MG Sports Cars

Hi guys,

After many years away, I'm getting back to working on my car, and I want to address a topic that has been talked about many times: IRS.

I know people use the JAG rear end, but for some reason it doesn't do much for me. I did a lot of research and in 2003 I purchased an IRS setup from Factory Five Racing. I never put it in, and I'm thinking I want to go back and do it now.

Has anyone else gone down this road in the last 10 years or so?

I found this article that talks about the setup. It's exactly what I have: [www.mustangandfords.com]

Here is a picture of the upper and lower framework



The upper framework is more narrow than the mgb frame rails, so it will need to be widened (no big deal).

The lower framework bolts into the Cobra at both the front and back of the framework. I know mounts would have to be fabricated for the front, possibly square metal tubing coming back from the middle crossmember beneath the seats. At the back, those two cross pipes bolt up to the cobra frame. In our cars, those pipes occupy the same space as the gas tank, so I'm thinking about cutting them off and using the rear differential cover from the 2002-2005 explorer that has mounts built right into it. See Picture:


The factory five setup is 54" from hub to hub, which is only about 2" more than the existing rear end.

I already own the framework, the hubs have already been drilled to an mgb bolt pattern, I've got a differential, brake rotors, coil over shocks... almost everything in hand except brake hoses and good cv joints to attach to the axle shafts supplied with the kit.

So? What do you guys think? Is this workable?

Justin
'77 B 4.2L Rover V8 with fuel injection.

wanna sell that outfit?

Your upper arms and frame rails will need to occupy the same space.
The rear mount will need to go where the fuel tank is.
The battery boxes will have to go.

Jim

I removed the battery box 10 years ago in anticipation of this conversion, so that's done.

Are you suggesting that even with removing the existing "x" pipes on the IRS frame, the mounts on the back of the explorer differential still interfere with the gas tank? In it's current form, the setup is 11.625" from the center of the axle to the back of their framework. That definitely interferes with the gas tank, which is why I considered using the explorer differential cover. I'm unsure of it's depth but it appears to be significantly less than the existing setup.

I already own a 16 gallon fuel cell that fits nicely in the trunk, so I could remove the gas tank completely if needed.

In the article I posted, they ran into the same problem of the frame rails interfering with the upper arms, so they cut a section out, and welded in an inverted channel to restore strength. Could that be done here as well?

I know the bump stops would need to be removed, but that's easy.

Thanks!
Justin

It's your car. If you seriously want to do this you will find a way.

Jim

I can't speak to the clearance on the diff rear mounting points, but the upper control arms should not proove to be too big of an issue to resolve. Have a look at the ones on mine... Simply bent tube (of appropriate wall thickness) with ends to mate with the rest of your set-up should solve the problem.

Do pay attention to the size wheels required to fit over the upright/knuckle/hub assembly as I would bet most Factory Five's are running bigger wheels than 15" like a lot of MGs use - especially if you are planning for 4 lug wheels in the MG bolt pattern

Thank you for the helpful response!

I found your pictures and your upper control arm looks perfect for what I want to do. I'm not wild about cutting frame rails, but I would do it if necessary.

Does that bend mess with suspension travel or geometry?

Factory Five specs 15" wheels for use on their cars, so I 'shouldn't' have any issues. Besides, the hubs are bone stock from a Ford Thunderbird Super Coupe IRS setup, and those definitely didn't use bigger wheels.

Thanks again!

Justin, I'm by no means a suspension expert, but I do not believe the bend affects the geometry. Here's why. Take your existing control arm, fix one end and move the other end through the arc it makes. Now, take a piece of wire lnonger than the control arm and bend it so the ends of the wire line up with the ends of the control arm and swing through it's range again. Clearly the arc is the same. So what matters is the straight line length between the ends and pick-up points, not whether the material between the ends is straight, curved or any other shape.

With respect to whether it affects travel, absolutely... But then, that was the objective - to allow more compression travel before the upper control arm hits the bump stop. Which reminds me... Not sure if my pics show it, but I removed the OEM bump stop and the added plate that's on rubber bumper cars to space the bump stop down an inch due to the higher factory ride height. I then welded a captive nut inside the frame rail (I also removed the bump stop bulge inside the wheel well so had access at the time) and used a generic urathane bump stop that is barely longer than the frame rail edges. That maximized my compression travel. I have only hit the bump stops once or twice.



Edited 1 time(s). Last edit at 05/30/2014 06:38PM by rficalora.

Rob is correct in regards to bending not altering geometry. As long as both end points are the same - it's treated as a straight linkage.