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Old 05-01-2021, 09:49 AM   #1
BigTire
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Question 1991 240 Sedan Speedometer Issues

I bought my son his first car, a 1991 240 sedan (with ABS) and we discovered it has a speedometer issue. The speedometer does not register until it hits 20mph. We looked into it and found that this is a common issue with this year. So...

We cleaned the connection at the speedo sensor, then did the tap test. It appeared the speedo sensor was fine, so we sent the cluster to a speedometer shop and they replaced all the capacitors, processor, and inspected/resoldered all the joints. They bench tested it and reported that everything worked.

We got it back and took the car for a test drive and the issue remains.

Does anyone have any advice on what else could be causing this issue? We going to the junkyard today to get a speedo sensor off another 240 just to make sure it's not the cause.

It's pretty frustrating since he's totally excited to drive the car but can't until we figure out this speedometer issue. If all else fails, I'll get him a GPS speedometer, but I'd rather fix the problem. Any advice will be much appreciated!

Last edited by BigTire; 05-01-2021 at 11:24 AM..
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Old 05-01-2021, 11:11 AM   #2
bobxyz
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Sounds like the speed sensor in the differential, what Volvo calls the Speedometer Impulse Sender, is too far away from the slotted wheel inside the differential. For the pre ABS cars, this can be adjusted with shim washers. If you don't have a copy already, get the Bentley 240 service manual. It's a great resource for maintenance and repair.

I vaguely remember there being 2 different sensor part numbers that might have been accidentally swapped at some time. I'm not sure if this is even possible.
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Old 05-01-2021, 02:28 PM   #3
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I think it's the 91 ABS system that has an extra converter box between the differential sensor and the speedometer. I've never seen one, but try looking behind the glovebox. What's the Kxxxx number on your speedo? If it's K9800 or close, versus K39200, then you have a pre-ABS speedometer with a converter box.

Also see the speedo writeups at cleanflametrap.com
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Old 05-01-2021, 07:27 PM   #4
BigTire
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Hey bobxyz, thanks for all the info! I've owned many 240s, but I'm not well versed on speedometers, so I'm really at a loss.

The number on the speedo is K10042
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Old 05-03-2021, 09:45 PM   #5
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I've never heard about a converter box between the sensor and the cluster. Is my 1994 940 Bendix/Regina likely to have this setup?


Thanks!
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Old 05-03-2021, 10:17 PM   #6
Khrrck
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Quote:
Originally Posted by Lazarus View Post
I've never heard about a converter box between the sensor and the cluster. Is my 1994 940 Bendix/Regina likely to have this setup?


Thanks!
-Lazarus
Shouldn't, it should already have the 48 tooth tone wheel in the diff which sends a compatible signal.

The converter box is for cars with 48 tooth tone wheels but speedometers that expect a 12 tooth signal. It just divides the pulses by four.
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Last edited by Khrrck; 05-04-2021 at 11:48 AM..
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Old 05-04-2021, 02:32 AM   #7
MasterBlaster
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Quote:
Originally Posted by Khrrck View Post
The converter box is for cars with 12 tooth tone wheels but speedometers that expect a 48 tooth signal. It just quadruples the pulses.
Pretty sure that's backwards.
48 tooth tone wheel > converter > 12 tooth speedo.

But, you can argue with 2manyturbos about it...

http://forums.turbobricks.com/showthread.php?p=4592715
1991 was the first year of "Optional" ABS on the 240. I don't think the cluster is any different, ABS vs. non-ABS for 1991. The reason Volvo was able to use the same cluster was they installed a signal converter before the cluster that turned the 48 tooth tone ring signal into the same signal the 12 tooth tone ring generates. That said, any K10042 with the service light reset button coming through the cluster lens should work. The ABS clusters that are definitely different from non-ABS clusters are the 1992-93 clusters. Those read the 48 tooth tone ring signal directly. If you install one in a non-ABS car, they read 1/4 the speed you are actually traveling.

Take a look at figure 6 on this 1991 240 wiring diagram and you will see the converter that changes the tone ring signal into something the speedo understands.
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Old 05-04-2021, 11:48 AM   #8
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Nah, you're right, I had it backwards lol. Edited
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