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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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Old 05-12-2021, 10:36 AM   #8
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[IMG][/IMG]

I think you may be right; looking back at my video of the rebuild, it appears it may be stuck in the tail hosing. (Judging from the difference in depth of the bearings between the '82 and '84)
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Old 05-12-2021, 05:52 PM   #9
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I swapped my 1982 85mph speedometer for the 1984 120mph speedometer.
The car reads approximately 5mph slower than it is actually traveling at 55mph.

I then removed and compared the speedometer gears that insert into the side of the Overdrive
Both have the same number of gears.

I am assuming the difference is in the speedometer gear that is inside the OD on the annulus output shaft?

Is there a plastic (side insert) gear that will make my 1984 Overdrive compatible with my 1982 dash cluster?
The 1982 dash cluster number reads "r0,960" and goes to 85mph.
The 1984 dash cluster reads "r,0980" and goes to 120mph

[IMG][/IMG]
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Old 05-12-2021, 07:49 PM   #10
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There are different metal speedo gears (the one on the output shaft) but that's not your problem. The speedo marked "r0,960" is for a wagon and the one marked "r0,980" is for a sedan. Sedan and wagons used different tire sizes so the speedos were calibrated differently. The "r" number indicates revolutions per mile.

FYI, the number of teeth on the metal speedo gear is stamped into the tail housing of the OD.
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Old 05-12-2021, 08:39 PM   #11
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Quote:
Originally Posted by hiperfauto View Post
Folks on here don't know a good deal when they see it.
how psi stock cna support?


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Old 05-12-2021, 10:07 PM   #12
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So once I have the Overdrive from my Sedan installed into my wagon, the speed will always be incorrect no matter what dash cluster I use?
Or is it as long as I have a wagon speedometer paired with a wagon overdrive and/or a sedan speedometer paired with with a sedan overdrive (no matter what car they are in), they will give me a correct speed reading?
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Old 05-12-2021, 10:15 PM   #13
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No you have the wrong instrument cluster in your car, and that is what is giving you the incorrect speed reading as hiperfauto so succinctly stated.

A 240 Turbo would have 373s and a red gear.

An NA 82 would have 354s and a blue gear.

An NA 84 would have 331s and a black gear.

The different metal speedo gear on the output shaft is an early / late [82+?] thing with 6 or 7 teeth iirc.

Last edited by Redwood Chair; 05-12-2021 at 10:23 PM..
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Old 05-12-2021, 10:23 PM   #14
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Ok, so as long as I match the speedometer and overdrive (either both from a sedan or both from a wagon) I should be fine?
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Old 05-12-2021, 10:33 PM   #15
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Think of it this way. The speedo gear(s) are matched to the rear end ratio and the speedometer is matched to the body style. Just remember tire size will have an effect on accuracy.

As long as the speedo gears are matched to the diff it doesn't matter which OD you use.
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Old 05-12-2021, 10:38 PM   #16
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The overdrives are the same for a given year / model.

IE: all NA 82 stick shift cars came with 354s and a blue speedo drive gear.

The sedan / wagon difference is in the speedometer itself a 25 or 26 tooth plastic gear is used to account for the different tire size 185R14 on the wagons vs the sedan size of 185-70-14.

Again you have the wrong speedometer head in your car.
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Old 05-20-2021, 01:44 PM   #17
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Thanks for the clarification, sometimes I have a knack of over complicating things, haha.
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