Quote:
Originally Posted by Tony Mathers
Thanks Gentlemen at this stage I will see how it cleans up, as most of the rust came off before I put the gearbox in the molasses.
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No doubt it will clean up OK, but personally I wouldn't bother with a rusty gearbox after it's out of the vehicle. I'd rather start with one that hasn't seen water, since they're easy enough to source. Or at least replace the rusty gears, which are often just the upper ones. The cluster gear never rusts if it's fully underwater, even after decades, because the oil layer seals out all oxygen.
The main consideration of course is tooth end wear/damage through crunching the gears, which mainly effects 2nd and 3rd gears. This damage is self perpetuating, because once the rounded ends are flattened and splayed and chipped they're much harder to engage without crunching. Eventually this can lead to a tooth breaking off, or even several stripped teeth. When that happens you need a complete rebuild, as the bearings are likely to be damaged by case hardened fragments of steel floating around in the oil, and likewise the seals may be abraded. In fact there will always be loose steel floating around inside a crash gearbox, so it's worth making sure you have a magnetic drain plug. They often get lost over the years.
As Phil says you can happily run a rusty gearbox provided the bearings are replaced. One of my Ford gearboxes was so rusted out it took me two days work with a crowbar and sledgehammer to get the gears and selectors moving again. It works fine now but makes a tremendous racket because the front bearing was completely rusted solid. It's OK in the back yard but would no doubt shatter if it were run at speed on the road for any length of time.
The gearbox in my road blitz was also rusty, and I didn't even know at first, because the truck had supposedly been restored. All I did was check the oil level, never dreaming there'd be a litre of water underneath! It wasn't until I did a 200 km trip and lost reverse gear along the way that I realized there was anything untoward inside. What happened was the oil/water/rust powder emulsion whipped up inside while driving caused the oil to lose its lubricant properties, and the reverse selector fork started to bind on its shaft when pushed sideways by the gear lever. It took me a while to figure out, because it worked perfectly when pushed gently with a finger, but every time I put the lid back on it stopped working! Anyway it was easily fixed by flushing with petrol and refilling with clean oil. The bearings seem to be OK for the moment so I have no plans to change the gearbox.
