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What is a "Dead Diff" ?
TimEllershaw - 17/9/13 at 10:17 AM

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]

beaver34 - 17/9/13 at 11:43 AM

not sure but ive got a spare open diff if you need one?

gavin174 - 17/9/13 at 12:49 PM

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

no idea, I would ring the seller!!

mcerd1 - 17/9/13 at 01:12 PM

if I had to guess I'd say its been welded up...

r1_pete - 17/9/13 at 01:14 PM

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

mookaloid - 17/9/13 at 03:05 PM

I've asked the question

mookaloid - 17/9/13 at 03:10 PM

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

TimEllershaw - 17/9/13 at 03:14 PM

quote:
Originally posted by mookaloid
Quick answer:

Easy when you know





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

Thanks.

Smoking Frog - 17/9/13 at 03:14 PM

quote:

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


That would make it a living dead axle, scary!

Litemoth - 17/9/13 at 03:18 PM

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)

TimEllershaw - 17/9/13 at 03:19 PM

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

britishtrident - 17/9/13 at 04:40 PM

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.