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1987 Speedometer is jerky and wild!

Momboy007

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Hello All,
I have an 1987 Ford Ranger, 2.3L and the speedometer is jerky and it will also act OK as I am on the gas, but when I let off the gas to shift gears (manual Transmission) the speedo will drop to zero, then, as I put in another gear and am on the gas, it goes back up, but is still a bit jerkly, how do I tell if it is the speedometer gear at the transmission or the actual speedometer guage, I pulled the cable and it is lubed and very smooth to turn

thanks all in advance,
Rick
 


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06RangerXLT

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sounds like a few missing teeth from the gear in the back of the cluster, or its releasing when theres no preassure
 

Momboy007

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Do You mean on the transmission side (gear) or on the actual speedometer?

Thanks in advance,
Rick
 

Spott

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I had a similar problem several months ago. Turns out the driving gear (on the rear output shaft of the transfer case, but also found on the output shaft of the tranny on a 2wd) was worn out.

Unfortunately, those driving gears are getting pretty rare these days. I saw one of each size on ebay, but the big transmission supply shop in town here found me a "good used" gear for cheap. Might have been the last one they had available, however.

I'd pull the end of the speedo cable from the t-case/tranny, and peer in there with a flashlight and mirror. The teeth on the driving gear should appear straight, from the side...if there's a dip in the center, it's time for a replacement. Replace the driven gear, too, they're readily available. The driving gear comes in a 6t or 7t gear, and the driven gears come in several sizes. You may be able to get your speedometer more accurate with a different gearing combination, too.

Spott
 

jhammel85

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It's a long shot but, Have you hit any hard bumps? I hit a huge pot hole at 65mph not too long ago and my speedo bounced and read incorrectly for almost a week.
 

Momboy007

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Hello All,
I have hit no large bumps lately, so I do not think that is what it is, I noticed on the transmission side of the cagble, the small white gear is nylon, wouldn't the gear inside the transmission be steel? How does it wear out? My truck is a 2wd, how would I replace the gear inside the tranny?


Thanks all in advance,
Rick
 

Spott

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The speedo driving gear in my truck, inside the BW1350 t-case, is a nylon gear cast around a steel sleeve. They come in 6t or 7t versions, colored burgundy and "natural" (off-white). I think the 7t gear is the natural color.

Let us know what transmission you have, and we can probably tell you how to get to the driving gear.

Spott
 

Momboy007

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Hello Spott,
It is a 5 speed manual, I have had the gear out, it really does not even look that bad, but it is the white gear, how do I inspect the inside gear?

Thanks in advance,
Rick
 

Spott

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Like I said, pull the driven gear (the white gear) out, and get a little mirror and flashlight up there, and look into the hole the driven gear was in. You might be able to stick your finger in and feel the driving gear.

Also, please check http://www.therangerstation.com/tech_library/ManualTransmission.html and see if you can ID your transmission.

Spott
 

Momboy007

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Spott, it is a Toyo Koygo 5 speed. While I have you here, what are the wires that come out of it, are they for neutral safety? actually there are 2 of them there

Thanks,
Rick
 

4.0B2

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my local ford carries both the drive and driven gears for the trans/t-case and vss..

the one for the vss costs me like $5 from my local ford...
 

Spott

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Sorry for the delay, my computer died and I had to wait until I had the money to repair it.

The wires coming off of the transmission are likely a reverse switch and a neutral switch. If you only have two actual wires, then one goes to each switch, and the switches are grounded through the case. If you have two sets of wires, then you have signal and ground for each switch.

I'm not familiar with the TK5's. They were made by mazda, but my '88 service manual doesn't cover them, as they were only used until '87. If they're anything like the other tranny's I've seen, then the speedometer cable hooks to the case at the very back, just ahead of the rear seal. If so, you can probably take off the driveshaft, undo a large nut in the center of the flange/yoke, remove the flange/yoke, pop the rear seal out, and slide the speedo gear out the back of the tranny, around the output shaft.

Again, I've never seen the TK5, and can't find diagrams for it, so I'm just guessing. You might try asking in the transmission forums for better instructions.

Spott
 

holyford86

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I've had this problem before, changed drive and driven gears, cable, found the issue was over the years trans fluid had worked it's way up into the back of the speedo and gummed up the assembly that ran the speedo (it basically consists of magnets spinning inside a steel cup) A little bit of careful cleaning had me back in buisness.
 

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