Hi I am building a chassis from the haynes book but got let down with my donor so have to change the rear as i can not find any irs rear axles so I am looking at going down the live axle route.

my question is

can the top trailing arm be longer than the lower trailing arm as I have already welded that part in my chassis as per the haynes spec.

and what sort of travel should the rear axle have from top to bottom.

thanks

Ive seen dissimilar length trailing arms, although I think the other way round (lower longer) is more common, but equally the effects all depend on pivot location, the exact lenghts of the arms, etc. I would certainly be very hesitant to stray from a know design with fully understanding the implications, and or, just because you happened to have a bracket in a certain place already.


Daniel

Can't help with the TA length I'm afraid, but a word of warning if you are modifying the axle yourself to take the arms: Be very careful about spreading the heat when you weld the brackets on, I did my own and guess I spent too long in one spot when welding because when I took the car for weight/alignment checks with my local chap at Track Solutions (blatant plug! ) we discovered that I have over 1deg of toe-out on the rear!! It seems the axle will bow if not done carefully. It can be sorted but I'd sooner have got it right in the first place.

Good luck with the build

The arms really should be the same length and parallel to each other. The trailing arm front pivot points don't actually need to be in line vertically when viewed from the side as long as the arms are parallel and the same length.

In the early days of book Locosts a lot of builders were making all 4 trailing links 25mm longer and increasing the wheelbase by 25mm but as most builds are now IRS this has been largely forgotten about. The advantages were the longer trailing arms gave slightly less roll steer and the nose of the differential intruded less into the cockpit area.

If the axle distorts during welding it is easy enough to fix by running a couple of dummy welds down the opposite face of the axle, in any event this was mainly (but not exclusively) a problem encountered on Escort English banjo axles which were fabricated from thin sheet steel.