|The MGA With An Attitude
3 PROPSHAFTS USED IN THE MGA -- PS-101
There were three different propshafts used in the MGA in various years. The first two are specially matched to the first two gearboxes for about half of all MGA cars up to January 1959 (excluding the Twin Cam model). The third propshaft serves the other three gearboxes for the other half of production.
MGA propshafts - Early 1500 on top - Mid 1500 on bottom
The female splines on these propshafts match the male splines on the early and mid 1500 gearboxes. Early 1500 is 1 inch 10-spline. Mid 1500 is 1-1/16 inch 10-spline. The polished outside diameter of the nose piece runs inside of the bronze bushing in the tail of the gearbox, and also provides the clean surface for the shaft seal. As the rear axle bounces, the propshaft changes angle, and the splined coupling moves slightly fore and aft on the gearbox output shaft. The gearbox rear seal is then subject to sliding motion as well as rotation of the coupling. It is important that the bushing maintain a close working fit to avoid radial motion of the yoke that would damage the seal.
The rotating and sliding bearing and seal surface is the same diameter on both units, even though the spline is larger on the later one. The dust cup on the early unit is a steel tube, welded to the yoke. The dust cup on the later one is stamped sheet steel and press fit on the yoke. This allows the later dust cup to be removed and replaced if it may be damaged, or if you need to have clear access to the OD of the coupling to clean or polish the seal surface. The one in the picture above came loose once in operation, making strange rattling noises. The two small tack welds holding it in place are not standard issue.
As the later gearbox is slightly longer on the tail end, the later propshaft is slightly shorter. Center distance between U-joints is 31-3/8" for the early propshaft, and 30-9/16" for the later one. Overall length from the mounting face of the rear flange to the tip of the front yoke is 38-3/8" for the early propshaft and 37-5/8" for the later one (3/4" shorter).
Late MGA propshaft front yoke
Introduction of the fixed output flange on the MGA gearbox meant the propshaft had to have a flexible length. The third model propshaft used on the MGA then incorporated a sliding spline aft of the front universal joint as shown in the picture above. The thread at the back of the yoke will carry a hand tightened dust cap with a cork seal to keep dirt out and grease in for the splines. This may be snugged up slightly by hand each time the propshaft is greased. Later replacement parts may provide a rubber seal in the dust cap (see parts catalogs). This same basic model of propshaft, using all the same hardware parts on both ends,was continued all the way through end of MGB production in 1980 (on 4-cylinder cars). Three different overall lengths were used on the MGB cars, none of which exactly match the MGA propshaft.
When switching between different models of gearbox in the MGA, use the engine rear plate that matches the starter position on the gearbox, the clutch disk that matches the splines on the gearbox input shaft, and the propshaft that matches the output drive of the gearbox.
Bill Spohn (thanks much) has provided the length measurements of the third model MGA propshaft, flange to flange, as 32-11/16" extended, 31-3/4" compressed. Working length then is nominally 32-1/4". Compression hits a stop when the nose of the male spline bumps against the grease plug in the front of the yoke. Any additional forced compression would dislodge the plug. The extension hits a stop when the seal and a metal washer (like a snap ring) in the threaded dust cap cap comes up against the back ends of the male splines. More forced motion in that direction would damage the seal and the dust cap. In between full extension and full compression is only about one inch total travel, so it is really important to have the correct length propshaft for your installation. This being the case, none of the MGB propshafts is long enough for suitable use on the MGA. Median lengths of the MGB propshafts are 30", 31-1/8" and 32".
Problems with using the wrong propshaft here are similar to the problems with the different 1500 type propshafts. Too much spline overlap may cause bottoming out of the male spline in the yoke. Insufficient spline engagement creates accelerated wear in the splines and could damage the dust cap and seal seal.