Discovery gearbox woes
“AT least the new gearbox works perfectly.” That was how I concluded last month’s story about replacing the broken gearbox in my newly-acquired Discovery 200Tdi with an R380 from a scrap 300Tdi.
If you describe anything on an old Land Rover as “working perfectly” you are just asking for trouble, and about a week after I filed my column I noticed that first and second gear were starting to become a bit stiff and awkward to engage. There was also an issue with the gear lever not self-centering in the fourth/fifth plane as it should, making it just as easy to select fifth as third. I took the top cover off the gearbox, fiddled about with the bias springs to no great effect, then realised there was a bit missing: the metal tab which should sit between the bias springs had broken off.
I had another R380 sitting under a workbench, so I swapped over the top cover assembly. The gear lever now self-centered, but the change quality still wasn’t great. A couple of days later I had to drive down to the village post office. I reversed into a parking space and then found that the gear lever had jammed in reverse gear. After mauling it about for a couple of minutes I managed to get it back into neutral, but then found I had lost everything in the forward half of the gate – first, third and fifth. First and third reappeared on the drive back to the workshop, but fifth was unselectable.
Taking the top off the gearbox again I could see nothing obviously broken, but the selector shaft had a lot of sideways play in it and was very stiff to rotate. Clearly the gearbox would have to come out again, but what to do after that? I had three choices: strip down the existing gearbox and try to repair it, fit another secondhand R380 (I had two to chose from) or try to repair the vehicle’s original LT77 gearbox which had lost fifth gear but was otherwise in good order. On the LT77, fifth gear and its selector mechanism can be accessed without having to disturb the main gearbox internal, so I decided to pull the extension case and see what I found.
It turned out that fifth gear had stripped all the dog teeth which engage with the synchromesh hub. Usually this kind of damage is caused by a weak synchromesh: repeatedly crunching into gear will take the tips off the dog teeth, especially if the gear is a cheap pattern replacement. The gearbox had certainly been rebuilt at some point and the mainshaft splines were in perfect condition, which isn’t what I would expect from an LT77 with 150,000 miles on it and a plain (not cross-drilled) input gear on the transfer box. I had a good secondhand synchromesh hub and a brand-new synchro ring sitting around doing nothing useful. So I ordered a new gear, put everything back together, then crossed my fingers and hoped none of the metal fragments from the mangled gear had ended up somewhere they could cause trouble. The LT77 has a magnet on the drain plug and a plastic fluid filter – both were clogged up with little bits of gear tooth, and the vehicle had been running for quite some time in that state.
This time I had no-one around to help me with the gearbox swap. First job was to remove the transfer box, using a couple of long studs in place of bolts to help me ease it back off the mainshaft. I left the bottom crossmember in place, jacked the gearbox just high enough to remove the rubber mount and bracket, then lowered it until it was just touching the crossmember. With the long jack under the back of the engine I was able to manoeuvre the gearbox backwards with the crossmember taking the weight. It is at times like this that I wish I had a big workshop with a four-post lift, long-reach transmission jack and all mod cons. People often ask me why I don’t have a four-post lift: the answer is that my workshop will only just accommodate four vehicles, and a lift would cut this down to two. All the same, I’m starting to get a bit old for crawling around on the floor. When I have done a hard day’s work my body certainly lets me know it. It is something I will have to look at before too long, I fear.
The repaired LT77 hasn’t done anything strange yet, but after what happened last month I’m not going to say anything more than that.