DIFF RATIOS ?

[grahamw48]

I've been wondering what the diff ratio is on my car (1980 280i).

Different figures seem to be given, depending on where you look.

Carfolio give 3.07 (seems high!), whereas the TVR handbook that I inherited with the car gives it as 3.54, same as the 350i, I believe. The book is 1984 though.

I know the old Capri 3.0 and 2.8i had 3.09 diffs on (usually) 13" wheels.

On Ford diffs there is a small metal tag/label which gives the ratio - very handy.
Is there such a thing on the Wedge diff ?

I'm asking because my car seems rather 'revvy', considering the somewhat high diff it's supposedly fitted with.

I know the diff has been out, as there is a nice picture of it in the 'history file', sitting in someones garage, all newly painted bright red.

Perhaps the rev counter is faulty, as that easily flies round to er hum, 7,000!

Any thoughts ?

[wedg1e]

The 3.54 is the standard ratio. Supposedly the 3.07 (or 3.09) was an option, but I don't know anyone who has one. You lot! Any takers?

The tacho on my Tasmin read progressively less, the harder you revved it, so it's possible yours is duff too.

[19560]

wedg1e said:

19560 said: My speedo is calibrated to 150mph and I appear to have an unusually tall top of 28mph/1000rpm. . IIRC a 3.04:1 diff ratio was an option? My (PAS-equipped) car has had some changes (perhaps not for the better) but based on 3.54:1 diff ratio and tyre circumference of 74 inches, it equates to 142.5 mph at 6000 rpm in top. Now I have never got it there, but I have seen about 5400, probably a realistic 130, and that was on 95 RON. It will, however, pull quite happily to 6000 through the gears which equates to 35, 57, 85 and 119 mph. Given that the 350s generally had the same diff ratio and tyre diameter, try this in your car and see what it equates to. Alternatively, take it that the car should do 25.5 mph per 1000 rpm in top and see what that produces (ie 4000 rpm is 102 mph, +/- a bit).

[kevsmev]

My early Tasmin has a 3.09 diff ratio according to the tag. I presume because it has an autobox(but not for much longer)
Kev

[shpub]

Yes there is a tag except I have seen several diffs where the tag does not match the actual ratio. When I replaced the diff on the 520, it was marked up as a 2.88. Easiest way to check is to jack up the rear wheels and turn them and see how much the prop shft moves.

[wedg1e]

19560 said:

wedg1e said: 19560 said: My speedo is calibrated to 150mph and I appear to have an unusually tall top of 28mph/1000rpm. . IIRC a 3.04:1 diff ratio was an option? My (PAS-equipped) car has had some changes (perhaps not for the better) but based on 3.54:1 diff ratio and tyre circumference of 74 inches, it equates to 142.5 mph at 6000 rpm in top. Now I have never got it there, but I have seen about 5400, probably a realistic 130, and that was on 95 RON. It will, however, pull quite happily to 6000 through the gears which equates to 35, 57, 85 and 119 mph. Given that the 350s generally had the same diff ratio and tyre diameter, try this in your car and see what it equates to. Alternatively, take it that the car should do 25.5 mph per 1000 rpm in top and see what that produces (ie 4000 rpm is 102 mph, +/- a bit).

Now you mention it, it's 3.04 I was thinking of, not 3.09...
The above applies to a V8, of course, not a V6.

[grahamw48]

kevsmev said:

My early Tasmin has a 3.09 diff ratio according to the tag. I presume because it has an autobox(but not for much longer) Kev

Funnily enough though, the diff usually has a lower ratio on autos, presumably to boost acceleration a bit.

Standard Ford V6 Capris had 3.09 diffs, whether manual or auto, very early ones slightly lower (the famous 'Atlas' axle)

[Chassis 33]

My 1980 Tasmin has a 3.54 diff, IIRC from a series II XJ6, i worked that one out from ordering new seals from my local Jag dealer, which are different on the series III's.

IIRC the later series III diffs are sensible metric dimensions compared to the earlier diffes that are "sensible" imperial dimensions.


If anyone is interested the Jag part numbers for the diff seals i got (exactly 3 years ago today, looking a the receipt) are

JRTC1348 - Spacer Collapsible - 2off - £5.70ea plus vat
JRTC1340 - O Ring - 2off - £1.87ea plus vat
JCBC6923 - Seal Oil Pinion - 1off - £24.74 plus vat

£50 on stopping my diff leaking...then i painted it black so cant tell if it leaks or not!!!

Regards
Iain