Subaru have used many different flywheel types to suit different clutch applications in their manual models. Some aspects of the flywheels have always remained constant, such as the crank bolt pattern, the pilot bearing arrangement and the starter ring gear arrangement. Others such as as their inertia, whether the torsional vibration damping is done by the flywheel (i.e. dual mass), clutch disc (single mass) or both, and the clutch attachment geometry have changed many times. Some variants have been used for a very long time in many models, and others only briefly, and / or in only one model.
With the 1990’s Subaru models flywheels were simple, as there were only two types. Multiple part numbers for each, but two types in terms of physical interchangeability. From around MY00 onwards it gets a lot more complex.
All of the Subaru flywheels used in 1990’s models were flat faced designs, where the pressure plate bolts to the same planar surface that the disc friction lining runs on. Some of them really are flat faced – with the same machining operation right across the gearbox side, and others have a very small step of around 0.2mm between the friction fave and the pressure plate bolt face. This 0.2mm step is irrelevant in terms of clutch operation. The difference between the two is the pitch circle diameter (PCD) that the pressure plate bolts and dowels are on. This and what each is used fr is explained below, and the difference is easily visible when buying flywheels once you know what you’re looking for:
‘Push to Release’ Clutch Flywheels for Normally Aspirated Applications
268mm PCD – used for all of the 1990’s normally aspirated Subaru applications with ‘push to release’ clutches (except the early EJ18 from about MY90 – MY92), and well beyond that with the same clutches in certain models. Most types have 2 clutch alignment dowels, some have 3. The same clutches fit either:
The MY90 to about MY92 EJ18 engine used a 215mm clutch with flat faced flywheel. They used a 254mm PCD which is physically interchangeable with the flywheels mentioned next for the turbo 5 speed models, but it has a much lower moment of inertia.
Both of these flywheel types were used for many years after the 1990’s too. For European / ‘rest of world’ spec models, they were usedin :
* Some, but not all MY00 – MY03 Legacy / Liberty models
‘Pull to Release’ Clutch Flywheels for Turbo Applications
Like the flywheels for the ‘push to release’ clutches, the ‘pull to release’ equivalents also all have flat faces, with some being truly flat, and others having a very small, inconsequential step (0.2mm). See above for more details.
254mm PCD – used for all of the 5 speed turbo Subaru applications up to MY04, with ‘pull to release’ clutches, and well beyond that with the same clutches in certain models. Both the 225mm and the 230mm Subaru ‘pull to release’ clutches fit the same flywheel. Most types have 2 clutch alignment dowels, some have 3. The same clutches fit either. Six speed EJ engined Subaru’s do not use these flywheels:
‘Push to Release’ Clutch Flywheels for Turbo Applications
Up to MY04 all Subaru turbo models used ‘pull to release’ clutches. For MY05 (in European / ‘rest of world’ models) they introduced a new ‘push to release’ clutch for the lower powered turbo models (up to around 250 bhp). It is not compatible with any of the previous ‘push to release’ clutch installations, as it requires a unique flywheel and release bearing. The flywheel has the same 254mm clutch PCD as the previous 5 speed turbo models, but is not flat faced. the friction face is recessed 2mm from the pressure plate bolting face:
‘Push to Release’ Clutch Flywheels for BRZ / GT86 Applications
For the new BRZ / GT86 in MY12, despite using what was effectively a Toyota gearbox with a Subaru shaped bell housing for the new FA20 engine, the BRZ / GT86 used a Subaru clutch arrangement. But one which has only one part and some geometry carried over. It used a new flywheel with the same geometry as the MY05 –> lower powered turbo ‘push to release’ clutch flywheel, with a much lower moment of inertia, and a new pressure plate. The BRZ / GT86 clutch / flywheel combination may not be the best suited to may VW conversions, for a couple of reasons – they have a relatively low torque capacity, and the lower intertia flywheels will not suit all VW bus applications well, so consider this before deciding to use them (although the flywheel inertia can be increased by using the equivalent MY05 –> lower powered turbo ‘push to release’ clutch flywheel):
‘Pull to Release’ 240mm Six Speed Flywheel for MY02 Onwards Higher Powered Turbo Applications
From MY02 onwards, when the stronger 6 speed gearbox was introduced for the higher powered turbo models such as the STi, Subaru introduced a new stronger clutch too. Bigger in diameter then any of the previous clutches at 240mm, the only part which interchanges with the earlier models is the release bearing. The flywheel is very visually different to all other Subaru flywheels, with 9 pressure plate bolts instead of the usual 6, and a 15mm step from the pressure plate bolting face to the friction face in a 15mm deep recess:
Subaru Single Mass vs Dual Mass Subaru Flywheels
Dual mass flywheels (DMF’s) in general don’t have a good reputation. This is for a few reasons:
- Because they are a service item. A single mass flywheel (SMF) in a vehicle which gets its clutch serviced correctly and which gets driven in a normal, non abusive way will often mast the life of the vehicle, but most dual mass flywheels are intended to be replaces when the clutch is worn out
- Because dual mass flywheels are much more complex than single mass, they have more failure modes. Without abusing the clutch, it is pretty difficult to damage a single mass flywheel, but the springs, dampers or other moving parts in a dual mass flywheel can fail.
- Because in many applications (including Subaru) the friction face of a dual mass flywheel is very much thinner than in an equivalent single mass flywheel, meaning is is less stiff, so less able to resist distorting if the clutch gets hotter than it should do
- Because the extra complexity of a dual mass flywheel means they are always far more expensive then single mass flywheels
….yet they have become more and more widely used by Subaru and just about all other makes since they were introduced (in MY00 for Subaru’s in Europe). Subaru have used a few different designs of dual mass flywheel, and all are a lot less versatile than many of the single mass flywheels are in terms of clutch choice. Typically Subaru used a much more limited range of clutches with the DMF’s and aftermarket clutch choice for them typically doesn’t exist – just the OEM selling their version of the genuine parts without Subaru part numbers.
There is a good argument for keeping dual mass flywheels in their OEM applications (i.e. not replacing them with single mass flywheels). However, in an aftermarket application, using a different gearbox, and often when using engines which were sold both with SMF’s and DMF’s in different models or markets for many years (as is the case with many of the more common Subaru engines fitted to VWs), using the Subaru DMF if the engine came with one makes very little sense. If the engine was from an auto, fitting a DMF makes no sense at all. You can usually buy a new SMF and clutch for far less than the cost of a new DMF. This is what we recommend you do for almost all VW engine conversions.
Petrol Subaru Valeo 230mm Dual Mass Flywheel
Used in some Legacy / Liberty models from MY00 to MY03, and all Legacy models from MY04 onwards, these were the first Subaru DMF’s:
This is a conventional dual mass flywheel, in that all of the torsional vibration damping is done by the flywheel with the disc hub being rigid.
Those who are not familiar with Subaru engines sometimes confuse these first DMF’s for an SMF. This is because they don’t look like many DMF’s do – in general mist DMF’s are more bulky than their SFM equivalents. Valeo made these DMF’s and their clutches for Subaru, and the intention seems to have been to squeeze the clutch and flywheel assembly into the same space previously occupied by the SMF and its clutch. This doesn’t seem to have been entirely successful, as they soon introduced a thinner release bearing for models with the DMF.
Diesel Subaru Sachs 240mm Dual Mass Flywheel
Used with all of the EE20 diesel engines, from MY08 onwards.
These Sachs DMF’s are a much less conventional in that both the flywheel and matching Sachs clutch disc do part of the torsional vibration damping each (i.e. the disc hub is also spring and damped). The damping properties of the disc and flywheel will be carefully matched to prevent resonance, so swapping the disc in this clutch would be asking for trouble. There is no suitable VW clutch disc that is compatible with this flywheel.
Subaru Flywheel to Crank Bolts:
EJ Series engines (and others where the flywheel bolts directly to the crank – i.e. no position sensor reluctor ring between):
All the Subaru single mass flywheels use the same 28mm long bolts as standard. They’re nice and easy to use as they have 14mm flanged hex heads. Dual mass flywheels and automatic torque converter drive plates used a few different bolt sizes, none of which match the single mass flywheels, so if you’re removing them to fit a single mass, you need new bolts too. We stock them – ours have a different hex size, and are 2mm longer, but they’re the same spec.
Valeo dual -mass flywheel bolts:
All the Subaru single mass flywheels use 14mm hex flanged head flywheel bolts, so they’re nice and easy to use. The dual mass flywheels and automatic torque converter drive plates used a few different bolt lengths, none of which match the single mass flywheels, so if you’re removing them to fit a single mass, you need new bolts too. But removing the Valeo dial mass flywheels. However, this presents a couple of problems:
If your engine has the Valeo dual mass flywheel and you’re removing it to fit a single mass, you’ll find removing it isn’t straight forward. The bolts for the Valeo DMF are not hex heads, they’re Torx Plus. Anyone who has not come across Torx Plus before will probably mistake them for Torx, and try to undo them with a normal Torx bit. This is a mistake, and often breaks the bolt heads (as does trying to undo them with an Allen bit). Torx Plus is a heavier duty version of Torx, and although they look very similar, they’re not interchangeable. The correct Torx Plus but size is TP50. Torx Plus bits used to be incredibly hard to get. Back in around 2003 we had to order a set from the US after not being able to find any tool brands who had them in stock in the UK. They’re easier to get now, but still not exactly common.
The other problem you’ll have if removing a Valeo DMF is that the holes in the clutch friction face do not line up with the bolts, so you can’t get the Torx Plus bit into the bolt heads square. If you don’t need to use the DMF again, you can remove the friction face from the DMF which gives perfect access to the bolts – but you’ll never get the DMF back together again. How to get the DMF apart is not immediately obvious. The friction face is held on by a circlip, but it’s very hard to see. It is in the groove highlighted by the red arrow in the picture above. Remove it and pry the friction face away from the rest of the flywheel. Once it’s removed you have perfect access to the Torx Plus bolts.
Using a refurbished, reground or reconditioned flywheel is never a good idea if a new one can be sourced for not much more. Flywheel which have been ‘restored’ like this generally were no longer flat enough to be used any more, and the distortion is caused by excess heat, from the clutch having been slipping more then it should have been. This could be due to bad driving or continuing to drive on a worn out clutch, or use in an application where the engine has more torque than the clutches torque capacity. Obviously it takes a lot of stresses withing the material (cast iron for all OEM Subaru flywheels) to distort them. Re-machining the friction face until it is flat again – usually by grinding does nothing to remove those stresses. It just removes the surface. Therefore unless whoever is doing the work also stress relieved the flywheel before grinding (if they do, they’ll certainly be advertising that fact that they do), what you’ll end up with is a flywheel which still has all sorts of stresses in it, so is far more likely to distort again – i.e. nothing like a new flywheel.
Be especially aware of those dishonestly selling reconditioned flywheels as new. There is a seller on UK ebay who always lists them as ‘new other’, which is simply untrue. It’s deliberately misleading.
When abused Subaru flywheels can distort in two ways, and or / crack. This is not uncommon, and it can be very hard to spot if buying from photos only. If you have the flywheel in front of you, all are pretty easy to spot when you know what you’re looking for, but are easily hidden in photos. The distortion can be either a local high spot, which will show as a large local area which is discoloured brown or purple or blue relative to the rest of the friction area, or the whole friction area can go conical – put a straight edge across it to check. This can sometimes be seen by a narrow discoloured band all around the friction face. A very slight conical shape so the outer diameter contacts the disc first can be OK, as long at it is very consistent all the way around the flywheel, but only a tiny bit (like maybe 0.2mm). If it’s gone conical the other way, so the centre of the disc contacts the flywheel first, that is more likely to be a problem.
When Subaru flywheels crack, the cracks are always in the surface of the friction face where the iron got hottest, and always radial. They can be from invisibly small, to wide enough to fit your finger nail into. They don’t seem to spread to the point that the flywheel falls apart, but it’s obviously best not to use one that is badly cracked.
Single mass flywheels are the simplest. They’re effectively a single part which does all of the flywheels’ jobs. Some, such as German VW Type 1 flywheels literally are one piece of steel. Most modern single mass flywheels are made from multiple parts, but non of them move relative to each other (for instance an iron flywheel with a shrink fitted steel ring gear). Driven without abuse, a single mass flywheel will usually last the life of the vehicle.
Damped flywheels are uncommon, but Subaru do use them in some applications. They are not the same as dual mass flywheels. Externally they are like single mass flywheels – they rigidly attach the clutch to the crank shaft, and no parts more relative to each other. However, inside they have a viscous damper. For the Subaru applications which use them, the damped flywheels always interchange with the equivalent single mass models and their clutches. They are just as reliable as single mass flywheels too, but do look different, especially from the engine side, with a pressed steel plate held on with many screws. Don’t undo these screws if you have one:
Dual mass flywheels do not rigidly attach the clutch the the crank shaft. They are effectively two flywheels with springs and / or dampers between then allowing a limited amount of rotation relative to each other. One of them attaches to the crank shaft and has the starter motor ring gear attached. The other has the clutch attached. There are many different types in terms of how the connection between the two flywheels work, with this pretty much always being hidden inside. If you hold the crank / ring gear side still, the clutch side always rotates slightly relative to it.
Two things are responsible for the short service life of most dual mass flywheels:
1. Wear of the spring and / or damper mechanism inside which couple the two flywheel halves together
2. To make room to fit all the extra complexity into space which in many cases was not originally designed for a dual mass flywheel, a lot of dual mass flywheels (including the Subaru Valeo petrol ones) make compromises to fit them in. A good example is the thickness of the iron face that the clutch disc runs on being much thinner than any equivalent single mass flywheel. This thickness is what gives the flywheel stiffness to resist distorting due to excess heat when the clutch is abused, so DMF’s which have very thin friction faces are always more prone to distorting than their thicker, stiffer SMF equivalents.
With most DMF’s the damping in the flywheel takes over the job traditionally done by the damper hub in the clutch disc (the ring of springs in most single mass flywheel clutch disc hubs and their associated other parts), so the clutch disc will be rigid (i.e. no damped hub). This is the case with the Subaru petrol Valeo DMF’s. Don’t ever try to use a disc from another application which has a damped hub in this type of DMF – even if you find one which fits, you could end up with a resonance which destroys parts.
In some DMF’s the flywheel does part of the damping, but the disc, which still has a damped hub does part of it too. This is the case with the Subaru Sachs diesel DMF’s. Don’t ever change the disc in a DMF which uses a damped hub disc for another damped hub disc intended for a different application, you could end up with a resonance which destroys parts.