Help! My Big7 is stuck in 1st gear!

[larrylamb11]

Argghhh! 
It appears a disaster has befallen my '38 Big 7....... I can't shift the gearbox out of first and the 'box has gone 'tight' 

I could really use some help or pointers - is there a typical failure mode with these 'boxes that might cause this?

I am resigned to stripping out the gearbox and dismantling (having already whipped the top cover off in situ and inspected with no obvious ailments) but it would be really useful if anyone might have any suggestions as to what I should be looking for.... 

Here's what happened.....

I went to use the car yesterday, it started as normal, shuffled it back and forth to get out of the garage, then pulled away in first, coasted down the drive in gear with the clutch in to approach the road (20m), got to the road and let the clutch out slowly to pull onto the highway and as it began to pull forward the car suddenly pulled up short (like the brakes had jammed on) and I couldn't move the gear lever. Thereupon I was stuck in the middle of the road, straddling the carriageway! I realised I was unable to move the car - I couldn't push it, couldn't get it out of gear and it would only move forward under engine power with difficulty (it would lurch forward when the clutch bite eventually overcame the high friction in the box) and that's where I was stuck.....

I managed to move the car to the edge of the road, whipped the top cover off the 'box to see if there was anything obvious (nothing, plenty of oil too), found I couldn't move the gear selector for 1st/2nd and that was it. I had to disconnect the propshaft to be able to move the car back to the garage. With that disconnected I can tell that the output drive flange on the gearbox is tight and won't move like it normally would, so the 'box has clearly gone tight internally somehow...

Help!

[John Mason]

It sounds to me that you may have got two gears selected at the same time. This sounds odd but in this situation because of the difference in the gearing it all locks up. My memory is a little vague now as I last came across this problem some 50 years ago. I would look at the gear selectors first and check the forks that engage and disengage the gears.

John Mason.

[Dave Mann]

This happened to me in our Seven 50 years ago, I stopped after descending a steep hill in bottom gear only to find on re engaging the clutch the transmission was locked and it was stuck in bottom gear. With the help of some passers by we picked the rear of the car up and wheeled it into a car park. I removed the gearbox top and with the aid of a crow bar put it back in neutral with the second gear synchro balls and springs flying everywhere. I drained the box to collect the balls & springs and put the oil back in. We then continued our holiday, It was some months later that I stripped the box to put things to rights. This happened to Peter Fearn going to Woolaton Park decades ago and to another Seven in Switzerland.

[Peter Sweeney]

Had the same problem with my Big 7. Son drove car first time on his own and kept in 1st. Jammed had to bring car home on trailer strip and rebuild gearbox. Tend now to get out of 1st at the earliest moment. Pete

[Chris KC]

Something like this happened to me on a campsite in Switzerland once - engine still running, but couldn't de-select first & car wouldn't move in any direction. With back axle jacked up (and handbrake released!) the rear wheels will turn.

In my case there was excessive free play in the box and the first gear cog had basically jumped over the detent springs and gone far enough off the end of the shaft to tilt slightly & jam against the inside of the casing.

Nothing inside was damaged, but it had to be stripped down, and even then took some effort to free the jammed gear.

[Simon Scott]

When my box did that it there were bits of synchro spring and the ball bearings in the oil when I drained it.

[larrylamb11]

Thanks for the thoughts 
It hasn't selected two gears at the same time luckily as I've checked that and the reverse and 3rd/4th selectors are still in the neutral position (and capable of moving therein).
It sounds most similar to the failures Chris KC & Dave Mann experienced - that's exactly what mine did, engine still running, can't de-select 1st, but rear wheels will turn... it feels like the cog is jamming on the casing as the 'box has gone so tight, yet will still turn with enough force from the engine. 

Hmmmmm...... it's not sounding too positive so far.

Are gearbox spares / parts available for these? or am I better sourcing another 'box do you think? (if indeed there are any available  )

[Peter Iddon]

Hi Larylamb11
I suspect the syncro indent springs and balls have become displaced on the first/second gear hub, when this happens it's quite usual for one of the displaced parts to jam in between the gears, locking the gearbox in the process.
It's not at all uncommon for this to happen on gearboxes when they develop a little end float on the shaft/gear clusters due to wear.

[Bob Culver]

As with other similar makes I am always intrigued by the arrangement of sliding parts and gear hubs. After 1st gear is engaged there is nothing to stop the gear hub wandering forward to its other extreme until the 2nd gear synchro cones contact. If 1st selector wear or adj allows the 1st to go well rearward, and the synchro cone is well worn the balls in the hub may start to emerge around the rim and wedge the 1st gear irretrievably rearward. The heavy rubbing synchro cone effectively engages 2nd gear at same time, more or less locking the drive. Some or all balls may pop out. Curiously cars seldom show signs of any synchro cones heavily rubbing for protracted periods.
 
(Javelin cars had a similar simple box. The makers took over final gearbox production but tolerances were poor. The steel on steel cones rubbed until they seized and the car locked in two gears, locking the wheels, terrifying the test drivers in winter, and leading to warranty and remedial work which finished the firm. Was “remedied” with an additional ring of grooves to capture the balls and limit hub wander. Curiously trouble with earlier boxes is almost unknown whatever the use)

[Chris KC]

It's quite possible there is no real damage (presumably you weren't going very fast when it locked up?) so it may simply be a matter of stripping down and re-assembling. If similar to A7 gearboxes they are not nearly as complicated as that might sound. Likely new detent balls or at least springs will be required, a good clean up, and perhaps new bushes / bearings to address any end float. There's only really one way to find out what needs doing. I wouldn't be in a rush to replace the box unless the one you've got is somehow beyond repair.