Midget Diffs
Posted: Mon Jul 26, 2010 4:28 pm
Which years of midgets, if any, have the suitable diffs that will drop straight into the minor axle? And what ratios?
948/1098 Midget had 4.22 ratio, 1275 had 3.9, 1500 were 3.9 and 3.7 for the later ones. All Riley 1.5 and Wolesley 1500 use the same 3.7 diff.
In principle any of the Midget/Sprite/Riley/Wolesley diffs will fit into the Minor casing, but it depends on what engine you have and the use you want to make of the car. If your current axle has the filler in the rear of the axle casing, then any Midget diff will fit straight in with no physical problems. If you have the earlier casing, with the filler in the diff nose, then to fit the later 3.9 and 3.7 ratios may need some local grinding of the casing to get them to fit (this is not always the case).
What can be a problem is fitting a 'later' diff into an 'early' casing - you end up with no filler at all! The solution can be to drill the early casing and weld on a boss for the filler plug, or fill it via the breather (need to be precise on what you put in).
The 4.22 ratio was available in both 'early' and 'late' versions, i.e. filler in the diff or axle casing, so first identify which axle casing you have , and go from there.
In summary:
Early casing (filler in diff) - can fit early 4.22 with no mods, later 4.22 and all 3.9/3.7 will fit, but will need new filler in axle casing, and may need local grinding to casing to fit 3.9 or 3.7.
Later casing (filler in casing) - can fit any of the ratios withiout any mods (early 4.22 will give you 2 fillers!)