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12-10-2006, 07:05 PM | #1 |
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Need help with wacky speedometer
Just got back from picking up a 79 SWB K10. It has 350/350/np203 combo and ran fine on the way home. Problem is when I was doing 65 the speedo said 90! It also goes up and down quite a bit, don't know if it's related but thought I'd mention it.
Any ideas or suggestions on how to figure this one out would be appreciated. Thanks. |
12-10-2006, 07:35 PM | #2 |
7000 #'s of american IRON
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Re: Need help with wacky speedometer
those are either some big tires or that speedo gear is missing teeth..
my vote is the speedo gear. |
12-10-2006, 09:20 PM | #3 |
Old Time Rodder
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Re: Need help with wacky speedometer
Don't know if this is what is wrong but I had the same problem with 2 speedo's and found that there was transmission fluid coming up the cable getting into the speedo itself. Drove me crazy for several months. Replaced the seal in the speedo drive gear housing and haven't had any more problems. Couldn't even clean the speedo and reinstall, only solution was to replace it. hope this helps
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79 GMC SWB Lowrider Stepside [81 cab] that thinks it a Chevy (since 6/1980) Replacement cab had A/C which now works, made a real truck out of it 84 MC 305 350TH 3.08 4 wheel disc finally My daily driver again |
12-11-2006, 10:18 AM | #4 |
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Re: Need help with wacky speedometer
Thanks guys. Lowseirra, where is the seal, in the trans? Also do you remember where you got a replacement?
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12-11-2006, 12:02 PM | #5 |
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Re: Need help with wacky speedometer
ScottH;
On a 4x4, the speedometer cable goes into the transfer case. On mine, there is an adpater that makes a right angle, and if I remember, there is no seal. Are you running oversize tires?, that will cause some error. low sierra, on yours, did your speedo bounce when the tranny fluid went up the cable. My 79 c-10 bounces and growls, but I haven't investigated what the problem is. Most likely my speedometer is going south. |
12-11-2006, 12:53 PM | #6 |
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Re: Need help with wacky speedometer
There is some sort of adapter between the transfer case and the cable, but it is straight. Tires are 31 x 10.50 x 15. The size difference should account for some, but 25 MPH over is excessive, isn't it?
Thanks. Scott Last edited by ScottH; 12-11-2006 at 12:54 PM. |
12-11-2006, 03:16 PM | #7 | |
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Re: Need help with wacky speedometer
Quote:
on a 85 f150, that I now own, the drive gear in the transmission (granny low) was worn out and it would do the same three things. sorry about the ford reference but the answer for it could be same for a chevy not having fluid up the cable problem.
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79 GMC SWB Lowrider Stepside [81 cab] that thinks it a Chevy (since 6/1980) Replacement cab had A/C which now works, made a real truck out of it 84 MC 305 350TH 3.08 4 wheel disc finally My daily driver again |
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12-12-2006, 02:36 PM | #8 |
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Re: Need help with wacky speedometer
Any other ideas or ways to figure this one out?
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12-12-2006, 02:52 PM | #9 |
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Re: Need help with wacky speedometer
My buddy had the same problem, there was transmission fluid coming up the cable getting into the speedo itself. He also replaced the seal in the speedo drive gear housing and has not had any problems since then. I have no other ideas right now, those small tires should not effect it that much.
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12-12-2006, 02:57 PM | #10 |
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Re: Need help with wacky speedometer
Looks like we have another vote on the fluid leakage being the culprit.
Can you tell me where the seal is? Is the drive gear in the transfer case, or the adapter between the cable and transfer case? Any idea if I can pick this up at a parts store or need to go to GM? Thanks for the help. |
12-12-2006, 11:41 PM | #11 |
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Re: Need help with wacky speedometer
it could also be a wornout speedometer cable...i've replaced them before when they acted up like that and it usually always cures it.... to change it you have to take the gauges out though...
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12-12-2006, 11:44 PM | #12 |
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Re: Need help with wacky speedometer
it could also be a wornout speedometer cable...i've replaced them before when they acted up like that and it usually always cures it.... to change it you have to take the gauges out though...
another possiblity is like in the case of my truck....my axles have lower gears and when i am doing 60mph the speedometer shows i am doing 85 or 90
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"Horsepower is how fast you hit the wall, torque is how far you carry the wall with you." '84 chevy half ton short box 2wd, 67,000 actual miles '03 chevy 1500 HD crew cab 4x4 standard box, 6.0L |
12-13-2006, 12:02 AM | #13 |
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Re: Need help with wacky speedometer
yea, you didnt say what you had for axles. 3.07 to 3.73 or 3.73 to 4.11 or something like that gets messy quick.
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12-13-2006, 10:34 AM | #14 |
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Re: Need help with wacky speedometer
Pretty sure axles are stock. Just not sure what stock is for a 4x4.
Gonna look at it this weekend. Starting to wonder if someone put an adapter on the cable. I came across one on the net to increase the speed to make up for larger tires. There is definitely something between the xfer case and the cable. Will probably take it off and see what happens. Thanks to all. BTW could still use some info on the seal referenced above. |
12-13-2006, 06:09 PM | #15 | |
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Re: Need help with wacky speedometer
Quote:
the seal is in the housing that holds the speedo driven gear. the speedo cable screws on to this housing. take it out of the transmission and pull the gear. clean it up and you will see where the seal is. it's just a small seal like would be around any shaft.
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79 GMC SWB Lowrider Stepside [81 cab] that thinks it a Chevy (since 6/1980) Replacement cab had A/C which now works, made a real truck out of it 84 MC 305 350TH 3.08 4 wheel disc finally My daily driver again |
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12-13-2006, 07:26 PM | #16 |
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Re: Need help with wacky speedometer
Thanks Low.....is this an O ring seal?
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12-14-2006, 02:51 AM | #17 |
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Re: Need help with wacky speedometer
My 78 with 350, 4speed, and 205 does the same thing. Kinda depends on the outside temp. I've replaced the cable with brandnew and the gear teeth in the 205 are fine and I don't think 90 weight gear oil is going up the speedo cable to the dash. In my case the speedo head is worn out and needs a replacement.
Bill |
12-14-2006, 02:53 AM | #18 |
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Re: Need help with wacky speedometer
maybe someone switched axles? that would also throw the speedo off but i went from 2.73's to 3.73's and i don't think the speedo was quite that dramatic
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12-14-2006, 04:06 PM | #19 |
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Re: Need help with wacky speedometer
it is a small seal like an axel seal with hard outside ring. go to a transmission shop and they will probably have lots of these since they don't usually replace them when you get a rebuild. I went to the shop that did my trans and asked for one. the guy is a friend and I asked him why they didn't put it in when they built mine (seal comes in kit) his reply was they don't think it is necessary because most people don't have a problem. cost me two speedo's.
hope this helps. but if you don't have an auto, you probably have a bad drive gear.
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79 GMC SWB Lowrider Stepside [81 cab] that thinks it a Chevy (since 6/1980) Replacement cab had A/C which now works, made a real truck out of it 84 MC 305 350TH 3.08 4 wheel disc finally My daily driver again |
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