5-Speed competition gearbox.
Posted: Mon Apr 07, 2008 2:39 am
The EMS is now off the road until the engine/gearbox is complete, stripped water pump and jack shaft have hurried it's rest to the garage.
The rest of the gearbox parts have arrived, so at least i can finish the box, just waiting on the UBV cylinderhead to arrive.
The gearbox will be a bit of a mongrel as far as parts are concerned, the main box is a chillcast from a 4-speed with a 5 speed primary housing. The final drive is a new special competition 5 speed 6:31, chillcast pinion housing, gear set from a 1989 900, type 4 primaries, this will give similar ratios to a 4 speed competition box, but just using 2nd to 5th. The selector shaft is a competition spec part with steel selector fingers and a quality universal joint. Short shift gear stick. The LSD is from Gripper Diffs and has been set up for tarmac. The clutch plate is a special light unit from Sachs tuning and motorsport, not available off the shelf, i wouldn't have usually chosen such a special clutch, but i will not be using any syncro rings with this this box, so the lightness will really help with the gears.
All i need to do now is modify the 5th gear selector shaft, with the competition fingers/selectors the 5th gear selector shaft is too long and this gets in the way of the 3/4th gear steel selector finger.
Because i have used the 4-speed chillcast box, the 5-speed layshaft cluster is a little too long, to get this to fit i had to remove a few millimeters from where the layshaft needle bearing sits, i removed the bulk of the aluminium in one go and slowly removed small amounts until i acheived a perfect fit with no play at all in the layshaft cluster, this took quite a while, the pictures hopefully make it clear as to what i had to do...
The initial pinion depth as stated on the end of the pinion is -15, i fitted a shim thickness of 1mm and checked it, it read -15 on the dial gauge, i must have checked it another 6 times and set up the gauge in the tool at least twice!
Here is the pinion with new bearings, the standard crush sleeve has been replaced by a solid sleeve, all sitting in the strong chillcast pinion housing...
This is really all you can see of the competition selectors in their position, the selection is very precise and very positive...
The clearance between the ring gear bolts and the internal selector shaft is very close and depending on the backlash adjustment, the bolt heads can even touch the shaft, to overcome this i just put the bolts in the lathe and took 2mm of the heads, i now have a clearance of 1mm between the bolt heads and the selector shaft.
This gearbox has had the syncro assemblies removed from gears 1 to 4, because the syncro rings/guide rings/springs and circlips have been removed there is a possibility the syncro hub can be moved to far, to stop this from happening the syncro splines on the gears need to be welded across two splines at three equally spaced intervals, all this is doing is replacing the space normally occupied by the syncro assembly, you can just see the welded syncro splines in the photo below...
The gears for this box are from a GM45612 gearbox (1989-90) and using the 6:31 final drive, but the intermediate gears have been swapped from an earlier 1981-1988 gearbox, this will give a much nicer spacing between the gears, in fact, using type 4 primaries will give very similar ratios in gears 2 to 5 as a competition 4 speed using special 30:35 primaries. I still have the option to change the primaries, but top speeds at 7000rpm will be around 100mph with type 4 and up to around 130 with type 8.
The rest of the gearbox parts have arrived, so at least i can finish the box, just waiting on the UBV cylinderhead to arrive.
The gearbox will be a bit of a mongrel as far as parts are concerned, the main box is a chillcast from a 4-speed with a 5 speed primary housing. The final drive is a new special competition 5 speed 6:31, chillcast pinion housing, gear set from a 1989 900, type 4 primaries, this will give similar ratios to a 4 speed competition box, but just using 2nd to 5th. The selector shaft is a competition spec part with steel selector fingers and a quality universal joint. Short shift gear stick. The LSD is from Gripper Diffs and has been set up for tarmac. The clutch plate is a special light unit from Sachs tuning and motorsport, not available off the shelf, i wouldn't have usually chosen such a special clutch, but i will not be using any syncro rings with this this box, so the lightness will really help with the gears.
All i need to do now is modify the 5th gear selector shaft, with the competition fingers/selectors the 5th gear selector shaft is too long and this gets in the way of the 3/4th gear steel selector finger.
Because i have used the 4-speed chillcast box, the 5-speed layshaft cluster is a little too long, to get this to fit i had to remove a few millimeters from where the layshaft needle bearing sits, i removed the bulk of the aluminium in one go and slowly removed small amounts until i acheived a perfect fit with no play at all in the layshaft cluster, this took quite a while, the pictures hopefully make it clear as to what i had to do...
The initial pinion depth as stated on the end of the pinion is -15, i fitted a shim thickness of 1mm and checked it, it read -15 on the dial gauge, i must have checked it another 6 times and set up the gauge in the tool at least twice!
Here is the pinion with new bearings, the standard crush sleeve has been replaced by a solid sleeve, all sitting in the strong chillcast pinion housing...
This is really all you can see of the competition selectors in their position, the selection is very precise and very positive...
The clearance between the ring gear bolts and the internal selector shaft is very close and depending on the backlash adjustment, the bolt heads can even touch the shaft, to overcome this i just put the bolts in the lathe and took 2mm of the heads, i now have a clearance of 1mm between the bolt heads and the selector shaft.
This gearbox has had the syncro assemblies removed from gears 1 to 4, because the syncro rings/guide rings/springs and circlips have been removed there is a possibility the syncro hub can be moved to far, to stop this from happening the syncro splines on the gears need to be welded across two splines at three equally spaced intervals, all this is doing is replacing the space normally occupied by the syncro assembly, you can just see the welded syncro splines in the photo below...
The gears for this box are from a GM45612 gearbox (1989-90) and using the 6:31 final drive, but the intermediate gears have been swapped from an earlier 1981-1988 gearbox, this will give a much nicer spacing between the gears, in fact, using type 4 primaries will give very similar ratios in gears 2 to 5 as a competition 4 speed using special 30:35 primaries. I still have the option to change the primaries, but top speeds at 7000rpm will be around 100mph with type 4 and up to around 130 with type 8.