Speedometer Issues
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Speedometer Issues
Hello Everyone! I'm a new member, long time follower of the forum. I've gotten lots of useful information from the wonderful people on this site and was hoping that someone could help me with an issue that I've been meaning to fix for a while!
She's a 1970 F100, 4 speed manual (NP 435), 4x4, with a 390 and a flatbed swapped in. Supposedly has 130,000+ miles,
So, when I bought my truck in the fall, the speedometer sometimes worked, but always very low, never reading above 35, and generally unsteady. The P.O. said that this was becasue of the driven gear on the speedometer cable and gave me another gear with the truck as well to try and see if it worked (Wine color, 16T) in addition to the currently installed 18T yellow gear. While the wine colored gear was installed, the speedo didn't read anything at all.Eventually one day the speedo ceased to work entirely, and has been that way since. Today I finally got arount to changing the speedo cable to see if that helped or fixed the isses. Turned out, when rotating the gear attached to the cable by hand, both with the new cable and the old, the speedometer moved and worked, as did the odometer. This leads me to believe that the problem is with the drive gear inside the tailshaft, not the speedometer or cable itself.
Does anyone have any thoughts or suggestions? And if it is the drive gear inside the tailshaft, how easy of a fix is that, and where is a good place to find the gear I would need to replace? I'm stumped as to where to go from here, and want to make sure I'm headed down the right path. Any advice or suggestions would be appreciated, especially if you've experienced this issue in the past
She's a 1970 F100, 4 speed manual (NP 435), 4x4, with a 390 and a flatbed swapped in. Supposedly has 130,000+ miles,
So, when I bought my truck in the fall, the speedometer sometimes worked, but always very low, never reading above 35, and generally unsteady. The P.O. said that this was becasue of the driven gear on the speedometer cable and gave me another gear with the truck as well to try and see if it worked (Wine color, 16T) in addition to the currently installed 18T yellow gear. While the wine colored gear was installed, the speedo didn't read anything at all.Eventually one day the speedo ceased to work entirely, and has been that way since. Today I finally got arount to changing the speedo cable to see if that helped or fixed the isses. Turned out, when rotating the gear attached to the cable by hand, both with the new cable and the old, the speedometer moved and worked, as did the odometer. This leads me to believe that the problem is with the drive gear inside the tailshaft, not the speedometer or cable itself.
Does anyone have any thoughts or suggestions? And if it is the drive gear inside the tailshaft, how easy of a fix is that, and where is a good place to find the gear I would need to replace? I'm stumped as to where to go from here, and want to make sure I'm headed down the right path. Any advice or suggestions would be appreciated, especially if you've experienced this issue in the past
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 783
From: Simi Valley, CA
Hello Everyone! I'm a new member, long time follower of the forum. I've gotten lots of useful information from the wonderful people on this site and was hoping that someone could help me with an issue that I've been meaning to fix for a while!
She's a 1970 F100, 4 speed manual (NP 435), 4x4, with a 390 and a flatbed swapped in. Supposedly has 130,000+ miles,
So, when I bought my truck in the fall, the speedometer sometimes worked, but always very low, never reading above 35, and generally unsteady. The P.O. said that this was becasue of the driven gear on the speedometer cable and gave me another gear with the truck as well to try and see if it worked (Wine color, 16T) in addition to the currently installed 18T yellow gear. While the wine colored gear was installed, the speedo didn't read anything at all.Eventually one day the speedo ceased to work entirely, and has been that way since. Today I finally got arount to changing the speedo cable to see if that helped or fixed the isses. Turned out, when rotating the gear attached to the cable by hand, both with the new cable and the old, the speedometer moved and worked, as did the odometer. This leads me to believe that the problem is with the drive gear inside the tailshaft, not the speedometer or cable itself.
Does anyone have any thoughts or suggestions? And if it is the drive gear inside the tailshaft, how easy of a fix is that, and where is a good place to find the gear I would need to replace? I'm stumped as to where to go from here, and want to make sure I'm headed down the right path. Any advice or suggestions would be appreciated, especially if you've experienced this issue in the past
She's a 1970 F100, 4 speed manual (NP 435), 4x4, with a 390 and a flatbed swapped in. Supposedly has 130,000+ miles,
So, when I bought my truck in the fall, the speedometer sometimes worked, but always very low, never reading above 35, and generally unsteady. The P.O. said that this was becasue of the driven gear on the speedometer cable and gave me another gear with the truck as well to try and see if it worked (Wine color, 16T) in addition to the currently installed 18T yellow gear. While the wine colored gear was installed, the speedo didn't read anything at all.Eventually one day the speedo ceased to work entirely, and has been that way since. Today I finally got arount to changing the speedo cable to see if that helped or fixed the isses. Turned out, when rotating the gear attached to the cable by hand, both with the new cable and the old, the speedometer moved and worked, as did the odometer. This leads me to believe that the problem is with the drive gear inside the tailshaft, not the speedometer or cable itself.
Does anyone have any thoughts or suggestions? And if it is the drive gear inside the tailshaft, how easy of a fix is that, and where is a good place to find the gear I would need to replace? I'm stumped as to where to go from here, and want to make sure I'm headed down the right path. Any advice or suggestions would be appreciated, especially if you've experienced this issue in the past
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Stick your finger in the hole where the cable and gear goes. You will feel (and/or see) the speedo drive gear. it should be square cut. If the teeth have a worn dip in the middle you have found your problem.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 783
From: Simi Valley, CA
1970 F100 would have a 9" rear axle. There was no 4.10 ratio available.
What is the AXLE code stamped on the 2nd line-far right of the Warranty Plate?
Warranty Plate riveted to the left door face below the latch.
What is the AXLE code stamped on the 2nd line-far right of the Warranty Plate?
Warranty Plate riveted to the left door face below the latch.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Mind jumped around also back in 1978 when, I got my 1971 4x4 f250 the cable at the TF case was always pulled on an angle because the cable was really to short having almost a kink in the outer cable housing.. My 4x4 TF case has a STEEL tooth gear not plastic it's a fixed drive gear to the internal shaft. My inner cable tip was also slipping so wrapped some aluminum foil around the tip to tighten it up some. Plus the cable housing that screws on coupler to the TF case coupler it not stay tight so I put a o-ring or was it a garden hose washer to help it to stop leaking. Not a regular rubber one though. My drive gear says (O1T-71) A-18 = is 18 tooth gear It does show wear in the middle tooth area..
You should pull the gear an check what you may need ,this was another reason I went to a electronic speedometer..
Orich
You should pull the gear an check what you may need ,this was another reason I went to a electronic speedometer..
Orich
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
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I bought the truck after it had been owned by a ranch family, and the axles have been changed to 4.10s at some point in the vehicles life. They at some point ran 35s on the truck. I've confirmed it using a tachometer and a speedometer app on my phone. She turns just below 3K RPM at 70 Mph, which is exacly right for 33s, 4.10 axles, with the 1:1 in the transmission, if internet calculators are to be believed. Otherwise, the best I can tell it that the axle code is an A, with the numbers 05 under the part labeled trans code.
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Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 783
From: Simi Valley, CA
I bought the truck after it had been owned by a ranch family, and the axles have been changed to 4.10s at some point in the vehicles life. They at some point ran 35s on the truck. I've confirmed it using a tachometer and a speedometer app on my phone. She turns just below 3K RPM at 70 Mph, which is exacly right for 33s, 4.10 axles, with the 1:1 in the transmission, if internet calculators are to be believed.
Otherwise, the best I can tell it that the axle code is an A
with the numbers 05 under the part labeled trans code.
Otherwise, the best I can tell it that the axle code is an A
with the numbers 05 under the part labeled trans code.05 = Ford 9" rear axle / 4.11-1 / No Limited Slip / 3,300 lbs axle capacity.
A is the TRANS code: New Process 435.
C8AZ-17285-A .. 7T Yellow Nylon Speedometer DRIVE Gear - TYPE 4a - Teeth run this-away: ///// / Obsolete ~ No one has any NOS
NP435 & 4.11-1 with 15" wheels = 1970/71 F100 2WD // 1970/72 F100 4WD // Also misc 1968/72 Passenger Cars.
Tuned
Joined: Mar 2002
Posts: 405
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From: Ft. Walton Bch 32547
Speedometer Issues
Has the OP ever solved the issue? I have a 71 F100 4x4. All factory NP435 and Dana 21, for now. New cable, and speedo works. Driven gear looks good. Can use a mirror and see the drive gear is in there. Not sure what to do, besides remove the transfer case and look in there. Just trying to avoid that.
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