I have a stock rearend with 3.92 gears in my 55 truck. I need to reduce highway rpms and was thinking the gearing may be the least expensive start. Can anyone tell me what gearing I should look for and where? Is there a site that sells them for my truck, or are there other axles that will bolt onto my truck? any help is appreciated. Its a 239 with a three on the tree. Thanks, Steve

55 F100  Summerville, SC

Steve, I have a 239 with a 3.92 rear. Are you driving faster than 65mph?



This winter I'm changing the 3.92 to a 4.27. Saturday I went out with the GPS and recorded rpm's at various speeds so I can compare them when the 4.27 is in. At 65 mph I'm turning 3000 , 55 mph 2400. When racing, at the finish line, I'm turning 3800 at about 73 mph.



3000 at 65 mph isn't bad.

  Dennis in Lititz PA

Thanks Dennis, I don't typically drive faster than 65 (had it to 82 twice though) but when I am on the interstate it stinks getting passed up by everyone. Also, with my truck being so close to original (no interior insulation) and the fact that I cannot get the driver's side door to stay closed all the way, at 65 it sounds like I'm pushing 100. I would imagine that I must be turning near the same rpms as you are with having the same set-up. any reason why you are going that direction with the gears and not the other way? I am getting closer to driving it on a daily basis and was looking at lowering the rpms to ease up on the engine a little.

55 F100  Summerville, SC

Steve:

Have you thought about putting a taller tire on the back, that will lower your rpm some.  Also, road noise and wind noise from a door that isn't closed tightly will not change when you change gears, only engine sounds will change.

John - "The Hoosier Hurricane"

An overdrive transmisson would solve your problem without really changing originality.

-Gary Burnette-

I have considered the overdrive/T-5 route and may need to go that way if the gearing change doesn't give me enough relief. I found a website from another post on the forum and they carry a set of 3:08's for my truck. My wife said Santa will bring it for me if that's what I want. I am really new to a lot of this and I certainly appreciate all of y'all advise. Is there a noticable difference in 3:08's from 3:92's? As far as the door noise goes, that striker plate just will not stay adjusted right. Even with a new plate and screws it still works loose.

55 F100  Summerville, SC

It will be noticeable. That change will shift your RPM down by about 750rpm at cruise speed. Make sure you don't want to haul anything if you go that route.


Lawrenceville, GA

Steve- I had the same problem with my stricker plate moving no matter how tight I was able to get it. How I finally fixed the problem was putting o rings over the bolts between the plate and the body. Never had another problem with movement. Cheap fix!

Ol'ford nutCentral Iowa

56 Vic w/292 & 4 spd.

Steve, I'm doing it for racing and parades. I have the borg warner R10 overdrive so going the other way doesn't hurt. With the 3.92 and overdrive it gives me about a 2.43 rear. With the 4.27, I'll be at 3.00. If you can go the overdrive route, that would be the best.

  Dennis in Lititz PA

Are overdrives plentiful out there or will I be hunting for awhile? I checked the classified in this forum for R10 and didn't see any for sale. I only mentioned the T5 earlier because I've read so much about them on this site. I'm trying not to repeat too many questions that others have asked but usually when I see something close to what I need to know, it's usually referring to a car instead of a truck. I like the idea of the 3:08's lowering the rpms but I do not want to give up the ability to pull/haul with my truck.

55 F100  Summerville, SC