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Author Topic: Diff ratio. How to identify.  (Read 666 times)

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OTeunico

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Diff ratio. How to identify.
« on: 16 March 2025, 05:16:24 »
Hi folks,
I will fit some oversized van tyres to my 2.5TD. As far as I know mine has a 3.45 diff ratio. 4.22 will suit perfectly my new tyre diameter...any clue on how to tell what ratio has a secondhand diff by its external look? Do they have some ID plate/tag or something?
TIA
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TheBoy

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Re: Diff ratio. How to identify.
« Reply #1 on: 16 March 2025, 10:13:19 »
Can't answer your query, but thought TD's came with 3.9?
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zirk

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Re: Diff ratio. How to identify.
« Reply #2 on: 25 March 2025, 20:22:39 »
Fairly sure the if my memory serves are the 2.5TD had a 3.45 Diff.

The bit I can't remember is wether this ratio is for Manuals and Autos, or wether the Autos were higher ratio, don't think they were.

If your just going up in one tyre size from normal then the profile normally is smaller, so I wouldn't worry about the ratio etc, or if going totally bigger sizes then your next choices are a 3.7 and 3.9
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Doctor Gollum

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Re: Diff ratio. How to identify.
« Reply #3 on: 25 March 2025, 22:46:59 »
Six pot diesel diff ratios might be listed in Haynes :-\
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cam.in.head

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Re: Diff ratio. How to identify.
« Reply #4 on: 25 March 2025, 22:55:57 »
or you could just turn it and count the rotations
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Nick W

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Re: Diff ratio. How to identify.
« Reply #5 on: 26 March 2025, 10:08:27 »
If you're going to fit a used diff, wouldn't you unbolt the cover to check there's nothing bad*** inside? Then you could count the teeth on the ring gear and pinion and know what the ratio is.




*** damaged teeth, sparkly oil, not enough oil, weird new life forms living on the oil that's left, whatever
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Doctor Gollum

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Re: Diff ratio. How to identify.
« Reply #6 on: 26 March 2025, 10:55:48 »
Quote from: cam.in.head on 25 March 2025, 22:55:57
or you could just turn it and count the rotations
True enough...

4 turns of the prop shaft would be 3.9 and 3.5 turns would be tother ::)
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Enceladus

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Re: Diff ratio. How to identify.
« Reply #7 on: 28 March 2025, 13:36:04 »
There should be an ID tag on the bottom of the diff. The ratio should be at the bottom right of the tag. Something like 38:9=4.22.  That said given the age of these diffs the ID tag might well have disappeared.
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OTeunico

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Re: Diff ratio. How to identify.
« Reply #8 on: 14 April 2025, 20:23:41 »
Unfortunately I cannot check the diff since it  is not in my city. It will be purchased from a reputable breaker with warranty.
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Doctor Gollum

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Re: Diff ratio. How to identify.
« Reply #9 on: 14 April 2025, 21:35:05 »
If they're that reputable they should be able to send you picture or perhaps supply the vin of the car it came from.
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Mr Skrunts

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Re: Diff ratio. How to identify.
« Reply #10 on: 19 April 2025, 13:48:03 »
https://www.autobahnstormers.org.uk/mainmenu-about-the-cars

Sure there was info about diff ratios on here.

Looks like the site has changed and sadly I have not got the time to help and look. :y
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Doctor Gollum

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Re: Diff ratio. How to identify.
« Reply #11 on: 19 April 2025, 16:30:04 »
The basic ratio options are listed in Haynes.

If I remember when I get back home, I will have a rummage.
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