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I know everyone is excited about have a new poster here and even more excited about having yet another topic about IRS in a classic mustang, so here I am.
I was directed here from a classic mustang forum and have been knee deep for the last couple days reading about everything I could find. I found the infomation about the history of IRS in the early mustangs really interesting, and it made me more excited about the prospect of putting one in my project. Of course, that led me to CTM and Duane's bolt-on design. It's great to have someone putting in the effort to dig up history like that and bring it back new and improved. I'd love to be able to buy one of his units one day, but the "I can do it myself" stubborn part of me wants to at least explore the idea of finding a used Jag unit to make work.
There isn't a shortage of posts on here about Jag units, but I'm not quite ready for all the technical geometry stuff quite yet (baby steps). What I am looking for is more information about what years to look for?
What years have what widths?
What years have outboard brakes?
What years are stronger?
What years are better designs?
What are good sources to find them?
...that kind of stuff.
I appreciate the help in advance. I look forward to being a part of this site, and, one day, I hope I can be a contributor and not the newbie who asks the same old questions.
Andy
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first of all welcome to the forum!!! Can you provide me with a link to the post that brought you here?? I just like to go look and see what people are saying about my forum and such 
Your questions lead me to believe that you have not yet seen my web page. go to you will find 6 long pages on my install and should give you lots to read and look at
- Putting Independant Rear Susprnsion (IRS) in a Classic Mustang
Page I: Why make the upgrade and Fords original IRS design
Page II: Where to find a unit, and then taredown, and cleaning.
Page III: Narrowing of the LCAs and half shafts and converting the Jaguar bolt pattern to a Ford bolt pattern.
Page IV: The differential rebuild, the drive shaft rebuild, and the rebuilding of the hubs.
Page V: Installing the IRS unit in the car
Other: Rebuilding a Jaguar differential with Danna 44 parts
as to ror questions:
What years have what widths? 
What years have outboard brakes?
The XJ40, X300 and X308 all have outboard discs but the XJ40 does not have vented rotors. I just moved a post from the old forum on the subject:
What years are stronger?
Jaguar built all the XKE and XJ6/12 to be rock solid. handle 600 HP easily. I recommend staying away from the XKE because of the spin on wheel hbs and the fact that they will cost you big $$$
What years are better designs?
same basic design from 60-87 with the exception of the XKE hubs and the XKE coil over shocks
What are good sources to find them?
best source I know is David Bogger at I have purchases two units from him. he has great prices and is a great guy.
Once again welcome to the forum. Let me know what you think of my web pages and we would love to see some pix of your project.
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Thanks for all the info, daze. I've been reading up on all your articles. It's nice to have some else do the the hard work for once. I'm sure I'll have more questions.
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Here is where someone linked your site:
It seems not everyone is a fan of independent rear suspensions.
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Are the xj40, x300, and x308 units newer than 87?
Ideally, I want a 3.25 to 3.50 gear, outboard brakes, and traction lock.
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37ford wrote:
It seems not everyone is a fan of independent rear suspensions.
Oh, of course not...
The more moving parts you've got in something, the harder it is to get completely sorted. Any time you're putting together a bunch of parts from different cars it's going to be a significant sorting exercise.
Stick-axles on early Mustangs are well-understood and folks have been tuning them for forty-plus years; there's certain combinations that are known to work pretty well out-of-the-box. Nothing like that exists if you're playing with retrofitting an independent rear; you're on your own to make it work right.
Some basic considerations apply independent of the specific vehicle involved. Stick axles work great on smooth tracks. The rougher the surface, the poorer they stick and the more they beat you up. Some solid-axle suspension layouts work much better than others. And everyone has a different point they want to hit on the performance-vs-comfort chart.
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performance-vs-comfort chart.
I think that is the biggest difference. For autocross and circle tracks IRS and live axle can be made to work equally as well, if set up properly, but to get a quality handling rear end that also provides a smooth more comfortable ride, IRS is the only way to go. Don't forget however there is one down side to IRS and that is wheel hop under hard accelerations. That is one place where the live axle wins out every time.
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I have made it through all of your articles. That's great stuff. I haven't memorized it all yet, and I am sure I will be going back to the one adout the differential. All that was a little too much to absorb in one sitting.
I find it very interesting that the Jag units have no dedicated UCR. Seems like that simplifies things. I was reading about the narrowing process, and noticed that you shortened the half shafts and LCRs the same amount. Since you did that, I assume those are parallel to each other?
Did the original units not come with a sway bar?
As for pics of my project, I do not have one yet. I currently own a 37 Ford that I finished a couple years ago. I came to the conclusion that I will have to sell it before I can fund another project. Fortunately, it really cheap to daydream, plan, and do research on the next project.
Here is a build video of the '37.
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Are the xj40, x300, and x308 units newer than 87?
Ideally, I want a 3.25 to 3.50 gear, outboard brakes, and traction lock.
Sorry some how I missed your earlier post.
yes the xj40 x300 and x308 are the subsequent Jags offered after the series I, II, and III xj6/12. As to the combination you want... GOOD LUCK WITH THAT or at least good luck finding one unit that fits the bill. here is how I would do it. I would start with a rear end from a series I, II, or III xj6/12. Why because they are the easiest to modify to fit your specific application, fairly common, can be had for a couple hundred bucks, AND can be upgraded to have the things you want. The outboard discs can be purchased from a newer jag and it is a good idea to replace the differential carrier and the ring and pinion any way so why not get dana 44 parts and then you can pick exactly what you want.
I find it very interesting that the Jag units have no dedicated UCR. Seems like that simplifies things. I was reading about the narrowing process, and noticed that you shortened the half shafts and LCRs the same amount. Since you did that, I assume those are parallel to each other?
Nope, they are not quit parallel with each other. When I first was trying to figure out how much to take out I thought about using ratios to determine how much to remove and I looked at figuring the triangle created by the different angles to determine how much to remove, BUT I ran to a couple of major problems. the half shaft and the LCA are different length AND there pivots are in totally different locations which means as the suspension goes through its range of motion, the angle of the half shaft in relation to the LCA changes (this is how the camber curve was built in to the system) so I could never figure out what position to put it in, so that I could take my measurements and calculate out what I needed to do. The breakthrough happened when I had the opportunity to measure the half shafts and the wishbones from an XKE. even though the entire rear assembly was about 8" narrower than an xj6/12 unit the difference in length, wish bone to wish bone and half shaft to half shat was the same. in other word if the Xj6/12 half shaft was 4" longer than the XKE half shaft than the difference between the XKE and XJ6 wish bones was also 4" This is one of those situations where I felt totally comfortable in the idea of " Jag did it that way so I will do it too" In most cases I try to stay away from that reasoning because I am not doing it exactly as Jag did and it is an easy excuse to not think things through however in this case (relative to suspension travel and camber curve) nothing I was doing was any different than what Jag did so I felt confident in using this line of reasoning.
My thinking was shown valid when Joe ran the camber numbers for my suspension in relation to a stock Xj6/12 unit
Yes there is a minimal difference e but not enough to worry about and I am sure that was Jags reasoning. by simply lengthening the half shafts and wishbones the same amount they could still utilize the same differential and hub with out having to redesign new pivot points.
Did the original units not come with a sway bar?
Jag did offer a rear sway bar but they are not very common and would have been challenging to retrofit to my application. Also in my case I had the sway bar already since I had replaced it with a bigger one in the front, and I am a firm believer in a rear sway bar being smaller than a front sway bar, so it was the perfect solution.
Thanks for the build video!!!
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looks like it was a fun project. I especially like how all the way through you kept taking the "same" picture it really tells the story that way
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"I would start with a rear end from a series I, II, or III xj6/12. Why because they are the easiest to modify to fit your specific application, fairly common, can be had for a couple hundred bucks, AND can be upgraded to have the things you want. The outboard discs can be purchased from a newer jag and it is a good idea to replace the differential carrier and the ring and pinion any way so why not get dana 44 parts and then you can pick exactly what you want."
I've been going back and forth from this thread to the other one about the outboard brake hubs to try to piece it altogether in my head. You suggest starting with a X6/12 complete unit because of the sheer quantity available and capatibility. You purchased hubs and half shafts from an X308 to have outboard brakes on a XJ6 main unit.
If I were to do something similar, I would likely still have to change gears and add a limited slip. If that were the case, I would only end up with the center housing, sone innards, and LCAs from the complete XJ6/12 I started with. Then, I would have the half shafts and hubs from a X308,X300, or XJ40. I may be misunderstanding or missing something, but it seems like, if you can manage to get those outboard parts from an X308,X300, or XJ40, then why not start with that whole unit and modify the width? Are the carriers on those not as good? Is there something about those units that make them harder to narrow?
It just seems like you would wind up with a lot less spare parts sitting around in the end. I'm sure there's a good explanation, but I was curious.
Last edited by Daze (10/25/2011 7:44 am)
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If you wanted to start with something that has the gear ratio and limited lip carrier than it could be done. Most likely it will come from an XJ12. This will make it a little harder to find and cost a bit more. Then once you get it who know what kind of shape the ring and pinion or carrier will be in. For a performance application on such a complicated rear end, I don't know that I would even consider a used limited slip carrier unless I knew its full life history and I new that the miles on it were low. If it were a Ford 9" where the entire center section can be replaced in 30 min I would risk it, but on a Jag unit where the entire suspension has to come apart to replace the carrier, I personally would just start with new parts and not worry about it.
The Xj40 X300 and X308... also XJ8 which I forgot to mention before have a different rear end configuration. The cage was eliminated and the center section mounts differently. The following pix are from an early XJ40 still similar to the XJ6 unit but different
Then as you get to even newer rear ends the the wish bone disappears and is replaced with a stamped LCA which is going to be even harder to narrow (pix from the post XJ40 IRS into an Aussie falcon
It just seems like you would wind up with a lot less spare parts sitting around in the end. I'm sure there's a good explanation, but I was curious.
That can be avoided. Contact David Boger at www.everydayXJ.com tell him I sent you and ask him what he would charge you for a complete rear end assembly then get another quote for the rear end assembly with out the half shafts, calipers, or hubs. If it is a significant reduction in price than buy just those parts. If not then get the entire unit and then list the half shafts, calipers, or hubs on eBay. I bet you could sell them for almost as much as you will end up paying for the same parts from a newer car to upgrade to outboard discs. make sense???
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Ah. I see that it looks like a completely different beast alotogether. The XJ6/12s look much simpler.
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if you decide to get just part of an XJ6 unit, make sure you get the old inboard disc brake rotors. you will need to cut the center section out of them to make a spacer to go between the drive axles and the half shafts. I am ready for more questions, fire away
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Are the LCAs inteneded to be level at ride height?
The stabilizing arms you show in orange in your sig pic...I assume you fabbed those yourself. Was there something that had the same function within the cage fron the factory or were you just beefing up the system?
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Are the LCAs intended to be level at ride height?
yes, on a Jag they sit parallel with the ground and in line with each other at normal ride height. Even when the car is aligned it is done by locking the wishbones parallel with the ground and then camber is set to 0º
The stabilizing arms you show in orange in your sig pic...I assume you fabbed those yourself. Was there something that had the same function within the cage from the factory or were you just beefing up the system?
I did fab it up my self to replace the OEM arm. there is a tab near the end of the wishbone that is designed to bolt up the trailing arm. The OEM jag units went strait forward and used big rubber bushings to absorb the binding cause by 2 different arcs moving in perpendicular directions. You can see the OEM Jaguar arms in the following pic
The OEM mounts as well as the cage mounts were in theory there to add anti squat but I really don't see how they would be very effective. The bushings on the trailing arms are so big that they should absorb most if not all force that would be applied to create anti squat. I mounted mine as I did to strengthen the unit and have as little bind as possible. buy putting my arms in line with the wish bone pivots I have effective turned the wish bone in to a 3 pivot a-arm
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I got another one for you. The main reason for getting the wheel hubs from an X300, X308, or XJ40 is to have hubs with brake mount provisions. That openes up a new set of challenges, (according to your posts).
1. Finding the parts.
2. Making them work with the the older parts.
3. Changing the bolt pattern.
4. Being stuck with Jag brake parts.
Any of these may or may not be difficult, or may not even apply. In my case, I will definetely be chanign the bolt pattern, and I won't be satisified with using Jag brake parts. I like using stuff more readily available. Finding the parts will probably be a problem. That's the case with everything once I actually start looking with money in my pocket.
Now, I'll just get to the point. Why not just weld a provision onto the XJ6/12 hub for the brake caliper brackets? The hub looks plenty beefy enough for the torque, if done properly. Then:
1. You can use whatever brake parts you want.
2. You won't have to locate and buy parts from two different cars.
3. If you have to change the bolt pattern, you can can just drill out the flange on the XJ instead of having to use a spacer.
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A bunch of good thoughts, I am going to play devils advocate, not to put down your thinking but to further the brain storming and creative process. What I see is two different sides of the argument so I am going to address them separately.
I got another one for you. The main reason for getting the wheel hubs from an X300, X308, or XJ40 is to have hubs with brake mount provisions. That opens up a new set of challenges, (according to your posts).
1. Finding the parts.
2. Making them work with the the older parts.
3. Changing the bolt pattern.
4. Being stuck with Jag brake parts.
1. The parts are easily obtainable. I got them on eBay and didn't pay any more than I will be able to get for the parts from the XJ6 parts I won't be using
2. The only "challenge" is cutting the used rotor down to use as a spacer between the half shaft and drive axle. And the other issue is the different pin sizes which can be easily gotten around
3. Changing the bolt pattern is not an issue, simply run different rims 
4. You are not stuck with Jag parts, with the mounts already there any Brembo Wilwood or other brake calipers could be made to bolt up. Also by changing the bolt patter your rotor choices double you can drill out any chevy rotor or use a Ford rotor
Now, I'll just get to the point. Why not just weld a provision onto the XJ6/12 hub for the brake caliper brackets? The hub looks plenty beefy enough for the torque, if done properly. Then:
1. You can use whatever brake parts you want.
2. You won't have to locate and buy parts from two different cars.
3. If you have to change the bolt pattern, you can can just drill out the flange on the XJ instead of having to use a spacer.
Let me start by saying the idea is great, but there is IMHO one major flaw and that is the welding. I have designed several brake "upgrade" brackets and am good friends with several people on a Mustang forum who make and sell Mustang "upgrade" brackets and the general consensus when dealing with brake brackets, is to only weld as a redundancy. in other words only weld as an extra support structure. I know what you are thinking Wilwood and others make weld on brake kits, BUT for the most part those kits are designed for race application. Yes race breaking will put more torque and stress on the set up than spirited street driving, but on the race track the brakes may see a thousand cycles, but on the street it will hundreds of thousands of cycles which can lead to stress cracking. the other factor I see amplifying this issue is aluminum is by its very nature brittle and easily stress fatigues and having the different hardnesses created by the welding will amplify that issue.
1. I will give you the first one you will be able to use what ever brakes you want
2. even if you weld on tabs you will still have to source parts, rotors calipers and then you have the added task of coming up with a way to connect it all together, and then, if you weld on tabs how would you accommodate an e-brake??
3. I will give you that one too with one exception. I feel the option to weld up and redrill the modern flange is not really any more involved than redrilling the older stile flanges.
Any of these may or may not be difficult, or may not even apply. In my case, I will definitely be chanign the bolt pattern, and I won't be satisified with using Jag brake parts. I like using stuff more readily available. Finding the parts will probably be a problem. That's the case with everything once I actually start looking with money in my pocket.
When it comes to brakes my personal goal is to have pads, calipers and rotors that are easily replaceable. To that end I try to use OEM... or at least some ones OEM parts, maybe a different make or model than what I am working on but something I can easily get at a parts house of I need to.
OK enough with the devils advocate. Like I said before I think the idea is a good one but would like to see a different solution. what if it bolted on to the hub, or maybe clamped around the snout of the hub and then bolted to the hub for added stability??? I don't know I don't have an easy solution... at least not one that I like better than using a modern hub . I still think you could use the modern hub and then use what ever caliper and rotor you could fit to the application.
Like I said above I am not trying to bust your chops or be one of those naysayers so many forums have who never like ideas but there own. I just like to look at all sides and all issues so that we can come up with the best solutions.
Last edited by Daze (10/31/2011 9:06 pm)
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No offense taken here. That's how you learn. I like to throw stuff out there and get information from those who have been there. It's a lto easier than learning the hard way.
Concerning the ease of finding parts, you gave e a good source with "everdayXJ", and I plan to call him when I get everything figured out. I just have not had good luck finding parts on ebay. I have been looking since I started this thread, and there are a few complete XJ6/12 systems on there, but there just aren't many parts. Maybe I'm not using the right search phrase, but most of the X300, 308 stuff I see on there seems high and is located in England.
I have also looked for Wilwood, Brembo, etc. Jaguar disc brake kits online without much luch. Again, maybe I'm not looking in the right places. I'm typically pretty resourceful, but haven't really come up with much as far as calipers and brackets.
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When you get to eBay put in "jaguar rear hub" that should provide you with a better result. basically you want any hub that has the brakes at the hub. I believe they are all the same as long as it still has an aluminum hub
Last edited by Daze (11/01/2011 4:24 pm)
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here is a good price on a pair of hubs and the shipping is about as good as you will find
and here is a listing for the half shafts
Last edited by Daze (11/01/2011 4:26 pm)
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Hey guys...what a pleasure it is to go over your posts, I have an open question: I just picked up a jag rear and I was told it came from a 2001 xj40, I had a jag before under a 56 ford f100, but now I'm working on a 37 ford coupe and have plans for the xj40, this has vented rotors and 3.50 gears. How can I convert the Jaguar V-8/Chevy Yoke, 25 Spline, Open Drive to a chevy yoke????
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