My sister has an '84 240 her and my father figured out that her odometer and speedometer read about 15 percent high. So if it reads 75mph she's really going only 66. (no wonder the cops just passed her by when she thought she was going 80;)

Any thoughts?

thanks
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Ryan - '68 122, '88 240 DL (5 spd)

A 15% error isn't a result of tire size unless you are running 145-12's from an old Mini!

We have the same situation: my son's '81 also reads 14% high on the odometer and about the same on speed. The manual trans was replaced by a previous owner, and probably came from a later 240 with a 3.31 axle. So the speedo gear in that trans is set to show 60MPH at 2800 driveshaft RPM. With his 3.73 axle, that RPM comes at 53MPH and the speedo then shows 60.

I checked the speedo gear - it is Black and has 20 teeth. The Volvo parts guy told me that's the most they have. (The more speedo gear teeth, the slower the speedo will show). Pull your speedo gear and if it's less than 20 teeth, you can make at least a partial correction with a 20-tooth unit. Other options are: (1) live with it and do the mental math; (2) pull the trans apart and change the tailshaft's speedo drive gear ($$$ and big job); (3) get a specialist speedo shop to build a mid-cable reducing gearbox ($$$).
--
Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD; plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)

Renumberate the instrument cluster.

My original 245 instrument cluster was off by a lot too, so I printed up new gauge faces. With the wrong size tires and a screwed up cluster, it's 105 where it used to be 120. I gauged it the last time they put up one of those trailered radar + readout units to "remind" those who speed.

Then a few weeks later, I bought one off a '90, because it was there.

-- Kane
--
Blossom II - '91 745Ti/M46 ... Bubbles - '74 144GL/BW35 ... Buttercup - '86 245GL/AW70 ... The Wayback Machine - '64 P220/M40

Try taller tires. If she's got 185/70/R14's try 205/70/R14's or step up to 15 inch wheels. I once had a Mustang that I trashed the 4 speed. I got another one from the junkyard that came from a Mustang II. They used the tiny 13" wheels. I did not think this would be a problem until I drove it. The speedo read 5 mph slower than I was really going. You could also change the speedo gear in the trans if you could find the right one.
Note: smaller diameter tires - faster reading (also like lowering rear gears)
taller diameter tires - slower reading speedo
Ben

If the rear axle ratio/speedo driven gear turns out to be the culprit PROJECT 242 .COM sez:

3.54:1 uses #380754, 18Teeth - blue
3.73:1 uses #381681, 19Teeth - red
3.91:1 uses #380753, 20Teeth - black
--
'80 DL 2 dr

I had this same problem. I ended up changing the speedometer gear that is located in the overdrive unit. My rear axle is a 3.9:1 and I think it was put in by the PO. I put in the gear that matched the axle and now have an accurate odo and speedo. It is an easy fix. Your axle info is on a plate on the rear passenger side of the axle.
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Simon 80 240 296k 17 years.

What size tires are on the car?
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Regards,
Eric Staufer,
1989 244DL 125k,
My 240 Page (newly updated!), (opens a new window)