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MG MGB GT V8 Factory Originals Technical - jaguar independent rear narrowing

I'm installing a jag xj6 rear into my B and would be gratefull for any info on who could shorten the axles and control arms. The closest to my location the better. No one here in the Austin area want to touch them for fear of weakening them. Thanks.


I'm also installing a Jag rear end into my B, and I'm having Ted Lathrop, of Fast Cars, Inc, do the work. He hasn't started on it yet, so it's a bit early to provide tech details.

However, I have done a bit of research: First of all, the lower control arm is made exactly the same as a drive shaft, so having it shortened should be a simple process. The axle shafts, though, are made differently and shouldn't be cut and welded, at least not on most models. To shorten them, you should replace them with a steel tube of the same type and size as a typical drive shaft, and have new flanges welded to it on each end, to match the Jag U-joints. Most towns have a truck shop that specializes in drive shaft service, and can do the work for you rather inexpensively.

There is a company in California, called Concours West Industries, that specializes in Jag rear end work for street rods. Go to your local book store and browse through a copy of Street Rodder magazine - they will have an ad for CWI, and for a few others Jag specialists as well. You can buy a wide range of new units from them, including one that uses the differential from a Ford 9", and can handle gobs of power, or they will also provide shortened components as well.

I have a series of article on rebuiulding the Jag rear end from an old issue of Street Rodder - if you want, I'd be happy to copy them and send 'em on to you.
Dan Masters

More info from deep in the archives (contains some info from the Street Rodder article):

<<<Posted 02 May 1997 at 06:04:13 UK time
Eric, Dumfries, Va,

Other than the article (Faust and Hoagland) in "The MG V-8 Newsletter" and the reference "Aluminum Olds V-8/MG" in Petersen's Complete Book of Engine Swapping No.4, I don't know of anyone who has/is attempting to put a Jaguar IRS into an MGB, except me. (I'm sure there are others -- I just don't know who they are.) If you are going to use a Jag IRS, the first decision is which one to use. There was an excellent series of articles in the March, April and May 1995 issues of "Street Rodder" magazine discussing the Jag IRS. The article in the April issue provides details (there are a few minor errors) on the differences between the various E-Type, XJS and sedan rear ends. The 6-cylinder E-Types (Mar 61 - Sep 70) are 53 1/4 inches from wheel flange-to-flange, the V-12 E-Type and 3.8S sedan are 56 inches and the XJ6 and XJS are 61 3/4 inches. My 76 MGB rear axle measure 52 1/4 inches (the front axle measures a
bout 50 3/4 inches) versus 53 1/4 inches for the 6-cylinder E-Type so if you can live with the extra inch (I'm using wider alloy wheels with more back space.), then the 6-cylinder E-Type IRS is the way to go since it doesn't have to be narrowed. If you can't live with the extra inch, then you can use almost any model since all the rest will have to be narrowed anyway. By the way, narrowing the Jag IRS requires cutting and welding the lower control arm (called a wishbone in the E-Type shop manual) and the half shaft (which forms the upper suspension link as well as transmitting power from the differential to the wheels). All half shafts except for some pre-65 E-Types and probably some 3.8S sedans of the same vintage are forged from solid steel. Cutting and welding these is not recommended by CWI (Concours West Industries) who appear to have by far the most experience in the U.S. modifying these suspensions for use in other vehicles. Brake ro
tors on all 6-cylinder E-Types are 10 inches in diameter. V-12s and later cars are 10.4 inches. 1960-63 cars have 3/8 inch thick rotors while later 6-cylinder E-types (and other Jaguar models) are 1/2 inch thick. Therefore, since the swept area is the same, there should be no difference in braking between the various 6-cylinder E-Types other than those with the 1/2 inch rotors should be less likely to overheat and warp. Given that a well built MGB V-8 should have performance similar to a 6-cylinder E-Type and brake proportioning valves sell for about $40 (Summit Racing), I would recommend the best brakes you can get, including upgrading the front brakes as well. If you want to install the Jag IRS in its cage (or cross member) you will have to cut out the brackets that hold the top end of the rear axle rebound straps and relocate the fuel pump on the later model cars. On my car the flange on the IRS cage had to be bent out flat to clear the
rear part of the battery frame. At about this point I decided I didn't like the idea of having to bend flanges, cut brackets, drill holes in the floor, etc. to get the suspension in. I also decided that even though powder coating cage and suspension components as I did when I rebuilt my XJS several years ago looked pretty good, removing the cage and fabricating a tube steel cross member that would bolt to the two shock mounting holes on each side plus one additional hole added about 1 foot behind the rear shock mount hole would look much more professional (and also provide a better view of and access to the suspension, brakes, etc. so I've designed a cross member which is being built now. For those who don't want to design and build their own cross member and other mounting hardware, almost everything you need can be bought from CWI (644 Terminal Way, Costa Mesa, CA 92627, 714-642-9807). End pieces for the cross member will still have to be fabricated and
their radius arm kit will have to be modified to attach to the front mount where the leaf springs would normally attach or further forward. Many people don't bother with the radius arms; however, Jaguar thought they were necessary even on the 6-cylinder E-Type so I would recommend you do likewise, especially if your IRS is being held in with 6 bolts through the thin sheetmetal of the body shell. Also make sure you use rubber bushings like Jaguar did on the radius arms so the suspension will not bind as it moves up and down (the wishbone moves up and down in one plane while the rear end of the radius arm is traveling in an arc in another plane at nearly a right angle to the first which creates a geometry problem and something has to give). (The rubber bushings can be eliminated without causing a binding problem by locating the front pivot points for the radius arms in line with the wishbone inner pivot points; however, I don't know if there is room to do that under the MGB.%
29 By the way I paid $850 (plus $170 shipping) for my 69 E-Type IRS with 3.54 ratio, Power-Lok differential and steel wheel hubs. Jaguar uses five 1/2 inch bolts on a 4 3/4 inch circle -- same as Chevrolet. The hub can be redrilled to match the MG 4-bolt pattern. For wire wheels it looks like Moss's wire wheel conversion kit has hubs which bolt to the steel wheel rear axle. If that is true and Moss would sell just the special rear hubs, then there might be a way. I have no idea if the Moss conversion would really work. I expect to spend $500 to $600 more for parts, powder coating, and fabrication of the cross member/radius arms. I hope this, along with the other articles, helps. Sorry I wrote so much; however, I've only scratched the surface. I won't be able to report on the final results of my conversion for several more months.>>>


Dan and Carl,
thanks for the leads. I am temped to shorten them myself, but would rather leave it to someone more experienced in shortening jag rears. I contacted ERA replicas (Cobras) and they also told me to call Concours West Industries. Shame on me for not having surched archives first.
Dan thanks for the offer, but I have a subscription to ShopKey and all the info I need.
I'm custom fabricating a space frame from chrome molly tubes and aluminum panels.(the only thing still remaining are the outer body panels and sills for body allignment issues). Fully tubbed wheel wells to allow up to 345 wide tires on 15 inch rims. Currently only running 225/50/15 but plan to switch to wider slicks at track. Hope to run 12's naturally aspirated but should dip into 11's with twin turbos at full boost. Hope to have it finished by end of next month.
Joaquin Lopez


What is "ShopKey?" and is it something I would want?

Hey, it sounds like you are making one mean machine! I can hardly wait to see the finished product. Don't forget to send in a "how-it-was-done" article for the newsletter.
Dan Masters

If I didn't know any better, I'd say it sounds like about $1300 to get your hands on a jag irs, and all the parts necessary to get it under an mgb. Seems to be about $1300 to get a shortened rear axle with posi to go under a B.

Is this really a discussion we need to be having?

Shopkey is a repair/estimating/management program from Sun/Snap-On. Used to be Mitchell's "On-Demand". It is a quarterly updated dvd package subscription intended for automotive repair shops, so its pretty expensive. However, I don't know how I've managed without it in the past. If you work on modern vehicles it's a must have. It provides vast amount of info that makes a Haynes manual appear as if it was written for a child. Info such as detailed wiring diagrams, year/make/model/engine specific efi theory and operation, component testing, vacuum diagrams, belt routings, specifications/capacities, tips and technical service bulletins, subsytem info such as Air conditioning/ABS/Airbag - everything you need to repair a modern vehicle. It provides info from 1983 through current model year, and if the info is not available they can fax you any anything that is not yet included in your current update.
here a link:

prices go all the way up to $5000 for a jag rear last I looked around, but a little searching can land you a good used system for $400-$800 round here. The main reason I'm doing this is that I wanted better control in cornering and a posi for better launches. The way I originally installed the engine only allowed millimeters of clearance at rack, exahust, tranny etc. Under heavy breaking/cornering things would rub. I didn't realize the extend of the wear done until I remove the engine/tranny. I had originally hoped to finish this on my summer break, but we have been swamped in work and I only have time on Sundays to work on it.

I'll provide update upon completion.

MGC steel wheel hubs have a 5x4 3/4 bolt pattern also. If you can find a set of fronts (I would try the U.K. they are rare in the U.S.) They bolt right up to the B spindle. You'll also need MGC rotors turned to 10 3/4 dia. and MGBV8 calipers/pads. Bearings and seals are the same #s as a B. You could keep your 5 lug rear hubs, have better front brakes, and have a huge selection of wheels to pick from!

bill jacobson

This thread was discussed between 21/08/2002 and 22/08/2002

MG MGB GT V8 Factory Originals Technical index

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