98 GT speedometer off

[98DesertGT]

Was thinking either drive train or electronic.
But figured here is okay.

Okay worked out 95% of the bugs.
Took it for a drive and ran the GPS

5mph no matter the speed.
It's slow.
so 30 is 25, etc.

4r70w
Now tires are the 245/45/17s
checked the sensor all teeth are okay.
it was coated in fluid but appears to be purple/brown. Rotated the wheels measured 3.27s.
Can recheck but 99% certain it didn't spin 1/2 a turn past 3.

any thoughts?

AND YES, WELL AWARE OF THE SPEEDCAL
But If it won't read proper stock, that'll throw the speedcal off as well no?

 

[98DesertGT]

Little addendum.
AM has the Speedo gear chart, but I take 99% of anything they say with a grain of salt.

the 4r is listed to be 8 tooth.
based on the chart I'm supposed to run a 21 tooth/purple.

If the chart is right I'm definitely confused. Like I said coated in tranny fluid, but appears either dark purple or brown.
Any pictures I've seen online the purple gear looks very vibrant
But I trust an actual SN owner over AM claims.

Oh the tag isn't on the diff.
that's why I marked an rotated.

 

[Royal96]

Is it bone stock right down to wheels/tires?

It's worth noting that I haven't had this issue and have never had to deal with speedcal or anything but it's just something I could see easily being overlooked.

 

[lutter94]

Is the odometer off? The only way a speedcal will help, is if you are off by a percentage. To me it sounds like your needle needs to be adjusted. Maybe the po took it off once. If you drive down the interstate, and pay attn to mile marker signs, or your gps might work too, either or, and your odo is accurate, just pull the lens off, pop the needle off and try to reset it to a more accurate speed. I did this while driving in the middle of nowhere. I would just put it on cruise control, have a friend hold the steering wheel, allowing you to push the needle back on. Should be able to get it within 1mph.

 

[98DesertGT]

Is it bone stock right down to wheels/tires?

It's worth noting that I haven't had this issue and have never had to deal with speedcal or anything but it's just something I could see easily being overlooked.

Engine had the PI swap.
stock air box and filter.
stock headers/mid
stock catback with Flowmaster welded in.

let's see
at "65" it's a hair past 2000.

The wheels are the 17in premiums.
That odd looking design.
.when rotating the wheels, the driveshaft turned more than 3. not just a hair past, and based on my marks not even 1/2 so led me to the 3.27 conclusion.

now interesting enough, cruise doesn't work.
fuse and relay are good.
thinking it's the fenderwell piece.

But my only thought coincides with possible needle play. As the Speedo seems sluggish below 20.
as the odometer works just fine.

More testing is needed.
But that's currently the last issue to address as far as I can find.

 

[98DesertGT]

Is the odometer off? The only way a speedcal will help, is if you are off by a percentage. To me it sounds like your needle needs to be adjusted. Maybe the po took it off once. If you drive down the interstate, and pay attn to mile marker signs, or your gps might work too, either or, and your odo is accurate, just pull the lens off, pop the needle off and try to reset it to a more accurate speed. I did this while driving in the middle of nowhere. I would just put it on cruise control, have a friend hold the steering wheel, allowing you to push the needle back on. Should be able to get it within 1mph.

I'll verify Odometer accuracy.
then move the needle myself.
at 65 it'd be too easy.
bout a centimeter movement.
Not even really an issue, I'm just running out of "problems"

 

[lutter94]

Safe assumption with the rear end being 3.27's. When you say its 65, is that gps speed, or dash speed, since its off by 5mph. 4th Gear is 0.7:1.

 

[chris91]

Easiest way to get an accurate reading when spinning the driveshaft is to spin the wheel 10x. The you'll know for sure what Gears you have because it'll spin 37 times meaning 3.73 or 41 meaning 4.10 etc.

 

[98DesertGT]

Safe assumption with the rear end being 3.27's. When you say its 65, is that gps speed, or dash speed, since its off by 5mph. 4th Gear is 0.7:1.

the dash read 70, dead over the tick.
GPS registered 65.
Can account for 55, 60 as well. dash will read 60-65 accordingly.

I'm making a big deal from nothing currently, as I'm manual swapping as a first mod.
But seeing as I've addressed all issues, it's really all I have to play with til the parts are acquired.

 

[98DesertGT]

Easiest way to get an accurate reading when spinning the driveshaft is to spin the wheel 10x. The you'll know for sure what Gears you have because it'll spin 37 times meaning 3.73 or 41 meaning 4.10 etc.

ooh, good thought.
I'll try that in a few days when the weather sorts out!

I put four ticks...each different to make sure I didn't misread.
It definitely didn't go a full turn past 3. and definitely more than a .08 so I guestimated 3.27.
But I'll definitely give the full 10.
in theory should be just under 33 turns.