I have a 97 4x4 and recently upgraded to 285/75/16 from my stock tires. I had my truck radar tested and when my speedo reads 100 Km/h I am actually doing 112 Km/h. About a 10% difference. I also really notice a change in my shift points. I have to be careful when I set my cruise control because sometimes after going up a hill, my revs will stay up and not shift down. Will a new speedo gear solve all of this? I don't really care about the speedo being out it is the shifting that I would like to fix. All help is appreciated.

Thanks in advance.

 

I used to have the 285/75/R16 on my old truck with a 4.6. The speedo gear is easy to change but it won't do anything for the shift points. I find it odd that the 5.4 wouldn't shift down. I really didn't have much of a problem but then again, I had a stick shift and would remove cruise before i went up any major hills on the highway. The main reason i changed my speedo gear was to correct the odometer.

 

I only have 265/75/16's, but my speedo and odometer were off by about 5%. I swapped the speedo gear from a 20 tooth to a 19 tooth. Pretty much have them back to normal again. I am still off just a tad, but I'd guess by less then one mph now.

Maybe an 18 tooth gear would work for you? Before I changed mine, my speedo would show 60 mph, but I was actually going 64 mph.

 

MitchF150 -- how did you decide which tooth gear to change to, and how hard was it to change. I keep hearing how easy it is, but I haven't seen how to do it -- are there any special tools involved or anything? I've got a '97 F150 4x4 going from 265/70/17 to ProComp 33x12.5x17's. Thanks!

 

I just read it in another post. The guy was doing the same as what I did. 255/70 to 265/75. The 19 tooth gear is tan in color. That's the easiest way to tell the parts guy at Ford which one to get. It cost only $12.00, is plastic, and only takes two minutes to swap out. It's located on top of the transfer case, just above the drive shaft. One 7 or 8mm screw holds it in. Just remove it, then pull the whole unit out. Be kinda careful. It uses an O ring to seal itsef. Then the gear just pulls off. Replace it and put it back and tighten. Take for a test drive.

There was another post recently, that actually listed all the gear types/colors.

Basically, it's the larger the tire and NOT regearing, you drop the number of teeth. Regearing and NOT changing tire size, you would need to increase the number of teeth.

I think the range from Ford is 16 - 22 teeth.

 

buffalotr8,
I also have a 97 4x4 with 285/75r/16 tires. A black 20 tooth gear came with the original tires (255s). I installed a tan, 19 tooth gear for the 265s and it broght the speedometer right on the money. I now plan to buy a grey, 18 tooth gear for the 285s.
You are right about the shift points. I installed a B&M ShiftPlus Electronic Shift improver ($40) and it helps a lot. When installed, you can choose one of three settings: off (stock), setting 1 (optional setting) or setting 2 for much firmer shifts (perhaps for racing, but not recommended around town). No, it doesn't change your shift points, but it does feel much better than stock.

 

Phil
So the B&M shift improver really helps with the 285's. If so I need to get one. I hate the way the tranny will shift out of OD and sometimes drop a gear on the interstate, especaially with cruise on. What all is involved installing it? Also, thanks for mentioning the speedo gear too, now I know which one to get.

 

I have a 97 4.2L and went from the factory 255 tires to the 265 Michelen LTX, and my speedo is off by 7 mph. Is the tan gear that you are talking about, the same to change on a 2 wheel drive?

CJ

 

Installing the B&M wasn't too difficult. You basically have to splice into the wires that lead to the transmission. You can do it inside the cab, or (as I did), find the same wires right at the transmission sending unit. Sorry I can't be more specific than that, but I installed mine over a year ago and threw away the instructions. The instructions that came with the kit were clear. If you choose to splice into the transmission, space is limited, and you will need long needle nose pliers and lots of patience.
CJ797:
Sorry man, but I have no idea where the speed sensor is located on 2 wheel drive transmissions. I suspect it is no different than the one on the 4x4s, only installed in a different location. Pulling it out of the transmission should take no more than 3-5 minutes.

 

I thought the the newer "150"'s with the computer did not need the mess of a gear driven speedo. Dosen't a program modification to the computer solve the problem of bigger tires? Does that mean we can slow down the odometer also?

 

On 97-98's, they have the actual gear still. Newer ones are computer controlled.

With the stock speedo gear and taller tires, yes, your speedo and odometer run "slower", so you are putting less miles on the actual meter. But your speedo shows slower too. Personnally, I hated it because it actually made you think you were going 60, when you were really going 64. The mind will do strange things to you. I think the computer gets fooled too, and thinks you are going slower then you really are, so whatever all it adjusts, will adjust for the slower speed. Just my own theory...... No proof at all.

 

I would also like to know how to do the speed gear change,but i also have a 5spd and want to know if there is any difference in transmissions.


Tanman

 

Thanks everyone for the great advice. I am going to swap in the new gear in the next couple of weeks.

 

tanman,
Looking at my Haynes manual for 97-98 model F150s, there is a picture of your speed sensor on page 7A-3 (manual transmission chapter). It looks identical to the one I removed from mine. The tan gear is slightly different than the black one, but it should fit just fine.