[phantom 309]

i just bought a 94 crew cab 6.5l diesel dually 2wd, it has a 14 bolt corporate rear end i think,. it's geared slow,. rpm is 2600 at 65mph, with 215-85-16 tires, which is a better way to go?,. 19.5 tires and rims? or change gear ratio's,?? i think these gears are either 4.56 or 4.88's and i,d like 3.73's,
When this gets accomplished, how do i change the speedo to register right? truck is a 4l80e auto.
i did try searching for this info,. but maybe i,m using the wrong key words,.
thanks
nick

 

[FastCR]

Are you sure your getting to overdrive? I'm not sure, but it's probably got 4.11s.

 

[woodchuck2]

I beleive FASTCR is correct on the 4.11's, most 14 bolt's came with that gear unless it is military and then they came with 4.56's and a detroit locker. The only other time that i have found a 14 bolt with 4.56's was in a 74 3/4 ton with the 250 ci. straight six and sm 465 4 speed.

 

[phantom 309]

Thanks for your replys ,. i have slowly shifted the trans up thru the gears and i swear i,m getting all four gears plus lock up,. is there a 'for sure' way to tell? i do notice that there is no engine braking , when i lift off it seems the engine goes to an idle,.but it also goes right back to gear with a little throttle,. can you point me in the direction of what i should be checking?
thanks
nick

 

[Heartbeat Hauler]

I had a '94 crew cab dually with the 7.4L gasser and the tires on it were 235/85/16s this is a taller tire than what you have and could account for the somewhat higher rpms, but 2600 at 65mph is about right for your setup even in OD. In my 94 I was turnbing about 2400 RPM at about 65 mph and I had the 4.10s for sure. I think the taller tires is a good way to help. If you had 4.56 gears your RPMs would be way up there at 65 OD or not.
JP

OnEdit: If you do change gear ratios you can adjust the speedo via a tuner. Oh and you probably won't like the 3.73s when towing with a 6.5 oil burner.