MASCOT January-February 1987

ROADSTER NOTES - Replacement of lower wishbone pivot bushes 4AB/4AD

Bill Haverly

Now and again a fault on a car develops which is very difficult to diagnose. Sometimes it's a squeak or a rattle which is more an irritant than a serious defect, but it's wise to check it out. Where engines are concerned, the odd noise is more important to track downs but an intermittent knock can even leave the engineers scratching their heads after a complete stripdown. My 4AB is by nature a long suffering tyre squealer, and this is not due to excessive cornering speeds for I left the boy racer image behind a long while ago. Attempts to cure it have only been partly successful. A new pair of front tyres several years back helped enormously followed by setting up the tracking according to the book and getting the camber angles right, but by last year the squeals were recurring, nearside front tyre was uneven, and the car was far from sure footed in the bends.

At the Woburn Run I was changing the offending wheel for a better spare and having a nose round noticed chafing marks on the lover end of the suspension turret, which I figured could only have been caused by the coil spring. As the coil spring sits over 2" away at this points the conclusion was that to allow such chafing to take place there must be considerable wear in the lower wishbone inner pivot bushes. These are the same type rubber bushes as fitted on the top wishbone inner arms and in the leaf spring eyes and shackles, but on the IFS bottom wishbone pivots are none too easy to check for wear. They are well concealed and protected by the pivot and brackets and the gunge of ages, and with the coil spring under compression between the top bracket and lower arms (free length 12", compressed 8") it is very difficult to detect any lateral or end movement; even in my case where the bushes were in bad condition. Several years of MoT tests without comment or failure prove this point quite well. So, what to do about it?

The golden rule with a running restoration is only to tackle the work in hand that is necessary. Don't get diverted, otherwise you will be joining the ranks of the long term rebuilders and the car will be off the road for years instead of weeks. With this in mind, the stripdown began. Off came the outer track rod connection, the anti-roll bar link, and with the shock absorber bottom bracket nut and the 4 nuts holding the top anchor bracket removed, the shocker was lifted out with bottom bracket attached. Bottom trunnion locknut slackened off a few turns and clouted with a copper hammer to check for seizure. O.K., it moved. Next step was to fit two hook type spring clamps on opposite sides of the spring, and lock on tight as near to the ends of the spring as possible. Slacken off the swivel pin top nut after removing split pin, and keep a firm grip on the brake drum/stub axle assembly as it drops out of the top trunnion and pivots away. Remove coil spring with clamps attached, top and bottom rubber insulating pads, coil spring bottom carrier and spacer. Pop swivel pin back into top trunnion and replace locknut. Now the bottom trunnion pin can be drifted out. I kept the nut on for as long as possible, using it as a thread protector during this operation. Remove the swivel nut again, and the hub assembly can be rested on a block of wood to avoid any tension on the flexible brake hose. The bottom wishbones should now be free to pivot, but mine were still bonded to the pivot bushes and took a lot of penetrating oil and up and down movement to loosen. Now for the moment of truth - the anxious time when the inner pivot nut is slackened off and attempts are made to free this 10" bolt which passes through the large chassis cross member. Before tackling this undo the nuts holding the pivot end brackets to the frame.

Either I was, in luck or Holt's penetrating oil is very powerful stuff, but with some determined soft hammer work and plenty of squirt, the pin eventually came out. True, it was a bit bent at both ends and the thread was slightly damaged, but it came out. As for the rubber bushes, one was three-quarters missing and the other in a very sorry state. Checking the stripped items for wear, swivel pins and bushes were free of any side play, but the bottom trunnion pin was a bit sloppy, so I pressed in a new 3/4" bush and reamed it out to size. The pin itself had little wear, only some pitting on the top side where there is no grease outlet. The inner pivot bolt was straightened out, cleaned up and thread recut with a 7/16" BSF die nut, then trial fitted to the cross member prior to reassembly. I knew the brake assembly was O.K., for new cylinders and shoes had been fitted in the earlier days of restoration. Before assembling the lower wishbone, remove the tab washer and slacken the two set bolts holding the arms together, to give enough clearance for the new shouldered rubber bushes. The only fiddly part was replacing the bottom trunnion. Here the same approach as dismantling was adopted, i.e. hanging the stub axle temporarily onto the top trunnion to take the weight. Other points were smearing the inner pivot bolt with rubber grease to give some lubrication and perhaps prevent the bushes sticking in the long term, and fitting a new shocker. I picked up a pair last summer at an autojumble (where else) which are standard fitting on the front end on the Morgan Plus 4, Plus 8 and 4/4 sports cars.

Armstrong recommend them as being compatible with the Roadster spec. and the part number is 62/0130. Price from the Morgan agents is around £20 each + VAT but by jumbling around you should pay less than this for a pair.

One further point, regarding the use or non-use of spring clamps during this overhaul. Whilst it is certainly possible, if a bit dangerous, to remove the coil spring on a sort of explosion principle, I'd like to hear from anyone who is either immensely strong, or ingenious enough, to have replaced a coil spring without the use of clamps.