What size gear do I need to recalibrate my speedo? I changed from the stock 235/70/26 to 265/75/16 tires. Also, would I be correct in assuming that gears for a 1998 mustang would also fit my 98 F-150? I have the 4R70W. Thanks.

 

Well, that depends. If the Mustang has an 8.8 inch rearend and so does the truck, then they will fit. As for the gears, I don't know what size you'll need, but we'll find out before long.

 

If you do the math, roughly a 3.90 gear would get you back to stock (assuming you ment 235/70/16!). Don't know of the availability of that ring and pinion, though. 4.10s would be easy to find, however . . .

 

I think he means what VSS gear he needs. In mine, the stock gear was a 20 tooth one. I put in a 19 tooth gear to get my speedo and odo back in sync. I did the same tire swap on mine. The only thing is I have the E4od trans (early version of the 4r100).

If you do mean a rear end gear change, then that will cost a bit more and I don't think the mustangs use a 8.8 rear end.

 

Boy, don't I feel like an idiot now . . .

 

Yeah, I meant the VSS gear. BTW, how hard is it to replace the gear? I'd rather do it myself than have to pay somebody to do it. Also, where did you get your gear from? Thanks.

 

Took me about 5 minutes to swap it out. I got the gear from the Ford parts counter for around $12.00. Sorry, I don't have the part number, but it was tan in color......

You'll want to clean the area around the VSS so no dirt gets inside. Just remove the single nut and pull it out. It has an "O" ring on it, so be careful. Mine had a "C" clip holding the gear on, so pulled that off and the gear came off the shaft. Put the new one on and replaced the clip and put it back in.

That was almost three years and about 55,000 miles ago too!

 

Hmm.....that sound about like the gear I'd need. I went from 255/70/16s to 285/75/16s. I did the calculations and doing the tire swap you guys did gives a 5.11 speedo inconsistancy. Doing the swap I did gives a 5.08 difference. Mitch, or anyone else you know if that sounds about right? If so then going to 1 less tooth than I have now should make the speedo read right........I think. I know when I pulled my speedo gear before it was red but I never bothered to check the gear count. I don't feel like crawling under the truck right now due to the snow we're getting right now. I also seem to recall that Ford color codes the gears so only 1 tooth count is red, tan, etc.

 

Hey Powerstroke,

If you still have the stock VSS gear in place, no offense, but that thing must shift like crap........ Mine did with the 265's that are only 31" tall and your 285's are pretty close to 33" tall....

I don't know the exact percentage mine was off, but I figured it to be pretty close to 5%. Basically for every 20 mile posts I went by, my odo would show I should have only gone past 19 of them.

It's been awhile, and I don't recall the exact numbers, but after I went to the 19 tooth gear, I can go past a whole bunch of mile posts before it'll be off by only .1 of a mile. So, I'm still going faster then my speedo shows, but I don't think it's any more then 1 mph.

IMO, If you go to the 19 tooth gear, you'll be closer, but still off by a bit I'd think. An 18 tooth gear would then put you just over. Maybe if you had 3.73 gears and used the 19 tooth gear, that would be just about right?? I figure if I had the 3.73's, I would have to put my 20 tooth back in..... But don't feel like spending a grand for such a small gear change.

Good luck!

 

Shoulda ridden in it with the 315s on it. Its been so long since I've had the stock tires on it that I've pretty much forgotten how it used to shift (went to 265/75/16s in 2000 I think, it was in the middle of the Wilderness AT recalls). The stock gear is still in there.


I only increased tire size by .03" more than you did with your swap so by going down 1 tooth on my gear should give me the same results as you.

235/70/16 = 28.95"
265/75/16 = 31.65"
Difference = 2.7"

255/70/16 = 30.1"
285/75/16 = 32.83"
Difference = 2.73"

Now I realize all this doesn't take gears into effect. I have not been able to find a calc online that takes that into effect. Its cheap enough that I'll probably see if I can get a gear tomorrow. Hopefully I'll have either 4.10 or 4.56 gears in this thing before too long. Right now with 4.6L 285s 3.55 gears pulling an 18' trailer with a Ranger on it flat out SUCKS!!! So you're saying you've got less than 1mph variability now Mitch?

 

Yep. I don't know "exactly" what the difference is, but it's pretty darn close. Close enough for me anyway.

I can lock it in cruise at what shows as 60mph on my speedo and it will click off one mile for every one minute for quite awhile before it will show .1 difference (slower). Same deal with counting the mile post markers. I'll pass a mile post just as the one minute is up until it gets too boring to do and still be within a .1 of a mile....

Shifting is much better (stock). While my truck came with the 235/70/16's, the door jamb lists the size as 255/70/16. I did swap the 235's for some 255's and I could not tell a difference. I didn't do any mile post checks either. It was only when I went to the 265's that it really changed noticably.

I can tow my #4500 travel trailer all day up and down hills in third gear and only be pulling around 2300 rpms. Rarely does it even need to downshift on a hill either. Sure, on a 6% grade, it'll downshift and I just go 50 mph only because I don't want to rev the motor as high as it would take in second to maintain 60 mph.... Which it would do.....

 

I stopped at the larger of the local dealers today to try and find that gear. They don't carry any on hand so I'll have to make my drive tomorrow without it. I was hoping to try and get it in before I leave tomorrow morning to help with shifting during towing. I'll probably have to try and see if I can find one at the really big dealers in Cedar Rapids.

 

Don't go to a "really big dealer" just because they're big.

Find out who the "really big" SVT dealer is and go there. They swap these things all the times for Mustangs and usually have them in a box under the counter.

In St Louis, that would be Sunset Ford.

Steve

 

The reason I said a "really big dealer" is because out here in the sticks its mainly small dealerships that don't usually deal with these kinds of parts on a daily basis so they don't have them on hand. A larger dealership in a city like Cedar Rapids is more likely to have these parts on hand since they would do a larger variety and frequency of these kinds of repairs. Closest SVT dealer would be Willey Ford in Ames which I won't be going anywhere near today. Guess I'm gonna have to settle for my "really big dealer"