Hey all,
I have finally gotten my 73 xj12 running with a blown small block chevy 383, (yeah, I know) and I am having a problem with the rear tires rubbing as I am running a 255/60/15 tire on the back. I was wondering my options to get the back of the car raised up some?

 

As for raising it up you can add a spacer to the IRS cage mounts but that will only get you so far. It doesnt help with drive shaft angle and oil pan clearance though. You could run stiffer springs and raise the rear suspension but that will through off your ideal geometry which is important when your upper control arm is also the drive shaft. That said... I don't think 255's will clear with stock sheet metal but I don't know for sure with 15 inch wheels.


For me...255/50/r17 would not clear stock sheet metal even with tucked in wheels. So out came the metal working tools. The wheel arch was raised 15/16's, flared and extended then blended in to the body so it appears OE. You cant tell from the pictures but the whole rear 1/4 panel has been "fattened" 1 inch. I like the subtle curvaceous look of the **** end even more now.


This is a 27 inch setup, OE is 26. The 255's were the largest size that ticked all the boxes for this build. I wanted to run 275's but the 255/50/r17 has the same contact patch as a 275/40/r18 because of the larger diameter.


The last pict shows the suspension compressed and at the bump stop.

If you do get the rear to hook you will have to contend with IRS cage roll next and that's a whole 'nother discussion.

 

8XJ ,be aware that the XJ rear suspension was NEVER designed for hard acceleration,it was/is for smooth,quiet ride!

i have experienced ,them actually being ripped out from under the car,all cattywumpas, cocked sideways, time to call the tow truck and haul backwards!

any one serious about racing has done a complete change to a custom rear suspension setup, 1st one i seen was by Group44, at the Daytona 24hrs races, back around 1978-1982.
must have worked ,they won some Trans-Am races also, against some bad *** Corvettes and mustangs.

 

Would it be possible to use a universal type air shock, like the ones I have on my nova? just keep two of the stock shocks and replace two with air shocks... I am mainly looking to get the back up a couple inches.

 

[QUOTE=Blownv8XJ;1186759]Would it be possible to use a universal type air shock, like the ones I have on my nova? just keep two of the stock shocks and replace two with air shocks... I am mainly looking to get the back up a couple inches.[/QUO


knowing what I know...nova air shocks or a jacked up rear end wouldn't get it done. It's bad for weight transfer , think gassers with their squat rears and high fronts. Also geometry will be compromised as previously mentioned. You'd be solving one problem and creating 2 others.

What you can do is run 235's. I ran 235's on a previous incarnation of my car and remotely located the battery to the trunk for weight transfer. You will need to trim and pry out the rear wheel arches a bit for clearance but it all can be done with some wood and a angle grinder with a 40 grit flap disc. For me a set of 235's did ok but 1st gear was useless with a 406, 700r4 and 3:54 rear ratio. If you'd be running a trans with a taller 1st gear and taller rear ratio and a cam that's a little soggy on the bottom end then you'd be fine with 235's.

 

I moved the engine back as far as possible... have 383 with 470# torque and use 200R trans and 2:88 gear (since mine is a fun daily driver) and the stock sized tires are fine. It is true that if you get the big tires to "stick" you will probably rip out the IRS. All rubber mounted for a nice riding car... see all the post from others about this subject. There is a good site for the Mustang folks that used the Jag IRS.. but they solid mounted things. You can make it work and it is strong...

It is too tall in the front as I have not removed the spring packing parts yet... the front is several hundred pounds lighter than with the Jag stuff... all
aluminum parts where possible.

The car will attempt to lift the front wheels and then plant the rears well and the burn out is very short... and we are off...

 

Raise rear suspension with coil overs not air. Realign rear each time raised or lowered. There is a reason why Jag used 4 shocks for over 30 yrs.