1985 C30 Crew Cab 6.2L Diesel, 3speed granny gear with 411 rear

[Fatmanz85]

Question.....my truck has the 6.2L diesel, 3 speed granny transmission and 411 rear...... it seems to do well at 60 to 65 mph but today had to get her up to near 80 to get away from a bad situation........ surprised to feel it smooth out and continue to pull past 80mph. I was told how "slow" these engines were and to keep it between 55 and 60 mph when I got it.... my question is what is a good safe rpm/mph range to run it? Will it run 70 on the interstate pulling a load without destroying or hurting the engine? I want to take care of it but still work it.....just dont know how much it'll take before it is damaged..........

 

[Fatmanz85]

Is this a dumb question? Been a gas engine person for 45 years, if you dont know .... ask Right?

Nevermind...........................

[fitz]

Id say 70 mph is pushing it a little hard.
My M1028 has a 6.2, turbo 400/208, and 4.56 gears.
The sweet spot on mine is 53 mph. I don't have a tach, but I've talked to other owners with the same truck and they agreed.
Mine will go faster, but it don't like it.
Someday I might get a Gearvendors overdrive for it.

[FlatBlack77]

how many rpms is it at when doing 70mph? or however fast you are wondering about

[Fatmanz85]

I dont have a Tach but Iwith the 411 gears she seems most comfortable at between 60 and 65...... I have a Tach ordered, hopefully it will be here in the next few dats and I will have a better guide for our first camper pull. My 5th wheel weighs in at 11,000 loaded, I've pulled  it to the local State park and did very well, in two weeks I'll be putting it on the interstate and wanted to find out about how hard to push it. Thanks for the insight.

[Irish_Alley]

i know its old but i want to chime in. fitz would be turning 2700 rpms or so at 53. fat man for you to turn the same rpms you would be about 60 mph. but from what i understand the 6.2 can go 80 with no problems. but i just took my 91 v3500 with a 350 4l80e up to 75+ with the rpms didnt seam to bad with od but it didnt feel the smoothest. think my 79 with 38s rides smoother at those speeds lol. fitz i would stay away from gearvenders not because they have a bad rep but a 4l80e would be much better since you would have to replace both drive shafts anyway. you prob are looking at 800-1k for the trans and stand alone if you find one out of a 91-93 diesel (you can use that tcu for yours)

[roundhouse]

Crying out for a 5 speed OD
It's a easy swap in a 2WD