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Author: Subject: What is a "Dead Diff" ?
TimEllershaw

posted on 17/9/13 at 10:17 AM Reply With Quote
What is a "Dead Diff" ?

I've seen a couple of adverts for "dead" diffs ( English Axle Genuine Ford 3.9 Dead Diff (39/10) Very Good Condition Rally Race )

I'm guessing that "dead" in this case doesn't mean broken or not working, as they all seem to be described as being in good condition. Have they have been locked up in some way for racing (more no-slip-diff rather than limited-sli-diff )


Any idea what they mean ?



Thanks,

Tim.




[Edited on 17/9/2013 by TimEllershaw]






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beaver34

posted on 17/9/13 at 11:43 AM Reply With Quote
not sure but ive got a spare open diff if you need one?
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gavin174

posted on 17/9/13 at 12:49 PM Reply With Quote
is it because it goes in a live axle......

no idea, I would ring the seller!!





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mcerd1

posted on 17/9/13 at 01:12 PM Reply With Quote
if I had to guess I'd say its been welded up...





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r1_pete

posted on 17/9/13 at 01:14 PM Reply With Quote
I'd contact him, they are usually referred to as welded or locked diffs if the planet gears have been welded.

Immediate thought was Dead = knackered

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mookaloid

posted on 17/9/13 at 03:05 PM Reply With Quote
I've asked the question





"That thing you're thinking - it wont be that."


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mookaloid

posted on 17/9/13 at 03:10 PM Reply With Quote
Quick answer:

Hi Mark,
All this means is that the Number of teeth on the Crown wheel and Pinion work out exactly to 3.9 and not 3.89 like the majority do - This is sometimes important for racing purposes i.e. Hot Rods or Autograss etc, Regards
Ian Evans
E A S R S

Easy when you know





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TimEllershaw

posted on 17/9/13 at 03:14 PM Reply With Quote
quote:
Originally posted by mookaloid
Quick answer:

Easy when you know






Ahhhh, I see. Obvious once you know what he means.

Thanks.






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Smoking Frog

posted on 17/9/13 at 03:14 PM Reply With Quote
quote:

is it because it goes in a live axle......



That would make it a living dead axle, scary!

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Litemoth

posted on 17/9/13 at 03:18 PM Reply With Quote
As said above, I think the advertiser is saying it's 3.9:1 dead-on and not a fractional ratio - (39/10 = 3.9 exactly)
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TimEllershaw

posted on 17/9/13 at 03:19 PM Reply With Quote
quote:
Originally posted by beaver34
not sure but ive got a spare open diff if you need one?


Thanks for the offer.

Mine has quite a bit of play in it, but not sure if I'm just going to replace it, or get it repaired/reconditioned. I need to drag it off the car and have a look. ( I also need to think about ratios : don't know what I've got, or what I want )

This guy seems to get good reports : http://www.arrowautoengineering.co.uk/page4.htm






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britishtrident

posted on 17/9/13 at 04:40 PM Reply With Quote
The reason why you get funny ratios such 4.18:1 is because it is desirable to use prime numbers of teeth as this evens out wear and aids quieter running.

If you made a 4.2:1 ratio by use an 42 tooth crown wheel and 10 tooth pinion the wear would be not equally distributed

Using a 46 & 11 to give 4.1818 is better as because the were is shared out more evenly it will be quieter quieter and because the pinion has an extra tooth in partial contact it is stronger.





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