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Old 04-27-2021, 08:57 PM   #1
VolvoScout
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Default Overdrive Speedometer Compatibility

My 1982 Volvo 240 D24 Overdrive needs to be swapped with the overdrive from my 1984 240 D24.
I am wondering if these are interchangeable...

Similarities:
1. Both cars are the D24 Diesel.
2. Both cars have the same "K" number on the dash cluster
(the '82 goes to 85mph, where as the '84 goes to 120mph)
3. Both cars connect to the overdrive via the speedometer cable on the side of the OD
4. Both cars are the M46 transmission.
5. Both overdrives feature the smaller speedometer gear that inserts into the side of the OD, connecting to the cable.

Differences:
1. The Overdrive on the 1982 features an additional speedometer gear on the annulus, where as the 1984 does not have the additional annulus speedometer gear (see photo)
2. The '84 has the "later" relief-valve design.

Are these overdrives interchangeable as-is?

How exactly does the '84 determine speed without the larger, annulus gear?

[IMG][/IMG]
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Old 04-28-2021, 06:14 PM   #2
hiperfauto
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The speedometer gear just slips onto the output shaft of the annulus. Some of them have a separate spacer that needs to go on as well. The space between the bearings needs to have something there or the bearings will bind when the flange is tightened. Cars with a speedo sensor in the diff just use a spacer in place of the speedo gear.
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Old 04-28-2021, 06:41 PM   #3
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So if I understand correctly, my '84 derives speed from the rear differential, but my '82 derives speed from the overdrive? And the small speedometer gear on a post, that inserts on the side of the '84 OD is just a "spacer?"

And so, if I swapped overdrives, the '84 OD would work on the '82 car, but it would not give me a speed reading? (Ultimately trying to determine if I have to take apart and rebuild my '82 OD again)

Is the later-style relief valve on the '84 OD a superior design to the '82 OD?
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Old 04-28-2021, 06:57 PM   #4
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They didn't go electronic speedo until '86 so either one of your overdrives should work. The metal speedo gear was replaced with a spacer and the plastic gear was eliminated as was the hole for it in the tail housing (some early ones came with a plug).

If that's a pic of your '84 annulus the metal speedo gear (and bearing) are not on the shaft. If you assembled it without the metal speedo gear you will definitely have to go back in.

There were actually 3 different styles of relief valve. Newer valves have less parts but they all seem to work fairly well as long as the oil isn't full of debris. I wouldn't stress out about which style it has as it can be changed with the overdrive installed if there's a problem.
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Old 04-28-2021, 08:03 PM   #5
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Weirdly enough, my 1984 OD was missing the speedometer gear & bearing present on the annulus output shaft when I disassembled it...how then was it working?
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Old 04-28-2021, 08:14 PM   #6
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I don't think that's possible. Are you sure the bearing and gear weren't stuck inside the tail housing?
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Old 04-28-2021, 08:22 PM   #7
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I'll have to double-check the video footage of my OD disassembly when I'm back home this weekend.
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