highway speed issues.

Just got my m715 in jan. and is going to be my everyday driver, it has a ford 460/c6 combo in it. and i just got back today from a trip out to the desert to do some off roading.

off road the thing is a wonderful.
getting to the off road some 180 miles from my house was not so wonderful.
top speed of around 50-55 at 3000rpms. and gear oil leaking out of the t-case everywhere.

was curious what the best options are to go about getting much more manageable highway speeds but still have it crawl rocks well.

-over drive unit bolted to the back of the c6 tran.?
-no doubt reading around on the fourm i will have to change the t case?? to a np205 will it be able to handle the highway speeds?
-and should i change the stock axle gears?

alot to think about already and i just bought it...

dan

The NP205 is a great swap.

What you do about getting more speed does depend on how much more speed you are looking for...want to do 60 all day? Or 70? At what kind of RPM?

i would like to cruise on the freeway at 75 doing no more than 2800 rpms. as to keep the gas milage reasonable.

OK...

With stock tires, that means you need:
axle gears of 4.56, which is the lowest numerically the stock axles can take without a carrier change.

AND a .83 overdrive.

This equates to 2806 RPM (approx.) at 75 MPH.


If you go to a true 38 inch tire:
4.56 gears
AND
.93 overdrive
results in 2813 RPM at 75 MPH.

With a spring over and 39.5 in tires:
4.56 gears
AND
.96 overdrive
results in 2794 rpm at 75 mph.

Without changing the axle gears:

With a stock tire:
.65 overdrive
results in 2829 RPM at 75 MPH.

With a true 38 inch tire:
.72 overdrive
results in 2804 RPM at 75 MPH.

With a spring over and 39.5 in tires:
.75 overdrive
results in 2810 rpm at 75 mph.



Then you HAVE to beef up the brakes over stock...at least in my book...stock brakes at 75, especially the single line master, wouldnt cut it.

Handling on these trucks isnt that great either...speed like that would be a little nerve racking in my mind...for a long trip anyway...more than was intended stock...

I think this is a little more than you were looking at, but the vehicle (stock) was really never designed to do what you (and myself) want to do with it.

The drive train is happiest at lower RPMS. Mine screams, leaks, and is generally unrully at higher speeds. There's a lot of reasons for the unrulliness, but it's not happy.

If I were going to try to keep it sort of stock, I would change the gearing on the diffs and swap out the t-case for a 3:1 low. I am not a fan of the NP200. This solution requires a fair amount of work and not an inexpensive route, but I think you will be happier in the long run.

Body swap, if high speed and daily driving is your thing. Even with brake upgrades and gear changes your still working with 40 year old equipment. Find a 97 f350 with the 460 and the auto and bolt your body to it.

I have a similer setup. just got done putting on some 38x13 tsl. i only gained about 7 miles per our. 55 mph is it top speed. I am fine with that. But if you are wanting to go faster than 55 mph you will also have to chang your caster angle to. And put on a brake booster.

mine is not on the road, but i did some calculations for it. it will have 39s 4.56 rear end gears, and a .73 OD. i figured that i could cruise at 75 somewhere around 2100 rpm. i have done all of the other upgrades to make the truck less scary at those speeds. i have d60/14 bolt with disk brakes and power assist and dual circuit master. 2100 rpm is nice for a BBC.

i am not an advocate for the body swap. i sy swap the newer driveline into the 715 if you want to get up to those speeds and make sure all of the equipment is safe for that kind of speed
Ryan

Quote:

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Originally Posted by jeepcj

Body swap, if high speed and daily driving is your thing. Even with brake upgrades and gear changes your still working with 40 year old equipment. Find a 97 f350 with the 460 and the auto and bolt your body to it.

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Do an axle (modern 1-ton GM or Ford) and t-case swap (NP205) and you should be fine.

My truck is quite happy with the cruise set a 75-80mph all day long. In fact, even at an observed top speed of 115mph it was still quite manageable (but not recommended with Michelin XZLs). Fuel economy suffers greatly above 45-50mph due to the flat windshield.

That was with stock 715 body/frame, '85 GM 1-ton axles (D60/10.5"), 4-wheel discs, Saginaw PS w/ rock ram, mild-cammed EFI 460, 4R100 (E4OD) auto-od, Ford NP203/GM NP205 hybrid doubler setup & rear CV driveshaft from High Angle Driveline.

My semi-annual $0.02...

i cant imagine 115 in m-715 how was the pucker factor?

I'll bet the mark on the driver's seat still shows it!

Quote:

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Originally Posted by chadriley5

i cant imagine 115 in m-715 how was the pucker factor?

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Not much drama at all. Like I said it's not something you want to do for any length of time due to the low speed rating of the XZLs but for a quick romp up there and back no worries. I spent many, many hours refining my M715 to drive like any other modern 1-ton pickup, possibly better than some...

I have driven and ridden in Mudog715's truck...it is a well built piece of machinery that moves like the wind if you flatten the gas pedal...amazingly strong...and he has built it higher since I have seen it...that was in 2000...

I just bought a 715. It has a chevy small block v8 in it and an auto tranny from a corvette. I need to do a little research to find out exactly what the hp for the motor is and which tranny it is. I want to change out the gears to get a little better high end speed. Could someone hazard a guess as to what the cost would be to have a garage put in the 4.56 gears vs the 4.10 which seems to be more involved.

Thanks--just trying to get an idea of what I'm up against.

Quote:

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Originally Posted by chadriley5

i cant imagine 115 in m-715 how was the pucker factor?

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try running 100 in a 725 on boggers, scary and all over the road but the emergency required it to get my step daughter to the hospital.

Quote:

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Originally Posted by brute4c

I have driven and ridden in Mudog715's truck...it is a well built piece of machinery that moves like the wind if you flatten the gas pedal...amazingly strong...and he has built it higher since I have seen it...that was in 2000...

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Thanks John for the fine compliments. Hopefully I can make it to a future FE and give you an opportunity to drive the "version 3.3" of The Beast... I'm still waiting for the engine builder to finish my freshly-stroked 460 (now 521) which dumps the "mild" flat-tappet cam for a "moderate" roller cam. I've been distracted by other, non-M715 projects for the last 9 months but I'm anxious to get The Beast back on the road if only because I miss driving it around town and off-road.

Quote:

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Originally Posted by dave

try running 100 in a 725 on boggers, scary and all over the road but the emergency required it to get my step daughter to the hospital.

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A stock 725 is kinda spooky to drive on the highway stock, let alone at 100mph on Boggers. That would be REAL pucker-factor!

Mudog, I would be honored to drive yoursagain...would love even more to spend time with ya!!