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Newbie Question “Swing Spring definition “

Paul H

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Saw this ad on fleabay

******Triumph Spitfire 1500 3.63 ratio differential.  Smooth diff with very little backlash. Obviously difficult to check to know how quiet it is without driving the car which was just not possible but I have no reason to suspect there is anything wrong with it. If it was found to be faulty I would have it collected and refund in full. Diff casing is a four hole type for the spring so needs to be used on a swing spring car****


Whilst I am not looking to change from my 3.89 ratio diff on my Vitesse mk 2 which has  6 hole type,  does swing spring mean transverse spring and are 4 hole and 6 hole interchangeable ? 



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All the rear springs are transverse in the Herald, Vitesse, Spitfire, and GT6 family - they go at right angles across the chassis / line of drive - but swing spring means a spring that pivots in the middle and is not fixed in place.

Fixed springs are bolted with all six studs into the diff, but swing springs, because they pivot in the middle and must be free to do so, are held on with the outer two pairs of studs only. A swing spring will have the centre leaves bent to allow a pivot bolt, and fixed with a box-like housing, whilst a non-swing or fixed spring has no hole through the leaves and is held in place with a six-stud plate on the top only. Top photo is fixed, lower is swing with the mounting box attached, and then without showing the bend for the through-bolt.

Re the diff casing: it's common to have a six-stud casing used for a swing spring upgrade, simply by blanking off the two unused holes, but it's rarer for a swing-spring diff casing to be used for a fixed spring as this either means using only four studs or having two holes drilled and tapped. Other than that, the casings are nearly all identical. 





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Indeed. Earlier cars with the "fixed" spring are usually referred to as swing axle.

Other option is to swap the rear case between 4 and 6 stud diffs, really simple to do. Plus a great opportunity to clean it out and add a drain plug.

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and having put a hopeless swing spring on the Vit6  and a 4 hole 3.89 diff ( was 4.11) when reverting to a fixed courier spring it was easy to drill the case 8.3mm and tap 3/8 x 24 unf using the spacer block and clamp plate as a drill jig,

drill down 25mm  use a plug tap and its done , didnt break through into the internals , used a battery drill and drilled On car..

takes about 15mins 


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