Jag Rears

By Geoff Kremer

Jaguar rear axle radius arms and torque bars

The rear radius arms serve to locate both the hubs and axle. There are those who may argue that these arms are not necessary given the size of the bottom arms, trouble is that without them all the loading is then taken by the diff mounting pad and the torque arms so all the suspension and torque stresses are fed into a small area of the chassis. In order for radius arms to work effectively they should not bind or hang up throughout the suspension travel. I’ve noticed many Jag radius arms are located on the chassis in a way that will do just that, this is O.K. if the whole thing is mounted on rubber bushes as on the Jags but if the diff is solid mounted a whole load of additional stresses are going to be fed into the chassis causing flexing and possible cracking of welds in addition, during power take offs it will cause the wheels to move back and forth, not good for getting all them horses to the ground.

The torque bars play a very important part in distributing the loads over a large area of the chassis. Try and mount them at a 45 degree angle with respect to just about everything. This is called “triangulation”. What you are aiming for is to produce the strongest and lightest method of installation. The diff and its relationship to the chassis forms the major triangle, other things like the torque bars and radius arms are then linked into that relationship spreading the loads over a large area of the chassis. Unless you are rubber mounting the diff there is absolutely no point in having “rod ends” or bushes fitted to the bars because they shouldn't be moving around anyway.

My diagrams are only for guidance and your chassis may force you to do things differently but if you “think triangles” you wont go far wrong

Here is how I would mount them

The setting of the pinion angle has been under much discussion, when using say a Ford 302 V8 the engine and trans are decline at angle of around 5 degrees, to help submarine away from the cab and its occupants in an impact. Now the pinion should in theory be incline the same amount so the two UJ's run parallel so not to invoke undue wear. Many go with the set up as above, but some are also now disputing this as the best set up and say to incline the pinion to match the E/T decline. I guess you pays ya money you takes ya choice, if you wish to read more try this http://www.nsra.org.uk/forum/topic.asp?TOPIC_ID=40688&whichpage=1 Your input would be much appreciated, I will add the above method is how UK rodders do it.

Here are the specifications for the Jag
Usually the diff ratio is stamped on a little ally tag which often gets lost then all
you can do is whip the cover off. Count the number of crown wheel and pinion
teeth then divide the crown wheel by the pinion.
To find out If you’ve got a Power Lock (LSD or Possi!)
Turning one hub will turn the other in the same direction even if you try and stop it.

Tech Section