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Thread: Diff Ratio??

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    Diff Ratio??

    I have a Mk2 Escort english back axel, no idea what the ratio is, but i can see all of the numbers in the casting... How can i identify this and what set of numbers and where are they which tell me the ratio?

    Im assuming (although one must never assume) that 1.3 1.6 1.8 etc etc all have specific ratio to the engine size, so what went with what i.e ratio to engine size?

    I hope that all makes sense

    Thank you

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    Re: Diff Ratio??

    Casing / casting numbers won't tell you ratio. Sometimes axles still have an aluminium tag on them - that will have a ratio stamped on it but that doesn't mean what's inside is correct!

    Only way to check - without removing the diff and counting teeth - is to jack the back end of the car up (chock the front wheels), put it on stands, and then mark the tyres and propshaft with reference points. Both tyres will need to be rotated together the same amount (in the same direction ie either both forward or both backwards to mimic driving on the road) to work out the ratio otherwise you will get a proportion of the ratio due to the planet and sun ie differential gears. Count one full revolution of one wheel (but turning both wheels together) and count how many turns the propshaft has made. This will give you a very near figure if you've been accurate with your marking, turning and counting.

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    Re: Diff Ratio??

    Thank you very much, how does this work out, how many wheel turns to prop turns am i looking for to calculate it?

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    Re: Diff Ratio??

    you simply need to know how many turns the prop has to do to get one whole turn of the wheels. 3.5 turns of the prop for one turn of wheel +3.54 diff.

    point to note this only works out correct if BOTH wheels are turning, if you do it with only one wheel jacked up the sun and planet gears become a reduction ratio, and the number of prop turns will double

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    Re: Diff Ratio??

    Thats fair enough, so its really a 3 person job? or push the car in a straight line while looking at the prop... thats all do'able

    Is there a standard? how many ratios are there? I have a 1.6 so what is the best diff ratio to have

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    Re: Diff Ratio??

    standard ratios for a mk2 were 4.4 4.1 (van) 3.9 (1300) 3.54 (1600+2000) mk1's also used a 3.7

    there is not such thing as "best" ratio. it all depends on the spec of your car, what you use it for and what you most want, ie if you want acceleration then a 4.4 is the way to go, if you want reasonably relaxed motorway driving then its a 3.5
    Last edited by Graham; 22-06-2019 at 12:40.

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    Re: Diff Ratio??

    The most accurate way to check is with the diff out and and count the teeth and then divide. Counting wheel and prop reveloutions is all well and good but it's going to be very difficult to determine a 3.9 against a 3.7 or a 3.7 against a 3.54 unless your markings and counters are spot on.

    4.1 and 3.9 were the most popular ratios of the family cars back in the day with the 4.4 of the 1100 vans being very rare. Some of the Capris had 3.7 diffs and some of the later larger engine ones had 3.54 including Mk2 Mex and RS 2000.

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    Re: Diff Ratio??

    Mk2 Mex is a 3.77

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    Re: Diff Ratio??

    Quote Originally Posted by Erikmex View Post
    Mk2 Mex is a 3.77
    According to Jeremy Walton's Book RS The Faster FORDS, the transmission and diff ratios for the MK2 Mexico are the same as the RS 2000, 3.54.1 the same diff ratio was also fitted to the 1600 Sport. Having changed 2 of them years gone buy I remember both were 3.54.

    The Mk1 Mexico had a 3.7 diff fitted.

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    Re: Diff Ratio??

    ah, i thought it was the Mk2 also

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    Re: Diff Ratio??

    Quote Originally Posted by Erikmex View Post
    ah, i thought it was the Mk2 also
    i didnt say anything as i wasnt 100% but my recollection was that 3.7 was mk1 only, especially as mk2 1600ghia/sport was 3.54

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    Re: Diff Ratio??

    Okay, i did the test!

    But i have 13" wheels on... is this correct? is that original?

    I had 3 turns and then 2 o'clock, so im guessing 1300?

    How much could i get for this axle, with brand new brake shoes, and dums? axle works a treat, but i just think i might want to change it.

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    Re: Diff Ratio??

    wheel size makes no difference!

    dont get 2 o'clock, the minimum number of input turns to get a whole turn on the output will be will be 3.5

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    Re: Diff Ratio??

    The propshaft did 3 complete turns, then when the wheel came to its marker the prop stopped at this point. Im thinking this must be a 3.9? so 1300




    Click image for larger version Name:	IMG_20190625_135949.jpg Views:	116 Size:	123.9 KB ID:	84040

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    Re: Diff Ratio??

    Looks like 3.89 to me (if you've been accurate).

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    Re: Diff Ratio??

    Hi, what do you want the car for ? Fuel economy, 3:54. Little more happier, 3:89. Track Day, 4:44

    Cheers

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