An idler pulley guides the belt from a fixed mount, while a tensioner pulley is pressed against the belt by a spring or hydraulics to keep it tight. Neither one drives anything. For a Barra Falcon or a petrol Territory, our Falcon 4.0 idler pulley set is one 76 mm ribbed pulley and one 76 mm flat pulley.
Know your engine? Go to the fit table. Holding the old pulley? Check its face (flat or grooved), outside diameter and bore first.
| Idler pulley | Tensioner pulley | |
|---|---|---|
| Job | Guides the belt round a longer path, takes up belt length, steadies long spans | Keeps the belt tension constant as the belt stretches and wears |
| How it's held | A fixed mount (some fixed idlers can be moved to set tension) | A spring, hydraulics or pneumatics |
| Drives a component? | No | No |
| Face | Grooved or flat on the inside of the belt; flat on the back of a single-sided belt | Same rule |
| What we list | Pulleys and pulley kits for cars, and idlers for Cox ride-on mowers | The pulley only, not the tensioner arm |
Source: belt makers' technical manuals, Greenfield's FastCut owner's manual and our product listings (see Sources).
Match the pulley, not the name
In our range, the name on the box doesn't settle it. Our GMB tensioner and idler pulley has two fit lists on one listing: one headed "Tensioner Pulley" (the Colorado RG diesels among them) and one headed "Idler Pulley" (the Captiva CGII 2.4 among them). Our Falcon 4.0 set calls both of its pulleys idler pulleys, and the listing doesn't say which, if either, sits on the tensioner arm.
What we sell is the pulley, not the spring-loaded arm it's bolted to. So match on four things:
- The face: ribbed (grooved for a multi-rib belt), V-groove, or flat.
- The outside diameter, across the face.
- The bore, the hole through the middle.
- The width, and then the vehicle on the fit list.
Our Falcon 4.0 set and both Commodore kits give the face, outside diameter, bore and width of each pulley. Where a listing doesn't (the GMB pulley gives none), order from its fit list.
Flat or grooved: which side of the belt runs on which
On an ordinary single-sided belt (a ribbed belt or a standard V-belt), the working side runs in grooved pulleys and the back runs on flat pulleys only. Double-sided belts, such as AA section, are made to drive from both sides.
- Inside the belt loop, an idler can be grooved or flat. On long spans a grooved idler is the better choice, because a flat one can let the belt start to shake sideways.
- On the back of the belt (an outside or backside idler), the pulley must be flat. It runs on the top surface of the belt and wraps it further round the other pulleys.
The same rule shows on a V-belt mower. Greenfield's FastCut manual has the drive belt run round a V alignment pulley, a flat alignment pulley and two flat idler pulleys, and says the back of the belt runs on all the flat pulleys. On the same mower, the cutter belt has a self-adjusting tensioner, and its tension can also be set at a fixed idler pulley with seven bolt positions. So a "fixed" idler can still set tension, if its mount moves.
Our Cox ride-on idlers come in both faces: a V-groove idler that takes an A-section belt, and two flat idlers. Belt makers rate Kevlar (aramid) belts for drives where the belt bends backwards round an idler, though a back idler on its own doesn't settle it, and 99% of the deck belts we sell are Kevlar (see our Kevlar mower belt guide).
Signs a pulley or belt is worn
A belt maker's fault chart for ribbed drive belts gives these causes and fixes:
- Play in the pulley's bearing, or a damaged running surface: replace the idler or tensioner pulley.
- Uneven wear across the belt's ribs: pulleys out of line, or strong belt vibration. Check the drive and line up or replace the pulleys, then fit a new belt.
- Belt running noise: tension too low, or the belt is past its life. Re-tension it or fit a new belt.
Belt makers also say a worn belt often isn't the only worn part, and recommend a close inspection of the tensioner and idler pulleys when you replace it. For when to replace the belt itself, use your service book.
Follow the vehicle maker's instructions, fit belts with the right tools and not by levering them on with a screwdriver, and on a mower, pull the spark plug lead before you touch the belts. Most of our car pulley listings say the parts should be fitted by a professional and to the vehicle's specifications. If you don't have the workshop manual and the tools, book a mechanic.
Which Bearings Express pulley fits
Cars and 4WDs
| Vehicle (as listed) | Engine (as listed) | Years (as listed) | Our part |
|---|---|---|---|
| Falcon EF, EL and XH ute; Fairmont EF, EL; Fairlane NF, NL; LTD DF, DL | 4.0L six, engine code H or Z | 1994 to 1999 | Falcon 4.0 idler pulley set: 76 mm 6PK ribbed steel and 76 mm flat polymer, 17 mm bore |
| Falcon, Fairmont, Fairlane BA, BF; Falcon FG, FG X; G6, G6E | 4.0L Barra (non-turbo and turbo; FG X also EcoLPi) | 2002 to 2016 | Same Falcon set |
| Territory SX, SY, SZ (petrol); FPV F6 Typhoon, F6 Tornado, F6, F6 E, F6X, Force 6 | 4.0L Barra, incl. turbo | 2004 to 2012 (Territory) | Same Falcon set |
| Territory SZ diesel | 2.7L V6 diesel, 276DT | 2011 to 2016 | Territory SZ belt and pulley kit: 6PK1975 belt, water pump pulley, tensioner pulley, idler pulley |
| Commodore VS, VT, VX; VU ute (VX and VU up to VIN L661775; not supercharged) | 3.8L V6, LG2 or LN3 (L36) | 1996 to 2002 | Commodore V6 steel pulley kit: one 76 mm 6PK ribbed and two flat pulleys (76 and 90 mm), 17 mm bore |
| Commodore VT, VX, VY II, VZ; Berlina and Calais VT to VZ; Statesman and Caprice WH to WL; Monaro; Crewman and Adventra VY II, VZ | 5.7L LS1 and 6.0L L76 V8 | 1999 to 2007 | Commodore LS1 pulley and belt kit: four pulleys (one 6PK ribbed, three flat, incl. two air conditioner pulleys), 6PK1995 and 4PK1100 belts |
| Colorado RG and Colorado 7 | 2.5L and 2.8L diesel (LVN, LKH, LWH, LWN) | 2012 to 2020 | GMB tensioner and idler pulley, "Tensioner Pulley" list |
| Captiva CGII | 2.4L, LE9 | 2012 to 2019 | Same GMB pulley, "Idler Pulley" list |
| Jackaroo U8, Monterey U8, Rodeo R9 and RA | 3.2L 6VD1 or 3.5L 6VE1 V6 | 1998 to 2005 | Jackaroo and Rodeo V6 pulley kit: 6PK2300 belt and two pulleys |
| Pajero NF, NG, NH, NJ | 3.0L V6, 6G72 | 1988 to 1997 | Pajero V6 pulley set: two 90 mm flat steel pulleys and one 82 mm V-pulley; our GMB air conditioner pulley also lists the 6G72 Pajero (NF, NG, NJ, NK). The two model lists differ, so send us your VIN. |
| Landcruiser HZJ70, 75, 78, 79, 80 and 105 series | 4.2L 1HZ | 1990 to 2007 | GMB air conditioner pulley (it also lists Hilux, Hiace, Dyna, 4 Runner, Pajero and others) |
Source: our product listings' titles, contents and "Fits" lists, read 8 October 2026. Rows sum up longer lists, so check your exact engine and dates on the listing. The LS1 kit's VZ and WL 5.7L lines carry a VIN note, so for those, send us your VIN. None of these listings says which pulley sits on the tensioner arm.
Cox ride-on mowers
| Cox part (as listed) | Face | Bore x outside diameter x width (as listed; two listings give an inner width) | Ours |
|---|---|---|---|
| PIVBB20SPA90 | V-groove, takes an A-section belt | 20 x 90 x 12.7 mm | Cox V-groove idler with bearing (also as a pair) |
| PIFBB02 (lists model 5398A) | Flat | 17 x 117 x 25 mm | Cox PIFBB02 flat idler with bearing (also as a pair) |
| PIFBB126598A | Flat | 12 x 75 x 25 mm | Cox PIFBB126598A flat idler with bearing (also as a pair) |
Source: our Cox idler listings, read 8 October 2026. The listings say "for selected Cox mowers", so match the Cox part number on the old pulley or in your parts list.
More car pulleys are in engine pulleys.
Not in our range: we don't list a pulley for the AU Falcon you can order straight off the page (two of our listings name the AU, split by VCT), the VY and VZ V6 Commodore, the VE and VF, or chain tensioners and idler sprockets. For an AU, or anything not in the tables, send us your VIN or registration with the old pulley's face, outside diameter and bore, and we'll check it from the make, model, year and engine.
Questions people also ask
What is an idler pulley?
A pulley that guides the belt and drives nothing. It routes the belt round a longer path, takes up belt length or steadies a long span, and on the back of a single-sided belt it must be flat.
Do you sell the whole belt tensioner, arm and spring?
Not for drive belts: our listings are the pulleys and pulley kits above. The hydraulic tensioners we sell come in timing belt kits, named in the kit's title (Subaru, Toyota, Mitsubishi, Holden Rodeo V6 and others, in timing belts and kits).
Do your idler pulleys come with a bearing?
Our Cox idler listings say "with bearing". Our car pulley listings don't say, so ask us before you order if that matters for your job.
Related reading
- Car fan belts and drive belts: sizes and kits
- Do I need a Kevlar mower belt?
- AX vs A, BX vs B, XPZ vs SPZ: what the X means on a V-belt
Sources
- Optibelt, Technical Manual: Ribbed Belt Drives, "Tension/guide idlers", printed p. 33, https://a.storyblok.com/f/192292/x/818f0c788a/optibelt-tm-ribbed-belt-drives.pdf, read 8 October 2026.
- Optibelt, Automotive Technology Compact Catalogue (AT/COMPACT CATALOGUE/EN/0926): "optibelt SUR tension and guide idler pulleys", p. 13; "optibelt KIT RBK repair kits", p. 15; "Problems, causes and remedies, optibelt RBK" and "Safety tips", pp. 40 to 41, https://a.storyblok.com/f/192292/x/4c1220a0ab/optibelt-compact-catalogue-automotive-technology-catalogue-en-digital.pdf, read 8 October 2026.
- Gates Australia, Industrial Power Transmission South Pacific Catalogue (2018), printed p. 97 (aramid-corded V-belts for back-idler lawn and garden drives), read 30 September 2026 (as cited in our Kevlar mower belt guide).
- Greenfield, Owners Manual, FastCut: "Cutter Belt Adjustment", p. 14; "To Replace Drive V Belt", p. 16, https://greenfield.com.au/wp-content/uploads/2023/11/Greenfield_OwnersManual_FastCutTractor.pdf, read 8 October 2026.
Checked against the belt makers' and mower maker's documents above and Bearings Express product listings on 8 October 2026.
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