Well, I might as well, I now have it reasonably figured how the diff works on my car(s) and what I can do to resolve the issue I have.
What's the issue I have?
What you're seeing is a tiny little collection of gears with a huge mo-fo gear around the outside.
And here's the money shot - that little set of gears is the bit in the pic above, the $500 part.
And... the gearing/ratio is set by the big ring round the outside.
I can use the outside gear from my manual car, on the auto good diff.
With me?
Action time:
What's the issue I have?
- I have a manual car, with welded diff - not drivable.
- I have an auto car with open diff - with crazy ratio.
Ready?
320i ratio for a manual car is something between 3.45:1 (rare) and 4.27:1, the ratio for an auto is 4.45:1
What does this mean, the number of turns the prop-shaft will do before a wheel completes a revolution.
So, basically if you're cruising at 100Kph in a standard manual (diff) and fitted an auto one, you'll be going slower, or rather revving higher to get to the same speed. I.e. lower ratio diff. Excellent.
Got it? It's all in the gearing. What's confusing is that the gearing is largely outside of the diff bit.
Here's an interesting video on how diffs work:
Fascinating I think you'll agree.
So what does this all mean (I'm losing track myself actually)?
Well, I've been looking at these online, ebay has them:
This would fix my welded diff, but for $500 (the same pretty much I spent on Ron Burgundy) I reckon I must have the parts.
Consider this video... it's how a diff gets welded up :
What you're seeing is a tiny little collection of gears with a huge mo-fo gear around the outside.
And here's the money shot - that little set of gears is the bit in the pic above, the $500 part.
And... the gearing/ratio is set by the big ring round the outside.
I can use the outside gear from my manual car, on the auto good diff.
With me?
Action time:
- Pull off my locked diff.
- Pull it apart, check that it's welded in the 'tiny bit'.
- Pull that out.
- Pull out the auto-diff.
- Pull out it's 'tiny bit' that we know is open and works.
- Affix manual gear ratio to the auto 'tiny-bit'.
- Reassemble as the diff for my good car (that's not the auto, did you see the woosh comment below?)
- Never mention diffs again.
One thing I have to consider, is what the ratio is for the manual car - if it's 4.1 that's OK. But I'd like to have lower ratio gearing.
Why? Well you're into GT5, shorten the final drive in transmission settings and see what it does to your car's acceleration.
The one massive caveat to all this is how the ratio is worked out. But, ebay has the outer rings too, so I can replace them if I have to!
So there it is, I can buy the parts to sort my world, pull apart two diffs and probably get there. And in any situation there are ways forward that aren't going to break the bank.
Wear on the diff in the manual is going to be a factor - it's been welded after all. So I may invest in the ratio above and have that onto the auto diff, and ditch the risk of the track trashed one. Sound thinking actually.
I need a beer.
[Update]
This page has had a massive update. Why?
Well, like a proper religious zealot I had it in my head that the ratio was the divisible number. I.e. the bigger the number the higher the final drive gearing. But it's not, it's simpler than that. It's just the number of turns of the prop shaft before the wheel makes one revolution.
And it's been hard to change my way of thinking, I had a belief system around it, a sound hypothesis and generally made everything work with my world view.
I can't stress how confronted I was when I did the only thing that I knew would convince me... that being on the removed diff I turned the prop-shaft and looked to see if the wheels would spin faster or slower.
Slower obviously.
And now, as an enlightened soul I can see it's obvious. The gears are small to big... fast to slow. Easy.
[Update]
This page has had a massive update. Why?
Well, like a proper religious zealot I had it in my head that the ratio was the divisible number. I.e. the bigger the number the higher the final drive gearing. But it's not, it's simpler than that. It's just the number of turns of the prop shaft before the wheel makes one revolution.
And it's been hard to change my way of thinking, I had a belief system around it, a sound hypothesis and generally made everything work with my world view.
I can't stress how confronted I was when I did the only thing that I knew would convince me... that being on the removed diff I turned the prop-shaft and looked to see if the wheels would spin faster or slower.
Slower obviously.
And now, as an enlightened soul I can see it's obvious. The gears are small to big... fast to slow. Easy.
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