Surely I'm not the only OCD person on this site.
Speedo is approximately 10% fast. This has to be fixed.
This is likely the 3-ish percent fast from factory, plus the question of "correct" OE tire size on wagons accounting for the rest?

1982 245, 3.73, m46. So, cable speedo system

What are my options? Any reasonably priced ratio adapter known to fit? Are alternative speedo gears available? Coles notes on the face markings' meaning?

So far I found a US speedo shop who will do a recal, but he notes the "odometer will always be off" which made me hesitate.
I saw a DIY page online somewhere on electronically modifying the speedo head, but I presume that was for later cars, and I didn't save it.

Hi Ian,

There are different speedo gears...you'll have to count the number of teeth and see what you've got. Not much else you can do other than change the diameter of the tire.

Every 2 and 7 car I have owned has been 10% low except for a 1990 745Ti (not the current one unfortunately) that was bang on. Wish I knew what was different about that car as the speedo error is one of my top annoyances. The only speedo gear I've ever seen is the 25 tooth upgrade for the OG 240 that always break?

This is why I always chuckle when people on Brickboard and such tell someone not to change their tire size because the speedo will be off. I've never seen an accurate one with original tire sizes, and 10% is not unusual. My 86 740T is now right on with 205/55/16 on it.

Oh, and you're definitely not the only OCD person on the board... it's a badge of honour here.

Any reason NOT to change the tire size? 10% diameter change isn't going to affect fit, handling or anything else as far as I can tell...

More likely to change the rear axle than tire size. The K cam is going away, and if b230F's pulled 3.31 rear gears and OD, then a b23E with a downsized (X lobes ground by Delta on both exhaust and intake, with close LSA) cam I had made years back, should pull fine. I dunno if I'd notice the change to 3.54, though that's a much easier swap (1030 OE 127hp turbo). Looking at a parts car with a 3.31 -late housing/1031(?) being the only availability, AFIAK- there's a lot of detail they changed. A lot.
I do know the ratio of the axle of 3.73x4.03 firstgear is the thing I liked least about the car from new. 4.03 x 3.31 and a light flywheel *might* pass with me. It's 13% less multiplication and about as far as is practical to go. AFIAK doing an early ratio m46 isn't really practical even though it almost doubles the change 12.6% to 22%.
I don't want to lose the overdrive, as it's a unique feature of the car. I think the 3.73x.80 is actually a little deep for high way cruising, so willing to experiment...popping out of OD is really easy, and 3.31 in forth seems just right for daily-driver highway acceleration...where 3.73 was a little deep, IMO.

Tire size is... well, the stance (blech) is chosen already in my head. What a lightly modified car of the era would have had. 225/50r16 tires purchased, still dealing on the exact finish and availability of very accurate BBS rep's I'll get.

So what was the earliest equipment level to come with 3.31's?
IE whats going to be bolt in? Trailing arms changed what year? The tabs are different on the axle when the trailing arms changed, or are they?

You're more likely to find one in an '86+, though I'm not sure if it would be more likely behind an AW71 or M46/M47. The control arms are interchangeable, though the pinion of the 1031 axles is a bit longer than the 1030 axles. Don't ask the visual differences, because there are mutants out there too.

I think I still have a Mk1 IRS center section with a 3.31 gear set in it. They should work in a 1031 axle, if you want to go through the trouble of finding one and setting it up.

Well, yeah... I was hoping it was a known thing...that I'd forgotten. I'll check the owners manual for the car see what other ratios were listed. The sales brochure might also tell me. I have both.
Just not near the car right now and sick as a dog.

A change in driveshaft & trailing arms to go to a 1031 adds potential follow-on changes. Since this is a one family owned car since new I also am reluctant to making a parts-muddle underneath. Even having the speedometer setup there and not used bugs me. Having to redo brake hardlines, etc... Prefer this to be a leave no tracks kind of deal.
I might have the old Truetrac I have yet to use in the 140 installed, so getting in there is not out of the question, and there are a couple ways that might happen.

But your gears- IRS is 1031 pinion length though, no? So doesn't fit the OE housing for 1982?

Sorry, Ian - I have nooo idea.