As some of you know I have rebuilt my original D engine and was planning to fit a later synchro 126 gearbox.
I had stripped the 126 gearbox and made sure it all aligns to the D bell housing as the earlier casings only had the 2 bolt holes for the starter motor.
The gearbox has all been vapour blasted and the main box assembled.
I originally had 25mm driveshafts on the D.
It turns out the D's originally had 19mm driveshafts. The flanges that bolt onto the flexi drives are smaller diameter than the F/L/R as they changed the rear swinging arms to allow for a larger diameter flexi drive.
I ordered a new set of 25mm D driveshafts but they were out of stock and they sent me the 19mm ones.
So eager to build the gearbox so I could put it away until the shell was rebuilt I thought I could use the 19mm ones.
Then it hit me. There seems to be some differences between the D & later differentials.
Looking at the original specs:
The D had the 8/41 5.125 ratio.
The D sport had the 8/39 4.875 ratio.
The L/126 had the 8/39 4.875 ratio.
However when comparing the D diff to the L/126 diffs the D ones are a lot smaller.
Ring Gear:
D. 145mm outside diameter, 85.5mm inside
L/126. 154mm diameter, 80mm inside
Bevel gears:
Flange 58 & 62 mm diameters
The ends of the driveshafts are also smaller.
Across the spigots 44 & 45.5mm
Across the flats 19.6 & 21.5mm
The actual diff assembly is different in size as well so you cant change the ring gears over.
So I thought not a problem I will fit the later diff which matches my pinion gear. Trouble is the later crown wheel wont fit in the D casing, its too large a diameter.
I made a cardboard template to determine the inside shape of the casing and then tried it in the L/126 casing and you can clearly see the later casings have been designed to accommodate the larger ring gear.
I wonder if the 500 D sport ring gear which is the same ratio as the later ones was the same diameter as the early ones?
I don't think there is enough material in the 500D casing to machines some out to make space for the later diff. You can see from the picture where I have drawn the size of the 2 ring gears and laid them in the 500 D casing that I need to remove a minimum of at least 1mm to allow clearance.
So I have come to the conclusion that I will either have to rebuild the original D gearbox (But I don't want non synchro), See if I can use the original layshaft with the synchro gear assembly, fit the synchro gears in the D box, or I could use a F/L bell housing.
The later would mean I have an additional hole for the starter motor, or I could have this welded and then reshape the top to look like a D housing.
I had stripped the 126 gearbox and made sure it all aligns to the D bell housing as the earlier casings only had the 2 bolt holes for the starter motor.
The gearbox has all been vapour blasted and the main box assembled.
I originally had 25mm driveshafts on the D.
It turns out the D's originally had 19mm driveshafts. The flanges that bolt onto the flexi drives are smaller diameter than the F/L/R as they changed the rear swinging arms to allow for a larger diameter flexi drive.
I ordered a new set of 25mm D driveshafts but they were out of stock and they sent me the 19mm ones.
So eager to build the gearbox so I could put it away until the shell was rebuilt I thought I could use the 19mm ones.
Then it hit me. There seems to be some differences between the D & later differentials.
Looking at the original specs:
The D had the 8/41 5.125 ratio.
The D sport had the 8/39 4.875 ratio.
The L/126 had the 8/39 4.875 ratio.
However when comparing the D diff to the L/126 diffs the D ones are a lot smaller.
Ring Gear:
D. 145mm outside diameter, 85.5mm inside
L/126. 154mm diameter, 80mm inside
Bevel gears:
Flange 58 & 62 mm diameters
The ends of the driveshafts are also smaller.
Across the spigots 44 & 45.5mm
Across the flats 19.6 & 21.5mm
The actual diff assembly is different in size as well so you cant change the ring gears over.
So I thought not a problem I will fit the later diff which matches my pinion gear. Trouble is the later crown wheel wont fit in the D casing, its too large a diameter.
I made a cardboard template to determine the inside shape of the casing and then tried it in the L/126 casing and you can clearly see the later casings have been designed to accommodate the larger ring gear.
I wonder if the 500 D sport ring gear which is the same ratio as the later ones was the same diameter as the early ones?
I don't think there is enough material in the 500D casing to machines some out to make space for the later diff. You can see from the picture where I have drawn the size of the 2 ring gears and laid them in the 500 D casing that I need to remove a minimum of at least 1mm to allow clearance.
So I have come to the conclusion that I will either have to rebuild the original D gearbox (But I don't want non synchro), See if I can use the original layshaft with the synchro gear assembly, fit the synchro gears in the D box, or I could use a F/L bell housing.
The later would mean I have an additional hole for the starter motor, or I could have this welded and then reshape the top to look like a D housing.
