Crunching into reverse

[Paul_S]

My 240Z gearbox (5 speed) has a noisy habit of crunching into reverse. I've never succeeded in a silent selection into reverse gear. All the other gears are fine but possibly a little 'notchy' if I were to be critical. I've never drive another to know if that's normal or not.

So far I've replaced the clutch fluid (the old stuff was really grim) and had a go at adjusting the rod on the slave cylinder but it's not made any difference. I haven't yet replaced the gearbox oil as I'm waiting for a new speedo pinion gear before I do. Also I've made no adjustment to the clutch pedal itself, but I'm not sure that will make any difference since the clutch engages about half way through its travel.

Is there anything else simple or cheap to check before I start thinking about difficult and expensive solutions?! Is it a common thing on these cars or something out of the usual?

To be honest, I can live with it for a good while because I don't reverse that often and select reverse before starting the car in the garage. But it would be nice to get it fixed, or understand if it's an early sign of something serious that might occur in the future.

 

[jonbills]

I'm pretty sure they don't have synchro on reverse. Even the later C boxes don't. So might suggest your clutch is dragging just a little.
Does it have any inclination to move in gear with the clutch in?

 

[Paul_S]

I'm pretty sure they don't have synchro on reverse. Even the later C boxes don't. So might suggest your clutch is dragging just a little.
Does it have any inclination to move in gear with the clutch in?

I did wonder if there was no synchro.

I also wondered if there was any drag, which is why I tried adjusting the rod on the slave cylinder. There's no sign of the car wanting to move when the clutch is in.

 

[jonbills]

What engine speed is it idling at Paul?

 

[Paul_S]

Around 800 revs give or take

 

[jonbills]

Well that's no problem. Mine idles at 1100+ and no crunch.
Have you checked oil level?

 

[Paul_S]

Well that's no problem. Mine idles at 1100+ and no crunch.
Have you checked oil level?

I've not checked the oil yet. I have fresh oil for the 'box and am planning on changing it when I receive a new speedo pinion gear.

That shouldn't stop me checking the current level I suppose!

 

[jonbills]

I think from memory the reverse gubbins is on the upper half of the box so low level might have an impact. Can't hurt to check. It's easy enough for them to lose oil out of the rear seal.

 

[Paul_S]

I think from memory the reverse gubbins is on the upper half of the box so low level might have an impact. Can't hurt to check. It's easy enough for them to lose oil out of the rear seal.

Thank you sir! I'll give it a look

 

[johnymd]

My old 240 box from my blue car would always crunch when selecting reverse or just not go in. I got used to selecting 5th then going straight into reverse.

 

[Paul_S]

My old 240 box from my blue car would always crunch when selecting reverse or just not go in. I got used to selecting 5th then going straight into reverse.

Ah, interesting. I'd never thought of trying that.

When I next fire her up I'll let you know if the trick works

 

[Rob Gaskin]

You can't go from 5th to reverse on later boxes.

 

[Paul_S]

You can't go from 5th to reverse on later boxes.

Ah, that will make mine an early one then.

My old 240 box from my blue car would always crunch when selecting reverse or just not go in. I got used to selecting 5th then going straight into reverse.

Well I had a little test and that worked a treat!

I'm obviously hoping some fresh oil topped up to the correct level will fix it but this is an excellent workaround that I can live with on a daily basis. Much better than turning it off and on again!

 

[jonbills]

That's very interesting. I suppose it's using the 5th synchro to get the shaft speed in sync before selecting reverse.
But why is the main shaft turning in the first place? Maybe the pilot bushing is stuck to the input.
Or maybe I don't understand well enough how it all works[emoji18]

 

[Paul_S]

That's very interesting. I suppose it's using the 5th synchro to get the shaft speed in sync before selecting reverse.
But why is the main shaft turning in the first place? Maybe the pilot bushing is stuck to the input.
Or maybe I don't understand well enough how it all works[emoji18]

Don't ask me mate, I haven't got a scooby