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Hey all,
Man I was just thinking, wouldn't it be great if there was a forum dedicated to IRS. I found it!
I've got a '69 Datsun mini truck project that I'd like to convert to IRS.
My track width is small, at around 50", so most of the typical IRS candidates are probably going to be too wide. However, I might be able to deal with either shortening or leaving it extra wide. I may not use the original bed of that truck so I don't need to worry too much about bed clearance in the rear. Any and all suggestions for a good IRS donor candidate are welcome. I noticed in the Classifieds someone selling a BMW rear end that said it would be good for a mini truck.
Also, here's s twist. I would like to know if it's possible to take out the diff from some IRS and replace it with a VW trans. Has this ever been done? Are there any reasons why it couldn't be done, or why it would be ridiculously complicated? I don't know how wide the VW trans is, but wondering if anyone knows the diff widths for any of the common donors, like Jag.
Thanks!
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Welcome to the site !
I'm sure the gurus here can steer you in a direction with info. If you have time to go thru all the pics, Im sure you'll run across something to give you an idea. I know my jag RA was 62 1/2 " wide to start with from an Xj series and am thinking the XKEs might be in the 56-58" range. Saw an older XKE set up last nite at a cruise in under a 2 dr ford coupe thing, someday I'll remember my camera.
Sounds like a fun project !
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Hey thanks Digz,
Yeah, 56-58" would be great. I'm seeing that people are shortening them too.
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Lowfriction,
There are more factors than track width. For instance depending on how large of wheels you use, may allot you to also use shallow dish wheels and elongating your halfshafts. Then with some ingenuity you can some what alter the camber curve. The C4 Corvette has the ability to do so. If you move the inner pivot point of the camber rod you can vary the CC. You can find some pics here of cars narrowed in big amounts. The question is how level do the tires stay on the road. Wide tires and deep dish wheels would cause some issues. IMO
The big issue for some is where to stuff the coilovers?
Did you see post #9 on the below page link?
Builders page.
Ralphy
Last edited by Ralphy (6/09/2012 5:40 pm)
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Hey Ralphy,
I had been looking through that post, but somehow didn't see #9, thanks for the heads up. That's quite involved.
Actually though, I've been going back and forth in my head between two different IRS projects to take on and the Datsun is now on the losing end of the battle. The other project is wider and so there will likely be little to no modifications needed. Since I can't to the fab work myself, I'm trying to keep it minimal. I can't rely on volunteers and don't have too much money to burn.
I'll keep the board posted as things develop.
BTW, I'm sure this has been asked before but are there any available designs that allow for air bags?
Thread StarterOffline
There are guys that have bagged an IRS. It's been discussed here and a couple of guys have even inquired. One issue is ride height and the wheel camber. When you start to change the ride height your wheels will be cambered differently depending on where you're at. A way to remove or reduce this is to run equal length control arms or a closer length between upper and lower.
Back to narrowing and a small car. To me the issue of any IRS install is tire width, it's the guys wanting to run say 12" wide tires on any car that throws a curve. Look at it in ratio's of tire width vs. car width. If you have a wide bodied car and you have X amount of up and down motion you have less angular change in the body. This is to say 2" body lean is greater on a Caddy than a VW Golf. The Golf will be at a higher angle so it will require more camber. So as you do narrow an IRS you will automatically get more camber due to the fact you changed the geometry. But now stuff a 12" tire under under that Golf and now you have issues. Maybe!
Last edited by Ralphy (6/11/2012 5:51 pm)
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It's funny, suspension is one of those things that when you first look at it, you think man this is pretty simple, I could design one pretty easily. But, then the more you study things, the more you realize the devil is in the details and one change may cause unwanted changes in other places. A lot of complex geometry.
What you say about car width, tire width and camber all make sense. In fact, not only does camber get affected, but I believe your drivetrain losses increase as those axle angles increase as well. How significant that is may be up for debate, but it's something to consider too.
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Careful MAN. You'll over-think it - again and again, and again.
That's the voice of experience whispering in my (your) ear! 
I'm now cutting metal and committing. Still have upright designs to complete - but have pretty much settled on the LCA/UCA placements.
My point - try and consider the key elements and know that even the experts still sometimes miss the mark a bit too.
Cheers - Jim
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I'm doing the bag thing on mine right now. Problem is , it will more than likely be a year before I actually find out how it works in the real world. Yep, narrowed with fat tires,, but I intend to set the camber after I get an established "NORMAL" ride hieght figured out. I'm seeing them as a Just For Show/Fun type thing more or less on this van. A little different than my first thoughts on this build but changing bodys has led me this way.
So what s the end goal of your truck build?
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Nope - no truck - just sharing observations on my corvette track-car build. I've carried 10 foot 4x2 timbers and 4x8 sheets of ply with it though! Jim
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The big problem is that I love thinking and dreaming. So, you kind of nailed me there Jim. 
This car project has been on my mind for years but I haven't had time/space/resources to really begin until semi-recently. Resources and time are still a bit slim but I have a workshop now! So there is progress.
Basically, from the 30,000ft view of things, my goal is to build a unique cool looking car that has modern technology employed (ie: 4-wheel independent suspension, disc brakes at least in front, rack and pinion steering, and electric drivetrain) but is also a throw back to older car aesthetics when the machines were simpler. As such I've considered a number of more modern "rolling chassis" platform swaps to older bodies.
I originally thought that the Datsun truck platform would be simplest and most practical due to it's light weight, but I'm getting away from practical and more toward unique and fun. I would love to do a slammed 40s or 50s COE chevy truck cab on top of a Jaguar platform. There are other ideas of course.
But as Jim so wisely pointed out, until you begin to cut metal you're not going to get anywhere. So, clearly I need to start cutting metal!
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No - don't be too rash! WHAT did Mom Always say? "If Jimmy jumped off a cliff - Would You?"
No, I'm with you, you need the 30,000 ft overview, and be ready for changes. And frankly, I'm a bit glad I've had some percolation time. I have revised my rear sub-frame 4 times - and fortunately all timber and plywood mockups! And THAT was after a Major Mod to the rear Suspension, "Jim's Giovanni" [Google if you like]. And that time gave me more time to do a bit of analysis, reframe my desires -- and Now I'm near READY! I've defined mine as a TRACK CAR, maybe occasional but not Daily Driver - and NOT Drag, but sometime Show-Car, because its unique.
The Pro-Touring approach of making your car -- YOURS -- is the Holy Grail to automobiles for me.
Take a car you like, make your compromises, your mistakes, your work. Its your effort the design, the thoughts, the build, and eventually, YOURS to DRIVE. Enjoy every minute of it.
I relish even those I, "Waste just looking at it." But you need to define what you WANT it to be.
I finally have started to Zero in - after a few years.
It is; The Journey, The Learning- and, The Destination.
ENJOY!
Cheers - Jim
Last edited by phantomjock (6/12/2012 3:28 pm)
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Haha. All in good fun. Don't worry, I still need to buy my metal cutting tools before I can start cutting myself! Likely I'll run my designs by an expert welder friend and see if I can get them on board for a few weekends later on.
But we drink the beer AFTER the welding!
Couldn't agree more that half of the fun in these projects is solving all the problems and the process. The other half is driving it.
Thread StarterOffline
Hay guys looking help ,i'm building 1971 datsun w/300zx tt motor and tranny is in . now to rear using tt zx irs need to narrow it alot , i use stock subframe using rear chassis section i kept in need to make jig using it or start from scratch and measure and start bending tubing .please any suggestion or input on better way to attack this! thanks for any help....
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Hey DART - Welcome aboard!
For me, I kept the rear section in place as long as I could when building my new subframe. Then, I took a lot of measurements so I could keep the axle (half shaft) placement in the same position (fore/aft). I think I came pretty close. Not really a perscription - but it seemd to work.
I really got to post those pics.
Cheers - Jim
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Thanks for the info ,it is nice to be on a forum were your not talked down to for your build and ideas ,but others give support in anyway they can.i have one thing on my side all 3 control arms are adjustable . thing is datsun rear 50" /300zx 62.5" so i've gotta lose some width .so measure ,measure then center the diff. then see where i am . thanks again !
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Dart - I know what you mean. I've had a few shops ask why I'd do what I'm doing. Some were custom shops that just don't seem to want money. Half the reason anyone does what they do is because it is there and because they can.
I'm putting a Jag IRS in a '59 El Camino, not always easy.
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A friend directed me to this site. Although I like my 620 the way it is, I know someone who has done serious mods to a 520 pickup and in the middle of modifying a datsun 411 wagon.
htt p://community.ratsun.net/topic/7446-project-mx520-top-secret/
htt p://community.ratsun.net/topic/52056-misinformation-look-here-to-get-the-411/
without the space.
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so started the narrowing found stock subframe will not work and with angle of lca ,looking at team 321 lay out ,going to do a thin mtl. mock up first to see how it goes . any words of advice .i've lots of long travel, hybrib axles for off road . few pro tour set up 4link /3link. this is fisrt irs set just want to make sure square wheelbase stay equal ,able align .
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