Fixed Pins for MITSUBISHI TRITON ME - MJ 4WD

The fixed pin is the smallest fastener in a leaf spring pack and the one that holds the axle on your ME - MJ 4WD TRITON where it belongs.

Lose it and the axle moves on the spring, which is a different class of problem to a worn bush or a tired damper.

What Your ME - MJ 4WD TRITON Fixed Pin Is

A fixed pin, listed almost everywhere as a leaf spring centre bolt, runs through a hole drilled at the midpoint of every leaf in the pack.

Tightened, it clamps the leaves together and holds them aligned relative to each other. The clips along the length of the spring keep the leaves from spreading sideways, and the centre bolt does the locating that matters.

How long that bolt needs to be comes down to the leaf count, because it passes through every leaf and still has to take a nut on the end.

The names vary between catalogues and they all describe the same component. Fixed pin, centre bolt, centre pin, leaf spring pin and locator pin are the same thing, and a leaf spring bolt usually is as well.

Why the Centre Bolt Locates the Axle on Your ME - MJ 4WD TRITON

This is the part most people do not realise, and it changes how seriously a sheared pin should be taken.

The head of the centre bolt protrudes below the bottom leaf and seats into a locating hole in the axle seat. With the U-bolts torqued down, that protruding head is the only thing stopping the pack sliding on the axle.

The U-bolts clamp the pack down and the centre bolt head locates it. Those 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 shifts along the spring. On a vehicle that changes the wheelbase on one side immediately, which affects alignment and makes the vehicle track crooked.

It is also why the head has to seat fully in the axle hole during assembly. Assemble it with the head resting on the seat instead of dropped into the hole and the pack shifts the first time the vehicle is worked.

Long Head Centre Bolts and Caster Wedges for the ME - MJ 4WD TRITON

Worth knowing before ordering, because it is the most common reason a standard pin will not do the job.

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

Adding that wedge increases the distance between the bottom leaf and the locating hole. A standard centre bolt head is not long enough to reach through the wedge and into the seat, which leaves the pack with nothing locating it.

A long head centre bolt solves it, with an extended head sized to pass through the wedge and still seat correctly.

If caster wedges are going on as part of a lift and the centre bolts have not been considered, that is the part that gets missed.

ME - MJ 4WD TRITON Centre Bolt Sizes and Fitment

Five measurements decide whether a fixed pin will do the job.

Shank diameter follows the hole drilled through the leaves, and 5/16 inch and 3/8 inch cover most applications.

Overall length has to suit the number of leaves in the pack, with a longer pack needing a longer bolt.

Head diameter is matched to the locating hole in the seat, and an undersized head lets the pack rattle around in it while an oversized one will not drop in at all.

Head length is what determines whether the bolt actually reaches the seat, and it is the one dimension separating a standard pin from a long head version.

Thread length matters on packs with many leaves, since more of the shank needs to be threaded for the nut to engage properly.

Measure the original rather than estimating, especially on a vehicle that has had suspension work before.

Signs a Fixed Pin Has Failed on Your ME - MJ 4WD TRITON

• 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 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
• U-bolts that will not hold torque despite being correctly tightened

A sheared centre bolt announces itself rather than developing quietly. If the axle has moved, your ME - MJ 4WD TRITON should be looked at before it goes any further.

Why ME - MJ 4WD TRITON Fixed Pins Are Replaced With the Spring

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

The bolt sits clamped under high load for its entire service life and has usually corroded over the years it has been in there. Reusing one after the pack has been apart is a false economy against the labour already being spent.

Supply is usually a pair with nuts, which suits the work, because you are never doing one side of a vehicle on its own.

The same 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 fixed pins is the correct approach whenever a pack comes off.

Clamping the Pack When Fitting Your ME - MJ 4WD TRITON Fixed Pin

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

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

Check 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 later.

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

ME - MJ 4WD TRITON Fixed Pins Against U-Bolts and Shackle Pins

Three fasteners sit around a leaf spring pack and they get confused at the ordering stage.

A fixed pin runs through the middle of the pack, clamping the leaves and locating them on the axle. There is one of them per spring and no more.

U-bolts wrap over or under the axle and clamp the whole assembly down against it. There are two per spring and they are a separate purchase doing a separate job.

Shackle pins and spring eye bolts sit at the ends of the spring where it attaches to the hanger and the shackle. Different components again with their own sizes and their own bushes.

Where a listing just says leaf spring pin without qualifying it, check whether the measurement given is the shank length through the pack or the overall length, because the two differ by the head.

Corrosion and ME - MJ 4WD TRITON Fixed Pin Service Life

A centre bolt lives in the worst position on the vehicle for exposure, and that is what ends most of them.

The head sits below the bottom leaf directly in the path of whatever the rear tyres throw up. Water, grit and salt collect around it and sit against the steel.

The shank itself is rarely what gives up. It is the thread and the nut at the bottom, which corrode until the fastener cannot be undone without cutting, and the corrosion also thins the section where the bolt is doing its clamping.

Boat trailers and coastal vehicles reach that point fastest, since salt water accelerates everything. Agricultural use sits close behind those two.

Protection caps over the nut and thread are the cheapest way of delaying it, and they are worth fitting at the same time as new pins.

Find Fixed Pins for Your ME - MJ 4WD TRITON

Choose your ME - MJ 4WD TRITON to bring up the fixed pins and leaf spring centre bolts listed for it, standard and long head. Have the shank diameter, overall length and head dimensions off your existing pack before you order, and go long head if there are caster wedges in the build.