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Land Rover SI - SIII 3rd/4th Gear Problems.

Those Dreaded Synchro Clips

If your gearbox suddenly starts crunching gears going into third or fourth gear, or you cannot select 3rd or 4th, then you have possibly broken some synchro clips in the 3rd/4th synchroniser. There are three clips or detent springs that keep the synchroniser floated correctly between the primary pinion and the main shaft. Usually the broken clips drop into the bottom of the gearbox and you notice them when you change oil. Occasionally a broken clip will jam and stop you being able to select 3rd/4th.

The solution

If you have a jammed 3rd/4th, try selecting between 3rd, 4th and neutral, declutching between tries hoping to make the broken clip drop out. The good news, is that is is possible to replace the clips without taking the gearbox out. You will need to gain access through the selector cover and insert new clips (worth about 3). Quickly, the steps are :-

Remove the both floor plates, gear box cover and fire wall transition cover.
Select third gear, then remove the gear stick. Temporarily replace the selector cover bolts and clutch inspection plate.
Thoroughly degrease and clean the top of the gearbox and selector area.
Drain the oil from the gearbox.
You need to be able to raise the seat box about four inches. You do not need to remove it completely, just unfasten the bolts around the base, and the two each side at the back, and lift the base and use a block of wood to keep it in position.
Carefully remove the detent spring covers each side of the gearbox (they are held by two small bolts and are right-angle shaped). Put some light grease into the holes with you finger tip to stop the balls rolling out.
Remove the central detent spring. It is held in place by a brass threaded plug.
Undo the nuts and bolds holding the selector cover (6 in all) and lift it free.
Carefully remove the three detent balls and the interlock pins between the selectors.
You will need to remove the selectors next. Take a moment to note where the the selectors engage into the drive train to that you can put them back in the right position.
Remove the 3rd/4th selector (left hand side). It should be back compared to the others. If your problem was a jammed 3rd/4th, you can still lift the selector enough to see where the broken clip is jamming the synchroniser. You will need to use a lifting and twisting motion to get the selector out.
Remove the 1st/2nd selector (middle), and finally reverse gear.
Have a close look at the 3rd/4th synchroniser (see sketch). It has three guide posts with a notch in the middle and cutouts in the gears beneath them. The clips sit in these channels.
Select neutral in the transfer case.
Push the 3rd/4th synchro into the neutral position, with the selector place centered.
Rotate the synchro until one of the posts is to the right and horizontal.
Select high range to lock the gears again.
Push the synchro into 4th gear (that is, the movable plate to the front).
Insert a new clip into the gap between the post and the gears, with the bent ends towards the shaft.
Using a pair of angled nose pliers, push the clip down and twist anti-clockwise and it will snap into position.
Move the selector into 3rd gear to centralise the clip. You may need to rotate the shaft slightly.
Repeat these steps for the other two clips. It will get harder to move the selector as you add clips.
Replace the gear oil by pouring back through the top.
Reverse the steps to reassemble the gearbox, seat and floors.

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