Called Ford dealer and they said they don't show gears by tooth number. I have to come up with a Ford part number for them to order. I see the part numbers for the 19 and 17. But I think I need an 18 tooth (going from 255/70 - 16 to 285/75 - 16). Does anyone have the Ford part number for the 18 tooth gear? thanks....

 

Update: I kept calling Ford dealers until I found a smart one. I found a parts manager that knew what I needed. An 18 tooth, grey, gear; part number is: C7SZ17271C. $6.50 US. He had to order one. Now, hopefully it will solve my speedo problem with my new tires.

 

HAHA I had the exact same problem finding mine......unfortunatelyI wasn't smart enough to hold onto the part number for you.....hope you notice the inprovement I did. Cheers

 

Just Checking Pic

 

Thought I would pass along more information on speedometer reading before and after the tire change. I just got done changing the speedo gear and finished the road testing. Also, noticed that it shifted better with 18 tooth gear. So far I'm impressed with these Firestone Destinations. Mean, aggressive grip with relatively low road noise.

1997 F150 with 4.6L - 3.55 limited slip

original - 255/70 - 16 Goodyear Wrangler tires - original 20 tooth black speedo gear

Speedometer Reading -------- GPS MPH Reading

55 mph ------------ 56 mph
60 mph ------------ 61 mph
65 mph ------------ 66 mph

New - 285/75 - 16 Firestone Destination M/T - original 20 tooth black speedo gear

Speedometer reading -------- GPS MPH reading

55 mph -------------- 61 mph
60 mph -------------- 66 mph
65 mph -------------- 71 mph

New - 285/75 - 16 - Firestone Destination M/T - 18 tooth grey speedo gear

Speedometer reading ------ GPS MPH reading

55 mph ------------ 55 mph
60 mph ------------ 60 mph
65 mph ------------ 65 mph

So, it looks like the 18 gear took the speedometer reading to perfectly dead on (better than original Ford match-up). Appreciate everyones help.

 

Hey guys, I had posted a similar message regarding fixing the speedo gear a year or so ago and had it done by a speedo shop. I'm not sure what the guy used but he said it was probably within 1mph accuracy. My stock tire size was 235/70/16 and I went up to a 285/75/16 a few years ago. Does anybody know what number tooth gear he should have used (and probably did)? Just curious.

https://www.f150online.com/galleries...TOKEN=37026799

 

Based on my calculations, I would guess he went with a 17 tooth gear. I went from a 255/70 - 16. The 18 tooth grey color gear resolved my 5 mph difference. Your difference was probably more like 8 mph. So, there is a good chance he used a 17 tooth green color gear. You could satisfy your curiousity by spending 10 minutes and pull the speedo gear assembly and look at the color or count the teeth. One 11 mm wrench and you can have it off.

 

I've got a 1999 f150 4.6 manual with a 10% speedometer error because of smaller tires. I purchased a superchips 1715 microtuner thinking that I could change the tire size on the computer and cure my speedometer error, but so far that hasn't worked. Does anyone know when exactly it was that Ford changed from speedometer gear?

 

I am pretty sure 98 was the last year the speedo gear was used before they changed to electronic.

 

Well OK there is, but the wife isn't around at the moment.

Anyway I was searching this out and thought that this information might be useful to someone else too.

I finally found a formula to figure out the correct gear to use.

(8 x Diff Gear Ratio x Tire Rev. per Mile) / 1000 = Gear Teeth.

I have it all in an image I pulled out of a cataloge including part numbers for all the verious gears. But it seams they won't let us attach images to our posts any more.

Thanks Jake, got it figured out.

 

you have to link the pics now with [img]before and [/img] after.

id like to see the pic since ill need to do this ones i put 35's on

 

bump image now viewable.

 

question on this guys someone noted that newer vehicles aren't using these. I have a 2004 f150 heritage basically a 2003 and Im about to put on 285 75 16 like many of the guys here. Would getting a new speedo gear work or do I even have one in my truck?

 

No you don't have one in your truck, it is electronic. 98 was the last year for the speedo gears.

 

thanks buddy looks like I will just have to get a tuner or something