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7/11/2013 11:15 pm  #1


Hi, I have two IRS projects to work out.

Not sure how active this forum is, but I'm giving it a shot.

I have two IRS projects I am pursuing.

The first is a 1968 El Camino, pretty warm 350 and TH400 with a 2400 RPM stall converter.
Since I'm not rich a custom made rear is out of the question.
Looking into C4 Corvette or Jag.
Jag is easy to find, but the ratios from am XJ6 tend to be way too high.
I know that to get the result I want will take more than just getting it under the car.
Ideally I wold like to find an "S" rear if I go with Jag, they are narrower and have lower gears.
Most C4 Vette rears that come around at a reasonable price are the weak ones from an automatic trans car.

The other less immediate project is my Krait®, an almost street legal 1974 Spitfire Hill-climb / Autocross toy along the lines of a mini-Cobra.
Hot Buick 225 V6, Muncie (Or?) manual trans, gutted body, etc.
The original IRS would be vaporized by this engine.
I've been looking at BMW units but they are just a bit wider than I would like, 55" rather than the 50" ideal.
Also peeked under Mercedes and Audi, they are very similar but harder to find.
A personal bias rules out Japanese sourced rears, the Miata does not appear to be that great anyway.
Anyone ever narrow a BMW rear?
Anyone know which BMW's come with any sort of posi?
Seems hard to find any IRS less than 55" wide.

Open to suggestions, hints, expertise.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
 

7/12/2013 2:28 am  #2


Re: Hi, I have two IRS projects to work out.

Welcome aboard!  One more post and you can hang some pictures of those cars!
The Krait sounds like a fun build.  For the Krait  - Have you considered using C5/C6 Corvette A-Arms, Rear end etc?  Cant speak to the width - most likel over your 55" width requirement, but you could work that with some judicious fabrication.
There are a lot of bits and pieces youcan get together to scratch build an IRS for either.  Happy to help - as we can.
Cheers - Jim


UNDERCONSTRUCTION! Highly Modified C3 Corvette
         Dual Wishbone IRS w Subframe + Custom Uprights
 

7/12/2013 8:38 am  #3


Re: Hi, I have two IRS projects to work out.

Are you the same Richard who used to visit here:
http://www.348-409.com
Your 200 mph speedo and handle look really familiar.
Any way, regarding the gear ratios  from an XJ6 being too high, they are the same gears as a Dana 44.  There is a huge range of gears from 2.88 past 4.11.  There is a change in carrier size between 3.73 & 4.11 though.
There are companies which will narrow a Jag rear, it involves the half shafts and Lower Control Arms (LCA).  There are a few posts from folks here with experience either narrowing themselves or companies which have done the narrowing.
How good is the traction in your Krait?  Power is one thing, traction is another.  If you've got good traction, you'll find the weekest link in your drive train very quickly.
Good luck with your project, can't wait to see pics!

 

7/12/2013 9:52 am  #4


Re: Hi, I have two IRS projects to work out.

Krait is still in the parts gathering stage.
I have the car, TITLE, engine, and a line on a Muncie trans at a very good price.
Have to decide what rear to use.
Trying to do it on the cheap, the base car is ugly, banged up pretty bad on the drivers side.
I will not worry about the body until all the drive-line Fab. work is configured.

Body might even be changed out for something in fiberglass, or even a quasi-Lotus 7 sort of affair.
I want to keep it light, hoping to disprove the old "No substitute for cubic inches" malarkey.

Jag and Vette rear are probably a bit heavy for this, and clearly too wide.
An early E-Type rear would be excellent for width, and expensive.
The BMW rears are plentiful and 55" wide, some are a 4.10 ratio, lots of 3.73's.
They are very self contained within a cradle so I am surprised more here have not used them.

The El Camino is the more pressing project as it is a runner.
This may have to wait for winter as whole junk Vette's get pretty cheap then.
My major issue with the Vette rear is that cart spring, might have to fab my own coil-over conversion.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

7/14/2013 9:30 pm  #5


Re: Hi, I have two IRS projects to work out.

Well I found the guy who bought my Jag 420 rear.
He's not using it and I want to buy it back.
He beat me down on the price when I sold it, guess what he wants to do on selling it back to me? 

Not sure I can pay that much, I lost a lot when I sold it to him after having to buy a whole car to get it.
According to Wiki they are 4" narrower than an XJ6.

So would work OK in the Spitfre or great in the El Camino with fat tires.
Think I'm going to see if I can locate another, even if I have to buy another abandoned restoration.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

7/15/2013 6:33 pm  #6


Re: Hi, I have two IRS projects to work out.

Good luck!

Ralphy

 

7/15/2013 7:07 pm  #7


Re: Hi, I have two IRS projects to work out.

It seems a C4 'Vette rear is a little too wide for the '68 El Camino.
A C3 would work better, but is harder to find.

The Jag 3.8S/420 rear looks like my best bet.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

7/16/2013 7:23 am  #8


Re: Hi, I have two IRS projects to work out.

How wide is the frame on your '68 vs the 'vette rear?  I know the bat wing configuration makes it difficult and requires a certain width.  On my '59, the Jag rear is the only easy install.
On your '68, a company called Snow White sells a universal cross member for the Jag Rear which mounts the rear pinion at 3 degrees, which is where most of the side mounts for the LCA sit at.  At $300, it is a bit pricey but it does come with adjustable shock mounts.  This might be something to consider since your '68 is a driver and down time is something it sounds like you're trying to avoid.
Here is a link to their site:
http://www.snowwhiteltd.com/products.html
You'll have to call them as they don't keep their web site upto date.

Last edited by 303Radar (7/16/2013 7:26 am)

 

7/16/2013 9:58 am  #9


 

7/16/2013 2:04 pm  #10


Re: Hi, I have two IRS projects to work out.

Got some measurements from the '68 El Camino today.
Rear frame is 46.5" outside, 40.0" inside.
Inside of the wheel wells is the same 46.5".
The 10 bolt is 54.0" inside the backing plates.
Currently have 53.0" inside tire to inside tire, with lots of room for wider rims to the inside.

Curious how this compares to the '59 mentioned above and how hard that was?

I'm looking for a spare frame to mock-up on, or even just a rear half.

Tried to measure the Jag XJ6 I have here, but with the rear in it that did not go well.
It's beginning to look like an XJ6 rear may work best, the narrower rear looks more likely to have to notch the frame for the uprights.

Found a clean XJ6 3.54 ratio positive traction rear for $500.00, and five hundred miles of shipping. 

Snow White is now Speedway and they say they do not have a kit that will work for the El Camino.
Could not locate Concourse West, looks like they are gone?

Most guys build these as "Muscle Cars", with big engines and go drag racing, not what I am after.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

7/17/2013 8:03 am  #11


Re: Hi, I have two IRS projects to work out.

I'm suprised about Speedway not selling the universal kit, I only ordered it a year'ish ago.  They still show vehicle specific cross members on the link above.

My '59 El Camino hasn't been too difficult.  I am having a 3rd party weld in the cross member to make sure the alignment is correct.  I'm a little gun shy on this part, I'm sure it will be money well spent.
One problem I kept making is, the center of the pumpkin is about one inch behind the center line of the axles.  This is more important for the X frame on my '59 than the square frame like I think you have. 
Left to my own devices on a square frame, I'd buy some 2x3 or 2x4 square stock, make an isolation mount, ask Daze if he is still selling the top plate he had water jetted, find some 3/4 inch round tube, threaded bungs (shock mounts), and pick up some grade 8 bolts.  All told, probably out of pocket less than $80.  Much easier to do when the frame isn't coming out at at 23 degree angle and a hump over the axle.
The stock axle on my '59 was 58 - 60 (I'll double check sometime) inches between backing plates.  Which doesn't include the space for the drum brakes.  The Jag Axle I picked up is 61 3/4 between the wheel flanges, whic should leave me lots of space.

Even though I'm going to punch out the 348 to a 434 (only reliable crank), I prefer cornering ability and ride comfort to straight line ability.

CWI - Concourse West Industries went out of business.  Mike, the owner had a fire sale last year, not enough business.

 

7/17/2013 7:19 pm  #12


Re: Hi, I have two IRS projects to work out.

May have made some progress of sorts today.

Went looking for a '68-'72 "A Body" frame or rear half to use for mocking it all up.

Found a good one in a wrecking yard, $700.00.
I don't think so!

A "Slightly damaged in the front" at $400.00 on CL.
Better, not a winner.

"Wrecked in front but the rear is fine, $200.00"
Hmm, maybe.

I only need the portion over the axle and it can be from any "A" body of the correct years.
With patience I should be able to find a damaged or partial one just about free.

I already have a spare rear sheetmetal clip.
Once I have the spare frame section I can get serious about working out the fabrication.

Also found an overpriced C3 'Vette rear which the seller cannot even describe properly.
Cannot say which center section it has, ratio, or if it is a posi unit.
Pretty sad from a "Professional".


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

7/18/2013 12:25 pm  #13


Re: Hi, I have two IRS projects to work out.

Where are the shock mounts on your '68?  I'm thinking if you don't already have a cross member, you may be able to put one in w/o needing something to mock up.  If possible, post a pic, I'm curious what you're working with.

 

8/31/2013 10:24 pm  #14


Re: Hi, I have two IRS projects to work out.

Off to buy a good frame on Tuesday for $200.00.
Sometimes patience pays off.

Since it's supposed to be a good one I will get it checked and adjusted if necessary at a local shop.

I'm getting another El Camino/Convertible frame, they are fully boxed to be stiffer than sedan or coupe frames.

So once I get my conversion figured out I can just swap frames if turns out I need to do very much modification.
Still leaning toward Jag over Vette, much better prices and simpler install.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/04/2013 11:15 pm  #15


Re: Hi, I have two IRS projects to work out.

Okay, got pics of the rear of the "New" 68-72 El Camino frame this morning.

Original is a live axle with unequal length trailing arms and coil springs.
Looks to me like the spring perches will have to go, so much for a bolt in conversion.
Also seems all the 'Vette rears I find are Dana 36 from automatics, or overpriced.
If I really want a Dana-44 'Vette rear it looks like I would have to buy a whole car this winter, then sell what I do not need.
Looking even more likely to be a Jag set up.
Just need to determine which to use, XJ6 or 420.

Also intend to fully weld all seams and add some cross bracing for added stiffness.

Some pics to show what I'm working with.
 

As seen from the front with the rims I want to use.
Tires will be replaced with the same size in a modern equivalent, 265/60-15.
http://www.specialinterestarms.com/DSCF0490.jpg




3/4 angle from the front.
http://www.specialinterestarms.com/DSC00585.jpg




Close up of the cross member and spring pocket from the front.
The bracket to the front on the main rail can be removed with IRS.
http://www.specialinterestarms.com/DSC00589.jpg




Looking forward from the rear.
http://www.specialinterestarms.com/DSC00586.jpg




A low angle looking from the rear.
Might remove some brackets and box this in if I can.
http://www.specialinterestarms.com/DSC00588.jpg




That spring pocket sits right at the top of the frame arch.
http://www.specialinterestarms.com/DSC00587.jpg


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/05/2013 1:25 am  #16


Re: Hi, I have two IRS projects to work out.

Okay, "Edit" still not working for me so here's a late update.

After much web searching I find that the XJ6 rear is stated to be 61.75" wheel flange to wheel flange.
The original El Camino rear is 62.50".
The Jag is 3/4" (.75") narrower.
Divide by 2 to get the difference per side, 3/8" (.325").

So an XJ6 or XJ12 rear should be about perfect and no modification to width is needed.

As I measured an original XJ6 wheel the back rim edge to the mounting face is 4.8"
The mag wheels I want to use are 3.5" but are also 8.5" wide.
I have trial fit them on the car and they fit with plenty of space to the inside, and adequate clearance on the outside.
Gaining 3/8" on the outside will make them about perfect!
If I've done the math right my new track will be 63.9" at the center of the tire.
The original rear track was 59" using skinny little 14" rims and tires.

It's possible I might even be able to get away with 10" wide rear wheels (295/50-15 tires!), if I could find a set with the correct back-space.
Probably will not go to the 10" wide rims, would look great but tire selection and speed rating get pretty poor.
This is to be a fast road car, not a dragster.
 


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/05/2013 1:51 am  #17


Re: Hi, I have two IRS projects to work out.

Final thought for tonight.

The last item I need to check is frame and wheel clearance for the hub carriers.
I happen to have a nice '87 Jag XJ6 sitting in my yard, so I can try a wheel on it to see how that looks like it will go.
At worst I may have to notch the El Camino frame a little, it's getting modified anyway so would not be a big deal.
Yah, this is NOT going to be a bolt-on adapter.
I will probably cut out the original spring perches to fit the Jag rear diff mount since they are centered on the kick-up over the axle.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/16/2013 7:48 pm  #18


Re: Hi, I have two IRS projects to work out.

Unless the other guy back out I have a good trade going.
My tired SB Chevy 400 for his 3.54 and posi XJ6 rear. http://cdn.boardhost.com/emoticons/happy.png


Once in a while CL works.
I will be anxious until the deal is done this coming Thursday.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/17/2013 9:12 am  #19


Re: Hi, I have two IRS projects to work out.

Good luck!

 

9/19/2013 6:01 pm  #20


Re: Hi, I have two IRS projects to work out.

Got it tonight.
No shocks or springs but I did get both diff's.
The 3.54 posi diff looks like it will probably need to be rebuilt.
Still not a bad trade for an engine I only wanted $150.00 for.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/19/2013 8:21 pm  #21


Re: Hi, I have two IRS projects to work out.

Still cannot edit my prior post.

Here are a couple of pics of what I got.
No brakes, so I probably have to visit a local Pick n Pull for cores.

I did get two diffs, one 3.54 and posi.
Glad to find it is MUCH cleaner inside than out.

All bearings/pivots have to be rebuilt and the LCA's probably reinforced.
Glad that I can avoid having to shorten anything.
I did confirm that my 8.5" wide wheels clear the hub carriers with room to spare.

So I'm going to be looking at what can reasonably be done for the best mounting and lower trailing arms arrangement.
Not sure about the need for a watts link.

Main use is improved handling over the GM 10" live axle.
Hoping to use one coil over and one air shock per side.
The El Camino is lighter than an XJ6


http://www.specialinterestarms.com/DSC00614.jpg
http://www.specialinterestarms.com/DSC00616.jpg
http://www.specialinterestarms.com/DSC00615.jpg


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

9/20/2013 7:44 am  #22


Re: Hi, I have two IRS projects to work out.

Congrats on the deal! 
One design consideration to keep in mind is, where are you going to place the bump stops?  I'm going to have a braket come off my frame to stop the hub.  This will affect my wheel and backspace choice.  Some coil overs have built in bump stops but cost more.
I'd be curious to see what you experience for wheel hop, if any by having two different shocks.  The front and rear shocks will load/unload differently.  I just don't know if this will affect anyting.  Could be a non issue.

 

9/20/2013 8:31 am  #23


Re: Hi, I have two IRS projects to work out.

Not drag racing, much more acceleration from a moving start, IE, going to 120 MPH quickly from 70 MPH.
Doubt I will have enough power to worry about wheel hop under those circumstances.

The air shock will vary depending on the pre-load as it is adjusted to level ride height when carrying cargo.

My XKE's all had the ability to spin a tire but never hopped.
I was not burning the tires for a whole block, just a few feet.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

10/06/2013 11:10 pm  #24


Re: Hi, I have two IRS projects to work out.

Well that was a surprise.

Had not realized that the Jag rear uses heavier wheel studs.
Have to buy different lug-nuts to put the wheels on for mock-up.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

1/10/2014 9:25 pm  #25


Re: Hi, I have two IRS projects to work out.

Just picked up a complete XJS rear at the local Pick N Pull for $170.00
This one came with 2.88 gears and a bad pinion bearing.
No loss as 2.88 is junk to me.
So long as it will bolt up to my other diff's it's fine.
Have to figure out what type each is so I can decide which to rebuild first and get the right brake set-up.

Off to pick up a Triumph GT-6 in the morning.
It had a turbo Buick of some sort in it and the rear has already been converted to ???? IRS instead of the original.
Big ugly hole in the bonnet will have to be cleaned up.
Getting it pretty cheap so breaking my vow to stop buying more projects.
It gets a hot-rod 225 Buick V6 and Saginaw trans, Muncie or maybe a T5 WC if I can find one cheap enough.

MUST STOP BUYING PROJECT CARS NOW!


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

1/11/2014 5:25 pm  #26


Re: Hi, I have two IRS projects to work out.

Got the GT-6.
All good glass and the body parts that have not been hacked are good and rust free.
No longer IRS though, some sort of posi live axle that is a little too wide.
Horrible conversion, looks like they used any available scrap and no engineering.

Lots of potential and no shortage of work to be done.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

1/14/2014 8:27 am  #27


Re: Hi, I have two IRS projects to work out.

Good luck and post some pics!

 

1/25/2014 8:16 pm  #28


Re: Hi, I have two IRS projects to work out.

Got a chjance to identify may Jag rears.
All are Salisbury!

Posi unit center is 60-63 XKE, first model type.
Also an earlier XJ6 open diff that is much more complete but still missing brake calipers, cage,and some other small parts.
The complet unit I just got from an XJS turns out to have an open diff, not the posi it should have been. 
At least it was complete despite having a bad pinion bearing.
In theory I can put the gears or center from the early unit into the late cradle and axles.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

1/27/2014 1:10 am  #29


Re: Hi, I have two IRS projects to work out.

In a bit of a hurry to sort out parts for the GT6.
Seems a Mazda Miata rear may be a fairly easy swap?
Maybe put an RX-7 diff in it?
Anyone here familiar with them, or their strength - weakness?

I will be using an about 200 HP Buick 225 V6 and T5.
Might put a 300 HP 231 in it some day.


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

1/27/2014 6:28 pm  #30


Re: Hi, I have two IRS projects to work out.

Well, nuts!

Mazda Miata is still 6" too wide.
Really do not want to get into a complex modification scheme. 

Any suggestions for an IRS at or near 50" track?


At these prices I want my gas 100 octane, leaded, and my windshield washed!
     Thread Starter
 

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