Why radial grooves on clutch disk ?

[DippedHeadlights]

VW Karmann Ghia. Normal diaphram clutch with friction plate. I have here two clutch disks (friction plates), one made in Europe and one made in South America. They are both Sachs brand who were the OEM but there is a difference, on one the friction material is continuous all the way around, on the other there are 24 radial grooves, each about 3mm wide.

What do they do ? They obviously reduce the overal friction area but what is the benefit, could it be to reduce chatter somehow, maybe clean the surface, or something else ?

DH

[GavinPearson]

It's just a way of shedding debris to maintain clamp load and eliminate judder.

[Trooper2]

Don't they also aid in clutch release by ensuring the friction disc doesn't stick to the flywheel (vacuum effect), by helping to equalize air pressure on both sides of the disc?

I thought I read that in a patent description somewhere.

[GavinPearson]

Trooper2 said:

Don't they also aid in clutch release by ensuring the friction disc doesn't stick to the flywheel (vacuum effect), by helping to equalize air pressure on both sides of the disc?

I thought I read that in a patent description somewhere.

The effect of the grooves would be miniscule compared to the ability to get air through the disc hub springs, or the hub 'windows' in some clutches.

[DippedHeadlights]

I've spent a while Googling and still not found an answer. What is also confusing is the radial grooves are on the cheaper clutch. Something else, the grooves don't quite reach the outside edge of the disk, they stop about 1mm short, so they can't be to spin off contamination.

[tribbles]

Two things I can think of:

1) It could cool the clutch (but it'd normally spend most of the time spinning with the engine)

2) It could be cheaper to make (in parts cost) with minimal impact on performance. Would be more expensive for tooling though.

[GavinPearson]

DippedHeadlights said:

I've spent a while Googling and still not found an answer. What is also confusing is the radial grooves are on the cheaper clutch. Something else, the grooves don't quite reach the outside edge of the disk, they stop about 1mm short, so they can't be to spin off contamination.

You might find that the disc hasn't been manufactured correctly, which is not uncommon.

Having dealt with most of the major clutch manufacturers in a professional capacity I would say that they all have issues to some degree, it is not uncommon.

If you REALLY want to know about clutches try to get copies of LuK clutch symposium books, they showcase the latest in clutch and dual mass flywheel thinking.

As fr the clutch you have, if you are going to grease the splines be VERY careful about overgreasing. It WILL kill a clutch. You want to grease the gearbox splines, then use a piece of paper towel to then wipe the grease off, the surface will then remain tacky. That really is ENOUGH, any extra WILL get into the clutch damper if not the linings and then idle chatter or total failure is a sure thing.