MASCOT March 1991

DOES YOUR ROADSTER SUFFER FROM WIGGLY REAR?

Dave True

You will recall in last months Issue that I gave details of an additional chassis cross member on my 4AD Roadster and queried what purpose it actually served. I had a telephone call from Leo Raby in Birmingham and the following information is based on what. he told me.

Apparently the Management of Singers at Small Heath began to get progressively more worried about what became known as 'wiggly rear' and damage caused by chassis movement to the ash framing. at the rear of the car. With a standard 4AD chassis (body removed), if you were to jack up under the rear end of the main chassis member on the right hand side and carry on jacking until the roadwheel on the left hand side was off the ground, then the main chassis member on the right hand side would be 9" higher from the ground than the main chassis member on the left hand side. It follows that if a chassis twists to this extent, then enormous strains are put on the ash framing particularly at changes in direction adjacent to the four corners of the boot lid, and fracturing of the framing will inevitably result.

Sometime during 1953 Singers began to experiment with strengthening members to the chassis. A bit late in the day you might think, considering the back end of the Roadster chassis had remained virtually the same since Roadsters were introduced in 1939; but it could be that the back end twisting was accentuated when the much heavier 1497cc engine was fitted in 1951 in lieu of the earlier 1074cc. The heavier engine would probably stop the front end of the chassis twisting, which would make the back end twist more if jacking were applied on one side at the rear end. The beefing up of the front end of the chassis in 1951 to take the independent front suspension of the 4AB and 4AD Roadsters would also transfer the twisting further back in the chassis. Earlier beam front axle cars with the 1074cc engine would probably twist their chassis right up to the front end.

It seems slightly eyebrow raising that the factory experimented with various strengthening methods on cars for sale. I understand from Leo that no cars were actually recalled to the Works to have strengthening members fitted. Leo has been talking. to an 'old hand' from the Singer Factory and all work was carried out there. This, of course doesn't preclude owners making private arrangements with local garages to have their chassis strengthened. It seems to me not to be conclusive that my own 4AD was strengthened in the factory. If it was, why not use the same diameter tube for the additional cross member as for the original one? Mine are 1 7/8" and 2 1/16" outside diameter respectively. Also I would have expected a better job to have been made as regards the access holes in the boxed in chassis to get at the front fixing of the rear springs.

So can I modify my request and ask all 4AD owners with cars built after mid-1953 to look underneath to see what chassis strengthening there might be towards the back end please. It would be interesting to see how many varieties of strengthening there are.

Leo has had his previously unmodified chassis strengthened with a cross member to the rear of the original tubular cross member and this is fixed low down between the main chassis members so as to clear the underside of the propshaft. He has also had his main chassis members boxed in with welded steel plate from the cruciform member right back to the extreme rear end of the chassis, with provision for getting at the rear shock absorber fixing bolts.