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1988 Dodge Dakota LWB RC 3.9V6 3 speed auto
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1,478 Posts
Discussion Starter #1
Howdy!

My stepson owns a 1988 Dodge Dakota SE, 3.9L V6, automatic (not sure which one, haven't crawled underneath to verify which of the three listed in the service manual it is).

It has cruise control.

It also, through three speedometers, and replacing both of the speedometer drive cables, runs a good 15% LOW on speed, with the needle bouncing around.

Since this year used a combined servo/sensor arrangement for the cruise control (unlike the 90+ where the sensor on the transmission was also used for the cruise control), I'm having a dickens of a time finding a cruise control sensor (or servo).

Are there other vehicles that use the same sensor?

I'm about to bypass it to get the speedometer up to snuff ...

Although cruise WOULD be nice.

RwP
 

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Home School Valedictorian
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4,225 Posts
The low reading could be from taller than OE tires.
 

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The Anti-RUB
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1,752 Posts
It may be a tire size issue. But I would plug in a good scan tool that can read live data and drive around for a little bit. It should have a reading for the current speed the computer thinks the truck is running at. If it doesn't match the speedometer, then the speedometer is bad. If it does match, then its a sensor or tire problem. You can get a scan tool from your local autoparts store. Good luck...
 

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Registered
1988 Dodge Dakota LWB RC 3.9V6 3 speed auto
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1,478 Posts
Discussion Starter #4
Two things.

1) Factory issue was T215/75R15s, we have P215/70R15s on the back now. So the tire's SHORTER.

2) 1988. OBD1. No live data available off the OBD port (not OBDII). And no, the local autoparts stores don't sell scan tools for this gen Dakota, drats.

Sorry I didn't mention the tires. But the new ones, while taller than the smallest tires on a 1988 Dak from the factory, are still shorter than the factory issue on THIS Dakota.

I'll add that the speedometer is rather spastic, like the line is binding and releasing. But I've got all new drives from the transmission to the cruise control unit and from there to the speedo. If it ain't the cruise control unit (and with the cruise control VERY flaky, it needs to be replaced anyway), it's the transmission drive. Which I just don't see.

RwP
 

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Premium Member
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17,622 Posts
On the '88 Dakota's, the way you adjust the speedo for different tire sizes was with the drive gear for the sensor that goes into the transmission. If you have a gear with the incorrect number of teeth on it for your tire size your speedometer will be off no matter what you try to do. I'm not sure where you would get the correct size gear for your tire size though or how you would determine which one is the correct one other than trial and error.
 

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#19 ƃop ǝnןq ǝןʇ&#
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13,196 Posts
I have two 88 Dodges...a Shadow and a Reliant...I can get live data from both....with a Snap-on scanner...but not the cheaper scanners

Bryan
 
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