Speedometer
- Thread starter Vetman
- Start date
Roscobbc
Moderator
Broken cable
It will ba a bad cable sticking and the odometer gear in the head unit has worn out, a common thing, I have the parts cheapest in the uk
I would agree on the odometer gears being worn or broken. I think I am right in saying that this is quite a common failure as the original worm gear is plastic and wears away over time when used against the metal gear. You can see the plastic plastic particles at the bottom of the unit in the photo below.
The other photo shows the damping mechanism and spring which maybe faulty but if the gears are clicking on each other rather than meshing you may get the wobbly effect you are seeing.
Getting the speedo unit out and dissembling it is a bit of a piglet but it can be done. As stripping the speedo is quite fiddly I highly recommend decaf coffee and a box of beta blockers. And if you have eyesight like mine, a decent magnifying glass helps too.
There are some more pictures on my projects 'blog' on pages 4 and 5. Hope this helps.
The other photo shows the damping mechanism and spring which maybe faulty but if the gears are clicking on each other rather than meshing you may get the wobbly effect you are seeing.
Getting the speedo unit out and dissembling it is a bit of a piglet but it can be done. As stripping the speedo is quite fiddly I highly recommend decaf coffee and a box of beta blockers. And if you have eyesight like mine, a decent magnifying glass helps too.
There are some more pictures on my projects 'blog' on pages 4 and 5. Hope this helps.
Chuffer
CCCUK regional rep
You will always be going faster than you think you are .
Mine packed up a couple of weeks ago too but haven`t the time to delve into it yet . I am currently relying on RPM matched to what gear I am in which is probably more accurate than the way the speedo bounced about before finally packing up .
Roscobbc
Moderator
Speedo on mine has always been under optimistic......70 will read as 50 for example. In over 20 years I've checked the drive gear in the gearbox - that is correct for the 3.08 rear end. Earlier-on I simply learned the specific 30, 40, 50, 60 and 70 mph rpms in top gear......must admit that learning/remembering them in lower ratios was a struggle. Nowadays I use an old TomTom for a speedo function. I'm sure others on here will testify to the fact that with a more powerful car (in my case, perhaps considerbly more powerful) the very last thing you have time to look at is the speedo......just too much going on keeping it all in a straight line - aftermarket shift indicator light/rev limiter helps........
No it's doable but time consuming and the parts are not expensive
Chuffer
CCCUK regional rep
I have long maintained that with our draconian and almost zero tolerance speed camera infested roads , drivers are at bigger risk of causing accidents by constantly studying their speedo`s than concentrating on the road ahead .
CaptainK
CCCUK Member
I gauge my speed in the Vette by how easily I can hear the wife. If I can hear her talking, I'm below 70mph. If I can hear her whilst very loud talking, I'm doing 70mph. If I can't hear her at all, then I'm doing more than 70
Jokes aside, my speedo is wrong too as the rear diff has been changed from 3.70 to 3.08 at some point in its life. Like Ross, I've learnt roughly the revs to speed ratio, and sometimes use my phone with a GPS speedo on it.
Jokes aside, my speedo is wrong too as the rear diff has been changed from 3.70 to 3.08 at some point in its life. Like Ross, I've learnt roughly the revs to speed ratio, and sometimes use my phone with a GPS speedo on it.
Chuffer
CCCUK regional rep
My exhaust is loud enough to hardly hear my wife at 30 mph so at 70 mph + I got no chance . Heaven !I gauge my speed in the Vette by how easily I can hear the wife. If I can hear her talking, I'm below 70mph. If I can hear her whilst very loud talking, I'm doing 70mph. If I can't hear her at all, then I'm doing more than 70
Jokes aside, my speedo is wrong too as the rear diff has been changed from 3.70 to 3.08 at some point in its life. Like Ross, I've learnt roughly the revs to speed ratio, and sometimes use my phone with a GPS speedo on it.
Roscobbc
Moderator
I laugh when people talk about the OEM GM radio. Mines even a AM/FM unit but with its merge 2 watt or similar output the way way you can hear anything is when the car is stationary with the engine off. In this weather the roofs are off, rear window out, side windows down and at cruise speeds I can't even hear the mobile phone (or hear anyone talking if I picked it up)
teamzr1
Supporting vendor
I gauge my speed in the Vette by how easily I can hear the wife. If I can hear her talking, I'm below 70mph. If I can hear her whilst very loud talking, I'm doing 70mph. If I can't hear her at all, then I'm doing more than 70
Jokes aside, my speedo is wrong too as the rear diff has been changed from 3.70 to 3.08 at some point in its life. Like Ross, I've learnt roughly the revs to speed ratio, and sometimes use my phone with a GPS speedo on it.
There are vendors who sell the gears to swap in to regain the correct MPH being reported like this one
Speedometer gear driven drive pinion speedometer gear odometer gears
700r4 Speedometer gears, and USA made rear wheel drive and 4x4 cars and trucks plus odometer gears 700r4 th350 th400 aod e4od 727 518
www.laspeedometergear.com
Or Speedometer Driven Gears
Read this Is Your Speedometer Inaccurate? Here Are A Few Tips To Correct It
Doing the math
TCI Auto Speedometer Gear Calculator - TCI® Auto
Use this TCI Auto Speedometer Gear Calculator Formula for any GM, Ford or Chrysler vehicle. This is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line!
www.tciauto.com
Read attached PDF
CaptainK
CCCUK Member
Thanks Team, I've read up on that previously and know I need to change out the speedo gear. Just keep forgetting to check what I've already got in there, so I can do the maths to work out what I need.There are vendors who sell the gears to swap in to regain the correct MPH being reported like this one
Speedometer gear driven drive pinion speedometer gear odometer gears
700r4 Speedometer gears, and USA made rear wheel drive and 4x4 cars and trucks plus odometer gears 700r4 th350 th400 aod e4od 727 518www.laspeedometergear.com
Or Speedometer Driven Gears
Read this Is Your Speedometer Inaccurate? Here Are A Few Tips To Correct It
Doing the math
TCI Auto Speedometer Gear Calculator - TCI® Auto
Use this TCI Auto Speedometer Gear Calculator Formula for any GM, Ford or Chrysler vehicle. This is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line!
Read attached PDF
Vetman
CCCUK Member
As a ‘temporary’ solution I have fitted a gps speedometer. This uses a 5v usb power supply. Cheap on Amazon. I am surrounded by 20 mph traffic zones so didn’t want to risk having to take a ‘speed awareness course’ for racing along at 23mph.
I fitted a different type to my regular car for the same reason.
