Speedometer is off 5mph
Methanoholic
Joined: Mar 2009
Posts: 6,442
Likes: 8
From: Maine (NorCal Native)
There are many calculators available to do this ... if you must there are also inline calibrators, however A smart person would head to their local Ford dealer with the following info in hand:
And they will be happy to fix you up with the proper speedo gear.
-Enjoy
fh : )_~
- Tire size
- Transmission
- Rear Gear ratio
And they will be happy to fix you up with the proper speedo gear.
-Enjoy
fh : )_~
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
The speedo gear is held into the tranny or transfer case via one little screw at the end of the speedo cable. Take the screw out, pull the cable and gear out, and the gear comes off with a clip. Lots of places like Ford, LMC, etc sell them and IIRC they are about $7. If you pull it and count the # of teeth you can buy one with 1 tooth less and probably be as close as possible. But, give me the actual speed, indicated speed, and tooth-count of the current gear and I'll tell you the gear that'll get you the closest. Oh yes, and what the transmission is.
Thread Starter
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Senior User
Joined: Dec 2012
Posts: 103
Likes: 1
My dad does not want me taking off the speedo cable right now... (we are going to rebuild the transmission in the future)
Where there different speedo gears in 1982?
(note: the truck was made in the end of 1981, but is a 1982 model)
From driving the truck I can tell that the truck is off by almost exactly 5mph.
Does this help you out any?
Thanks for your help.
Where there different speedo gears in 1982?
(note: the truck was made in the end of 1981, but is a 1982 model)
From driving the truck I can tell that the truck is off by almost exactly 5mph.
Does this help you out any?
Thanks for your help.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
There were several speedo gears in all years. The reason being that there were many different rear gear ratios and many different tire sizes.
If your truck is reading slow, meaning the speedometer shows a slower speed than you are going, then you need a smaller speedo gear. But, to say it is 5 mph slow w/o saying at what speed doesn't tell much as if that is at 10 MPH then you are off 50%. But if that is at 100 MPH then you are only off 5%. I doubt that your 5 MPH error is at either of those speeds, but you get my point.
If I assume it is off 5 MPH at 60 MPH actual then you have an 8% error. And if your speedo gear is an 18 toothed one then you need to drop 1 tooth. (You really need to drop 1.5 teeth but that's an impossibility as there are no gears with 16.5 teeth.)
So, when the time comes you need to pull the speedo gear and find out what you have. Then go to Ford or LMC or someone and buy a gear with one less tooth - for your transmission or transfer case. There are several styles of gear and you must get the right style. Show yours to the parts guy at Ford and he can get you the right one.
If your truck is reading slow, meaning the speedometer shows a slower speed than you are going, then you need a smaller speedo gear. But, to say it is 5 mph slow w/o saying at what speed doesn't tell much as if that is at 10 MPH then you are off 50%. But if that is at 100 MPH then you are only off 5%. I doubt that your 5 MPH error is at either of those speeds, but you get my point.
If I assume it is off 5 MPH at 60 MPH actual then you have an 8% error. And if your speedo gear is an 18 toothed one then you need to drop 1 tooth. (You really need to drop 1.5 teeth but that's an impossibility as there are no gears with 16.5 teeth.)
So, when the time comes you need to pull the speedo gear and find out what you have. Then go to Ford or LMC or someone and buy a gear with one less tooth - for your transmission or transfer case. There are several styles of gear and you must get the right style. Show yours to the parts guy at Ford and he can get you the right one.
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pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
Doesn't help unless you know what color gear is on there now...
(they are all color coded)
I think Summit Racing sells them.
(they are all color coded)
I think Summit Racing sells them.
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Thread Starter
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Senior User
Joined: Dec 2012
Posts: 103
Likes: 1
Ok thanks anyway.
When I drive 70 on the highway, it reads 75.
I had someone drive 70 and I followed, however I did not test other speeds.
I hadn't put much thought into it. It is a certain percent, which makes sense. I just thought it was always off by 5mph.
The rear end is a 13 code (9" 2.75 gear)
I'll figure it out when the time comes.
Thanks
When I drive 70 on the highway, it reads 75.
I had someone drive 70 and I followed, however I did not test other speeds.
I hadn't put much thought into it. It is a certain percent, which makes sense. I just thought it was always off by 5mph.
The rear end is a 13 code (9" 2.75 gear)
I'll figure it out when the time comes.
Thanks
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
Do a search.
There are a lot of threads here about this issue.
Be sure to get the correctly 'handed' gear.
You, nor your sig say if the truck is 4wd.
if it's 4x4 it will be driven off the transfer case.
Just follow the cable.
There are a lot of threads here about this issue.
Be sure to get the correctly 'handed' gear.
You, nor your sig say if the truck is 4wd.
if it's 4x4 it will be driven off the transfer case.
Just follow the cable.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
We need the color of the speedometer gear so we can tell you which one you need. They are color coded for the number of teeth, and the pitch angle of the teeth, either right or left handed pitch. The whole purpose of the different gears is to calibrate the odometer/speedometer so it reads as close as possible. It takes about 1 minute to check and/or replace. It's not a major job that would need to wait for a transmission overhaul.
Originally Posted by Gary Lewis
If I assume it is off 5 MPH at 60 MPH actual then you have an 8% error. And if your speedo gear is an 18 toothed one then you need to drop 1 tooth. (You really need to drop 1.5 teeth but that's an impossibility as there are no gears with 16.5 teeth.)