Series 3 Strange gearbox goings on.

Hello,

Here's one for you. At the beginning of the year I lost 3rd & 4th on my 1984 Series 3. I managed to get it back home and was manoeuvring it into it's parking space when there was a "thunk" from the direction of the box and I could select all gears again. I checked the oil which was a bit low and told myself that must have been the problem.

All seemed well for a few months then I lost third, which was odd as all the failures I have read about on the internet have mentioned synchro clips coming off resulting in inability to select 3rd or 4th. Nothing mentions only losing 3rd gear.

I drove it around over the summer like this with no trouble. Unfortunately whilst out last Friday I fluffed a gear change into fourth with a nice graunching sound. I stopped, picked my eldest son up from Air Cadets and then found I was stuck in Fourth. I tried dropping the clutch a bit to jar it out but no effect. I was stuck in the traffic having to use the Hi & Low ratio to give me a second gear. I got home but nothing has shifted it out of 4th.

Any ideas? One friend has suggested it's simply a selector problem. I'll try and get the floor and seats out this weekend to have a look. Any pointers wrt what to look for would be great. I already have a nice pile of sheared off seat base bolts. The four that fit behind the base of the B pillar/seat belt mount were a right b*stard to get out. No access and nasty captive spring clips on them that didn't capture anything, just stopped you getting the spanner on the square rusted in nut. Rant over, I feel better now, apart from my thumb. That still hurts where I hit it with the hammer trying to wedge a spanner on the nuts.

Give rusty threads a good soaking in penetrating oil a couple of days before undoing them, it can work wonders. No idea about the gearbox problem but I would start with looking at the selector too.

Col

Stainless replacement bolts and clips available.

Check the castle nut on the back of the main shaft. Can be accessed from the PTO cover o on the transfer box.

Rest assured that I am familiar with the properties of WD40 & Plus Gas. I must have used a few gallons over the years. This lot were too far gone. I previously soaked the ones under the floor but the WD40 only freed off the portion in the nut. They turned until you got to thicker corrosion on thread at the end of the bolt then sheared off anyway!! I couldn't really get in the gaps with a wire brush to clear the threads.

I've already been to Screwfix and got a nice selection of Stainless fixings. Next job is to see what state the hand brake components are in before freeing them off to get the seat base out.

You can see the selectors without taking seat box out , although it’s always nice to have new fixings
Just need to remove both floors and the gearbox tunnel cover could be loose pinch bolts on the selector fork for 3rd and 4th

Check the mainshaft nut hasnt come loose, common issue where someones just tightened it with a punch and hammer, the nut comes loose and the mainshaft can move back and forth

Check mainshaft nut first, but in my case the synchro springs failed, changes got harder, then I missed a gear and stripped the gear teeth off which then fell into the constant mesh gears and seized the box. So drain the oil and see what comes out, if its bits then box out.

Thanks.

I now have the box out. I'll try the main shaft nut.