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well, ive looked at more jag IRS units than i care to remember, and recently i found a XJ40 unit available cheap woth a 3.54 power lock diff. Now this has really thrown a spanner in the works. This unit could potentially solve all the main issues i have with the old XJ6/12 unit. Outboard brakes, no trailing arms, but still a jag design with no upper links. The OEM cradle assembly leaves a little to be desired, in that it all mounts down low, which could potentially complicate exhaust system installation a little, but it got me thinking, theres no reason a crossmember cant be fabricated and mounted to the top much like the older IRS units, theres some decent mounting points on the top of the differential
does anyone have some more pictures they could post up? Does anyone know of any short comings of the later units? are they a dana 44? 
heres a few slight variations, i think there newer versions, drive shaft flange is a bit differnt, whereas the pictures i posted above had a flange identical to the older units and solid discs
this one is newer again, with a short sway bar and a tubular rear mounting system
Gareth
Last edited by KLR250 (5/11/2011 2:03 pm)
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Sorry, some how I missed this post otherwise I would have answered it right after you posted it. I am about 90% sure the unit is Salisbury and that like the earlier units Dana parts can be retrofit in to the case. Unlike the earlier XJ6 all the bolts are metric rather than SEA. As far as I know the strength is comparable to the earlier units. I believe the main reason Hot Roders stay away from them is they want the inboard brakes for the unsprung weight. If you decide to go with that unit I think it should work really well for you. I would recommend however upgrading the rotors and calipers to X300 or X308 units because the rotors are vented. I think if I was going to do another IRS project and one of those was available I would use it
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Thanks for the advice Daze. Its looking really attractive at this stage, IMO there a really nice looking unit
the other reason rodders steer clear is because there trickier to narrow to, although width isnt a concern for me, i can use every bit of it
this guy installed one into a MK1 jag and shortened it 60mm each side
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Daze you are right in saying Hot Rodders like the inboard brakes. But what I have seen Racers move them to the outside. Removing unsprung weight is great but when you are really pushing a car the heat and hard ability to change parts is a deterent. I see very few to no race cars with inboard brakes.
Unsprung weight reaches a point at which you will get minimume returns by reducing anymore. Suspension harmonics, the rate is app. 40 to 55 pounds.
They just look too cool!
Last edited by Ralphy (5/15/2011 8:12 am)
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KLR250 wrote:
the other reason rodders steer clear is because there trickier to narrow
I don't think that would be that much harder to narrow. The half shafts could be narrowed just like the older units. Unless I am missing something the LCAs would be the only "tricky part" and I don't think that would be to hard, I would just fab up some tubular units and replace them all together.
Daze you are right in saying Hot Rodders like the inboard brakes. But what I have seen Racers move them to the outside. Removing unsprung weight is great but when you are really pushing a car the heat and hard ability to change parts is a deterent. I see very few to no race cars with inboard brakes. Unsprung weight reaches a point at which you will get minimume returns by reducing anymore.
I think a big reason rodders do is because "thats what has been done before" when I was first looking in to my IRS project I talked to several sources and they made it sound like old school was the only way, now that I am more well versed on IRS units I realize that one of these newer units would work fine. Outboard discs are not jut for racers. I was corresponding with a brit and he said that outboard discs are a common "upgrade" to series I II and II jages across the pond. They do it because of the bigger rotors and easier maintenance.
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Hot Roders stay away from them is they want the inboard brakes for the unsprung weight. If you decide to go with that unit I think it should work really well for you.
Daze, I was responding to the above comment. I think it's as much the cool look of inboard brakes that creates the appeal. However if you really need to be concerned about unsprung weight IE, racing. The negatives of inboard brakes far outweigh the positive of less unsprung weight. Hot Rodders may think, but racers know. If a person thinks they push a car hard enough to be concerned about unsprung weight on the road I think they are overly estimating the need. It's always one of the most iconic angles to hot rodding. Everyone has seen those pics of an IRS with inboard brakes/quick change, all chromed up and four shocks, FOUR! Yeah Man! Ooooh! I WANT!!!!!!!!!!
In my opinion, it's truly form over function. I think I nailed it, right square on the head! This is a great post! XD
Last edited by Ralphy (5/15/2011 7:50 pm)
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Something else I had read. In a study, a good racer can get just about the same performance out of a solid axle compared to an IRS setup. The major improvement with an IRS is that it is more forgiving, more user friendly if you will. I had read this in a university study where they tried many combinations.
Then this is in an article Daze posted:
"When put to the test on smooth tracks there was little to no change in performance time even though ride quality was significantly improved."
Last edited by Ralphy (5/16/2011 5:02 am)
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It really comes down to builders wanting what they think is better. It is common in the classic Mustang community for people to put in an engine that has a huge cam, put on the stiffest springs they can find, and then they wonder why the car isn't any fun do drive in town. its an issue of what they think they want rather than what they actually need. With a Jag IRS It was the first easily accessible IRS unit and was available for so many years that it became the standard choice for a retrofit. now that president has ben set there are those that believe it is the "only" way to go, but having the most retrofits does no make it the best. The classic Jag IRS is a good unit but there are other units out there that are just as good.
As for the handling of an IRS you are correct a quality 4-link when properly adjusted will perform as well on the track as an IRS and has the added advantage of being able to launch harder. For me IRS is not just about handling but also as much about ride quality. I not only want to go fast, but I want to be comfortable doing it 
Last edited by Daze (5/16/2011 9:14 am)
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Daze there are guys at the Club Cobra site that always want more. Some building 700 plus HP motors, in a car that weighs 2,600 lbs.! Truly a beast hard to control. A fella near me is building a Factory Five kit all aluminum motor with app. 750 HP. Here's the catch, it weighs 2,100 lbs. That's only 2.8 lbs per HP. The kit builders even say 500 to 550 HP is the sweet spot for power.
I (we) as a AC Cobra owner have a special need for an IRS. My driveshaft is only 10 inches long. So that is one reason an IRS is so desired with these cars.
Funny also I remember in my younger years reading an article. It was taking a Jag and tossing the entire drive train, motor on back. They transplanted it with a C3 Vette drive train.
Last edited by Ralphy (5/16/2011 9:41 am)
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Finally found another car with XJ40 IRS, they do look quite nice
looks like an interesting project. I sent the poster a message inviting him to the forum so maybe he will stop by.
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Well, hopefully I can make this work, i just bought the IRS for $250
going to pick it up on the weekend, Ill be sure to take lots of pics
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SWEEEEEEET!!!!! I set up this forum to be about all kinds of IRS but being that my web page is the main advertising we have been old school Jag heavy (there are others but those of us doing old jag far out way every one else) and even though this is still Jag it is different so I cant weight for you to add to the diversity. Also if you could take lots of pix of the parts that make this set up different, that would be fantastic!!!
Last edited by Daze (5/17/2011 7:11 am)
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Cant wait to get stuck into it! I'll be sure to take lots of pictures and measurments
first cab of the rank will be drilling out all the spotwelds so i can remove the original watts link bracketry, put this assembly on a jack and sit it in place to see whats going to fit where
im hoping i can utilise the factory cradle and the forward mounts sit on my rails....but that might be to easy lol
Last edited by KLR250 (5/18/2011 5:58 am)
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Off to pick up my IRS unit tommorrow, ill keep you all updated
very exciting lol
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I love the excitement of getting new parts
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Picked up the IRS today, So far im very happy with it, Looks to be a well engineered bit of gear. The lower arms are bullet proof and Lighter than i thought. The guy threw in a spare set of arms, a spare mounting cradle, spare half shaft, and the drive shaft yoke.
Pictures soon
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where are the pictures???
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None yet, Its still on the trailer, about to go and pressure wash it down at the local car wash
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None yet, Its still on the trailer, about to go and pressure wash it down at the local car wash
we don't mind a little dirt and grease, you don't have to clean it just for us 
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I think you guys might be missing the point on inboard brakes just a little. There's more to it than hot rodders and racers. For the racers, pad changes and cooling are major major issues, and the heat cooks the stub shaft seals letting oil get on the rotors so it really isn't that good of a choice. Hot rodders are more about appearance. What you're missing though is the appeal for a daily driver, which explains why they are there in the first place. Here, every pound you remove from unsprung weight makes for a smoother ride. It doesn't have to be faster to be better in other ways. Of course, with a modern brake package weighing under 20 lbs per wheel and sometimes down around 15 or less there is less to be gained by moving the brakes inboard, but even so the difference is enough to notice.
JB
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I don't think I missed that point. I never mentioned it, what the mfg. intended. I think most here view pros and cons in the conversion sense. Also, most if not all here are not building daily drivers. 
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hey Jim got any pictures of your IRS install??? I would love to see it
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Im still alive guys, I missed this place lol
Been really busy leading up to christmas, and unfortunatly i havent been busy on the car. But, i should have some decent updates soon, been working on the rear suspension, made some carboard templates up for my cantilever system......some teaser shots for now. Ive actually revised the bell crank angles again after these photos were takin, but the plan is to use some ride tech 1000 series airbags with 2.6" stroke, 1.5-1 bell crank ratio, which will give me the suspension travel i need, and still keep the system compact. The reason for the cantilevers was mainly because i dont have a whole lot of room to run the airbags under the car, and i figured what the hell, a bit more wow factor.
Like i mentioned i have revised the bell crank, as i had the angles wrong causing a decreasing rate on the spring instead of a rising rate, im pretty much making sure i keep the pushrod to bell crank angle @ 90deg and the airspring to bell crank @90 deg (at ride height)
Last edited by KLR250 (12/31/2011 2:15 am)
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