What Is the Best Front Idler for Volvo MCT85C Track Loaders?

Three measurements decide whether a front idler fits a Volvo MCT85C, and none of them is the model name. The bore it mounts on, the mounting-hole spacing, and the overall height of the assembly are the pivot dimensions - and a part that is right in two of them and wrong in the third will bolt up and then put the track out of line. That is why the useful question is not "which idler is best" but "which idler is the right one", and the answer comes from the part you are removing.

Last updated: October 5, 2026 (the photograph shows the Volvo undercarriage part class in this catalogue; confirm your own idler's part number against the serial number)

This guide covers what the front idler does on this machine, the dimensions fitment actually turns on, how to read the wear on the part you are replacing, the replacement sequence, and how to decide between OEM and aftermarket.

What the front idler does

On a compact track loader like the MCT85C, the front idler - sometimes called the front roller - is the wheel the track runs around at the front of the undercarriage. It supports and guides the track, holds the belt in line, and carries the tensioning load that keeps the track in contact with the drive sprocket and the rollers. On this class of machine it is one of the two components, with the sprocket, that decide whether a track runs true.

Its construction is simple: a machined wheel with flanges, an axle or spindle, and a bearing behind a seal. A sealed idler cannot be re-greased in service, which is why the seal is the part that decides how long the assembly lasts rather than any maintenance routine.

The dimensions that decide fitment

Three measurements, all taken from the idler you are removing. The bore diameter - the dimension that has to match the shaft or axle it mounts on, and the one that is invisible once the assembly is together. The mounting-hole spacing, including the bolt count, because the assembly has to seat squarely on the frame; a mismatch here cannot be corrected with washers. The overall height, which sets the height the track runs at relative to the sprocket and the bottom rollers.

Two further properties are outside those dimensions and belong in the same conversation: the flange height and spacing, which are what actually hold the belt in line, and the bearing and seal design. Add the part number, cross-referenced to your machine's model and serial number, and the fitment question is closed.

Reading the idler you are replacing

With the machine raised and the track slackened, four observations cover most of it. A groove worn into the running surface is normal end of life, but check alignment before fitting a replacement - an idler running out of line wears into the same pattern. Wear concentrated on one side of a flange means the belt is not running centred: a tension, alignment or roller-flange issue rather than the idler itself. Oil or grease weeping means the seal has failed and the bearing is losing its lubrication; since there is nothing to re-grease, this is a replace-now symptom. Cracks in the wheel or mounting mean impact or fatigue - replace it, and check the frame for distortion before the new part goes on.

Where play can be felt with a bar under the wheel, the bearing or shaft is worn, and it is worth measuring rather than judging by feel: the idler's entire job depends on holding a precise line.

Replacing it

The sequence is the same on this machine as on any compact loader. Park on firm, level ground, chock the machine and support the raised side on stands rather than on the jack alone. Release the track tension through the grease cylinder - slowly, with your hand clear of the fitting's discharge path - and support the belt before breaking the master link, because a slack track on a raised machine is heavy and moves when the link releases.

With the belt clear, unbolt the old idler assembly, then clean the mounting area before fitting the new one: an idler seated on packed material never runs square. Fit the replacement, align it properly with the belt's run, and tighten the mounting hardware to the manufacturer's torque figure. Refit the track, set tension to the figure in the manual - measured where the manual says to measure it, on both sides - and run the machine briefly to confirm the belt tracks straight before it goes back to work. Re-check the mounting hardware after the first hours, because fasteners on a tensioned component settle.

OEM or aftermarket

Both routes are legitimate, and the decision turns on the same three factors as any undercarriage part. Documentation: a dealer supplies the factory part with the factory's warranty; a specialist supplies an equivalent fitment with a stated material, bearing and seal design and written warranty terms. Where a supplier can state those, the part is comparable; where they cannot, the price is the only information available. Availability: a machine standing still costs more per day than the difference between the two parts usually does, so a part in the country with a delivery date often wins. Consequence of failure: an idler failure wears the track, so a marginal saving on the idler is rarely worth the risk to a belt.

Where the machine's own warranty is still in force, confirm with the dealer how a non-OEM idler affects coverage on the components it touches - a question to ask before ordering, not after a failure. And where the idler is being replaced because of alignment wear rather than ordinary wear, correct the cause first: the surrounding parts are listed by number and machine for exactly that reason, and this guide to choosing an aftermarket front idler follows the same method on excavators. Shimming is a related detail where the frame or the mounting face has worn - how to shim a front idler correctly covers it - and how to choose an idler by part number shows the same cross-reference exercise on a different machine.

Two further lines of comparison are worth the time on a machine that works hard. Surface treatments and coatings are changing what undercarriage parts are made of in this class, and how advanced coatings are changing undercarriage design explains what that means for a wear part's life. And where a fleet runs mixed brands, it is worth understanding how parts are sourced across them - what Volvo EC15V parts are used for in this market is a fair example of how a machine-specific part list is built, and the fitment discipline is the same whether the machine is a Volvo or not.

This article is part of the idlers guide, which covers what the front idler does, how to confirm the right wheel and how to read wear.

FAQs

How do I know which front idler fits my Volvo MCT85C?

By the part number cross-referenced to your model and serial number, then confirmed against the bore diameter, mounting-hole spacing and overall height of the idler you are removing, plus the flange height.

How long does replacing a front idler take?

A few hours with the machine properly supported and the right tools: releasing tension, supporting the belt, unbolting the assembly, fitting the replacement and re-tensioning. The inspection around it - rollers, sprocket, belt - takes the same afternoon.

What are the signs the idler needs replacing?

A track that will not hold tension, noise under load, the machine drifting to one side, a groove or uneven wear on the idler face, cracks in the wheel or mounting, and a weep at the seal. Treat the weep as replace-now.

Does the idler affect track wear?

Directly. The idler sets the track's line, so a worn one lets the belt run off centre and the misalignment transfers into the links, the rollers and eventually the sprocket. That is why an idler is the cheapest undercarriage part to replace early.

Should I replace the idler and the tracks at the same time?

Inspect the idler whenever a track is off, and replace it if it is due. The preparation is identical, so doing both in one job costs far less than returning to it a month later.