Speedo and Odo out by 20%

[Khyron]

I've been searching some of the common speedo problems, and I couldn't find one like mine. Lots of people have sticky cables, weak return springs or their speedo/odo is off by a set amount (20mph etc).

My 84-ptype with digital dash speedo reads pretty much 80% of true speed. It says 100, I'm going 120. It says 40, I'm doing around 48. My odometer seems to be out by not as much - my highway tests using "Next town" signs show around 15%. I also drove a circuit in my 02 jetta, then same in the supra, compared trip meters.

Any ideas? I have recently got stock wheels/tires back on it, but because the PO was such a witch doctor anything is possible. Could be another tranny from a Camry under there.

Khyron

[SilverMk2]

The rear axle was probably changed out for another with a different ratio. It can be fixed with different speedo gears, but you have to know what you have. W58s in Supras all have the same ratios, but other W series trans are differents. Tire size and inflation also matter. HTH

[Dean]

Sounds like your digi dash speedo was made for a 4.30 rear end ratio, and the car now has a 3.73 rear end.
You'll need to change the speedo gear in the tranny or live with it.
This thread gives a lot of useful info.
http://forums.celicasupra.com/showthread.php?t=3634
Hope that helps a bit.

[Khyron]

http://www.nexus-point.net/vehicles/supra/IMG_3804.JPG

I will go pace my other car again - I think I am just under 3K at 115km/hr (which is around 65ish?)

So maybe I don't have an LSD after all. My car is kind of a zombie anyway, the PO did lots of mods, but most of them poorly. So it's entirely possible he broke the original rear and put in another.

But does the swapped out rear explain why the odo and the speedo are out by different percentages? Or is that technically impossible and my measuring just isn't accurate enough?

Khyron

[turbogoo1]

What size tires are on there? They almost look like 235's on there. Which will throw off the speedo.....

Stock size is 225's

And im my opinion...that trim is aweful...sorry if you put it on...

[CelicaSUPRAMK2]

When I first began using my 84' L-Type that my dad had been sitting for a year & a half on one of his house's front lawn, it had the same problem - where it was inaccurate in rpm/speed & even would flicker off & on to lower or higher speeds spontaneously. Thinking that maybe it was the grounding (just in case) I bought myself a [performance] ground wire kit.
Like these >> http://cgi.ebay.com/ebaymotors/TOYOTA-LEXUS-SCION-G3-UNIVERSAL-EARTH-GROUND-WIRE-WIRES_W0QQcmdZViewItemQQcategoryZ33692QQihZ006QQit emZ160025578093QQrdZ1QQsspagenameZWDVW
And what do you know, problem solved for both issues! May I suggest them?? Cheap, help fuel economy, add hp, help transition vehicle at higher RPMs, and even illuminate vehicle lighting! hehe And no, I'm not tryingto lure you into an advertisement.

[Khyron]

Trim was previously mentioned crazy PO, as was the cheap re-spray with no clear coat. Stuff you can't tell until you actually see the car in person. AC removed, but no heater hooked up. 2.5 inch headers mated to a 1.75 inch cat/exhaust, bent strut tower.. I was in for too much money to bail, but I'm happy with it now. A few gremlins, but so be it.

If it's just the axle, I will live with the difference, but I am clueless about drivetrains and so I'm wondering about how a speedo can be 20% while the odo/trip is out by a different percentage. Those wheels came off another car, and I'm pretty sure they were correct spec when I looked it up (the ones that came with the car were definately larger)

Grounds seem fine - no flickering, or cutting out.

Khyron

[Dean]

Speedo and odometer are driven by the same cable. They should be out by the same percentage. It's hard to be that accurate in your tests.

[RedP85]

They both are from the same rotating cable: need to be same error, unless
you are very unlucky, and someone changed the odometer part only in the cluster, on top of the rear diff change.