Adding a rear spacer
This shows how to make and add a 1/2" spacer to the rear leaf pack which is a good technic if you are levelling the car front to rear without altering the spring rate or adding a half inch lift all round like me. Can be used to compensate for heavy bumpers or springs that have sagged a little.
I used high density plastic but you can use steel, old cut down leaf springs maybe even a plastic chopping board. Cut to a width of 64 mm or 2 1/2" and a length of 120 mm or 4 3/4". It is then just a matter of drilling a 8 mm or 5/16" hole in the middle of the packer for the centre bolt. The easiest way to find the centre is draw a line to opposite corners to form a cross and where the lines intersect is the middle.
Start by jacking up the car once you have chocked the front wheels and place stands under the towbar if fitted or under the frame as shown. Next place a couple of bottle jacks under the axle without using blocks if possible so you can then lower the axle as low as possible when the wheels are removed. Be careful as the axle will pull forward and can fall of the jacks. Remove the wheels and then the 'U' bolts and lower the axle making sure that all the tension is out of the springs and you have enough room to put vice-grips on the centre bolt head under the spring. You may have to remove the shocks from the axle stud if they prevent you from doing this.
Make sure that you place clamps over the springs as shown before removing the centre bolt otherwise they could suddenly fly apart when the bolt is removed. It is a good idea to let the bolt rotate a few times while un-doing the nut to free it up before using vice grips on the bottom bolt to stop it from turning while removing the nut.
Check the new centre bolt head that it is not too thick and bottoms on the axle in the middle of the spring perch with some of the head still exposed. I was alright as have a two degree shim which the head passes through to keep the angles the same after lowering the transfer case. Cut the head to half it's thickness if it doesn't sit all the way in otherwise when you replace the springs you wont be able to sit the leaves on the spring perch because it will be resting on the bolt head.
Insert the centre bolt through the spacer and then into the leaf pack. Then spin the nut down holding the bottom of the bolt with vice-grips and then tighten the nut. Cut off the excess and then tighten to 20 ft-lbs for the 5/16" or 32 ft-lbs for the 3/8" bolt if you have a torque wrench.
Do the other side and add the shims at this stage with the thin side forward if you have a setup the same as mine with a transfer case drop as well. It will also give you a little more slip yoke insertion. If you have extended shackles then you would face it the other way to bring the pinion down instead of up.
Then jack up the axle to just under the centre bolt with slight tension and then pull the axle back with the jack until the it falls into place. Replace the 'U' bolts making sure you have enough thread ( torque to: 28-32 ft-lbs for 3/8", 30-35 ft-lbs for 7/16" ). Keep the nuts even making sure that the U bolts come through the same length. Use a cross hatch pattern to keep it even left to right and front the rear. Put the shocks back on and the wheels and remove the jacks.
I didn't think that it would be very noticeable just going from 4" to 4 1/2" but even my wife picked it straight away. With the 1" transfer case drop ( make your own here ) and the two degree shim I have no vibes at all. After 100 miles make sure you re-torque the 'U' bolts because they will settle and loosen.
If you measure from the wheel centre to the bottom of the flare you will see how much you gained. Stock is 17 1/2" inches at the front and 17" at the rear. If you have removed your flares you can then measure from the flat round bumpstop area inside at the bottom of the coil spring up to the top of the spring isolator, where it meets the bottom of spring tower at the front. Front stock is 11 1/4" this way. For the rear you can measure from the top of the axle to the bottom of the frame rail, right above the bump stop. Stock is 6 1/4" for the D35 and 6" for the 8.25 and D44.