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how to work out your diff ratio

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is there a simple way of working out what ratio your diff is without removing everything on the front? was thinking there must be a way of measuring how many revolutions of the wheel you get per turn of the prop. any suggestions more than welcome. thanks.

post-3069-1177109403.jpg

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If the rear diff is a known quatity (or one in another car for that matter) you could chock one side of the car then spin the diff noses and compare the number of revolutions of the road wheel for a given number of propshaft/diffnose revolutions

Lewis :)

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sounds pretty good, the problem is ive got myself into a real situation. i blew the front on a play day. i then replaced this with another, i compared the old and new before putting them in and they looked the same (pretty stupid now i think about it). i put it in and went for a test drive on some green lanes. after about 1/2 hr the back blew which makes me think that either the rear was either severely weakened in the incident that blew the front or ive been a real dipstick and put the wrong ratio diff in the front. the only way to tell is to do what you suggested and compare it with another before i take it out of a donor vehicle. the problem im having is tracking down second hand ones. thanks for your quick reply.

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The diff will most likely only be either 4.7:1 Series diff or a standard 3.54:1 and you should be able to tell the difference between them using the prop revolutions: 10 wheel revs will either produce 35 or 47 prop revs.

Counting the pinion and crownwheel teeth is of course the "correct" way but unless you have a "special" there are only two factory diff ratios and the vast majority of diffs out there will be the 3.54:1 which is what has been fitted in all 90/110/Defender, RR and Discovery vehicles.

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The diff will most likely only be either 4.7:1 Series diff or a standard 3.54:1 and you should be able to tell the difference between them using the prop revolutions: 10 wheel revs will either produce 35 or 47 prop revs.

Counting the pinion and crownwheel teeth is of course the "correct" way but unless you have a "special" there are only two factory diff ratios and the vast majority of diffs out there will be the 3.54:1 which is what has been fitted in all 90/110/Defender, RR and Discovery vehicles.

Hope this isn't classed as highjacking a thread as on other forums.... I was just about to post a similar question, can you mix axles..?

I have a 98 110 TD5 bent rear axle, it looks to have tubes pressed into the diff housing, the 2nd hand one I just bought has a moulded all in one casing, if the ratios are the same I guess it can be fitted...?

If it turns out to be wrong and it will fit yours maybe we can help each other out here...??

Regards Dave

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Counting the pinion and crownwheel teeth is of course the "correct" way but unless you have a "special" there are only two factory diff ratios and the vast majority of diffs out there will be the 3.54:1 which is what has been fitted in all 90/110/Defender, RR and Discovery vehicles.

I have a pair of 4.1 ratio diffs from an ambulance, aparently a few 4.1 factory diffs were produced

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I have a 98 110 TD5 bent rear axle, it looks to have tubes pressed into the diff housing, the 2nd hand one I just bought has a moulded all in one casing, if the ratios are the same I guess it can be fitted...?

That sounds like a Salisbury axle, only fitted on the back of LWB's from late S2 to late 110's. No you can't mix diffs from them as they're physically different to the Rover axles.

Diff_Diffs.jpg

As for the original post, if it's a Range Rover, Defender or Discovery diff then it will be 3.54:1, I would think a Series one would be obviously different next to a coiler one as the ratios are different. Jack one wheel up and spin it to count prop revs, it's not rocket science. Everything coiler is 3.54:1, everything Series is 4.7:1 with the exception of Stage 1 V8 (3.54:1) and 101/FC which you wouldn't have one of anyway.

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Hope this isn't classed as highjacking a thread as on other forums.... I was just about to post a similar question, can you mix axles..?

I have a 98 110 TD5 bent rear axle, it looks to have tubes pressed into the diff housing, the 2nd hand one I just bought has a moulded all in one casing, if the ratios are the same I guess it can be fitted...?

If it turns out to be wrong and it will fit yours maybe we can help each other out here...??

Regards Dave

further to Fridge's reply, so you've bent the axle housing and you want to swap another in ?

sounds like the one you have aquired is out of either a 90, Disco or RRC which is a Rover axle and no where near as strong as a Salisbury 8HA, which is what you would have in your 110. Also the pinion nose is shorter on the Rover housing, so the tail shaft will be too short to fit, although it will physically bolt in.

How bent is the housing ? Is it easier to straighten and repair it ?

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A salisbury is cheap enough to find, they don't damage easily (I'm impressed you bent one) and you can make a drum-braked one disc-braked using off-the-shelf parts (search this forum for how). Pay no more than £50 for a salisbury axle, usual rate is about £30 as most people can't be bothered tripping over them / moving them out of the way :lol: disc braked ones may be a tad more but eBay & the forum classifieds are your friends ;)

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A salisbury is cheap enough to find, they don't damage easily (I'm impressed you bent one) and you can make a drum-braked one disc-braked using off-the-shelf parts (search this forum for how). Pay no more than £50 for a salisbury axle, usual rate is about £30 as most people can't be bothered tripping over them / moving them out of the way :lol: disc braked ones may be a tad more but eBay & the forum classifieds are your friends ;)

not quite that cheap here.

at those prices, some enterprising soul over there should start buying them up and flogging them to the Yanks as lightweight Dana 60's :lol: Freight could be a killer, 'though :blink:

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IIRC a Salisbury is a dana-60 if that helps you any? Salisbury were bought by Dana (or they were bought by someone who was then bought by Dana) and I'm almost certain the Sals is a (not super strong) incarnation of the D60.

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actually, I think the story went it was made under licence by GKN for Rover.

CWP is interchangeable, carrier bolts are 12mm instead of 1/2" UNF, I think the pinion bearing is slightly different and the pinion spline count is different.

Oh, and a Sals uses the weak Rover axle diameter and spline count. Axle tube diameter/wall thickness might be a bit lighter too.

Was all said very tongue in cheek.

Yanks wouldn't go for 'em anyway as a Sals is too narrow for their tastes. :lol:

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Real story.........

The differential in question was designed by the Salisbury Axle Company, which was purchased by Spicer in the 1918. Spicer became Dana in 1946. The "salisbury" axle used in Rovers have a Dana Model 60 differential. The axle assemblies are built by GKN which has many close ties with Dana.

http://www.dana.com/centennial/timeline/early.shtm

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not quite that cheap here.

(...) Freight could be a killer, 'though :blink:

Ditto!

BTW,I'm after a Salisbury axle to fit a coiler...

:)

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Does a 1994 Discovery rear diff have the same ratio that a 1996 p38 has as Im looking to swap the diff out of my P38 RR. Thanks

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They don't fit, unless you do a load of machine work.

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I think they are the same ratio. However the P38 casing is different and the bolt pattern is different.

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On 21/04/2007 at 5:24 PM, BogMonster said:

The diff will most likely only be either 4.7:1 Series diff or a standard 3.54:1 and you should be able to tell the difference between them using the prop revolutions: 10 wheel revs will either produce 35 or 47 prop revs.

 

Only if you jack up the whole axle and spin both wheels.  If you just jack and spin one wheel, expect half that number of prop revolutions.

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On 18/04/2017 at 1:11 PM, Snagger said:

Only if you jack up the whole axle and spin both wheels.  If you just jack and spin one wheel, expect half that number of prop revolutions.

Think he probably fixed it or chucked it by now :wacko:

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Yeah, I saw the date after replying, but I thought I'd leave it as someone had resurrected the thread and it may have been relevant for anyone with the same question.

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