Help Me Solve This Speedo Cable Flucuation
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Postmaster
Joined: Apr 2001
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Help Me Solve This Speedo Cable Flucuation
At issue is a standard, gear driven speedo cable on an A4LD transmission giving the most bizarre readings when cold weather arrives.
When the sitting overnight at temperatures around 30-45 degrees, the speedometer reads approximately 10 mph too slow, then corrects as the transmission warms. So far so good, sounds normal for an old box. However, when it is really cold outside, nearing the teens or below, the speedo reads way high, 30+ mph too high.
I recently rebuilt the transfer case and had occasion to pull the speedo gear driven off the TC. Expecting it to be worn or at least minus a few teeth, it was perfectly normal on both gear surfaces. The entire unit was well lubricated and the cable turned easily by hand with no evidence of the inner cable catching or dragging on the outer housing. The transmission is factory original, never opened and cold weather does not affect it's operation. It still shifts normally, only the speedometer is affected.
With onset of winter here, the strange gyrations have begun anew. Reading low when cold makes some sense, but the severe overage when very cold has me baffled. Can anyone explain the physics of this?
When the sitting overnight at temperatures around 30-45 degrees, the speedometer reads approximately 10 mph too slow, then corrects as the transmission warms. So far so good, sounds normal for an old box. However, when it is really cold outside, nearing the teens or below, the speedo reads way high, 30+ mph too high.
I recently rebuilt the transfer case and had occasion to pull the speedo gear driven off the TC. Expecting it to be worn or at least minus a few teeth, it was perfectly normal on both gear surfaces. The entire unit was well lubricated and the cable turned easily by hand with no evidence of the inner cable catching or dragging on the outer housing. The transmission is factory original, never opened and cold weather does not affect it's operation. It still shifts normally, only the speedometer is affected.
With onset of winter here, the strange gyrations have begun anew. Reading low when cold makes some sense, but the severe overage when very cold has me baffled. Can anyone explain the physics of this?
Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
Help Me Solve This Speedo Cable Flucuation
What vehicle, year, gears, tires, mods, repairs? How do you know it's reading over? Does it show 30mph (30 over) when you're stopped, or does it show a percent over at all speeds? When it transitions from 10 under to 30 over, does it jump or progress? There are 2 gears - the DRIVEN gear on the end of the cable and the DRIVE gear on the trans tailshaft. Have you checked both?
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Postmaster
Joined: Apr 2001
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Help Me Solve This Speedo Cable Flucuation
>What vehicle, year, gears, tires, mods, repairs? How do you
>know it's reading over? Does it show 30mph (30 over) when
>you're stopped, or does it show a percent over at all
>speeds? When it transitions from 10 under to 30 over, does
>it jump or progress? There are 2 gears - the DRIVEN gear on
>the end of the cable and the DRIVE gear on the trans
>tailshaft. Have you checked both?
Vehicle in question is '91 Aerostar, E-4WD, 3.73, no mods, standard tire size. When very cold, pulling out onto the highway and accelerating to average traffic speed (55mph), at approx. 15-20mph the speedo reads around 50mph and when traveling along with traffic reads about 75-80mph. The speedometer motion is steady, not erratic as with a worn cable. The Dana-28 transfer case appears to drive the speedometer cable directly from the T. case itself.
Any possibility the problem could lie on the other end, i.e. within the odometer/speedometer gearing at the dashboard end?
>know it's reading over? Does it show 30mph (30 over) when
>you're stopped, or does it show a percent over at all
>speeds? When it transitions from 10 under to 30 over, does
>it jump or progress? There are 2 gears - the DRIVEN gear on
>the end of the cable and the DRIVE gear on the trans
>tailshaft. Have you checked both?
Vehicle in question is '91 Aerostar, E-4WD, 3.73, no mods, standard tire size. When very cold, pulling out onto the highway and accelerating to average traffic speed (55mph), at approx. 15-20mph the speedo reads around 50mph and when traveling along with traffic reads about 75-80mph. The speedometer motion is steady, not erratic as with a worn cable. The Dana-28 transfer case appears to drive the speedometer cable directly from the T. case itself.
Any possibility the problem could lie on the other end, i.e. within the odometer/speedometer gearing at the dashboard end?
Senior User
Joined: Dec 2002
Posts: 364
Likes: 0
From: Minneapolis USA
Help Me Solve This Speedo Cable Flucuation
I have the same issue my 91 F150 reads about 50 mph faster than it should, ie: when i'm going 30 or somewhere around there my speedo reads like 70 to 80. I'm curious to know how to fix this issue.
Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
Help Me Solve This Speedo Cable Flucuation
There is no gearing inside the speedo head for the needle - it's directly driven. The gearing at the head is only for the odometer and is independent of the needle. Sounds like both of you need new speedos.
Senior User
Joined: Dec 2002
Posts: 385
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From: airdrie canada
Help Me Solve This Speedo Cable Flucuation
i had something similar happen about 5 yrs ago was -30 and my spedddo read about 40 mph fast only for a min or so never happened again. does anyone know if an early 351w with a c6 will bolt up to the transfer case on a 91 f150 4x4 sc?
Junior User
Joined: Jul 2002
Posts: 81
Likes: 0
From: The Rock, BC
Help Me Solve This Speedo Cable Flucuation
yep shouldn't be a problem, ford's pretty standard when it came to tcases. 31 splines and 6 bolt circular pattern on all the full size married cases
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