I guess I haven't been around here lately.  

No time tonight, but yes I've been working on this, check some of my past threads around here and I'll try to comment more tomorrow sometime. 

John.

Double-cardan joints I think have rotational-speed limits, so do your calculations on what the driveshaft RPM will be at the max speed you want to be able to run.

Many cars these days use Rzeppa-type ball-and-cage CV joints in the driveshafts, BMWs typically have one at the rear for instance, the '08 GT500 shaft I've got in the shop has one BMW-type non-plunging CV at the rear and a big Porsche-axle-type plunging CV in the middle.

303Radar wrote:

Frankenford, you might want to double check your rear end ratio.  Mine has a tag for 3.31 gears but the input turns three and a half time before the hubs have a complete revolution.  After I opened the diff cover, I saw the ratio on the ring gear was 3.54:1.  Also, Kugel Komponents http://www.kugelkomponents.com/ used to make/sell high density poly urethane bushings to replace the bearings on the control arms.  There might be some other companies as well.  Just letting you know you have options.

Why does anyone want to take out the bearings on the control arms?  They're a much more positive locating element than any sort of bushing would be, and that's a horrible, horrible place for polyurethane in any case.    There's a whole lot of applications for which the aftermarket sells urethane bits for which they're not at all suited - anything involving rotational motion, in particular.

I'm thinking, though, since I've got access to the CNC mill now, that I might as well go ahead and make a better mold for my urethane '64 Galaxie body mounts and maybe start selling 'em if I can figure out a proper way to vacuum degas them while they're curing, the set I made for my car had a 50% scrappage rate 'cause my de-gassing wasn't very good.

elgemcdlf wrote:

I have a Limited Slip carrier out of an Explorer which I understand are 31 spline axles. The MN12 is  28 spline. Does anyone know where I can get 28 spline spiders for the Limited Slip diff for the MN12?

Let me see if I understand what you're trying to do. 

You want to dismantle the Explorer limited-slip and swap the spider gears so you can run 28-spline inner drivers with it?

Hrmm.    I would have suggested just finding a 28-spline diff.    What year Exploder is that diff from?

28-spline Trac-loks are not hard to come by (I've got one sitting on the shelf, though I'm more or less hanging on to it for future use, now that my 31-spline Cobra axles showed up I won't be using it in the '64 wagon).

And if you're spending new money you can have an 8.8 Truetrac in 28 or 31-spline form for $400-ish.

tyrellracing wrote:

The U-Pull it' Auto wrecking yards  here in Oregon are loaded with all kinds of IRS equipped cars. From Toyota Supra's,to Datsun Z's as well as  BMW;s of all types Ford T-bird's and Mustangs to name a few.

I chose to use the MN12 'Bird setup in my '64 Country Sedan largely because (a) it was the right width  (b) it was Ford and (c) the Thunderbird underbody and subframe mounting arrangement appeared to be fairly compatible with the old Galaxie frame. 

The downsides being that the subframe is bulky enough to push the gas tank out of its original location, it required a little surgery to get the front mounting legs where I needed them on the Galaxie frame rails (this was a case of six weeks to figure out what needed to be done and a day to do it...) and Ford being Ford a lot of parts are no longer available new from Ford. Fortunately, there's only a few things on the assembly that seem to wear particularly quickly, so I'm just making sure I collect three good used examples of everything for my spares inventory...

The only Mustangs that ever got IRS were the '98-04 Cobras, and mostly those get parted  before ever hitting the junkyards; going rate for a complete '03-04 Cobra IRS is around $1000.

A little junkyard snoopery hints that the '90s Toyota designs - including the MkIV Supra, but more commonly the Lexus GS and LS, which are dirt-common in the pick-n-pulls here now - are a straightforward but modern design, the total package is reasonably compact and mounting doesn't appear to be too troublesome.  If I were going to do something else I might look at one of those.

The E38 and E39 BMWs ('95-01 7-series/97-03 5-series) are starting to show up in the cheap yards now, and while their rear suspension is a very good design it's also designed for an underbody shape not typically found in old Detroit iron.   

The  E21/E30 3-series, E12/E28/E34 5-series and E32 7-series all use various flavors of semi-trailing arm rear suspension, which

Ralphy wrote:

Just came across this info from the Factory Five FAQ.

http://www.ffcars.com/FAQ/irs.html

That came in handy today, as I'm sorting out what to do for axle shafts in the '64 and started dismantling a '91 'Bird manual transmission "fat shaft" to see if I can figure out how it was made. 

I've got one pair of '94 Lincoln shafts, one pair of '89 'Bird SC automatic shafts, and the aforementioned asymmetrical shaft.   All have the 28-spline inner drivers.

I can put together the old 'Bird 28-spline Trac-Lok and run some combination of the existing shafts, it'd really be too weak for the engine but it'd at least get the thing drivable that way.   Or I can bite the bullet and spend some money, get the 31-spline Truetrac and a set of '03 Cobra axles, which should be just about strong enough for most everything I plan to do with the car.   And if I did hit wheel hop with that combination (possible, but less likely with the automatic) then I could play with the asymmetrical shaft arrangement.

Progress!!!!

The modified MN12 IRS is hung on the frame now, it's bolted up under the car, and it's been sitting on its wheels.    A little bit of proof:



Modified MN12 subframe bolted up to '64 Country Sedan frame.  Front mounts and rear crossmember tacked in place.  Subframe bolted up using aluminum solid mounts I'd had made for setup purposes; when it's done I'll go back to the original steel-hat-with-rubber-insert mounts.   The crossmember had to be very thin vertically because the body floorpan hangs down between the frame rails at this point, the ends are a downward-pointing C-section that saddles over the mount bushings.   Fairly shallow (3/4in vertical ribs on the front/rear) but thick material (cut from 3x6x.250 steel) and ribbed on the underside around the mount bushings.  Maybe overkill, but...

The 8.8 pumpkin in this assembly is a scrap Mark VIII aluminum housing - the local pick-n-pull most often drains rear axles by punching a hole in 'em, and this one they managed not only to puncture the rear cover (about which I didn't care) but bugger one of the bearing caps in the process.   'Sokay, when it all goes together I'll be using the iron Thunderbird SC case anyway.

The pumpkin has an '02 Explorer rear cover (infintely more solid than the stock beercan-gauge early 8.8 rear cover) but the wings on the Explorer cover are too wide for a decent-sized isolator to clear the side rails of the subframe.  So the rest of the mount consists of a piece of C-channel bolted to the Explorer cover wings, and a pair of E38/E39 BMW rear diff mount bushings pressed into a fabricated steel mount assembly that bolts to the subframe.   We'll see how it all works out.

The '02 Explorer rearend assembly is an 8.8 and much beefier overall than the earlier units but very different in shape and critical dimensions; the axle shafts, side bearings, etc. are all different and it would not have been easy to a

On the early XJ rear the trailing arms are there to take acceleration/brake torque loads off the cage mounts (they can't handle it) and to 'steer' the cage and induce roll understeer.

The later design gets rid of them entirely, the new mount design is much more solid and spreads the loads further and roll understeer is a function of the revised pivot angles of the lower arms.

The later design also removes the vehicle weight from the cage and its mounts, it has a single long coilover assembly that mounts directly in the upper fender structure - something typical of modern IRS designs e.g. BMW.

Pastorpat wrote:

I did some measuring and the with of the front spring perches is 40 inches.  Each perch is 3 inches wide.  The subframe rail mounts on the inside of the front spring perches, then it gets wider until it reaches the rear of the carn.  The front of the Mark VIII mounts are 41 inches wide so i dont think that will be to hard to make weld up brackets for.   The Gas tank does seem to be the issue.   I will need to cut down the mark viii cage.  More details to come and some photos.

My biggest concern there is that while the front subframe legs are the proper distance apart, they slope downward to get there; in order to readily mount the stock pads under the Mustang spring hangers you won't be able to get the axle and suspension tucked up enough under the car.

I may be wrong, but I'm guessing that to get the whole thing far enough up under the car you'll have to cut off at least the front mounting legs and fabricate new ones out of 2.5in x .125 steel tubing to extend down and under the frame rails.

Just a guess.

Pastorpat wrote:

My son and I are looking to place a 1996 mark viii IRS in a 1971 mustang.  Wondering if anyone has seen it done.

Not in a Mustang.

I'm putting one in a '64 Galaxie (actually Country Sedan wagon) and I've known folks who have put them in F-100s as you've noted.

The MN12 'Bird/FN10 Mark rear suspension is pretty wide.  If I remember correctly your stock axle is 60.25 over the flanges.  My wagon's rearend was an inch wider than that, and I still had to have my rear wheels made with an extra inch of offset to accommodate the rear.    You might get away with it.  I think - have not tried it - the subframe could be narrowed maybe 2in in the center, where the diff mounts.   

The MN12 subframe is quite bulky and heavy (80lb or so for the bare subframe - the early SC subframes have more reinforcement inside, Marks and other 'Birds did not get this.)   Mine is not a bolt-in; I put pie-shaped cuts in the front legs of the subframe to narrow them 2in, lower them 2in, and move them back 1/2in which more or less centers the mount bushings on the frame rail just behind the point at which the rails kick up to go over the axle - I'm fabricating weld-on mounts for the frame rails at that point.  The rears barely fit between the frame rails; I'm fabricating a new welded-in crossmember to pick those up.  I'll also have to deal with the gas tank, which won't fit in the stock location due to the subframe and sway-bar location.

The '98-03 Cobra IRS might be a closer fit, it should be just about exactly the right width, the tubular subframe is less bulky, and the mounts would be easier to adapt.  They're more expensive on the used market but I think they're all 3.55s and Trac-Lok whereas only the SC 'Birds got 3.27 Trac-Lok gears and all the Marks were crappy 3.07 open diffs.

Pics a little later, have to run right now.

The real impact of rear roll-oversteer is what it does to the steering, and any significant amount of rear roll-oversteer is going to make the car twitchy.

Ralphy wrote:

The lower forward link adds some roll steer.

I don't see anything from the picture that would indicate that.

Ralphy wrote:

Lincoln Mark VIII Bagged IRS

That appears to use the Thunderbird/Mark VIII uprights (so does the Factory Five rear and the Hurricane one pictured) and diff pumpkin but all the rest is fabricated.    Maybe they borrowed some of the geometry but, given the layout of that upper arm, I'm betting it's not too similar.

So I got a new battery for the Sawzall and was back at the pick-n-pull for half-price day, and the Capri I was there to scrounge some Cortina parts from had been sent to the crusher.

Bah.

So I went off in search of the '77 XJS I'd seen the last time I'd been out there, to try an experiment.

Someone had already been wrenching on one side, the exhaust was gone on that side and one of the cage mounts had been unbolted.

Attempt to unbolt driveshaft, bolts too tight for my poor selection of box wrenches, note it's a one-piece shaft (it was an SBC conversion, not sure if the one-piece shaft is normal on an XJS) and decide to see if I can wrestle the thing off the slip-yoke once the cage is down - 3 min.

Pull the retainer and vertical bolt out of the front of the trailing arms - 1 min per side.
Arms won't come off (naturally) so sawzall the cone off the floorpan - 2 min per side. 
Sawzall the remaining exhaust behind the cage - 2 min.
Unbolt the sway bar from the floorpan - 5 min per side.
Sawzall the remaining cage mounts - 2 min each.

IRS falls to the ground.
Cut brake line and parking brake cable. 

Total time to this point right around 30 minutes.   Much quicker than wrestling with unbolting the cage mounts, trying to break the trailing-arm mounts loose from the floorpan or unbolt them from the LCAs, and the whole thing comes out completely intact.

Note - one of the cage mounts separated while I was sawing it, and I've seen others separated on junkyard cars - try not to put body parts under the cage while working on the car, if you do have to do work under the car e.g. driveshaft leave the trailing-arm bolts (and sway bar, if so equipped) until you're done under the car. 

I was working alone and this was more of an experiment than anything else so when I couldn't budge the thing from under the car by myself I abandoned it.   Looks to be a 3.07, by the books it should be an LSD but I can't confirm as I couldn't get the brakes loose enough to turn the hubs.

Ralphy wrote:

Gotcha. so the 8.8 uses a toe rod with one upper and one lower mounting point  at the hub? Then the 7.5 uses one upper mount and two lower mounting points at the hub?

Uh...no, not quite.

7.5 and 8.8 just refer to two different final drive designs. 

The 7.5 in stick-axle form was used in a bunch of different Fords - Mustangs, Rangers, etc.  IRS versions were used in the non-SC MN12 Thunderbirds and I believe the DEW98 Lincoln LS/Boringbird/Jag S-type also uses a 7.5 (might be wrong.)  The MN12 application is an iron case with two narrowly-spaced mounts on either side of the pinion snout and one V-block mount bolted to and cantilevered out behind the rear cover; I believe the DEW98 case is aluminum, and the mountings are certainly different and more typical of, say, BMW practice with one offset front mount and a pair of widely-spaced mounts in back.   I believe Ford's also had a 7.5-in ring gear axle in some of their (other-than-Jag) European products but I can't say whether it has anything in common with this one.

The 8.8's also been used all over the Ford product spectrum as a stick axle from Crown Vics and F-150s to Explorers and Mustangs.  The first IRS application was the '89 MN12 Thunderbird SC/Cougar XR7 and the FN10 Lincoln Mark VIII; it was subsequently used in the '99-04 Mustang Cobra and '02-09 Explorer.   The 'Bird SC case was iron, the Mark VIII and the Cobra shared an aluminum case design; both mounted as noted with the 'Bird 7.5 above.   The aluminum cases are not known for breakage, but the mounting arrangement and especially the thin aluminum rear cover ( used even on the iron 'Bird cases) are notorious weak spots.   The '02 Explorer unit is far beefier, a much stouter and heavier case with a very strong ribbed rear cover.   The Explorer assembly also uses a mounting arrangement similar to the LS, with a single offset mount forward and a pair of widely-spaced bushings in back.   

Just about everything about the Explorer u