This memo is about the springs used with shift detents in MGA and early MGB (pre-1968) 3-synchronizer gearboxes. During mid-production of MGA 1500 model there was as short period when the factory errantly installed incorrect short springs in the shift detents. This problem and the fix for it are detailed in Confidential Service Memorandum MG-241 dated 18 February 1959. The correct longer spring is and always was factory part number 2K4909, 1-3/16-inches (30.16 mm) long. The incorrect spring that was installed in some units is factory part number 22A75, 31/32-inch (24.61 mm) long. The shorter springs can cause a problem of popping out of 2nd or 3rd gear (automatic disengagement).

These are strong little springs with a high spring rate. Without getting into long engineering calculations using wire diameter, OD, free coils, etc, I will take a shortcut. Factory spec is 1.187" free length, and 20-pounds load at 0.75" test height. That deflection is .437", and spring rate is 45.8 pounds per inch. For perspective, that's about half of the spring rate of dual valve springs, and this is a tiny spring by comparison.

If the incorrect spring has the same number of coils and same wire size, it would have the same spring rate. But starting with free length of 31/32" and finishing with the same 3/4" test height, the working force will be much less.
(0.969-0.750) x 45.8 = 10.0 pounds final force.
That's exactly half of the intended spring force of the correct longer spring.

The kicker to this is that in more recent years there has been widespread cases of replacement part vendors (maybe most of the current vendors) supplying the incorrect shorter spring for this application. It has even been cited as being "industry wide standard practice" (possibly as an excuse for not correcting the supply situation). If you buy new springs you might inadvertently end up removing the correct long springs and installing the incorrect short springs, thereby creating a problem that did not previously exist. Any time you have these springs out of the gearbox for service you should measure the free length (and compressed length force if possible) and service the unit accordingly.

Another unfortunate side effect of this current supply situation is that many vendors use the same part number for this spring in the early MGB (pre-1968) 3-synchronizer gearbox (and maybe some additional applications as well). This can lead to the vendors supplying the wrong spring for the MGB gearbox, even thought the factory never had any problem with that one. Considering that this supply situation has existed for a long time, it bears checking length of these springs in any early MGB gearbox whenever it may be disassembled for service.

To make matters worse, this part is a very small sales runner where the larger vendors may only sell half a dozen pieces per year. Many customers never notice the error in length of the spring and use them as received. Other customers may notice the problem but use the part anyway or toss the cheap bits in the trash rather than bother to return them or ask for a refund. The complaints and returns rate is then notably small (nearly non-existent). With such a small sales volume and minimal returns the vendors don't have much incentive to fix the problem and may continue to sell the wrong parts for this application. In that case the only recourse for the customer is to not buy the parts, or always return or demand a refund for the incorrect parts. If you feel that you must use the parts, then file a complaint with the vendor anyway so they are at least informed of the situation and the level of customer dissatisfaction.