Speedometer not working, But odemeter is rolling fine |
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Speedometer not working, But odemeter is rolling fine |
Noodles |
Aug 3 2012, 02:01 PM
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#1
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Newbie Group: Members Posts: 37 Joined: 17-July 12 From: Seattle,Wa Member No.: 14,688 Region Association: Pacific Northwest |
So question for the experts! My speedometer don't regester mph's but my odemeter still seems to be turning. Was wondering if this is a common problem with 914s and if there was an easy fix. Like should I get a new angle drive or is it the speedo head itself that is bad? Any help would be much appreciated!
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TheCabinetmaker |
Aug 3 2012, 02:08 PM
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#2
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I drive my car everyday Group: Members Posts: 8,300 Joined: 8-May 03 From: Tulsa, Ok. Member No.: 666 |
Its in the head.
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ThePaintedMan |
Aug 3 2012, 02:28 PM
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#3
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Advanced Member Group: Members Posts: 3,886 Joined: 6-September 11 From: St. Petersburg, FL Member No.: 13,527 Region Association: South East States |
(IMG:style_emoticons/default/agree.gif) You can do what I did and find a "parts" speedo and try to salvage pieces from it. Make sure they're the same (ie. 120 mph, or 150 mph). Make sure to clean and grease the drive gears lightly. I've heard this is the cause of many broken speedos - the grease gets old, turns to glue and eventually something gives.
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Dave_Darling |
Aug 3 2012, 03:09 PM
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#4
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914 Idiot Group: Members Posts: 14,990 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
If the odometer works, the signal (the rotation of the cable) is getting to the speedo. The odo and speedo both take a single input.
The odometer uses the spinning of the cable to turn a bunch of gears that spin the wheels that tell the miles covered. The cable also spins a magnet that is close to a cup-shaped piece of aluminum. This aluminum piece is moved by the magnetic pull of the magnet, which turns it against a spring. The faster the magnet spins, the more the twist against the spring. It sounds like there is something disconnected inside the speedometer housing. Either the magnet from the cable, or the cup from the needle shaft, or the needle from its shaft, or the spring from the shaft. Once you get the speedo open, it should be straightforward (but possibly very fiddly) to find and fix what is wrong. --DD |
struckn |
Aug 3 2012, 06:36 PM
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#5
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Senior Member Group: Members Posts: 1,069 Joined: 9-November 11 From: South Central York Pennsyvania Member No.: 13,764 Region Association: MidAtlantic Region |
Slightly OT, but unless you're running stock tire sizes the speedo's and od's aren't accurate. Mines off at least 5-10 MPH!
I bought a GPS and stuck it over the speedo to track actual MPH. |
mrholland2 |
Aug 3 2012, 09:18 PM
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#6
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Senior Member Group: Members Posts: 750 Joined: 7-September 11 From: Santa Maria,CA Member No.: 13,531 Region Association: Central California |
Can't be made of aluminum. Aluminum is non-ferrous which means that it is not influenced by magnets. If the odometer works, the signal (the rotation of the cable) is getting to the speedo. The odo and speedo both take a single input. The odometer uses the spinning of the cable to turn a bunch of gears that spin the wheels that tell the miles covered. The cable also spins a magnet that is close to a cup-shaped piece of aluminum. This aluminum piece is moved by the magnetic pull of the magnet, which turns it against a spring. The faster the magnet spins, the more the twist against the spring. It sounds like there is something disconnected inside the speedometer housing. Either the magnet from the cable, or the cup from the needle shaft, or the needle from its shaft, or the spring from the shaft. Once you get the speedo open, it should be straightforward (but possibly very fiddly) to find and fix what is wrong. --DD |
bandjoey |
Aug 3 2012, 11:41 PM
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#7
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bandjoey Group: Members Posts: 4,926 Joined: 26-September 07 From: Bedford Tx Member No.: 8,156 Region Association: Southwest Region |
Many speedos for sale. Check the classifieds. (IMG:style_emoticons/default/biggrin.gif)
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mrholland2 |
Aug 4 2012, 08:29 AM
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#8
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Senior Member Group: Members Posts: 750 Joined: 7-September 11 From: Santa Maria,CA Member No.: 13,531 Region Association: Central California |
And contrary to what the creepy fat guy at the public pool says, speedos are NOT one size fits all. (IMG:style_emoticons/default/av-943.gif)
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Noodles |
Aug 4 2012, 04:34 PM
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#9
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Newbie Group: Members Posts: 37 Joined: 17-July 12 From: Seattle,Wa Member No.: 14,688 Region Association: Pacific Northwest |
Cool thanks for the informative replys, I'll tear into my speedo and see if I can just clean it out.
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bandjoey |
Aug 4 2012, 07:12 PM
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#10
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bandjoey Group: Members Posts: 4,926 Joined: 26-September 07 From: Bedford Tx Member No.: 8,156 Region Association: Southwest Region |
Cool thanks for the informative replys, I'll tear into my speedo and see if I can just clean it out. Ohhh Ouchhhh Geee Whizzzz, I didn't need to know....What's in the speedo????? Are you in that much pain? And what about your speedometer? (IMG:style_emoticons/default/av-943.gif) (IMG:style_emoticons/default/av-943.gif) (IMG:style_emoticons/default/av-943.gif) |
Dave_Darling |
Aug 4 2012, 08:44 PM
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#11
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914 Idiot Group: Members Posts: 14,990 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Can't be made of aluminum. Aluminum is non-ferrous which means that it is not influenced by magnets. Not completely true. http://en.wikipedia.org/wiki/Eddy_current --DD |
Drums66 |
Aug 4 2012, 08:58 PM
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#12
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914 Rudiments Group: Members Posts: 5,321 Joined: 15-January 03 From: Coronado,Cali Member No.: 151 Region Association: Southwest Region |
....Question #1, to your knowledge has it ever worked? #2 if so did it just
happen?? |
Noodles |
Aug 4 2012, 09:38 PM
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#13
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Newbie Group: Members Posts: 37 Joined: 17-July 12 From: Seattle,Wa Member No.: 14,688 Region Association: Pacific Northwest |
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slu234 |
Aug 10 2012, 12:43 PM
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#14
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Member Group: Members Posts: 57 Joined: 20-January 09 From: Staunton, VA Member No.: 9,949 Region Association: MidAtlantic Region |
I had the same issue with my speedometer, speedometer worked but the odometer didn't. The usual suspect is that the main drive gear (pot metal) will slip on the axle that it is supposed to be pressed on. The cheap fix is to remove the pot metal gear and distort the axle hole in the gear with a few strikes with a punch to tighten it back up. Reinstall.
I think PP has a good tech article on the 911 and 914 speedo problems. The good fix is to replace the main drive gear (the above mentioned pot metal gear) with a replacement that you can find at PP for about $25. Dave is right, messing with the speedometers/odometers is kinda "fiddly". The PP tech article at least gives you some guidance on how to open it up and give some good direction. Good luck. oh, btw.......link to the article here One watchout..I have read that you should not reset the trip odometer while the car is moving. Brian |
Dave_Darling |
Aug 10 2012, 05:04 PM
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#15
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914 Idiot Group: Members Posts: 14,990 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Brian, you've got it the wrong way 'round. If the odometer doesn't work but the speedometer does, then it's the pot-metal gear slipping.
The OP's problem is that the odometer runs, but the speedo needle doesn't read. That's also something wrong inside the speedo, but it doesn't have anything to do with the odometer gears. --DD |
scott_in_nh |
Aug 11 2012, 06:41 AM
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#16
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Senior Member Group: Members Posts: 808 Joined: 10-December 10 From: Hampton, NH Member No.: 12,471 Region Association: North East States |
related, but different:
my speedo is about 7% optimistic, but the odometer is pretty accurate (I have 195/65/15's on it). Is there a way to adjust the tension on the spring? |
r_towle |
Aug 11 2012, 09:26 AM
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#17
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Custom Member Group: Members Posts: 24,577 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
First time I have heard of it breaking in this way and not the other.
I have fixed plenty of Odometer gears...never had this issue. Question of the big brains. When you get the speedo re-calibrated for different size tires, what do they do exactly? rich |
slu234 |
Aug 13 2012, 08:51 AM
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#18
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Member Group: Members Posts: 57 Joined: 20-January 09 From: Staunton, VA Member No.: 9,949 Region Association: MidAtlantic Region |
Brian, you've got it the wrong way 'round. If the odometer doesn't work but the speedometer does, then it's the pot-metal gear slipping. The OP's problem is that the odometer runs, but the speedo needle doesn't read. That's also something wrong inside the speedo, but it doesn't have anything to do with the odometer gears. --DD woops!!! sorry for the mixup. |
914_teener |
Aug 14 2012, 10:40 AM
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#19
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914 Guru Group: Members Posts: 5,198 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
First time I have heard of it breaking in this way and not the other. I have fixed plenty of Odometer gears...never had this issue. Question of the big brains. When you get the speedo re-calibrated for different size tires, what do they do exactly? rich Rich, I think they de-mag the metal wheel on the drive "head" to make the need armature less "attractive". There is some mention on the Bird board of it. The housing is aluminum and guards the internals from any grease or junk getting in the housing when it spins is what DD already knows. Just dug into mine to fix the Odo. |
bbrock |
May 16 2021, 08:20 PM
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#20
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914 Guru Group: Members Posts: 5,269 Joined: 17-February 17 From: Montana Member No.: 20,845 Region Association: Rocky Mountains |
Reviving this thread to see if anyone has successfully repaired this problem. I just got back form putting the second mile on my car near the end of my restoration. This time I went fast enough to see that my speedometer is not working but the odometer is (hence, the 2 miles on it). Angle drive and cable are new (well, they have 2 miles on them now) and obviously working. Whats weird is that I tested the speedo with a drill about 3 years ago when I fixed the odo and it worked. I'm guessing I buggered something in reassembly so will be digging in to the gauge again. Thought I take a stab in the dark to see if anyone has gained new wisdom over the last 9 years.
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