Two speed rear ends.

180 gears, wow, you could start in NY and finally hit 180 in LA. Wouldn't be a boring ride.

 

You would have loved the Truck I drove for 3 Years then in the 90's 4X4 plus a set of 3 Speed Eatons. Truck was a 71 Transtar with a 290 Small cam that the boss used for Local work in IL trouble was he Considered Local in IL Chicago to Cairo IL. I ran all over the freaking state of IL hauling Feed Grain hell anything he could Plus Nursery Stock. Harvest was when thopse 3 Speed Eatons got a Work out. Low side on them plus 2nd and 1 I could crawl right along with the Combine at idle as it loaded me in the Field. Load me up and Off to the elevator I went.

The day I filled the Trailer all the way to the top and we had 8 foot sided Trailers with beans was FUN Never got above 3x1 middle in the rears on the road that trip. But at well over 135K what do you expect.

 

Those rear ends can be updated with lower gear ratios to increase fuel mileage. I accomplished this by having my machine shop retool(made the center induction shaft from billet alluminum, replacing the stock one....$1200 for milling alluminum) the gear ratio. Replaced the 6.85 low with the 3.55 that was on the high side. Found a 3.23 gear match out of an old White GMC cabover...installed in the place if the 3.55 position mentioned above. I know this sounds like alot of extra work, but with patience and the right drivetrain and machine shops...it is worth it. My 2009 387 Pete went from low to mid 6's to lower 9's high 8's (mpg). The addition of Airtabs to the rear sides and top of my cab raised those numbers up to almost 9.6(9.58 mpg). The lower gear ratio that was added is only for 14th/overdrive(13 spd Eaton Fuller + second differential gear). I have used it for other gears, but the mesh difference is too low for a smooth transition in low rpm situations(must be above 1600-1675 rpm before using the overdrive...rpms drop to just above 1175 @ 75 mph. If in hilly terrain..i dont even use it....but on flat ground...mpg is awesome! Hope this helps.

 

Speedometers don't like them.

 

Check out my solution on the 2nd page

 

Huh?...speedometer has nothing to do with rear ratio....my setup above....no change in speedometer/speed ratio....the speedometer runs off of the sensor in the transmission.....not one change in my speedometer(verified with gps vs speedometer)

 

I'm just going by my personal experience with the 3 Ford F700 tractors I drove at Pepsi. They were 1987 and two 1991's. The 1987 read right on the high side but the two 1991's read 20 mph off when on the high side.

 

You have to add on the air line for the actuator on the shifter which requires an 13/18 spd shifter control conversion..it allows for extra actuator selector switch for differential control. There is also an auto overdrive switch that does this autimatically above a certain rpm if transmission is in hi side(any gear, but that setup is expensive. The older ford F450's had an electric servo motor that was operated from a high side pressure switch, but that wont work on air operated brake systems because that switch worked off of hydraulic pressure from automatic transmission fluid. If you want to consider my setup, let me know. I can get you the info.

 

I could understand if the speedo gear/sensor was on the tailshaft...but if you had an aftermarket/pre '98 model truck...they were not BCM controlled....so to say all truck speedometers dont like this setup...especially when those year model trucks('91) are very rarely even seen on the road working anymore.....unless some mongrel was showing the truck(which would never have this setup anyway)...then your entire statement is based on a mechanical fluke or bad karma experience(tgat could have been easily solved with an aftermarket speed sensor kit from dana, spicer, rockwell, or eaton...which all mount inside the differential on a two wire insert with a magnetic pickup and ring gear insert. Now that this 33 year veteran diesel/gas/two\four stroke/encyclic/gear reduction/transmission building/overhaul tecnical specialist MECHANIC(not a parts replacer idiot you see @the dealers/truck stop wannabees) and 18 year Ol Skool trucker has taken time to redoubt your query....I CALL UTTER AND TOTAL ######## ON YOUR THEORY/STORY/COMMENT. Not that im trying to be a total azzhat...but if your gonna make assumptions...keep them @ the last/next truckstop dinner table/drivers room where everyone has to roll up their pant legs! Good day to you.

 

Sorry, I'm completely out of ####s to give tonight so I won't be able to give one to you for that long winded reply. Thank you come again.