Datsun 620 J15 4 speed stuck in fourth gear

[windowless66]

Got a bit of a problem my gearbox wont change out of fourth gear.

You can depress the clutch and the clutch disengages but the lever will not move out of gear. 

Two of the rubber grommets in the linkages were totally gone and I have made some bronze bushes to take their place. I made these after it was jammed.

I'm fairly sure the gearbox has just jammed up because of the slop in the linkages but does anyone know a good trick to unjam it?

I've tried rocking the car back and fourth in gear and moving the shafts for the gears by hand. its the front most lever that feels jammed.

The thing I was going to try next is removing the linkages and putting a big shifter on the shaft and use a bit of force.....Thats why I'm asking before I do any damage.

Any suggestions appreciated.

[69srl311]

When the brass syncros wear it allows the coupling sleeve to travel too far and the shifting inserts can pop up and that's all she wrote.  If you open the box, I would replace the brass syncros.  I didn't and it kept jamming in different gears, usually when it would get hot, until I replaced those wear parts.

[windowless66]

mmmm...Thats not really what I wanted to hear :) 

[datzenmike]

If this is the F4W63 with the removable oil pan... I had one do this also. It's worn out and I replaced it.

[windowless66]

If this is the F4W63 with the removable oil pan... I had one do this also. It's worn out and I replaced it.

Yeah its the one with the removable pan. Was it a big job? Theres a bloke up the road from me with a 720 with an L series engine not sure what size yet, I was going to go see him and try buying the whole car to do a gearbox swap.

If I did do the gearbox swap would it be worth putting in the L series? Is it a lot more work? I mainly just want the car back on the road.

Thanks for your help

[datzenmike]

J and L series transmissions won't swap but the internal parts will. I believe the motor mount location for the J are way far forward than the L series... at least they are here.

[windowless66]

So a fair bit of work then, I might just have to chase up another gearbox or try and get the bushes.

[windowless66]

Thanks for the help guys, Ended up taking a gamble and putting in a second hand gearbox....condition unknown :P But it seems to be a really good box. Shift is way smoother than the original box was and have done a good 500k's hassle free. Good to be on the road again.