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Bigger hammer

Why Fenchurch was jumping out of first gear


Chewed morris minor first gearCloseup of chewed gears

The pair of gears on the left of the first picture are the first forward gear and the other two are the reverse idler. The bottom gear on the reverse idler has unworn teeth - they should all look like that. The Morris Minor gearbox doesn't have synchromesh on first or reverse, which means that it crashes loudly if you try to put it into either of those gears when the speed of the input shaft and the output shaft don't match. You're supposed to come to a complete stop, press the clutch, and wait a couple of seconds before changing into first at a junction or roundabout. It is possible to double-declutch down into first but it's a bit tricky to get right.

When you crash it hard, the corners get chipped off the teeth of the gears. Do it enough times and they become tapered as you can see in the photos, which means that when you apply torque the gears are pushed apart, popping the stick out of gear. In a slightly worn box this usually happens when you're climbing a long steep hill. On a badly worn box it does it all the time unless you hold the stick in with one hand while steering with the other.

The fact that the smaller of the two first-speed gears is in much worse condition than the larger illustrates an interesting principle - they've actually worn by about the same amount but the wear is spread out over more teeth on the larger gear.

The rest of the gearbox was in remarkably good condition. All the helical gears and the synchromesh units are perfect, the main bearings seem fine, and there wasn't much wear on the layshaft. I think it must simply have been repeatedly crashed hard into first gear until the teeth were chipped away.

Comments

Gosh. And damn. and....


I'm not going to follow a Morris Minor up hill again!
The first time it happens is a bit of a shock but you soon learn to hold the stick in when climbing first-gear hills :)
Well, don't let yourself be followed downhill by one either. I made an unfavourable impression on a Mondeo once when the brake pedal suddenly hit the floor.
LOL!
Ooo-er. Doesn't look nice at all.

I'm kicking myself now for disposing of my other defunct gearbox, as I could have been rebuilding it. i've always been daunted by stripping and rebuilding an apparently complex gearbox- is it really all that difficult?
I rebuilt my Landy gearbox myself, and admittedly that was a bit more complicated than a Minor one but the amount of time and cost meant I didn't want to do it again. Pressing bearings and bushes in and out without the proper equipment, repeatedly assembling and disassembling it all to adjust end-float with shims, and slicing your fingers open with big circlips that refuse to go into their groove. Then if you get it all back together and reinstall it in the car and it's noisy or is still jumping out of gear, what do you do next?
Torch it, then spend the rest of your life hiding in a small box, gibbering.

Maybe I won't rebuild it. You can't get the parts for 948 boxes very easily, anyway.

Or the boxes- hounds keep outbidding me on Ebay. I can only assume they have neither jobs nor life, as I'm invariably otherwise engaged when bidding ends.
There's somebody on the forum advertising a reconditioned 1098 box for £200. I think you just need a 1098 backplate, flywheel, and clutch to mate a 1098 box to a 948 engine. Or upgrade to a complete 1098 engine, box, and diff, and you too can overtake BMWs on the motorway! ;)
I think you do, yes. In theory, that should make it a bit nippier too, as the 1098 was a more long-legged 'box. I can get a 948 for £150, but as I'm tight, I'm shopping around before I do that. I do actually have a 1098 clutch that I picked up from a car breaker's with a load of other bits. The 'box had already gone from that car, though.
It's only 2nd gear that's very slightly higher on the 1098 box - the other gears are all the same. The big difference is that the 1098 cars came with a 4.22:1 diff instead of 4.55:1.

£150 sounds a bit high for a box that hasn't been rebuilt and has an unknown history.
I know nothing about diff' ratios at all. the boxes haven't been rebuilt, but they have been tested and come with a guarantee- I just wish they weren't so expensive. I can't keep throwing money at that car...
I'd try putting a wanted ad on the MMOC forum - there's a good chance somebody's got a good used 948 box sat around collecting dust.

(Anonymous)

Is the seller's name dennis? If so, it's AUpickup from the MMOC message board - I know he's selling one, and I know he's trustworthy :)
That's the £200 rebuilt 1098 box on the forum that I was referring to.