matts85vet

pale green is close to gray
definitely not red

looks like you have a gray 15t drive gear.
you have a 35t orange driven gear

tire size 315/35/17 2.59 gear ratio

according to various speedometer calculators, you will need:

17t red drive gear

36t white driven gear

you already have a 35t driven gear so it should be close, depending on you're actual tire height

what gears did you start out with?

WVZR-1

Disregard all references to the "DRIVE GEAR" - you mention you've an error that's something 2 - 5 MPH but you haven't mentioned SLOW or FAST! Your concern now is only to correct the error! That needs to remain your ONLY concern regarding the speedometer error.

Is it FAST or SLOW? How did you check it? GPS? Is the error you mention accurate?

Maybe post some comparisons. I usually suggest using a GPS and post the speedometer reading using 40/xx - 50/xx - 55/xx - 60/xx - 70/xx on the GPS. The error should reflect a consistent percentage.

You do need to be concerned with the VSS identity! You need to be sure that the VSS is correct for the tooth count of the driven gear you end up with. The correct one will reduce the wear on both gears. The VSS ID is important!

BonePhoenIX

I have the white VSS.

car displays slower than actual speed. Verified with GPS. its about 5 slower at speeds above 60.

WVZR-1

With complete disregard to what should be you've got a single "inexpensive" option. Since it's "slow" and you've got a 35 presently you can use a 34 tooth gear which is NLA but it appears to be out there. This will NOT correct an error as great as you indicate yours to be!! When you say "slow" speedo reads 60 and GPS is greater than that? Yes - NO?

Is your "exploded" rear still around? If it is it might be interesting to check the tooth counts on the ring gear and pinion or all of the information off of the perimeter surface of the ring gear. A possible explanation for the "mismatch" in your car could be that a gear change was done by a PO and when it was done the drive/driven was done to accomplish a correction.

I've PM'd you!

matts85vet

if it doesn't correct the error, why bother?


replacing the drive gear is NOT difficult or expensive.

the drive gear is cheap-$10
here's a how to

http://www.digitalcorvettes.com/foru...d.php?t=110978

if you want an accurate speedometer

BonePhoenIX

Well the shop is fixing it for free since I payed them and they quote "it left the shop wrong"
I suspect the PO changed the rear end ratio and the speedometer/tranny drive shaft gears to match.

I've been driving and I've noticed that the "car's speed" is about 5 mph slower than the GPS speed from 35+
Ex: 35 its actually 39-41
40 its actually 45-46
And so on.
I currently have an orange vss gear and green transmission drive shaft gear.
315/35/17 rear wheels 297/35/17 front wheels.
White vss from AutoZone. vss harness was repaired (caused erratic number display)

My mpg is matching that of stock now after resetting computer (removing negative battery terminal for 1min)

They are willing to work with me until the issue is resolved.
What is my next step to have my Speedo read -5 than the current displayed speeds?

matts85vet

have them order and install:

red 17t drive gear

white 36t driven gear

this is correct for

315/35/17 tires w/ 2.59 gears

however, actual tire size varies between brands, so the 35t orange gear may work with the new 17t red drive gear

BonePhoenIX

Update: speedometer spikes random numbers. As 5/5/2012 8pm
last week it would randomly "go off" from normal.
Is this because I didn't replace the drive gear to the red one? Have the gears worn down?

geno13r

hi. I heard you could maybe help me also. I have a 93 and changed from 3.08 to 3.55. my speedo is off 25mph to the high side. 70mph reads 95mph. now I know it looks great rolling down the road taking pictures but its driving me nuts. thanks

WVZR-1

Since a C4 never had a 3.08 (maybe you meant 3.07) and there was never a 3.55 (maybe you meant 3.54)

Are tire sizes 'stock'? If sizes are stock a 15 tooth (drive) and a 43 tooth driven would get you as close as possible mechanically. The console SPID info could be helpful. Look for D8L and maybe G92 & G44. Those options should be present I believe for a '93 with 3.07.

If those aren't present (all bets are off).Post tire size confirm axle ratio now.15 & 43 aren't difficult to source and if D8L is present you could use the same VSS>

***************You should have started your own thread and NOT used a 7 year old 'conversation'.

geno13r

thanks for the help. I will remember the correct numbers.