Technical Tips for the 346 / Star Sapphire Page 3

Advice and guidance for the maintenance of Armstrong Siddeley cars. If you have other technical advice for Armstrong Siddeley owners you would like to share here, please contact sphinx@siddeley.org

Please note, technical tips are given by individual members and ASOC Ltd does not warranty the accuracy of them or endorse them in any way.

More tips can be found by using the links to the right.

Keeping your 346 handbrake freely operating - Supplied by Keith Dewhurst

The 346 handbrake as originally specified is capable of very effective working. However, upon release on MKII models it relies on the two expanders contracting under the pressure of the small spring spanning the expanders across the outside of the wheel cylinder and the one light spring on the rear of the leading shoe; that is to say not much spring pressure. Many owners (myself included) have found it helpful to fit an additional full-sized spring that spans between the shoes on the side of the wheel cylinder, as was the practice on the MKI.

When it comes to lubricating the handbrake cable via the grease nipples on each side, the service book suggests these are lubricated with 140 oil.  However, I always use thin engine oil, as I feel the 140 gives too much resistance.

Despite all of this it is quite common for handbrakes on MKIs and MKIIs to stick on or not fully release, causing warm brake drums and wheels and poor mpg. If this does occur, as an emergency response, it is an easy job to release the handbrake by lying under the rear of the car and pushing the expander linkage back into the drum by pressing a large screwdriver against the clevis pin, immediately behind the brake back plate, that holds the cable clevis to the bar coming from the expander / cylinder assembly.

The cause of sticking is usually internal corrosion between the metal and alloy parts of the expander / wheel cylinder assembly. This is easily rectified by cleaning and greasing with the cylinder in situ on the car.

First loosen the wheel nuts of the rear wheel, support the car with the rear off the ground and remove the rear wheels. With the handbrake off, slacken the square brake adjusters anticlockwise by a counted and noted number of ‘clicks’ and remove each rear brake drums by removing the two brake drum securing screws adjacent to the wheel studs. If a drum is sticking it can be freed by screwing two suitable BSF bolts in to the two threaded holes on the wheel face of the drum, again close by the wheel studs. Do not hit the drum fins with a hammer as this will likely crack the fins.

With the drum off remove the small spring that spans the handbrake expander across the cylinder (MKII only). Now remove the four screws that hold on the steel plate on the outer side of the cylinder to expose the expander mechanism: two wedges or handbrake tappets (as they are called in the parts book), two rollers and the draw link to the cable. It may be useful to make a sketch of how they are fitted before removing these as if the wedges / tappets are fitted the wrong way round they will not work. Almost certainly corrosion and pressure from the shoes will hold all in place while you do this.

It is also likely that when you remove the expander components one or both shoes will force the wheel cylinders to further contract causing the brake fluid level to rise in the reservoir under the bonnet. So, check to see if there is room for this first. It is also possible for the bottom shoe to be easily dislodged on an unmodified MKII and drop down letting the lower wheel cylinder piston escape, as only a light spring pressure is applied by the spring at the front end of the shoe. So please take care.

Remove the two wedges / tappets and two rollers from the side you are working on. With the draw link free it is now an easy job to remove the split pin from the clevis behind the wheel cylinder assembly, remove the clevis pin itself and pull the draw link free. The draw link, rollers and wedges/ tappets and their cover plate are all made of steel and should be thoroughly cleaned up with fine abrasive paper. The wheel cylinder housing in which they run is made of an alloy, and should similarly be cleaned up.

At this point it is worth checking that the wheel cylinder is free to slide against the back plate. It is secured by three ¼” BSF studs and nuts held from coming loose by double coil spring washers, (bearing on a plate MKII), behind the back plate. These should be tighten just enough to remove any slackness between the wheel cylinder and back plate, but not so tight that the cylinder cannot slide and find its own central position for even braking. If the cylinder will not slide when lightly tapped with a soft mallet then further dismantling will be needed to clean up and suitably lubricate the joint. Start by slackening the three nuts and see if a little ‘exercise’ will free it up. If not you may have to completely remove the cylinder and clean up the mating faces.

Now is also a good time to inspect the brake shoes for excessive or uneven wear. Be sure to look across each shoe at it leading and trailing edges to ensure it is wearing evenly between its inboard and outboard edges. If it is not, then the steady pins need adjusting to tilt the shoes closer to, or further away from the back plate, but this is really a subject in its self.

With all the handbrake parts cleaned up, reassemble using suitable grease. I always use Copperslip. Refit the clevis pin using a new split pin and wipe any excess of grease from the outer surfaces to be sure that this is not transferred to the drums or shoes by being thinned by heat. If all is well the draw link should be slightly proud of the cylinder and when pushed in should expand the shoes and spring back allowing the shoes to contract when released.

With both wheels done, replace the drums and tighten the expander on each side by the noted number of ‘clicks’ you first slackened them by. Next apply the foot and handbrake a few times each to centralise the shoes and check drum rotation. With the handbrake off set the adjusters so the shoes are just, but only just, catching the drums by the same amount on each side when rotated by hand in the direction of forward travel. Once set, reapply the foot and handbrakes and, with the handbrake off, re check all is well. Finish the reassembly and road-test.

In my experience these parts need stripping and cleaning every three years, although I expect different climates and storage environments will cause this to vary.

Modifying panel lights so you can see your dials at night - Supplied by Keith Dewhurst

This applies to all the Sapphire range that use the ‘ultra-violet’ panel light system. When new this no doubt worked well, but is does rely on the phosphorous luminosity of the markings on the gauges. Unless you are lucky enough to have a car that has been stored in the dark for most of its life, then it is likely that your dials will have lost much of this luminosity and are therefore rather difficult to see at night. I have tried a number of differing bulbs in my 346, but none really gave me a good clear view, so in the end I decided to convert to conventional illumination. As well as carefully removing the red glass domes in the centre of the multi instrument cluster and the one in the base of the speedometer I also fitted a rheostat to replace the original two position switch. Before you start any such modification be sure to disconnect the battery.

To gain access to the back of the instrument cluster on a 346 the three Dzuz fasteners on the face of the instrument board need to be released and the whole assembly of dials and switches pulled forward. Feed any slack in the speedo cable and oil gauge pipe through the bulkhead to aid this and as soon as it is adequately exposed remove the speed cable from the back of the speedo. Also take care with the mileage trip and clock adjusting knobs which hang down through the millboard beneath the dash from their respective instruments. To gain access to the red dome in the multi cluster there is really no alternative but to remove the whole instrument cluster. This necessitates releasing the oil pressure gauge feed pipe and the electrical connections from each of the two terminals on the ammeter gauge, fuel gauge and petrol gauge  I usually mark all with a tag of masking tape suitably labelled). There will also likely be an earth lead attached to the instrument cluster mounting screws.

With the connections removed and the existing instrument light pulled out you should be able to unscrew the 4 securing wood screws taking care to capture the alloy spacers beneath them. With the unit on the bench it is easy to remove the 4 instrument gauges (for safety) by releasing the two screws holding each in place, and to dismantle the cluster to gain access to the red glass. Fortunately the speedometer is much easier to address. The red dome is held in a metal fixing which, once the mileage trip adjuster is unscrewed can be easily released by removing its 2 fixing screws. With regard to the switch, I made up a metal plate, screwed to the back of the instrument board, to hold a Smith’s heater rheostat in place of the existing switch. Rheostat switches of this type were made with the same hexagonal shaft as is used on the original switch and which will enable the original knob to be easily fitted. In my case I only had a rheostat with a round shaft, so I cut the shaft on both switches and spiced them together with some small BA screws! It is possible the Stores may be able to help supply a suitable rheostat as the 16 / 18 hp range used a heater with rheostat. Anyway once assembled I found that 2.2w bulbs in the speedo and 5w in the clock and multi cluster gave a terrific light and I can adjust the illumination to suit the ambient lighting I am in.