First gear
jumping out when moving off, especially on hill starts, is a common problem on
all ‘Sevens’. The remedy is quite simple but involves removing the gearbox and
so the job is best left until a major task, like clutch renewal, is required.
The problem is usually caused by a broken spring, that holds the 1st/2nd
selector fork in position on the speed fork rod.
It is
possible to check this with the gearbox in the car if you can access the top of
the box. This is possible with ‘Box Saloons’ and the Ruby and Big Sevens if the
floor panel is removed. Remove the gearbox cover and interlock plate. Viewing
from the rear of the gearbox the 1st/2nd gear selector fork and rod are on the
right; try sliding the brass forks back and forth by hand. There should be
NO MOVEMENT.
If there is movement then the detent ball and spring are “not doing their job”
and should be replaced. This repair applies to all 4-speed gearboxes.
Once the
gearbox is out remove the top cover and the change speed gate with interlock arm
and pivot, exposing the selector forks and rods.
Above the
prop-shaft flange there are three nuts and washers at the ends of the three
rods. NB on later gearboxes there is a locking plate linking the 1st/2nd and
3rd/4th shafts. Remove these nuts and washers and locking plate, if fitted,
carefully noting its position. so that 1st/2nd speed shaft rod can be
withdrawn. On the earlier gearbox without the locking plate it should be
unscrewed from the bell-housing end. On later gearbox with the locking plate it
should be gently drifted forward taking care not to damage the threads. If the
rod is tight and not easily moved try some WD40; if it is still tight apply a
little local heat using a hot air gun.
On the
later gearbox with the locking plate take
GREAT CARE
as there is a set
of shims on the selector rod INSIDE the gearbox at the back which must be caught
as the rod is withdrawn from the housing. Initially only move the shaft forward
about 1/2” by which time you should be able to see that the shims are arranged
for their capture! Slowly remove the rod and expose the hole where the ball and
spring below it are situated. With luck these can be drawn out with a magnet;
however if the spring is broken and firmly stuck then it is probably necessary
to remove the speed fork completely and tap it out. This requires the removal
of the other two selector forks and rods from the gearbox. This may be
worthwhile as there is now an opportunity to check that all the balls are
functioning properly.
When
replacing the spring and ball it is essential to make sure that the correct size
spring and ball are used; some on the market are too small or the spring is
weaker.
Once the new spring
is in place it will force the ball a little proud of the fork arm
surface. Apply a little oil to the selector fork rod before sliding it back
into the selector fork holding the ball into its hole with a thin screwdriver
whilst the rod is moved over it. Replace the shims at the appropriate moment as
the rod enters the end housing. As the ball comes to the correct position in
the grove of the speed fork rod you will hear a firm clunk; if you don’t then
something is wrong, probably the wrong size spring and/or ball.
Replace the
locking plate, if fitted, washers and nuts and tighten; replace the change speed
gate with interlock arm and pivot adjusting the position of the forks, if
necessary, by screwing the rods in or out as necessary so that the interlock
plate can move freely across the gate without fouling the forks. Replace the top
cover and check movement of the gears. Replace the gearbox in the car and, if
necessary, replenish the oil.
This article, written by Doug Castle and Andrew Jarmin, originally appeared in CA7C Seven Focus in
Oct 2009 pp21-23.
When
replacing the spring and ball it is essential to make sure that the correct size
spring and ball are used; some on the market are too small or the spring is
weaker.