Help me plan - better highway capability

[Finnegan1008]

I would like to drive my m1008 over 55mph on the highway and am weighing out pros and cons of various options. I want to keep the truck as true to form and original as possible with the exception of some aggressive off-road tires (in the 32” range) and highway gearing.

The truck will remain stock otherwise. Please weigh in your opinions and experiences with the below options. (Or any others Ive missed)

re gearing the axles:
Pros - truck remains completely stock and I can keep the stout (and perfectly good) TH400
Cons - re gearing means new carriers which is pricey.

Questions- Would I be giving up some low end grunt with the setup?

700r4:
Pros- cheap and somewhat straight forward, stock drive shafts, stock mounting hardware, same dimensions as the TH400 ect

Cons - durability especially when towing and TV cable mounting is not and exact science and can lead to catastrophic failure

Question- is the durability concern blown out of proportion? Can these be built to be really stout?

4L80e:
Pros - stronger than the 700r4
Cons- expensive, not the same size as the TH400 so drive shaft mods needed, linkage won’t bolt up, shift Column needs replacing or modifying. Needs a computer

NV4500:
Pros- manual transmissions are awesome, gearing is great for this platform. Same dimensions as the TH400 (I think?). It’s a strong setup

Cons- expensive, lots of junk yard searching, pedal setup is hard to find, changes the concept of the truck.

gear vendors OD:
Pros: bullet proof, simple, and keeps the truck basically stock
Cons: pricey

Again please school me on my logic here, trying to figure out the right option.

 

[adf5565]

I went with a "Level 2" 700r4 built by Bowtie Overdrives. It has only been a year but no issues so far, and it is rated for 450 hp/tq which unless you're doing serious motor upgrades is plenty strong for the 6.2. I can cruise on the highway with ease. Check out my build thread starting on post 41. It is relatively easy to install and Bowtie will provide you with just about everything to swap the 700r4 in.

CUCV M1008 Build

Over the weekend I pulled the oil pan and replaced that gasket. Not a difficult task but by the end I was a little sick of laying on the ground 😂 Hopefully that’s good for many years now. Also tonight I pulled out the transmission. The 4 of the 6 bolts fastening it to the engine were oddly...

steelsoldiers.com

With regards to the TV cable, i outline that in the thread and it is easier than you think. The steps are included with the trans purchase and involves pressure testing to confirm it is set up correctly. The rare 6.2 specific tv cable rod/bracket is helpful but in my opinion not required, you could use/adapt a generic tv cable bracket found all over the internet and connect the tv cable directly to the IP instead.

2INSANE also outlined a step by step install guide which matches very similarly what I did so you know what you're getting yourself into.

The One Stop 700R4 Swap M1009

Overview Please give many thanks to the 10+ SS members for giving me the motivation to create this thread. Chuckg, 4sdair, forest522, computer54, dezertdemond, Dsilverline, Chevymike, ssdvc, TheMod, Mullaney, royalflush55, 1love, Sharecropper… By popular demand! This is a REAL M1009 1984...

www.steelsoldiers.com

Many threads are here on 4L80E installs which is a good option as well. In my opinion a trans with 4th gear is a better choice than just changing the gearing.

 

[Finnegan1008]

Thanks for the input! Just edited my original post my truck is a M1008 with stock 4.56 axle gearing

 

[Finnegan1008]

Ok new thought…

a built 700r4 from a reputable company is about $2500 when you include the core charge. I would also need a new torque converter.

the price is now creeping towed gear vendors pricing. Granted the GV would require a shortened drive shaft. But this makes the choice less obvious. That GV unit can handle a good amount of work.

Only downside to the GV OD is no lockup.

 

[nyoffroad]

I did a 700R4 and never looked back! What's not to like better MPG, lower first gear, lock up converter and cheap.
I took a core tranny to a local shop and paid CASH and had it totally rebuilt and upgraded for about $1000. (was a few years ago) but the cash was the money saver. At that time truck had 32" tires and would cruise 70MPH with stock 4:56 gears.

 

[87cr250r]

The M1008 will cruise at 65 on 33 inch tires but it's really loud.

The early civi trucks had a muffler on the air intake and an exhaust crossover in the intake manifold. These both help mitigation noise. Consider adding a crossover or H pipe in your existing stock exhaust pipes to make the truck more tolerable at freeway speeds.

 

[Finnegan1008]

The M1008 will cruise at 65 on 33 inch tires but it's really loud.

The early civi trucks had a muffler on the air intake and an exhaust crossover in the intake manifold. These both help mitigation noise. Consider adding a crossover or H pipe in your existing stock exhaust pipes to make the truck more tolerable at freeway speeds.

Thanks for the tip, an H pipe wouldn’t be a bad mod and may even gain a little power.
I really mostly am concerned with achieving a lower highway RPM while keeping up with traffic.

 

[87cr250r]

I took a little more extreme of a route. I put 37 inch tires on and that solved the speed problem but it was still loud as heck. I'm in the process of turbocharging it as that works as both an exhaust crossover and intake muffler. I can't report on results yet.

 

[Valor]

I went with a "Level 2" 700r4 built by Bowtie Overdrives. It has only been a year but no issues so far, and it is rated for 450 hp/tq which unless you're doing serious motor upgrades is plenty strong for the 6.2. I can cruise on the highway with ease. Check out my build thread starting on post 41. It is relatively easy to install and Bowtie will provide you with just about everything to swap the 700r4 in.

CUCV M1008 Build

Over the weekend I pulled the oil pan and replaced that gasket. Not a difficult task but by the end I was a little sick of laying on the ground 😂 Hopefully that’s good for many years now. Also tonight I pulled out the transmission. The 4 of the 6 bolts fastening it to the engine were oddly...

steelsoldiers.com

With regards to the TV cable, i outline that in the thread and it is easier than you think. The steps are included with the trans purchase and involves pressure testing to confirm it is set up correctly. The rare 6.2 specific tv cable rod/bracket is helpful but in my opinion not required, you could use/adapt a generic tv cable bracket found all over the internet and connect the tv cable directly to the IP instead.

2INSANE also outlined a step by step install guide which matches very similarly what I did so you know what you're getting yourself into.

The One Stop 700R4 Swap M1009

Overview Please give many thanks to the 10+ SS members for giving me the motivation to create this thread. Chuckg, 4sdair, forest522, computer54, dezertdemond, Dsilverline, Chevymike, ssdvc, TheMod, Mullaney, royalflush55, 1love, Sharecropper… By popular demand! This is a REAL M1009 1984...

www.steelsoldiers.com

Many threads are here on 4L80E installs which is a good option as well. In my opinion a trans with 4th gear is a better choice than just changing the gearing.

I can vouch for Bowtie Overdrives. They rebuilt my 700R4 to a level 2 and it has been great for a year and a half now. They are great on support too. Daryl Smith was the guy that helped me there. Great guy.

 

[socalsrt]

700R4
I ran a built level two 700R4 from Bowtie Overdrives for about 3 years and 20000 miles behind a stockish M1028. Honestly, I loved that transmission. It shifted great and sharp at just the right time. The gearing seemed perfect for 4.56 w/ 33" tires with the 6.2 diesel. It would cruise at 70 mph all day long. Remember, you will need to swap to the NP208 27 spline input gear. It is not hard to do, just follow the TM as the transfer case gets fully disassembled. Don't let this run you off, it is easy enough with basic tools and some good, heavy duty, snap ring pliers. You will also need to source a 6.2 diesel flexplate that the 700R4 converter will bolt to. I got the converter from Bowtie Overdrive and it had a different bolt pattern than the stock TH400 one on the truck. The 700R4 flexplates were readily available on Rockauto and Ebay, just make sure it is for the 6.2l diesel. You also need the lock up torque converter wiring kit. Again, I got this from Bowtie Overdrive and it was easy to hook up. Unfortunately, the bad news... finding the TV cable bracket for a 6.2l diesel is very hard. They only came on factory 6.2l diesel trucks/SUVs equipped with the 700R4 transmission. I was lucky and have one from a civilian diesel K5 I bought before the M1028. I just used the factory cable and bracket. Honestly had no issues with it whatsoever. Installed it and it worked perfect. I can grab some pictures of it if anyone wants to see them. I do not know if there is an aftermarket TV set up, but I am sure with a little bit of thought you can make something work. I never asked, but I bet Bowtie could get you set up with this too, or at least get you in the right direction. Also consider adding an actual, separate, dedicated transmission cooler. For me, the driveshafts, crossmember, shifter, and everything else bolted together with no issues. If you are staying with a 6.2 diesel, I would highly recommend a Stage 2 Bowtie Overdrive trans. ***Forgot to add. You will also need the 700R$ to NP208 transmission to transfer case adapter. It is the square four bolt style for the 700R4. Also, you will need the tall one. Ebay is your friend***

4L80E
I went with a 4l80E when I did the LS engine swap. I had Bowtie Overdrives go through the 4L80E I am now running. Again, great shop with no issues. I did not use the 4l80e behind the 6.2l so not much advice I can give you there. I do really like the built LQ4 with the 4l80e and NP205 combo. The 4l80e is smoother and stronger than the 700R4. Remember for the 4l80E you will need a transmission controller and a before and after speed sensor input to the controller. I do not think the driveshafts would need to change. Also, not sure about the column needing replacing? I did not replace or modify my column and it manually can go into every gear. I did have to move the linkage pivot point about an inch back on the frame. You are on the right track with the 4l80E, expensive and some additional work is needed. ***Forgot to add the most difficult hurdle. The male lip on the front of the transfer case adapter is 1/8" too big to fit in the female grove on the rear of the 4l80e. The lip on the adapter needs to be machined down. It requires a fairly large lathe. I was able to do the NP208 Adapter this way, however I had to machine up a center bolted mount to get the NP205 adapter to stay in the lathe.***

I can't help with the NV4500 or Gear Vendors unit. I have never messed with or looked into either.

Bottom line, if I had stayed with the 6.2l engine, I would still be running the 700R4 and I cannot recommend Bowtie enough.

Also, I would not change the axle gears. The 4.56 gears is really one of the great points of the CUCV trucks. I also seem to remember the carriers being different for 4.10 gears and below. I am not positive but research this before doing a gear swap. It may cost a bit more than you think.

Feel free to reach out to me if you need any help or pictures....

 

[nyoffroad]

About a year ago I did see online someone was making and selling the TV cable bracket for the 6.2, sorry don't remember who.

 

[Curtisje]

I had a GV Overdrive on my M1008. It was there when I purchased the truck. It developed a "shuddering" vibration in the driveline while decelerating. I did some research and found out 2 things; 1 you can't get parts and repair a GV unit, they will only sell you a new one. 2 there is a 'reverse' band in there that is the weak point in the unit...not super weak or anything... just what a read that got me concerned since I do tow.

The other con is it can't be used in 4wd which you already know.

I'd go with any overdrive transmission that you've listed. I'm repowering my M1008 with a 6.5TD and a 4L80E.

Good luck.

 

[Barrman]

I love the 4L80E in my 3/4 ton CUCV clone Suburban. However, I learned after 2 weeks in the mountains a year ago that there are troubles with engine braking and the 4L80E. There is an over running band that even when new can smoke itself in a few minutes. I have yet to find any rebuild or race shop that can tell me a reliable unit for engine braking can be built.

I’m not trying to scare you into a 700R4. I have no experience with them except for having several stock ones fail on me while towing decades ago. I have stayed away from them ever since and have not researched them either. I thought the 4L80E was the better alternative.

 

[LT67]

Regardless of whatever you do, a 255 85r16 will easily fit the stock wheels. Depending on which brand of mud tire, they are all minimum 33in tall and 10in wide. I run that size on my 86 M1008 and my 79' K20 flatbed truck. I luv em. Great on the highway and killer traction off road when they are aired down

*personally I would prefer to swap out the carriers and go with 4.10 gears and a 255 85r16 tire