I just had carrier and pinion bearings replaced and while the rear end was apart, I had 4.10 gears put in to replace my stock 3.55's.

After getting the truck back I just drove it to work one time. Either traffic was moving at 75 - 80 mph or the gear change affected my speedometer. Can anyone tell me if changing the rear end gearing affects the speedometer? This is on a '98 F-150 with 4.6 engine.


Thanks.

 

Yes gear changes affect the speedo. If you still have the same sized tires that you did before the swap going to deeper gears makes your speedo read faster than normal. To fix it you will need to replace the VSS gear on the tailshaft of either the transmission or transfer case (4x2 or 4x4). You can't use a micro tuner to fix this on a 97/98 since they used the VSS gear and aren't computer controlled.

 

PS 73

Thanks for the info and the fix. I was having a hard time believing that traffic that normally moves at speed limit +10 was moving at speed limit +20 mph.


ENB

 

3.55s to 4.10s made my 2000 truck's speedo +10 mph.

 

PS (or any other smart folks):

I went ahead and pulled the VSS vehicle speed sensor from the tail housing of the tranny and counted the gear teeth. I also noted that the gear was red. Now I checked my speed and with the combination of gear change and tire change my speedo is reading 13.3% too fast. So, I went down to the big local Ford dealer ( they do everything from cars to trucks to medium duty to class 8 trucks. Anyway the parts folks said that there was no gear with more than 21 teeth. I then bounced around and talked to all of their 'experts'. The bottom line from them was: bring your truck in and we'll figure something out. Well, I'm NOT going to drop my truck off and let them run up 2-3 hours at $60/hour to figure out what I already now. They of course talked about reflashing the pcm. I told them that was the fix for the '99s and newer.

My question is then do I need to find some aftermarket company that has this gear or is there different teeth available on the gear that slips on the tail shaft? There has to be a fix as I know 4.10 ratio gears were an option on my '98 2wd. Any info here will be greatly appreciated.

I'll have to say that I really like that extra torque multiplication from those 4.10s. My truck is running lean right now and I'm really waiting to see what this thing can do once my new tuning chip arrives and I can finally get into the throttle.

Thanks for the help.


ENB

 

Peddler1000;

If you go to a speed shop, you will be able to find an aftermarket 23 tooth gear that will fit your VSS. It does however wear out quicker than the standard gears. It is not made poorly but because the gear teeth are packed more tightly onto the same pitch diameter gear, the teeth have to get thinner to work. Give it a try though, I think that it will work OK. GlennMc.

 

Glenn

Thanks for the help. This F-150 site is great - so many people with so much info.

ENB

 

You say your truck is running lean.....what makes you think that??
Did it throw a code maybe??

 

I have a question about a gear change and speedo as well. I tried learning some from the above threads but Im a little slow when it comes to this stuff. if I change to a 4.56 from a stock 3.55 (I have 315/75/16) will the gear change alone bring my speedo back to stock along with power and gas, etc?

Thanks for helping!

 

depends on your stock tire size. If you had the common 235/75/16's stock then the 4.56's with 315/75/16's i believe would be the equivelent of 3.73's stock. it would take 4.30's to make it real close to stock which is not possible with the 8.8 ifs. Here is a calculator page that can help you with such quesions. http://www.drivetrainsuperstores.com/calculate.asp