The Exhaust and U-Clamps section gathers two related but distinct families of clamping hardware. The first is the exhaust joint-clamp range, the U-shaped or saddle-pattern clamps that hold sectional exhaust systems together at the joints between front pipe, centre section, silencer and tailpipe.
The second is the rear-spring U-bolt range, the heavier U-shaped bolts that secure the rear axle to the leaf spring on live-axle classic-MG applications. Both are essential structural items, both wear or rust through over time, and both are typically renewed during the work that exposes them.
Exhaust Joint Clamps
Exhaust joint clamps come in two principal patterns. The standard U-clamp uses a U-shaped bolt that passes over the joint, with a saddle plate underneath drawn up by two nuts to compress the joint. The single-screw band clamp uses a slotted band drawn together by a single bolt or screw, similar in principle to a hose clip but built for the higher temperatures and structural loads of an exhaust system. The right clamp depends on the exhaust system: the standard cast-iron-and-mild-steel original systems used U-clamps at most joints, while the Double S stainless systems use a mix of U-clamps and dedicated flange joints.
The clamp sizes are matched to the pipe diameter at the joint, typically 1¾-inch and 2-inch for most classic-MG applications, with larger sizes for high-performance systems and competition applications. Mild-steel clamps are stocked for owners running the original mild-steel exhaust system; stainless-steel clamps are stocked for owners running stainless systems where matching the clamp material to the system avoids any galvanic-corrosion issues at the joint.
Rear-Spring U-Bolts
Rear-spring U-bolts are the heavier-duty fasteners that secure the rear axle to the leaf spring on the live-axle classic-MG applications, MGB, MGB GT V8, MGC, Midget and MGA. The U-bolt passes over the axle tube and through the spring perch on the leaf spring, with a saddle plate underneath drawn up by two nuts to clamp the axle securely to the spring. The U-bolt is stressed at every load reversal, every time the car goes over a bump, the axle pulls down on the spring through the U-bolt; every time the car bottoms out, the spring pushes up against the axle through the same U-bolt. Over the working life of the car, the U-bolt threads stretch and the cross-section corrodes from underneath, leaving a fastener that has lost a substantial portion of its original strength.
Any axle-out or spring-out work is the right time to renew the U-bolts as a matter of course.
Specifications and Locknuts
The U-bolts are stocked in the appropriate diameters and lengths for each application, the MGB U-bolt is sized for the Salisbury tube axle and the leaf-spring perch on the standard car, with longer variants available for cars fitted with lowering blocks or other axle modifications. Stainless-steel U-bolts are stocked for owners doing concours-level restoration work or for cars used in salty environments where the original mild-steel U-bolts would not last. The locknuts that hold the U-bolts to the saddle plate are stressed components in their own right, nylock or plain-nut-with-spring-washer patterns are stocked depending on the application. The torque specification for the U-bolt locknuts is important, under-torqued allows the axle to move under load (producing wheel-tramp and accelerated spring-eye bushing wear), over-torqued stresses the threads and risks failure at the next major load.
The workshop manual is the authoritative reference, and the technical team is available to advise.