speed trouble

[dragonmaster1369]

I have a 86 m1028 /w a 6.2 in it and I cant get it any higher then 45 for a mile or so then it seem like its loosing power I checked all the cylinders and I have great compression in all cylinders. does any body know how I can fix this to be able to drive 65 mph in the truck.

 

[Warthog]

Welcome to SS.

When was the last time you changed the fuel filter?

With the gearing in the truck, the max speed is usually around 55. 65 is pushing it as the engine will be close to the max rpms. Things can start coming apart at max rpms

 

[Speddmon]

What he said ^

Max speed you'll want to go in a 1028 is about 55 to 60 TOPS. Any more and you'll find yourself in search of a new engine rather quickly.

 

[MakersTeleMark]

Change the fuel filter.

 

[scottladdy]

Improve Highway Performance of CUCV Pickups

... does any body know how I can fix this to be able to drive 65 mph in the truck.

Welcome to the MV addiction.

So, aside from what is likely to be a fuel supply issue as Warthog indicated, in order to drive 65 steadily and avoid engine damage you will need to do one or more of the following:

1. Change the gear ratio of the front/rear differentials
2. Install Larger Diameter Tires
3. Install an overdrive like Gear Vendors
4. Install an overdrive transmission

Presented to you in no particular order.

You can use an online gear ratio calculator like http://www.grimmjeeper.com/gears.html to determine what RPM's your engine will be turning at a given speed. For this particular calculator plug in TH400, NP208 (M1028 standard TC), 4.56 as your axle gear ratio and your tire size. You'll note that your engine will be turning around 3300 RPM's at 65 MPH.

 

[wayne pick]

If the engine hunts or surges under load, there may be water in the fuel. When you change the fuel filter, check the old one for water contamination.

 

[chevyCUCV]

Sounds like a problem with fuel supply somewhere

Should be able to hit 70 easily if you hold your foot down.

 

[patracy]

Sounds like a problem with fuel supply somewhere

Should be able to hit 70 easily if you hold your foot down.

70mph in a stock M1008/1010/1028/1031 = 3650+ rpm.

Easy? Maybe. Bad? Certainly.

 

[2HIJOS2126]

Welcome to the site... I also have a M1028 with slightly larger than stock tires... I cruise at 55-60mph at around 2700-2850rpm... I can hit 65-70mph but I dont run my truck over 3000rpm very often... I would recommend getting used to being passed on the highway...

 

[wayne pick]

dragonmaster1369, Running these old trucks at more than 60 mph without modification is asking for trouble. To achive highway speeds, adding taller tires, an overdrive trans, or changing the axle ratio is the only way to get to get the engine RPM's low enough to avoid damage.

The 4.56 gear ratio limits these trucks to a slow top speed. No one, repeat, no one in the civilian world in their right mind went down to their local GM dealership and ordered a K30 with the 6.2 diesel and a 4.56 axle ratio unless they had a specific application for it. If you plan on running your truck at a consistant high RPM, replace the harmonic balancer and avoid scattering your crankshaft and other related parts all over the highway.