Do this first.
1. Put gear shifter in the car into neutral.
2. Remove the shifter cable linkages off the gearbox's gear selector arms from inside the engine bay.
3. Grab onto the gear selector arm of the gearbox. Now manually pull the arm as far as it will go outwards (towards front of the car) as possible. While holding it out, turn the selector fully left - it should clunk into gear, then let go. Left is Reverse. If it doesnt go in, then try pulling the lever outwards and all the way to the right. Right is 5th gear.
4. If you can confirm that it wont go into reverse, I suggest the next step would be to unscrew your reverse sensor switch from the top of your gearbox. It's the big switch with the wires and black plug going to it on top of your gearbox. Remove it fully and inspect the base of the switch. It should have a nice shiny silver ball bearing in it encapsulated all around by the sensor so it doesnt fall out. Press the ball bearing in and out with your finger. It should go in and out very easily as it is spring loaded. If the switch doesnt look damaged and the ball bearing is pressing in and out fine, then you know the switch isn't stopping the gears from selecting reverse. Now try step 3 again and see if it lets you get into Reverse now. If it still doesnt allow you to get into Reverse, then DO NOT screw the reverse sensor switch all the way back in. Simply just wind it back into the top of the gearbox a couple of turns but NEVER wind it in all the way down when the gearbox isn't actually in the REVERSE position as it will irreversibly damage the ball bearing tip permanently. Now go to Step 5.
4b. However, if your gear lever now does shift into Reverse gear with the switch removed, then you know the reverse sensor was wound in too far into the gearbox. Leave the gearbox in the REVERSE position and screw the switch back in gently hand tight. Then try moving in and out of reverse gear again. There is normally an alloy washer/spacer on the sensor that lets it sit about 1-2mm proud off the gearbox when it is fully screwed in. Make sure you have a washer in place, screw it in, now check that you can still select in and out of reverse. If you can, you're done. Put the shifter cable linkages back onto the gearbox, plug the reverse switch back in and its happy days - THE END.
5. Now that you know it still cant select Reverse gear with the reverse switch fully removed from the gearbox, there's something wrong internally. It's either going to be inside the rear end case of the gearbox (easy fix whilst gearbox can remain in the car), or the problem will be inside the bellhousing (PITA as you have to remove the gearbox to do the job).
6. Drop the oil out of the gearbox. Jack the front of the car up. Put stands under the chassis under the car (safety first). Remove driver's side front wheel for better view. Now remove all the bolts from the end case. BE CAREFUL. Next to the end case is a thin sandwich plate part of the gearbox casing that is now only held in position by sealant because you have just removed the bolts. DO NOT budge or break the seal between the sandwich plate and the rest of the gearbox. We only want to remove the end case/cap here in this step. Once you remove the bolts, pry off the end case/cap from the sandwich plate. Once you do a synchro ring will fall out. That is the reverse gear synchro. Yes, it loosely just sits in between the end case and the reverse hub. Get out from under the car and look inside the end case you just removed. There should be a metal circular ring on one side of the case, with a thin circular spring (called a 'wave spring') connected to it. This wave spring is what holds the reverse synchro up against the reverse selector hub when you put the gearbox back together. Check that the wave spring is not broken by gently pressing it in and out. If the wave spring falls out, it is easy to put back into the end case by aligning the 2 notches in the spring with the correct position in the end case. If the wave spring is broken or split (not a complete circle) then it needs to be replaced and could be the reason why you cant select reverse because it could have misaligned the reverse synchro to stop the hub from sliding onto the synchro. If the wave spring is intact, then check the condition of the reverse synchro. I don't need to explain how to do that, you can check that on the internet lol.... but if the shape of the teeth don't look like little houses from side on, then you need to replace it. A damaged synchro could be why you cant get into reverse gear too.
7. If both the reverse synchro and wave spring look good, then go back under the car and check that the synchro keys and spring (a big U-shaped arc that holds the keys in place) are sitting in the reverse hub properly. You could have a broken spring on Reverse. If you do, replace it. If not, and the keys are still in position and the spring is holding them in, get a mate (or yourself if you are capable), to now manually select between 5th and Reverse gear on the gearbox selector arms like we did in point 3 above.
8. As you are switching between 5th and reverse, watch how the shift rail and shifter fork moves in and out to select between both gears. If you find you can select reverse now with the end case off, then you know the problem is in the back end of the gearbox you are working in. If you still cannot select into reverse then the problem is internal. Most likely the little reverse idler arm with the shoe that drops down onto the input shaft that engages reverse, or the problem is a misalignment in the actual way the 5th/reverse shift fork end mates up to the reverse idler arm inside. Either way, if the problem is inside the gearbox has to come out and be pulled down to the bellhousing.
Edited by EVO-00X, 02 January 2016 - 04:23 AM.
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