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MG MGB GT V8 Factory Originals Technical - Anyone using Jag IRS?

Hello all,
I just purchased a cancerous '72 XJ-6 to donate the front suspension and complete rear for my '66 MGB project. Does anyone have experience with this swap?
Thanks,
Darren Jameson
Darren Jameson

Darren,You can't use the stock XJ-s set-up in an MG as it is now.You really need the earlier e-type(series 1 or 2 SIX cyl. only)complete unit,cage and all.The earlier cage will go up into a "B" like it was made for it.Then you still have to get the width narrowed.This is done by getting new halfshafts made and shortening the lower control arms to get the needed width of 52' hub to hub.This can be done at home,but the halfshaft tubing needed is hard to find due to it's odd size and thickness.the shafts have to be 2 1/2'OD and with the large series U-joint,the weld yoke required takes 2 1/2'X .156 thick tube.Try to find this tube,it is very difficult because it is not commonly used,at least around here.As a result,it is easier just to let CWI in WA make up a control arm/1/2 shaft set for me to my spec.This is the most difficult part of tho whole project.
Actualy the body mods are not extensive nor difficult.Remove the axle retension strap mounts,remove jounce bumper extension(rubber bumper only),cut the battery box at an angle to clear the E-type cage(just move down a size in battery,Group 24 from a group 26,the cca's are VERY close.Then,using rubber insulators 1/2' thick on top of the cage,offer the unit up to the flat area forward of the trunk pan.You will notice this flat area is <> 7-8' wide and the cage is 7-7 1/2' wide,it is a perfect fit.Then reinforce the panel with doubling up and gussets to the frame sections,and drill down and bolt through the body,rubber insulators,and the cage with 4-6 bolts.Then fabricate torque control brackets between the cage and the bolt holes for the shock bodies.
This not a very difficult swap,but really only can be done with an early 6cyl E-Type cage assembly.ou can't narrow the XJ-s or 6 cage effectively.It would be more trouble than it's worth.The E-Type units are available(sort-of expensive $800-$1200 for a complete unit used)but then if you are looking to be this different,then price usually is not a factor.
Good luck........Dave D.
Dave D

Darren:
There is a website by Nick Smallwood in England who has done a conversion using a Jag rear end. Go to:
www.mgbv8.co.uk
Cheers, Pete.
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Peter Thomas

Thanks very much for the reply! It was Nick's site which inspired me to purchase the '72 Jag. It appears to me that he has made this swap work quite nicely. I'm going to try and follow his lead without trying to create a Sebring look on my '66 roadster. I hope to attain the look of the latest Supersport creation from MGOC. This will necessitate narrowing even further than he has. This is also where I might run into complications. It also appears that Nick has the dual spring and shock setup in place. Wouldn't this be overkill on an 1800# MGB?
Darren Jameson

Hi Darren,
I saw that too and thought the same thing...great set up but do you really need it?
My thoughts are in a road car it is not required but in a racing car it might just be the advantage over the opposition you need to win.
By the way I emailed Nick who tells me the project is currently on hold due to other priorities.
Good luck with the conversion, Pete.
*******************************************************
Peter Thomas

Peter,
Thanks for the reply. I thought that since I discovered this XJ-6 for $200.00, I couldn't pass up the opportunity!
Having said that, I now have the daunting task of trying to engineer this correctly! Any pointers or gentle words of encouragement are greatly appreciated!
Darren Jameson

Darren,
I am happy to provide words of encouragement and whatever other information I can help with.
Some of the hotrod fraternity have used the Jag rear end in street rods for many years so that might be an avenue worth exploring.
If and when I find anything else I will pass it on.
In the meantime go for it......Pete
*******************************************************
Peter Thomas

Guys,Jag IRS in an MGB has been done before.In fact I ambuilding another now.The XJ-& S rear assemblies might look very temptind dur to low cost and availability,but the fact remains the the easiest and most geometrically correct way is to use the earlier 6 cyl(62-70) cage assembly.To narrow a 12cyl or XJ-6 or S would mean alot of re-engineering of suspension and mounting.Ask Nick smallwood about that and he will tell you that narrowing the less expensive XJ-6 cage assembly was a pain in the %$##,and if he had to do it again,he would use the E-type unit.Think about it,you are taking a rear that is 61 3/4" wide and trying to narrow it to 51 1/2 to 52" depending upon wheels used.The upper coilover mount for the XJ-6 is too far outboard.The E-type measures 53 1/3" wide.That is only 5/8" per side wider.When you shorten the control arms and axles,not much will change besides the coilover angle from 30deg to 22deg from vertical.Then just soften the spring rate to compensate for that and that is it.The XJ-6 unit will not go to waste however,there are plenty of parts that interchange between years including brakes,hubs,diff units,etc...Trust me Darren,using th E-type cage will be the easiest and it will look like it belongs there.It is worth the trouble and expense of finding one,which is not very difficult.Good luck Dave
Dave

As I say on my website, if I was going to do it again “I would dump the sub frame all together”. I looked into the E-type option, which would have been easier, but the cost put me off. In the end I spent at least as much having a standard XJ6 unit shortened.

When you shorten the XJ6 sub frame, the length of useable shock also shortens. This would be made worse if the shafts were shortened to fit under standard bodywork.

The Cobra kit car guys mount the diff directly to the body using a very substantial ˝ inch steel mounting plate. Then either don’t bother with radius arms or mount the forward attachments in line with the inner spindles to minimize fore/aft movement during travel. This option allows you to place the top shock mounts higher and in the correct place at around half travel at standard ride height.

I kept the dual spring set-up as I felt it was special, and I believe 4 lightly sprung and damped units would give a better ride than 2 heavier ones. It also gives me better senses of security incase one unit fails.

The rear end is out at the moment for powder coating and to replace the 3.3/1 diff with a 3.07/1 limited slip item.

Nick

Nick Smallwood

Geez this sounds like a lot of work. But IRS would be great; the stock MGB rear suspension is positively agricultural at times. Is the Trevor Taylor Conversions unit any good? I'm gathering it hasn't earned widespread acceptance.
Harry

I have not heard anything about the trevor taylor conversion either. But just becuase it has not been widely accepted does not mean it is not good or even perfect. I have noticed we MGer's are a very "DIY" group. We would rather spend $500 of some other car's rear end and re-engineer it into our cars than fork out $1000+ for a built to fit kit..
Larry Embrey

Is there really any advantage to using the Jag IRS though? Seems to me a decently set up MG axle does the job surprisingly well, and is easily replaced if broken. Pretty light for being as strong as it is too. The armstrongs are infinitely tuneable and there's a lot you can do with the springs if you want. Seems like a lot of reasons not to mess with it to me. There *is* the problem with torque wrap up of course. How is that handled in the Jag rear end btw? My brother's IRS TR4 squats in the rear when you get on the gas. Can't really see that being good for either tire loading or handling, does the Jag also have that characteristic?
Jim Blackwood

This thread was discussed between 04/08/2001 and 14/08/2001

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