New User with Truck(Speed Help)

[TheMountainCalls]

New M1008

Hi guys I'm brand new to these forums and I have just bought a 1986 M1008. Its also my first vehicle I've ever owned. I just wanted a great basic platform to improve and work on. It was a Coast Guard truck at Whidbey Island Naval Base until the early 90s and and until 2006 worked for the forest service for S&R according to the guy I bought it from and then he used it as a farm truck(Barely, only put about 2k on the truck in 10 yrs).

I know the truck's top safe speed is 55 mph and thats what I drove it at. But my head was vibrating for a couple hours afterward. I want to use this truck as a light to mid offroad rig and that means that I need to go through I90 fairly regularly(And 55 through I90 is pretty sketchy).
Now here's my question:
I want this thing to do 60-65 at around 2400 rpm. Whats my best option?
I was thinking 4.10 gears and 33" tires(I dont want a monster truck i.e. tires >35"). Will this work and will I be able to keep the rear detroit?

Thanks in advance

Edit: Also any advice is welcome. I probably need it.

Photos
http://imgur.com/PCAbbp2
http://imgur.com/dqLuIBH
http://imgur.com/tdkjnFv

 

[TheMountainCalls]

Photos
http://imgur.com/PCAbbp2
http://imgur.com/dqLuIBH
http://imgur.com/tdkjnFv

 

[TheMountainCalls]

Hi guys I'm brand new to these forums and I have just bought a 1986 M1008. Its also my first vehicle I've ever owned. I just wanted a great basic platform to improve and work on. It was a Coast Guard truck at Whidbey Island Naval Base until the early 90s and and until 2006 worked for the forest service for S&R according to the guy I bought it from and then he used it as a farm truck(Barely, only put about 2k on the truck in 10 yrs).

I know the truck's top safe speed is 55 mph and thats what I drove it at. But my head was vibrating for a couple hours afterward. I want to use this truck as a light to mid offroad rig and that means that I need to go through I90 fairly regularly(And 55 through I90 is pretty sketchy).
Now here's my question:
I want this thing to do 60-65 at around 2400 rpm. Whats my best option?
I was thinking 4.10 gears and 33" tires(I dont want a monster truck i.e. tires >35"). Will this work and will I be able to keep the rear detroit?

Thanks in advance
Edit: Also any advice is welcome. I probably need it.

Photos

 

[cucvrus]

OK. It will go 65-70 with no problem. I go 75-80 at times. That top speed 55 is a myth. I drive an M1008/M1028 in stock form daily. I drive on I78 and I81. I have been on I95 around the beltway in DC. I never have any problems with driving at highway speeds. I keep my vehicles serviced/maintained.I have stock LT23585R16 tires. I am not sure how this top speed 55 started but it is not true. Some trucks I have/had stenciled top sped 50 on the glove box. WOW. I would be driven over on the interstate at that speed. I have been driving these CUCV trucks for over 30 years. I have privately owned more at least 1 for 22 years. Never blew 1 up yet. Never. Biggest maintenance issue I ever had was a head gasket that corroded thru. And that was just that an easy fix. I resolved starter issues by keeping them tight,fresh batteries and the support tight and in place. Fresh batteries are one of the most important things and keeping the glow plugs operational. If you have poor batteries and a mediocre glow plug system. You are asking for electrical issues. Keep in mind this is a 30 year old vehicle. It has well passed the life expectancy that it was built and designed for. From this point you must care and maintain it. But save your money and get out there and drive it as fast as you are comfortable. But if you feel 70 is tops that is fine. I push mine day in day out. I check my oil every day. Every day. Add very little between service intervals of 2500 miles. Have a great day.

 

[blueblaze]

I'd say the absolute cheapest way to get the revs down is to up your tire size. I wouldn't regear. The differential carriers split after 4.10s. So you would be stuck buying a used or new set of carriers and you would lose your rear Detroit unless you bought another one. I've done a 700R4 swap in these trucks. Probably the next easiest step since a diesel parts truck would harbor all the parts in one shot. Or you could possibly do a 5 speed manual swap with a NV4500 from the later style GM trucks, 92 and up. But then your stuck finding hydro pedals from an 85-87 truck and converting over to manual. Which can be done. I've done all these swaps with great success. Although I favor the 5 speed swap more for obvious reasons. Most people don't want to push revs on these trucks. advertised redline is 3600 RPM. With the stock 235's, at 65 mph that's over 3100 RPM. Do you really want to run that close to 3600 RPM? ANY 6.2 diesel engine in these trucks will last longer with lower revs. That's basic mechanics. I've also run them at speeds up to 65 mph a few times, and when I did it, always made me cringe even not seeing a tach. That's too far for any V8 IDI diesel in my opinion.

 

[GunnyM1009]

If the truck is vibrating pretty bad at 55 I doubt it is because of the gearing. It could have bad tires that have flat spots on them or warped wheels. As far as gearing and tires go I have a M1009 which comes stock with 3.08 gearing. I run 33x12.50r15 all terrains and it will do 80 pretty comfortably and still has adequate off road capabilities. That being said your rig should do 65 with no problems as long as it is well maintained. Keep in mind that as far as suspension, axle, and trans servicing goes everyone that has owned your truck prior to you have more than likely been the if it aint broke dont fix it type. Plan to put a little time money and some reading in on these forums and it will help you in the long run.

 

[Recovry4x4]

100% stock truck turn 2806 RPM @ 55 mph. Going with 4.10 gears and 33" tires nets you 64 mph for the same RPM. The same 2806 RPM with only using a 700R4 nets you 83 MPH. Cruising at 70 MPH with a 700R4 has you at an ideal 2366 RPM.

 

[patracy]

100% stock truck turn 2806 RPM @ 55 mph. Going with 4.10 gears and 33" tires nets you 64 mph for the same RPM. The same 2806 RPM with only using a 700R4 nets you 83 MPH. Cruising at 70 MPH with a 700R4 has you at an ideal 2366 RPM.

This.

 

[cucvrus]

Vibrations can be drive shafts with dents and bad u-joints. Old tires cause vibrations. I have new tires every 20 K and like I said. I have run a M1028A1 170K + on the same truck and sold the truck to another man and he loves and drives the truck on a daily basis. He just told me it gets better fuel mileage then his 2013 Chevrolet Silverado 35500 4 X 4 dually. That is fine you can run yours as you see fit. I am just telling you it is a myth that they fly apart at speeds above 65. Never done it here and I drove them well over one million miles. Counting the M1009's I am probably over that in mileage. I drive an M1008 daily and M1009 several times a week. Maintenance maintenance maintenance. Neglect them and they will fail. They like to be greased and the fluids kept topped off. I gotta run. I have an M1008 idling and a trip to go on. Have a great day.

 

[GunnyM1009]

100% stock truck turn 2806 RPM @ 55 mph. Going with 4.10 gears and 33" tires nets you 64 mph for the same RPM. The same 2806 RPM with only using a 700R4 nets you 83 MPH. Cruising at 70 MPH with a 700R4 has you at an ideal 2366 RPM.

What is the formula you are using to figure this out. I would like to figure out what Gunny is pushing at 70 running the 3.08 and 33's

 

[patracy]

What is the formula you are using to figure this out. I would like to figure out what Gunny is pushing at 70 running the 3.08 and 33's

Great resource:
http://www.grimmjeeper.com/gears.html

About 2319 rpm.

 

[TheMountainCalls]

Thanks for all the help
I think Ill go with 35" tires and a 2"?(That will fit right?) lift to draw out the gears, the Detroit is worth more to me than speed. (Just to start, more will come)

To clarify the truck isn't vibrating anymore than a 30 yr old truck with 5 yr old tires should be. Its just the engine howling at hwy speeds.

 

[Recovry4x4]

The grimmjeeper site is the one I use exclusively. It's nice to be able to run 2 and compare them side by side.

35" tires with 2" of lift is doable but will require sawzall work.

 

[TheMountainCalls]

Two more noob question:
How much effect does hp/torque have on rpm with stock trans/alxe ratios?
Also what do you think the minimum lift would be to fit 35" tires for moderate offroad and minimal to no trimming?

 

[Gralmk]

I am not sure how this top speed 55 started but it is not true.

It all started back in the first gas embargo! Military put out orders that said everyone will not go over 55mph! Lasted a few years so units with painting it everywhere, like that helped! In the Army, that order has never been rescinded! Very few of the modern fleet will not go over 55, in fact a lot will do 75 easy!

 

[Recovry4x4]

Lift questions. Even with 4" of lift and no offroading, expect tire contact. A little nip and you should be OK. Rim width and backspacing plays a roll as well so think about that before you buy rims. Consider this! The 6.2 is anemic in the power Dept. It needs 4.56 gears to do any substantial work. The TH400 is stupid strong but sucks power that the 6.2 can't afford to give. Combine that with 4.10 gears and 35" tires and you just killed your out of the hole power and acceleration. Off memory the 400 has a 2.48 low gear. Compare that with the 3.06 low of the 700R4 and it actually increases seat of the pants acceleration and gives OD to boot. In my all but meaningful opinion, the 700R4 is the ideal trans for the 6.2/ 4.56 combination.

 

[GunnyM1009]

Lift questions. Even with 4" of lift and no offroading, expect tire contact. A little nip and you should be OK. Rim width and backspacing plays a roll as well so think about that before you buy rims. Consider this! The 6.2 is anemic in the power Dept. It needs 4.56 gears to do any substantial work. The TH400 is stupid strong but sucks power that the 6.2 can't afford to give. Combine that with 4.10 gears and 35" tires and you just killed your out of the hole power and acceleration. Off memory the 400 has a 2.48 low gear. Compare that with the 3.06 low of the 700R4 and it actually increases seat of the pants acceleration and gives OD to boot. In my all but meaningful opinion, the 700R4 is the ideal trans for the 6.2/ 4.56 combination.

I agree. I am planning on getting a M1008 down the road and the 700r4 is what I plan on doing. Its the easiest way to accomplish the goal in my opinion.

 

[TheMountainCalls]

Ok I see what you guys are saying. Ive already scrapped the idea of the 4.10 gears because it kills my power and causes me to lose my locker. Currently I cant afford a 700r4 or more hp so Im looking for potential work arounds with tires and anything else I can think of.

 

[GunnyM1009]

Just my opinion but by the time you buy a 4-6in lift kit and 35's plus the possible necessity for different wheels and you come out spending more than it would cost to get a junk yard 700r4 and have it rebuilt.

 

[TheMountainCalls]

Yeah I just crunched some numbers and you guys are right...
Looks like Im getting a new transmission... in a few months...