Help with gearbox issue

[Molly1966]

1966 Morris 1000 with reconditioned gearbox and less than 2000 miles on it. Looking thoughts from anyone familiar with these gearboxes.

Up until now gearbox was working fine with no bad noises and smooth gearchanges. Was out for brief spin yesterday and all going well until on the way home went to fourth gear and noticed an unusual short shift into fourth. Thought I had imagined it as car continued on in fourth - no noise or issues.

Came to a stop and had to go up through the gears again and once more noticed a short shift into fourth almost as if fourth gear was not fully selecting and something was restricting it. Car then proceeded to jump out of fourth when decelerating and reluctant to go back in. No bad noises or rattling/banging but obviously something up.

Got myself home with no issues. When parked up and going through and selecting gears it seems that fourth and also potentially third gear are not selecting fully. Shifter goes into gear but sensation is that its not fully engaged. First/second/reverse all engaging as normal. Not been out in car since and plan to investigate further tomorrow. Wondering if anyone has any ideas on what internals could be causing it if there might be any pointers on it.

I know this will likely end up with gearbox having to come out. Gearbox was receipted from around 4 yrs back at £750 so is out of warranty but car has only covered around 2000 miles with it since. Typical my luck!

[philthehill]

Check the condition of the rubber ring on the bottom of the gear lever and the plastic cup under the bottom of the gear stick.
Make sure that the selector arm(s) has/have not come loose on the selector shaft(s).

[Molly1966]

Thanks Phil - that looks like a good plan.

Have not got to it yet today. Might be tomorrow or later this evening. I suspect an issue with the selector arm/shaft on 3/4 might be the most likely issue. Car has always had good positive tight selection on gears with no sloppiness but I will check the gear lever first as advised in case something has happened in there.

A second potentially related question. The car has always had an issue where when the clutch was fully depressed i.e very tight to the floor I got a loud rattling noise. Only noticeable when sitting not when driving. This only came at the very last 1/2 inch or so of travel so I avoided heavy clutch use with the gear changes. When depressed without too much force there was no noise and clutch worked perfectly. Also have checked clutch travel for adjustment and it seemed to be fine. No issues when driving so I left it alone putting it down to over travel and that I would be careful with it.

Any thoughts on causes with this or potential relation to current problem?

[philthehill]

I take it you have a normal mechanical clutch release mechanism.
You could well be right about the over travel.
The pressure pad of the clutch release fingers could be fouling when depressed.
I would suggest that you check the clutch pedal slack against the workshop manual.
Saying the above - the clutch pedal does not have to travel all the way to the floor to be clear enough for non rattle gear changes.
Setting the clutch pedal clearance so that even with the clutch pedal right on the floor may be the way forward.

[Molly1966]

Thanks again Phil - really appreciate the help!

The clutch is standard mechanical - all running gear is standard 1098 on the car. I did check the clutch pedal slack and have about 1.5 inches as per spec and pedal sits up nicely so I did not take it any further at that time. I took a mental note to avoid aggressive depression of the clutch which was easy enough as the car had nice gear changes with a decent dab of the clutch and I had no need to fully depress it.

I will revisit it when I get a chance to look at the gearbox tomorrow to see if an adjustment to the clutch stops this happening. I am just hoping now that some clutch over travel (if that's what it is) might have in turn damaged the main input shaft bearing in the gearbox.

[Molly1966]

Just a further update to say I took the car out for a short distance this evening - still not had time to further investigate mechanically.

Car is now flat out refusing to go into fourth - all other gears are working perfectly with no noise. Mystery deepens.

[philthehill]

If the selector arms are secure then it could be a faulty synchro hub which means stripping the gearbox.

[Classiccars]

Ours was hitting the handbrake and eo popping out of fourth.Had to bend the gearstick slightly.

[Molly1966]

Thanks @Classiccars - its definitely not near the handbrake and is something internal to the gearbox I am afraid.

Phil - you could be right about the synchro hub. I have been speaking to a very good gearbox specialist who works on these gearboxes and said the same. Advised that it could be a broken spring in the 3/4 synchro effecting the 3rd/4th selector rod detent. Have been given some good pointers and a suggestion to remove the side cover and release the detent plungers in there on the off chance that this might resolve a potential sticky detent.

Its a bit of a long shot but still worth a try whilst box is still in the car. My main problem at the moment is finding the time to get to it. In any event I will report back when I find out more.