Fixed Pins for GREAT WALL UTE, CANNON ALPHA (LEAF SPRING)

A fixed pin, more commonly called a leaf spring centre bolt, runs through the middle of each leaf spring pack on your ALPHA (LEAF SPRING) UTE, CANNON and holds every leaf in position relative to the others.

It is one of the smallest components in a suspension and one of the few where failure means the axle moves relative to the spring.

What a Leaf Spring Centre Bolt Does on Your ALPHA (LEAF SPRING) UTE, CANNON

The bolt passes through a hole drilled at the midpoint of every leaf in the pack, clamping them together and keeping them aligned and correctly spaced.

That alignment is the entire purpose of it. Leaves slide against each other as the spring flexes, and without the centre bolt locating them they would spread apart along their length and the pack would stop behaving as a spring.

The clips and clamps along the length of a leaf spring assist with that, holding the leaves laterally. The centre bolt does the locating that matters, which is why it sits at the point of highest clamping load in the assembly.

Length depends on how many leaves are in the pack, since the bolt has to pass through all of them with enough thread left for the nut.

Why the Centre Bolt Also Locates the Axle on Your ALPHA (LEAF SPRING) UTE, CANNON

This is the part most people do not realise, and it is why a sheared centre bolt is a serious fault rather than an inconvenience.

The head of the centre bolt protrudes below the bottom leaf and sits in a locating hole in the axle seat. When the U-bolts are torqued correctly, that head is what holds the spring pack in position on the axle.

The U-bolts clamp the pack down and the centre bolt head locates it, which are two different jobs, and friction from the U-bolts alone is not what keeps the axle where it belongs under braking and acceleration.

If the centre bolt shears, the axle can shift along the spring. On a vehicle that produces immediate changes in wheelbase and alignment on one side, and on a trailer it is how an axle ends up sitting crooked under the chassis.

It is also why the bolt must seat properly in the axle hole during assembly. A pack fitted with the head sitting against the seat rather than in it will move the first time real load goes through it.

Long Head Centre Bolts and Caster Correction Wedges for the ALPHA (LEAF SPRING) UTE, CANNON

Worth understanding before ordering, because this is the most common reason a standard bolt will not do the job.

A caster correction wedge fits between the leaf spring and the axle seat on a lifted solid axle vehicle, rotating the axle housing to recover the caster that the lift took away.

Adding that wedge increases the distance between the bottom leaf and the locating hole in the axle seat. A standard centre bolt head is not long enough to reach through the wedge and into the seat, so the pack loses its location entirely.

A long head centre bolt solves it, with an extended head designed to pass through the wedge and still seat correctly. Head lengths around 22mm are common for this, against a standard head of roughly 8mm.

If you are fitting caster wedges and have not accounted for the centre bolts, that is the part that gets missed.

Fixed Pins, Centre Bolts and Locator Pins

The naming varies across catalogues and it causes confusion when ordering.

Fixed pin, centre bolt, centre pin and locator pin all describe the same component, which is the fastener through the middle of a leaf spring pack. Trailer suppliers tend toward centre bolt, while vehicle and 4WD catalogues use fixed pin more often.

What none of those names describe is a U-bolt. U-bolts wrap over the axle and clamp the spring to it, and they are a separate purchase doing a separate job.

They are also not a shackle pin or a spring eye bolt. Those sit at the ends of the spring where it attaches to the hanger and the shackle, and they are different components again with their own sizes.

If a listing refers to a leaf spring pin without specifying, check whether the measurement given is the shank length through the pack or the overall length, since the two differ by the head.

ALPHA (LEAF SPRING) UTE, CANNON Centre Bolt Sizes and Specifications

Fitment comes down to four measurements and all of them matter.

Shank diameter has to match the hole through the leaves, with 5/16 inch and 3/8 inch being the common sizes.

Overall length has to suit the number of leaves in the pack. A bolt too short will not take the nut properly and one considerably too long leaves thread protruding where it can foul.

Head diameter has to match the locating hole in the axle seat. Too small and the pack can move within the hole, too large and it will not seat at all.

Head length decides whether the bolt reaches through to the seat, which is where standard and long head versions differ.

Thread length is the fifth consideration on some applications, since a pack with many leaves needs more of the shank threaded.

Measure the original rather than estimating, and check the figures against the listing before ordering.

Signs a Centre Bolt Has Failed on Your ALPHA (LEAF SPRING) UTE, CANNON

• A bang or clunk from the rear under hard acceleration or braking
• The axle visibly sitting further forward or rearward on one side
• One wheel no longer centred in its arch when the other is
• The vehicle pulling or tracking crooked with no alignment fault to explain it
• Leaves in the pack visibly offset from one another at the centre
• A gap appearing between the spring pack and the axle seat
• Loose U-bolts despite having been torqued correctly
• On a trailer, the axle sitting out of square and the tyres scrubbing

A sheared centre bolt usually announces itself rather than developing quietly. If the axle has moved, your ALPHA (LEAF SPRING) UTE, CANNON should be looked at before it goes any further.

Centre Bolts for Trailers and Vehicles

The principle is the same across both, though the applications differ.

Trailer and caravan centre bolts are frequently imperial and relatively standardised, since trailer springs come in common sizes rather than being vehicle specific. Boat trailers are the application where corrosion matters most, since a submerged bolt in a salt environment will not last like a road one.

Vehicle centre bolts are more specific, varying with the number of leaves and the axle seat arrangement on each application. A 4WD with an aftermarket spring pack can need a different bolt to the original, since the leaf count has usually changed.

Classic and older vehicles frequently need these as individual replacement items, since the original has corroded or been lost during a rebuild.

Why ALPHA (LEAF SPRING) UTE, CANNON Centre Bolts Are Replaced With the Spring

New centre bolts should go in with any leaf spring work rather than being reused.

The bolt is clamped under high load for its entire service life, and it has usually been stretched and corroded over years. Reusing one after a pack has been apart is a false economy, since it costs almost nothing against the labour already being spent.

They are generally supplied in pairs with nuts, which matches the job, since both sides come apart together and both should go back with new hardware.

The same logic applies to the U-bolts holding the pack down. Those are single use by design once torqued into their yield range, and replacing them alongside the centre bolts is the correct approach when a pack comes off.

Clamping the Pack Before a Centre Bolt Comes Out

The pack has to be clamped before the old bolt comes out, since a leaf spring under its own arc will spread the moment nothing is holding it.

Use a clamp across the pack near the centre, remove the old bolt, fit the new one, and tighten it with the clamp still in place so the leaves are drawn together rather than pulled together by the bolt alone.

Check that the head seats fully in the axle locating hole before the U-bolts go anywhere near it. This is the step that gets rushed and the one that causes the problems.

Torque the U-bolts evenly and in sequence, then retorque after the first few hundred kilometres once the pack has settled, since that initial settling is when a pack is most likely to move.

Fulcrum has been working on suspension since 1976, across 16 Service Centres and 200+ authorised workshops nationwide, and leaf spring work is a core part of what the network does.

Find Fixed Pins and Centre Bolts for Your ALPHA (LEAF SPRING) UTE, CANNON

Exposed thread and nuts on the pin can be covered with protection caps to help keep corrosion and damage at bay.

Select your ALPHA (LEAF SPRING) UTE, CANNON to see the fixed pins and leaf spring centre bolts available for it, in standard and long head versions. Check the diameter, length and head dimensions against your pack before ordering, particularly if caster correction wedges are fitted. Warranty and a fitment guarantee come with everything we sell, supported by workshops in every state.