Setting up an IRS Question

maz duh i am not shure if you have started building yet but in my opinion have the axle length the same on both sides is more important then mounting the pinion flange on center. i actually cant think of any reason to do that other that looks and it will limit your suspension travel on the short side.

--------------------------------------------- Originally posted by BioMax  I suggest mounting the thirdmember so that the center of the CV is at aproximately half the overall height of your wheel/tire. That will help keep balljoint bind to a minimum. ---------------------------------------------maybe im just having a dumb moment here,  but when mounting it are u suggesting to mount it so the shafts are level at ride height? or  install the center pod  while its laid out  on the chasis table ensuring that the cvs and not binding?  maybe this is a dumb? but im just trying to wrap my head around this as well,

The center of the CV joint at the thirdmember should measure (to the ground) half of the wheel/tire height when the truck is at half travel. This also means that the axles will be parallel to the ground at half travel.

Edited: 3/15/2009 2:49:43 PM by lyinlow

Edited: 3/15/2009 2:48:58 PM by lyinlowthanks max!! i have some more ?s for you im just curious in the attached pic its a mrk VIII irs subframe flipped upside down im tying to determine how im going to make my lower mounts, as you can see here they have two different pitch's so i guess im wondering when i make my own would i be best off to make the lower control arms the longer one? (set the mounting inward  or would you suggest i make the lower mounts to the larger pitch? (making the lower amrs shorter also when you guys do your irs do you make a way to adjust toe? or do you set it up on the frame table and leave it what it is? just not sure if you use a adjustable rod end on one of the mounts? if so im curious as how you setup the other mount to accomodate the adjustability? hope this kinda makes sense...... Trevor

what you are dealing with is ford introducing caster into the suspension as it articulates...this was a question i posed to max about a year ago when i was doin my IRS and i was told for a mini it isnt necessary and a lil overkill......as for the toe adjustment i didnt do any in mine....i made sure everything was squared and that the mounting wurface was parallel to the frame itself and all is cool.

awesome so did you just pick a lower measurement for the space between the mounts (as i have marked in the pic) and make both  equal....also i noticed your setup and your using a markVIII rear as well.. crazy... i had envisioned the same ways  of making a arms as you have.. on your setup on the lower arms just curious why you have the tabs on the lower control arms angled up towards the spindle instead of just having them straight? one more thing did you keep the same width lower arm or narrow them a bit?

I would always suggest designeing some sort of alignment adjustment into your design. As for A-arm lengths, you should make a paper doll of your intended design and find the length that works best for your wants.

Thanks Max.. ill definately have to think this over and figure a way to also get toe adjustment in the setup.. you have any suggestion on how this would be acieved and the one mounting point of the lower arm would have to be non adjustable and the other would.. problem im seeing is when you were to adjust the one, the non adjustable would bind up.. only solution im thinking is to use a heim joint on them.   Trevor

I don't know what the knuckles looks like. I couldn't say.

when i setup my lower arm length i used the same idea as a front suspension in that UCA, LCA, and tie rod pivots are all in a line......for the rear i replaced the tie rod pivot with the CV pivot......as for width i lopped about 8-10 inches off the overall width....as for adjustment i have no clue how i would go about adding it now....without rebuilding the lowers....which has crossed my mind.....as for teh angle of the tabs it was purely to make the lower arm level with the CV since my inboard mount is a lil lower than the knuckle mounts...also it gives me a lil more room for the bag in there