Car slipping out of 5th gear

-crisp-

Hi

I've searched this topic to deth and its been asked millions of times but I cant find a question similar to mine.

I'm driving a honda civic with a 6 speed transmission. It was working fine but last night it woudnt stay in 5th. I can change into 5th and as I'm accelerating, not even hard, any acceleration at all is enough to keep it in gear but as soon as i let off the throttle it pops out half way and grinds. I can hold it in easily, it doesn't pop out with much force at all.
4th is fine and 6th is fine so I managed to get home.

I've found multiple answers to this question but all for 5 speed and not 6

One, which im hoping, is the transmission fluid needs changing.
that makes the most sense as yesterday I had the car jacked up to change the rear pads and rotate the tires. i had both wheels on the left side off the ground and then the same for the right.
I donk know much but could it have just knocked the fluid around the gearbox to revel that it need to be changed?

Other responses which i hope aren't my problem are new synchronizers, a new fifth gear or even a whole new gearbox. I'm terrified to drive it incase something comes loose and i mash the entire gearbox.

Any suggestions before I bring it into the garage and sign my life away with repair bills?

Thanks in advance for any help.

Nissan doctor

Does the gear stick move around a lot in all gears when you accelerate and decelerate?

-crisp-

Not even slightly. It doesn't even move around when it's in 5th. It sits in properly then slips out when I let off the power.
The only movement in the gear stick is the usual vibration from the engine. You can't even see it move just feel it.

Plug

There are very slight tapers on the dog teeth of the gear and the teeth on the baulk ring, it prevents the sliding hub from popping back out. Maybe they are worn.


Another possibility is the end of 5th gear is worn. This has helical gears and when two are running in mesh they want to pull away from each other on the axis, if there is enough play on the axis of 5th gear well then that explains why its popping out.

Worn gear linkages are another possibility. Im not sure if it has cables or a bar on the linkages.

-crisp-

I take it they are costly to fix?

Plug

Good few hours involved. Most garages won't tackle a gearbox but you should find a gearbox specialist or a any garage that will do a gearbox. Obviously we don't know what the problem is yet so get it looked at first.

-crisp-

Any guess if it's drivable? If I avoid 5th and go from 4th to 6th?