Drivetrain 90 LX Speedo Problem

Glliw

Member
Oct 21, 2019
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Hey all,

I've got a 90 LX 5.0 that has improper speedometer operation. From what I've read, I don't see this issue described elsewhere, but I'm sure I'm missing it as I can't be the first to have this problem.

The speedometer increases very slowly up to about 35 mph over time. It seems to not be impacted by the actual speed of the car. Going 70 mph also shows a max of ~35 mph.

I pulled the speedo gear out of the T5 and spun it with a drill. The cluster increments accordingly up to about 35 mph doing this but slowly drops back down.

The needle does not flutter, flicker, jerk, or jump.

What might the issue be here? I would think that the cable and gear itself are OK as it responds to input.

Would this be too tight of a needle? And if so, how the heck did that happen? Of course, I'm not the original owner, but why would someone tighten the needle? Or does the cluster just need lubricating?

Looking for some advice before I dig knuckle-deep into the dash.

Thanks,
Will
 
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Mustang5L5

i'm familiar with penetration
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Could also be the bushing in the speedo head. 90-93 clusters are relatively cheap. You can either swap the speedo head, or the entire cluster. The mileage is very easy to match up.

From the trans to the cluster, it's a purely mechanical system, but the speedo head allows for some slip.
 
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TheGrinch77

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Just had mine apart and I would suspect a issue in the Speedo head and or speedo “flywheel”. Is your odometer working correctly? Seems by what you said you ruled out the trans and cable. Might be time to pull the cluster for a look. I ended up replacing my cluster due to a bad speedo flywheel (as I call it ) it was warped which caused my speedo issue. I have only taken apart one 1992 mustang cluster but they use a similar design as some Mercedes and other cars I have taken apart over the years. I would think The issue lies in the wheel or mag area of the speedo.

Have you taken off the needle or done a gauge overlay recently?
 
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Glliw

Member
Oct 21, 2019
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Sheboygan, WI
Thanks for the ideas. The odometer increments though it does seem to be off some but I haven’t verified that. I’ll check the speedo itself.
 

7991LXnSHO

Now I want a 10 year badge
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I kinda thought it was a stretch
That’s a problem with Speedo’s.
And please don’t stab a Dizzy or Tranny in my car.
:O_o:
Mechanical speedometers can get gummed up or have parts wear out. I’ve seen plenty of bouncing needles in older cars from cables, but a steady slow reading seems to be more likely in the dash. Good luck and Please let us know what you find.
 

BlakeusMaximus

Still got to try a little lube on my speedo head
Jul 12, 2017
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I cleaned the head on the speedometer where their cable inserts into it with brake fluid, oiled it up with all purpose oil and mine is silky smooth. Hence my CT.
 
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Glliw

Member
Oct 21, 2019
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Sheboygan, WI
Update on this...I took apart the dash and inspected the speedo. It doesn't seem to me that the needle is bound up and there was plenty of grease on the cable's input.

This video shows the needle's movement and how free it is.
View: https://youtu.be/-aLWQ6hTKQ0



I re-lubricated and re-assembled. Took it for a drive and have a slightly different behavior below. Instead of rising to ~30mph and staying there, it now has the following behavior:
View: https://youtu.be/Unsm2YZJ1lQ

  • at a stop does not go all the way back to 0.
  • as accelerating, it reaches ~20 mph relatively smoothly but then bounces quite heavily around 20-25 mph.
  • increases to ~50mph, being a few mph off
  • Above 50mph the gauge does not increase. Going 70 mph the gauge stays at 50mph.
  • odometer is pretty accurate. over a ~5 mile drive, it was only off a couple of tenths.
 

Mustang5L5

i'm familiar with penetration
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Feb 18, 2001
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The needle being that loose is normal. I have 3 or 4 speedometers here and they are all the same. The other gauges use motors to move them, so there is resistance. The speedo needle is actually free floating. The needle connect to a flywheel with two magnets that circle it. There's no direct connection. As the speedo cable turns, it spins the magnets which "grab the flywheel.

The bouncing is caused by 2 things. bad bushings in the speedo head (or bushing in need of lubrication). Or a speedo cable that is binding up.

You can pretty easily pop that speedo out. The cluster is fairly modular so when you remove the gauge face, you can see how the speedo is it's own section and can be removed. I would try that and lubricate the bushings with some silicone lube, or ensure there is no binding or debris causing issue.
 
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