfortunately I don’t understand suspension geometry well enough to know what effect these changes would have. The comment about the uprights is irrelevant to the wishbone issue anyway, I think, as it probably refers to the stub axle needing to be longer to accomodate the thicker front hub. All I can assume is that if the V12 lower wishbone is shorter than the 6 to compensate for the vented disc and keep the track the same, and the upper wishbones are the same, as I believe they are, then there would need to be some change to the location of the lower balljoint taper to keep the static camber within spec. If the upper wihbones were shimmed out to get the static camber correct, would the camber and\or caster be affected on lock? Can’t see why it would, but as I say, I don’t really understand this in detail. Both beams were S1, so comment about S2s doesn’t really apply. So, is the S1 6 upright the same as the S1 12 upright apart from a different stub axle? S2 is different with regard to caliper mounts ( 4 pot vs 3 pot calipers)