Jumpy speedometer
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Jumpy speedometer
My speedometer intermittently starts flopping about 20 mph higher than actual speed, and sometimes pins, as though I'm going 100mph. It did this during the summer, then settled down for several months, then today started flopping again. What's the most likely cause? Cable? Gear? Lack of lubricant?
'86 F350 Crew 6.9L Diesel 4.10 C6 2WD 163k (at least)
'86 F350 Crew 6.9L Diesel 4.10 C6 2WD 163k (at least)
Post Fiend
Joined: Nov 2002
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From: Memphis, TN
Jumpy speedometer
Cable drag would cause it to be jumpy, but I think the only way for it to peg would be internal drag or bad bearings in the speedo head itself. Those problems & wearing plastic gears are why I went to the '92-97 style electronic speedo.
http://www.webphotos.com/list_photos.asp?mi=3&smi=1&a=13217
http://www.webphotos.com/list_photos.asp?mi=3&smi=1&a=13217
Post Fiend
Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Jumpy speedometer
Yes, it's in the '83 dash - there are pics that show it installed. I collect them when I find them cheap in junkyards - there's always someone that needs one. Right now, I only have 2 complete clusters, but I know where to get another loose PSOM if I need it.
It requires an '87-up rear axle to work, though...
It requires an '87-up rear axle to work, though...
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Jumpy speedometer
Superdave, the speedometer jumps or wanders up to the maximum peg point, and flops down again. It's most pronounced a highway speeds.
I was mostly trying to figure out where to start looking, the transfer case or the dash. I think I'll start with the transfer case end first, tomorrow morning. I gather that it's not too hard to release the cable, but actually working with the meter requires pulling the instrument cluster.
'86 F350 Crew 6.9L Diesel 4.10 C6 2WD 163k (at least)
I was mostly trying to figure out where to start looking, the transfer case or the dash. I think I'll start with the transfer case end first, tomorrow morning. I gather that it's not too hard to release the cable, but actually working with the meter requires pulling the instrument cluster.
'86 F350 Crew 6.9L Diesel 4.10 C6 2WD 163k (at least)
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Posting Guru
Joined: Sep 1999
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From: Indiana
Jumpy speedometer
pbrassey, I am understanding your meaning it bounces up there.I would be looking at the cable. As I said try lubing it, or it may just need replaced.
My dad's 78 F-150 4x4 did the same thing. It bounced everywhere. At approximate road speed, (had to guess, because you could not get a reading). It bounced from 40-85 mph. It bounced through the whole range of speed. Put up with it for a couple of years or longer, till I got serious about fixing it. One of my kids was going to start driving it as a daily driver.
New cable with housing from NAPA healed it right up. Still works fine now, probably 6-7 years later.
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Joined: Oct 2002
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From: The Big, Oregon
Jumpy speedometer
If it goes higher than your road speed, and hangs there for a while, and does it without first dropping a little, I would say it's in the cluster. I have access to a dash from an early 80's.
Jared
Jared
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From: Laveen
Jumpy speedometer
I've had the same problem a couple of times, once it was the cable and lube fixed it and the other was dust in the little magnetic coupling in the speedo itself. I blew all the dirt I could out with low pressure air and then washed the mechanism out with denatured alchohol, be carefull not to get anything on the face as some of the markings are easily washed off. Then I sprayed a little teflon dry film into the mechanism and put a little lithium grease on the little gears and stuff and it's worked since 1986.
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Jumpy speedometer
[updated:LAST EDITED ON 05-Dec-02 AT 07:29 PM (EST)]about the rear axle...you dont have to have a 87 or newer axle. you would just need to have a magnet installed in your ring gear. it can be done.
Post Fiend
Joined: Nov 2002
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From: Memphis, TN
Jumpy speedometer
Where'd that come from? The ABS sensor doesn't use a moving magnet, and one magnet would only produce one pulse per tire revolution. The PSOM needs over 100 (108 for light trucks; 120 for heavies) pulses per rev to work. But those pulses aren't produced by a magnet - they're produced by the change in the field intensity caused by the teeth of the tone ring passing thru the field created by the ABS sensor, which directly affects the current in the circuit. That's what the PSOM reads.
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Jumpy speedometer
Thanks for all the good suggestions. I pulled the cable from the transfer case, found it all mucked up on the outside with the usual mix of grease and dirt, cleaned it up the best I could. The cable had black oil dripping out of it. The plastic gears looked fine. After I cleaned it up I bolted it back in, and so far it's working fine, steady as a judge. One frustration: the little clip that holds the cable to the gear didn't want to go back in. I resurrected several choice words, and finally threw it out and replaced it with one of my son's old guitar strings.
'86 F350 Crew 6.9L Diesel 4.10 C6 2WD 163k (at least)
'86 F350 Crew 6.9L Diesel 4.10 C6 2WD 163k (at least)
