Magnette rear spring replacement

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The condition of the leaf springs on my ZA had become a little tired. Broken straps and leaves that no longer hugged their fellows were indicative of the need for replacement. Undoubtedly too, the springs would have lost some of their original tension after 65 years of use !

In preparation I ordered a pair of springs from BCC in Redruth, and from Peter Martin a set of (rubber) rear shackle bushes, shackle plates, new U-bolts, saddle plates, saddle plate rubbers, and axle buffer plates. It might be worth checking the condition of the rear shock absorbers and their bushes too, and replacing if necessary.

At face value it seemed a relatively straightforward job. In the best traditions of the Haynes manual, the instructions were clear – simply support the body on axle stands, undo the forward mount bolt, remove the rear shackle plate; undo the U bolts over the axle and withdraw the spring. I wish it had been that simple!

I found the rubber bung covering the top shackle bolt in the boot and removed it. For some reason, the nut on the shackle plate didn't line up with the hole; it was positioned high and in such a way that no spanner or socket could be fitted from the boot. That meant everything had to be done from underneath the car. The car was jacked up and axle stands placed under the side ahead of the front mount and to the rear under corner of the boot floor as a precaution.

The rear shackle plate nuts came off relatively easily but the shackle plate itself could not be removed from the spring because the outer bush was firmly "welded" to the pin of the shackle plate. It was left in place and attention focused on the U bolts over the axle. Firstly, I placed a jack under the axle casing to take the weight once the spring was released. Next, the lower shock absorber mounting was undone and the shock moved to one side. Both rear shocks had been replaced recently so neither the shocks themselves nor the bushes needed changing.

The U bolts were relatively easy to remove, but the lower saddle plate had become welded to the rubber saddle pad. A cold chisel was used to separate these components from the underside of the spring, and then the spring, with a little help from a hammer, dropped to the ground, pivoting on the front mount. The buffer plate that locates the top of the U bolts was very rusty, as were the saddle plates and U bolts.

The front mounting comprises a single bolt with nut on the inner mount face. This was completely immovable. No amount of leverage, penetrating oil, or even heat, would cause the nut to budge at all. Eventually, the nut had become rather butchered, as had the head of the bolt. Out came the angle grinder and cuts made to the bolt between the mount and the spring itself on both sides of the spring. Despite there being just the head of the bolt and virtually no shank, a drift was needed to remove the remains of the bolt. Similarly, the nut and the tail of the bolt presented the same problem. It took some time with the drift to remove the stubs but eventually, both came away. What makes this task more difficult is the very limited access to the outer face of the mounting point.

Now – a word of warning. It appears that the original Magnette silentbloc bushes (3/8" ID) were not available in the past and so MGA items (7/16" ID) were fitted instead by drilling out the front mounting holes to suit. My spring supplier had sent me the MGA size thinking that was the original size. After some confusion over several days, during which I considered drilling out the mounting holes to 7/16" as the supplier didn't appear to have the 3/8" ID bushes, it transpired that they did, and sent me the correct bushes. These were relatively easy to fit so all was back to "factory spec".

It is quite possible that some Magnettes may have had the front mounts redrilled to 7/16" so you will need to check which you need.
With the spring removed it seemed prudent to paint the forward mount, and the axle plate prior to refitting the new spring. For this I used POR15 – a rust converting paint which I have used in the past. It is very effective, albeit not cheap.

Once the paint had dried, I fitted the front mount and left it untightened as the front and rear mounts must be only tightened when the car is resting on its own weight otherwise the bushes may distort. At the rear, I fitted the top bushes using some rubber grease to aid their fitment. The bushes were a very tight fit in the holes but using an old 3/8" stud with large washers and nuts, I craned the top bushes in place

There isn't much of a gap between the inner face of the shackle plate and the body, so it is necessary to fit both lower bushes before moving the spring up to fit the shackle plate. The shackle plate itself is a tight fit and again, rubber grease was used to assist the fitment. Ultimately a rubber hammer was need to force the shackle plate through the bushes, and as far as the top bushes were concerned, a washer had to be fitted through the boot access hole, followed by a nut that was tightened on the shackle plate pins before sufficient thread was available to fit the inner plate, spring washer and nut. It really is quite tight but there is just enough of a gap between body and shackle plate pin to fit the lower washer and nut. Once again, the nuts should only be loosely fitted at this stage.
Now, with the spring attached at the front and the rear, attention turned to the U bolts around the axle casing. Trial fitting the U bolts showed that they were a tad narrower than their predecessors (presumably a metric size that approximates to the original imperial) and needed "easing" to fit the axle nicely. Failure to do this will result in the saddle plate holes being out of alignment with the U bolt legs as they will splay if not eased open. Use the old U bolts as a pattern. This part proved to be quite straightforward with the buffer plates placed on the top of the axle before the U bolts were slid over and then pushed through the upper plate, upper rubber buffer, beside the spring, and down through the lower saddle rubber, and lower saddle plate.
I used a jack to ease the spring upwards and back into place whilst tapping the U bolts down. Finally, the shock absorber mount plate was replaced, the U bolt nuts tightened, then the shock absorber bushes were replaced and the shock absorber bolted back. Lastly, the car was removed from the axle stands so that I could tighten the shackle plate nuts plus the forward mount when the car was in its normal position under its own weight.

Footnote

I initially opted to use rubber bushes as they are readily available but did find that the rear spring mount tended to creak rather when fitted – presumably when the shackle pins rotate in the rubber. As the rubber bushes are not very expensive, I chose to replace them with poly ones. You may find it difficult to find a supplier listing Magnette poly bushes, but the Superflex part number for the rear shackle is SPF0014 (also used in the MG Midget and MGB) available from MG Motorsport

Suppliers

Springs BCC Brakes & Suspension 01209 202820 (britishclassiccarparts.com)
Poly Bushes MG Motorsport 01442 832019 (mgmotorsport.co.uk)
Other parts Peter Martin 01580 763056 (mgspecs.co.uk)