Hey Guest!
Hi all,
As I start to set up the "priority list" of repairs on my new-to-me 1971 GT6 MkIII, the transmission is pretty quickly rising to the top. It's a standard 4-speed unit (no O/D). It drives/shifts fine currently, but it has some fairly significant gear whine and an intermittent, rotational grumbling noise at idle (sometimes). I suspect this means the cage bearing between the input shaft and mainshaft is on the way out, and the layshaft and needle bearings aren't far behind. I've rebuilt enough transmissions to know that loud needles typically mean shaft damage - so, assuming the damage is done, I'm anticipating the need for a new mainshaft, amongst other things. Seems like Spigot repair longevity is hotly debated.
I was surprised to find that parts for these transmissions are nearly non-existent... Or, in the 10 days I've owned the car, I just haven't figured out where to look yet... I guess I'll need to have a little less fun driving it, if these parts need to last a while!
Doing a bit more digging, I've noticed some folks mention a "hybrid" gearbox using the mainshaft from a Dolomite/TR7 4 speed with an 18mm spigot, and machining out the GT6 input shaft to accept it. Then, incorporating the lay-gear cluster, 1st/2nd gear and synchro assemblies, plus the reverse gear, from the TR7, along with 3rd and 4th gear from the GT6, which results in a more robust transmission with the same or similar close-ratios to the original setup. My goal is to keep this car (fairly) original if I can, so I'm not super keen to go the 5-speed swap route, but I generally like the idea of using later parts to improve the reliability/durability a bit...
The issue is I can't find a good list or full explanation of exactly what parts I need from which transmission. More importantly, it seems like the later era parts are just as difficult to source in the US. TR7's aren't littering the scrap yards, and Dolomites practically don't exist.
- Has anyone put together a "donor parts list" to build this "improved" GT6/TR7 hybrid transmission?
- Is my best route to look for a donor TR7 4-speed and a machine shop to do the work of widening the input shaft cavity for the larger spigot bearing? Do I need anything beyond a donor TR7 4-speed and my current transmission to kluge this together?
- More importantly - is there a vendor that is a reliable source of these parts here in the US that would actually carry these components (as opposed to hunting down questionable used parts and hoping for the best)?
I'd be interested to hear from anyone who's gone this route (or has rebuilt a late GT6 gearbox in general). This has certainly been an good introduction into the Leyland "mix and match parts" approach to car building...
As I start to set up the "priority list" of repairs on my new-to-me 1971 GT6 MkIII, the transmission is pretty quickly rising to the top. It's a standard 4-speed unit (no O/D). It drives/shifts fine currently, but it has some fairly significant gear whine and an intermittent, rotational grumbling noise at idle (sometimes). I suspect this means the cage bearing between the input shaft and mainshaft is on the way out, and the layshaft and needle bearings aren't far behind. I've rebuilt enough transmissions to know that loud needles typically mean shaft damage - so, assuming the damage is done, I'm anticipating the need for a new mainshaft, amongst other things. Seems like Spigot repair longevity is hotly debated.
I was surprised to find that parts for these transmissions are nearly non-existent... Or, in the 10 days I've owned the car, I just haven't figured out where to look yet... I guess I'll need to have a little less fun driving it, if these parts need to last a while!
Doing a bit more digging, I've noticed some folks mention a "hybrid" gearbox using the mainshaft from a Dolomite/TR7 4 speed with an 18mm spigot, and machining out the GT6 input shaft to accept it. Then, incorporating the lay-gear cluster, 1st/2nd gear and synchro assemblies, plus the reverse gear, from the TR7, along with 3rd and 4th gear from the GT6, which results in a more robust transmission with the same or similar close-ratios to the original setup. My goal is to keep this car (fairly) original if I can, so I'm not super keen to go the 5-speed swap route, but I generally like the idea of using later parts to improve the reliability/durability a bit...
The issue is I can't find a good list or full explanation of exactly what parts I need from which transmission. More importantly, it seems like the later era parts are just as difficult to source in the US. TR7's aren't littering the scrap yards, and Dolomites practically don't exist.
- Has anyone put together a "donor parts list" to build this "improved" GT6/TR7 hybrid transmission?
- Is my best route to look for a donor TR7 4-speed and a machine shop to do the work of widening the input shaft cavity for the larger spigot bearing? Do I need anything beyond a donor TR7 4-speed and my current transmission to kluge this together?
- More importantly - is there a vendor that is a reliable source of these parts here in the US that would actually carry these components (as opposed to hunting down questionable used parts and hoping for the best)?
I'd be interested to hear from anyone who's gone this route (or has rebuilt a late GT6 gearbox in general). This has certainly been an good introduction into the Leyland "mix and match parts" approach to car building...