Correct speedo gear

Reply Subscribe

Thread Tools

Search this Thread

Mar 30, 2001 | 01:31 PM

slikness

Thread Starter

Posting Guru

Joined: Jun 1999

Posts: 1,100

Likes: 0

From: Durham

Correct speedo gear

OK, I need a math wizard for some help. I just swapped out my 2.75 for a 3.50 posi. Now I need to know what speedo gear to change to. I have the 3.50 posi with 26.7 inch tall tires behind a C6 tranny, 31 spline axle. Can anyone help?

Thanks,

'82 F150 2WD w/351W (orig 300 I6)
Slik

Mar 30, 2001 | 02:31 PM

cgl

Posting Guru

Joined: Apr 2000

Posts: 1,345

Likes: 0

From: NorCal

Correct speedo gear

Oh this can get fun... I just had a run in with the CHP over this. It seems I went up a tooth when I shoulda went down. What gear do you have in there now (color)? I believe it should clip onto the tranny end of the speedo cable.

About how much is your speedo off by? It should be reading faster than you're actually traveling.

Mar 30, 2001 | 03:04 PM

RGAZ

Senior User

Joined: Aug 1999

Posts: 343

Likes: 0

Correct speedo gear

I believe you have a Pink installed and you need the Yellow.

This is funny. I have the Yellow and I need the pink after adding my 32" tires. My speedo reads low.

I have the 3.55 LSD gears and 32" tires.

Randy

Mar 30, 2001 | 06:08 PM

cgl

Posting Guru

Joined: Apr 2000

Posts: 1,345

Likes: 0

From: NorCal

Correct speedo gear

Boy are you in for a surprise. I had the yellow (18 tooth) with my 3.55 and 30" tires. When I aded the 32" tires, my speedo was slow (obviously) about 5 MPH. So I got the pink gear (19 tooth) hoping to speed up my speedo. Wrong! I tried explaining that to the highway patrol, but my speedo read 55 and he had me clocked at 64 (I saw the readout). So after getting a bit miffed, I followed a freind of mine who had a new pickup and a calibrated speedo. Sure enough, I was now about 10 MPH slow. So I got a grey gear (17 tooth) and I'm finally close (+-1 MPH) to being accurate again.

So now that I know, less teeth will speed up your speedo, while more teeth will slow it down.

One more thing. When you get the gear, make sure it's Right Hand pitch not left!

Mar 30, 2001 | 09:27 PM

slikness

Thread Starter

Posting Guru

Joined: Jun 1999

Posts: 1,100

Likes: 0

From: Durham

Correct speedo gear

Yeah, it looks like I'm reading real fast. I'll bet that I'm 15-20% different.

'82 F150 2WD w/351W (orig 300 I6)
Slik

Apr 1, 2001 | 07:37 AM

bige53

New User

Joined: Jan 2001

Posts: 11

Likes: 0

Correct speedo gear

I have a 81 f100 with a 300 6 cly T-18 4 SPEED 235/15 Tires white speedo gear. It does not regester at all. I hooked the gear to a drill and cable is fine. Oh yes I have a 3:25 ratio axel 2 wheel drive. Thanks for any help. Earl

Apr 1, 2001 | 03:33 PM

dave89f150

Junior User

Joined: Dec 2000

Posts: 55

Likes: 0

Correct speedo gear

I'm going throught he same thing right now. My 89 F150 has the 300 six and 4 speed manual. The previos owner had installed a lift kit and 33.12.50 tires. The speedo reads about 8 mph slow at 70 mph. The gear on the cable was an 18 tooth. The local Ford dealer didnt know which way to go (teeth count) to speed up the speedometer. They gave me a 21 tooth and it really slowed it down. I figure I will go to the 16 tooth and that should fix it. The dealer told me that on a 4x4, there is another plastic gear in the transfer case that drives the speedo gear and that it often times strips out. I dont know about 2wd other than it has to have a gear in the tranny to drive the speedometer gear. I am really nervous driving this monster on the interstate as the speed is very deceiving. What is stock RPM at 70 mph with a 4x4, 4 speed, six cylinder, and stock tires?

89 F150 4x4 300/4 speed 33.12.50 w/Rancho lift 3.55 gears
82 Mustang GT 302 C4 + nitrous=FAST
91 Mustang GT basic bolt ons- GM Eater