The only way to shift the transmission into any gear is by holding the shift lever down or up, then releasing the clutch. It then stays in gear. If i just shift (this was working previously) then release the clutch, it acts like the bike is in neutral, but the neutral indicator isn?t lit. What could be the problem?

There could be several reasons why a 2008 Astra may become stuck in 4th gear. Here are a few potential causes:

1. Transmission issues: A problem with the transmission itself, such as a damaged gear or a malfunctioning shift solenoid, can cause the vehicle to remain stuck in a particular gear.

2. Clutch problems: If there is a problem with the clutch system, such as a worn clutch disc or a faulty release bearing, it can prevent proper gear engagement and cause the vehicle to stay in 4th gear.

3. Shift linkage or cables: Issues with the shift linkage or cables that connect the gear shift lever to the transmission can result in difficulty changing gears, including becoming stuck in 4th gear.

4. Hydraulic issues: Problems with the hydraulic system, such as low fluid levels, leaks, or a malfunctioning clutch master or slave cylinder, can affect the proper operation of the clutch and transmission, potentially causing gear-related issues.

It is important to have a qualified mechanic inspect and diagnose the specific cause of the problem. They can perform a detailed diagnostic procedure, check for error codes in the vehicle's computer system, and conduct necessary tests to identify and resolve the issue with the 4th gear sticking.

It appears this is a 5 speed manual transmission. There may be shift linkage problems between the shift lever and transmission. also bushings. I strongly recommend a repair manual specificly for this transmission. possibly filespeep.com or manualslib.com
How is the clutch and throwout bearing?

Instructions

1. • 1 The gears on a motorcycle run in this order: first, neutral, second, third, fourth and fifth. When you are moving, shifting up from first gear will skip over neutral and shift you right into second gear. The only time that shifting up from first will get you into neutral is when you are not moving.
     
   • 2 Pull in the clutch lever and tap the gear lever down until it stops. This will signify first gear. Pressing the gear lever down will shift you down one step and pressing it up will shift up one step.
     
   • 3 Tap the gear lever up one click while still holding in the clutch. This will put the bike into neutral.
     
   • 4 Start the bike. The bike needs to be in neutral to start.
     
   • 5 Hold in the clutch lever and tap the shifting lever down to shift to first gear.
     
   • 6 Release the clutch slowly and give it just enough gas to get moving.
     
   • 7 Listen to the motor to know when you need to shift. If the engine is making a low grumbling noise, then it will need to be shifted down. If it is making a high squealing noise, then it needs to be shifted up.
     

Instructions

1

The gears on a motorcycle run in this order: first, neutral, second, third, fourth and fifth. When you are moving, shifting up from first gear will skip over neutral and shift you right into second gear. The only time that shifting up from first will get you into neutral is when you are not moving.
2

Pull in the clutch lever and tap the gear lever down until it stops. This will signify first gear. Pressing the gear lever down will shift you down one step and pressing it up will shift up one step.

3

Tap the gear lever up one click while still holding in the clutch. This will put the bike into neutral.
4

Start the bike. The bike needs to be in neutral to start.
5

Hold in the clutch lever and tap the shifting lever down to shift to first gear.
6

Release the clutch slowly and give it just enough gas to get moving.
7

Listen to the motor to know when you need to shift. If the engine is making a low grumbling noise, then it will need to be shifted down. If it is making a high squealing noise, then it needs to be shifted up.

On most motorcycles the shift drum has 2 levers and springs called a detents. One lever and spring(detent #1) holds the drum in nuetral and the second lever and spring(detent #2) holds the transmission in gear each time a gear is selected. The nuetral detent (detent #1) has a notch that it drops into when it is in nuetral only. If the spring for the nuetral detent is bad or the detent lever does not drop into the notch (for whatever reason) the transmission will not stay in nuetral. The detent levers and springs will be located to the outside of the shift drum, normally opposite the shift lever side of the engine and inside the engine cover.
If you can rock the bike back and forth and find nuetral with the engine off but have trouble getting nuetral with the engine running, the problem with finding nuetral is probably clutch related and is not the detent. Clutches that are not fully disengaging will make it hard to find nuetral with the engine running.

It sounds like your shifter pawl is broken. It's trying to roll the shifter drum but it's not rolling it quite far enough for the drum to index to the next detent. It is rolling it far enough to put out the neutral indicator light. If this is the problem, a teardown of the transmission is required to repair this.

There is one other possibility. From the foot shift lever, follow the shifter rod back to the shift lever on the transmission. This is the shift lever that connects to the shifter pawl shaft. I"ve seen lots of them get worn to the point that they feel like they are going to fall off. When they get like that, they don't shift well. To repair this, you will have to pull the complete primary to get to it. If the splines on the shaft are worn badly enough, you're back to pulling down the transmission to replace the shifter pawl shaft.

Good luck
Steve

With bike not running, rock the bike backwards and forwards and shift through all the gears. If it shifts all the way to fifth gear and back down, then the problem is not in the transmission. If you can't shift the transmission into any gear with the bike not running, just rocking it backwards and forwards, then you've got a problem with the transmission or the shift lever mechanism.

If it does shift but you still can't get it into gear something is strange. I've seen a clutch that the plates were locked together from sitting up, but it still would shift into gear. Of course, when it did shift into first gear, the bike would lurch forward and kill the engine. In this case, we had to disassemble the clutch pack and free the plates up. If you've had a new clutch put in the bike, it could simply need an adjustment. But, usually a new clutch will have a tendency to wear in and start to slip rather than drag. When a clutch causes the bike to lurch when put into gear or become difficult to find neutral with the engine running, it's dragging. I'd check the entire clutch adjustment to start with.

Slide the rubber boot on the clutch cable up, break the lock nut loose and turn the adjuster to make the cable as short as possible. Take the derby cover off the primary to gain access to the clutch release adjuster bolt. Break the large locknut loose, adjust the center bolt inward until you feel resistance. Back the screw back out and back in until you feel resistance again several times. You want to just take the slack out of the adjustment, not start to open the clutch up. Once you've turned the bolt in and feel the resistance, back the bolt back out 1/2 to 1 complete turn. Hold the bolt in this position and lock the lock nut again. Now, adjust the clutch cable back out until you get a freeplay of about an 1/8 inch at the lever. The clutch should be adjusted well enough to release at this point. If it doesn't, the clutch plates are probably stuck.

If the clutch plates are stuck, rock the bike back and forth and shift the bike into fourth or fifth gear. Now, while holding the clutch lever in, push the bike backwards and forwards far enough to "bump" the clutch. This may break the bond between the plates and free it up. If not, you'll have to disassemble the clutch in order to free it up. Good Luck.