While we were away in Victoria, just after Christmas, we had to have our clutch replaced. The reason being, the Thrust Bearing failed and damaged the fingers of the clutch pressure plate. The bearing failed due to incorrect free-play adjustment. The clutch face was in good repair, but the pressure plate was unserviceable due to the damaged fingers. Two points that came out of this exercise were:
- Clutch Type
- Thrust Bearing Free-Play Adjustment.
The standard clutch as fitted to all OKAs is a ceramic clutch and as OKA state in the owners manual, should not be slipped. If you do slip the clutch you will cause rapid wear to the clutch, pressure plate and flywheel. The ceramic clutch was fitted as early testing showed failure of an "organic" clutch. An organic clutch plate is what most people would recognise as a normal clutch plate.
It was recommended by Andrew Kee of Whitehorse Trucks (ex OKA dealers in Morwell, Victoria) that I replace my clutch with an organic type. He had supplied some ten of these to various OKA owners and had had no problems. The advantages being that the clutch can take some slip without undue wear or problems, and it is much softer on the drive-train giving a smoother take-up of the load.
The new NT OKA has an Organic Clutch. I have since learnt that Paul Nott is a good source. The clutch that was fitted to my vehicle is made by Daikin and if you go on their website you will find they have a listing for OKA (WA) and the part numbers start with OK.2. Thrust Bearing Free-Play Adjustment
Terry of Eastside Trucks, Morwell, carried out the repairs to my vehicle. He explained that it is a common problem, that he has found a lot of OKAs have the free play on their clutches incorrectly adjusted. Too often the thrust bearing is under load and therefore working (turning) continuously, leading to early failure of the thrust bearing, or at worst a slipping clutch.To ensure that it is adjusted correctly the following procedure needs to be followed:
1. Remove the inspection plate from the bottom of the bell housing (6 screws). Some vehicles will have a grease nipple for greasing the thrust bearing.
2. With the plate removed you will be able to see the side of the thrust bearing. With a long screw driver you should be able to freely rotate the bearing with the clutch disengaged.
3. If the bearing turns freely, all is good so far. Have someone operate the clutch pedal. As they slowly push the pedal down, you keep on turning the bearing until it stops. At this point the clutch pedal should have moved about 25mm; if so your free-play is adjusted correctly.
4. If the bearing does not turn freely, you either have a seized bearing or more likely not enough free play. You will need to adjust the free play by adjusting the adjustment bolt, which is on the opposite side of the bell housing to the clutch lever arm. N.B. Too much free-play will make it difficult to disengage the clutch.
5. You will need to test your setting to make sure you can still disengage the clutch.