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#1
10-10-2013, 09:59 PM
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70 GTO speedo does not read correctly
So I did not find this in searching the forum. My 70 Goat will only show up to 20 miles per hour on the speedo. I checked the cable and seems to be connected fine but, is this a sign that the cable is bad or the speedo? The needle does not bounce and once I am over 20 miles an hour it stays at 20. I fear the speedo is bad but the car is 100% original so a new speedo is an option that is not terrible just a pain to replace. Thanks for checking out my question....
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 Make it go around corners, life's more interesting that way!  70 GTO White/Blue Project 
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#2
10-11-2013, 03:04 AM
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Yep, sounds like a bad speedo then if the cable is working properly.
I'm actually in the process of dong a speedo swap/rally gauge install on my '72, so I'm right where you are. Pretty easy swap, and small potato's compared to other projects the car will need in time. Good luck! 
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Eric Mitten '74 Bonneville 4dr Sedan (455/TH400/2.93 open) '72 LeMans GT (455/M-13/3.23 [8.5"] posi) '71 GTO Hardtop (400/TH400/3.07 12 bolt posi) ‘71 GTO Convertible (455HO/TH400/3.23 posi) '67 GTO Coupe (455/ST-10/2.93 posi) Deuteronomy 8:3 
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#3
10-11-2013, 06:43 AM
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I would guess its your speedo as well.
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#4
10-11-2013, 08:06 AM
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Quote:
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1971 Pontiac GT-37 Car is a junk yard dog and maybe one day will be restored. 
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#5
10-11-2013, 11:15 AM
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Is it accurate up to 20 or does it show 20 even though you are doing 40? I would also inspect the plastic cable drive gear in the tranny--they are cheap and easy to inspect/replace if needed.
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Knowledge is knowing a tomato is a fruit; wisdom is not putting it in your fruit salad. |
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#6
10-11-2013, 04:42 PM
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I would start by checking the speedo cable and gear in the transmission.
I recently changed the speedo gear in my M20 to correct for a new ring/pinion set and saw something similar, where the speedo needle would stay at a certain level and not move. The odometer worked fine. The new speedo gear came in a two pack, so I installed the other one and it works fine. What I found is the speedo cable end didn't seat fully into the trans gear. I'm thinking it forced the cable end to push in too far at the speedometer side of the cable.
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1970 GTO-vert, 461, eheads, stump puller, m20, 3.42 
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#7
10-13-2013, 11:54 AM
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Thanks guys, I will check the gear in the trans and look into the gauge. The Speedo seems correct up to 20 mph and the odometer works (although I have not really checked accuracy). I will check accuracy of odometer as well. Appreciate the feedback!
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Make it go around corners, life's more interesting that way! 70 GTO White/Blue Project
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#8
10-15-2013, 07:19 PM
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Before you do too much, just hook the speedo cable up to your drill. Give it a spin, at high speed you should be able to get it between 60 or 70. Easiest check.
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1964 GTO Auto 1970 GTO Ram Air III 4-speed 1972 Lemans Convert with endura option, 455, 4-speed |
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#9
10-15-2013, 07:57 PM
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If you have a drill and there is a click setting for 1,000 RPM. That would translate to 60 MPH on your speedometer during the test as long as the speedometer is working properly.
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Peter Serio Owner, Precision Pontiac |
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