If I have an 1152 speedo what diff ratio do I have?
My speedo is notated: SN6317/10 which is for a 3.54/1 rear axle ratio (1100 turns per mile)
The other diff for 3.4 and 3.8 litre engines was a 3.77/1 and had notation SN6317/08. This one was fitted to MOD cars. Expect you might be yours?
Got the above from my Mk2 Parts Manual.
/08 is 1152 is for 3.77.
On that list - yes - not listed. Mine is a 1963 and I think Andrew’s car might be later.
Thanks gentlemen. That is very helpful.
So looks like I have a 3.77 diff.
1961 originally 3.4 auto.
Standard for a 3.4 is 3.54. ( 4 speed and Automatic )
Only overdrive models used 3.77
So maybe 3.54 for me?
That might fit with the tacho readings, although I have little belief in the accuracy of any of my instruments.
The best way to be 100% sure is jack the rear, chalk the tyre and propshaft and rotate the tyre.
I find it safest to rotate the full number of suspected pinion teeth turns because
3.54 and 3.77 are too close to be 100% sure
Mark off each turn on a piece of paper for both, as its easy to loose track
This will also confirm if you have LSD
Its easier and quicker (and less messy) than taking of the cover to count the teeth, (certainly easier if its IRS diff cover)
Its really important when considering 4wd vehicles with mods & unknown parts
There should be a tag attached to the rear cover on the diff with something like 13
—
43
which identifies the diff ratio, in this case 43 divided by 13 = 3.31 May also be an extra tag with Powr Lok, indicating LSD unit within.
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13 is the number of teeth on the pinion, 43 on the crownwheel.
Ditto what @OldJagNut Kevin said. There’s usually a metal tag under one of the diff cover bolts that gives the number of teeth on the ring and pinion. Sometimes you will find a PL tag that identifies it as Power Lok limited slip.