M1009 Transmission options question: TH400 vs 700R4

[Tinman84]

I'm a bit of a CUCV greenhorn (I've had my M1009 about 6mos). I've learned lots already with lots left to learn, and I have a question for those that know more than me: I ran into a guy a while back who said a 700R4 transmission should bolt on directly (no modifications) as a replacement for the 3spd TH400 that came stock in these things. Is this true? I'm still trying to decide if it's worth it for the overdriven top gear for freeway driving. I'm also aware that these 6.2s are not meant to be powerhouses, so would it have enough power to turn an overdrive? Lastly, can they handle being turboed without shortening their lifespan? I'm not looking for a hotrod, but being able to drive up the mountain highway near where I live going faster than 30mph would be nice. Thoughts? Opinions? Smart remarks?
Thanks in advance.

 

[doghead]

Fact, everything you've asked can easily be answered with a bit of searching our site.

 

[cucvrus]

Tinman 84. If it was me and I had this issue. I would take the easy route. Just change the gears in the rears. I put a set of 4:10's in an M1009 Blazer for a customer. And the easiest way is change the complete axle assemblies. He lived in the the north east and pulled a utility trailer. It was a totally different vehicle after the gear change. And even 3:73 gears would make a huge difference. That is easier then changing the transmission to a 700R. And the stock 3:08 gears are a bit high but they do make it go fast on the interstate. The 4:10 and 3:73 gears are easy to find. They were in used a lot of the 1/2 ton GM pickups , Blazers and Suburbans in the 70's and 80's. That is the easy way to fix your issue. That is my opinion only. I'm sure you will hear more. I can hardly wait.

 

[MarcusOReallyus]

Tinman, a lot of folks here have swapped in the 700R4, and a lot have installed the Gear Vendor's Overdrive unit. I havn't touched any of these myself, but I've read a lot of threads on these mods. I haven't seen anything negative from anybody who has done either. Nobody says they wish they hadn't done it. Same for the turbo.

None of these are a straight bolt up. The bugger with the 700R4 seems to be sourcing the TV cable bracket. For the GV overdrive, you do have to have a custom shaft built. On the turbo, exhaust pipe routing is a bear.


Speedmon's thread on the 700 is probably the best. There are many on all three subjects. Do some searching - you have a lot of reading to do!

 

[Drock]

I did the Gear Vendors in mine. After much debate I decided to go that route rather then the 700R4. The 700 would have been MUCH more complex to install and in the end not quite as tuff as the TH400. From what I've read the GV & 700R4 would have cost the same ( around #$3500.00 ) but with the 700 you'd have to make ah cross member, drive shaft, custom linkage, and deal with the electronics, Not to mention take out, and install, ah big trans in ah tall 4X4 truck. I did my GV on ah blanket in the grass, It only weighs about 60lbs and goes together in 2 pieces. The GV will run in auto mode, but also has a manual foot controller so you can split gears or not use it at all. I'm very happy with it and consider it a must for these trucks.

 

[Recovry4x4]

I did the Gear Vendors in mine. After much debate I decided to go that route rather then the 700R4. The 700 would have been MUCH more complex to install and in the end not quite as tuff as the TH400. From what I've read the GV & 700R4 would have cost the same ( around #$3500.00 ) but with the 700 you'd have to make ah cross member, drive shaft, custom linkage, and deal with the electronics, Not to mention take out, and install, ah big trans in ah tall 4X4 truck. I did my GV on ah blanket in the grass, It only weighs about 60lbs and goes together in 2 pieces. The GV will run in auto mode, but also has a manual foot controller so you can split gears or not use it at all. I'm very happy with it and consider it a must for these trucks.

Clarification on the 700R4 swap. Factory crossmember works fine. No driveshaft mods are needed. No custom linkage is needed. Lockup electronics are easy and earlier models of the trans can be locked hydraulically. If doing the install at home it would run between $1500 and on the high side $2000. Both offer real advantages.

 

[cucvrus]

Gear Vendor on an M1009 Blazer? Hmm would you even be able to install a drive shaft? Or would it be yoke to ujoint to rear axle? i don't think an M1009 Blazer could have a much shorter drive shaft. The original guy was talking about options in an M1009 Blazer. That is why I mentioned the axle / gear swap. Does a gear vendor fit and operate in an M1009 Blazer?

 

[Skinny]

Since you have 3.08's in your Blazer, I would stick with what you have. Adding an overdrive to that even with the stock 31" tires would put you into a useless power band unless you cruise at 90mph on flat land. Now if you decide to step up to 1 tons with deeper gears, then you probably have good reason. Personally with that wheelbase, I would stay away from a GV because your driveshaft length is getting pretty short. At stock suspension height, you may run into vibe issues, require a CV rear shaft, or both especially if a lift is down the road.

 

[Csm Davis]

I'm a bit of a CUCV greenhorn (I've had my M1009 about 6mos). I've learned lots already with lots left to learn, and I have a question for those that know more than me: I ran into a guy a while back who said a 700R4 transmission should bolt on directly (no modifications) as a replacement for the 3spd TH400 that came stock in these things. Is this true? I'm still trying to decide if it's worth it for the overdriven top gear for freeway driving. I'm also aware that these 6.2s are not meant to be powerhouses, so would it have enough power to turn an overdrive? Lastly, can they handle being turboed without shortening their lifespan? I'm not looking for a hotrod, but being able to drive up the mountain highway near where I live going faster than 30mph would be nice. Thoughts? Opinions? Smart remarks?
Thanks in advance.

Okay Tinman I have had a civilian 6.2 with a 700r4 and they have even less hp but you would swear it had more than the military cucv. So yes it is worth doing and is a bolt in with factory parts. I will also say a built 700 can handle anything a 6.2 will put out even with turbo. A turbo will be a great addition to the 6.2.

 

[Skinny]

Agreed

Just be aware that with that gearing combination and 31's (which I presume you are running), you are pretty much right on the bottom side of the 6.2 sweet spot. Anything larger and you start to get into the chug zone.

 

[welpro222]

Yeah the 700r4 with 3.08 is worthless. I have one in my k5 6.2, I only use it when doing 70+ on freeway. The problem is 3rd gear with the 3.08 rear is worthless for towing anything.

 

[cucvrus]

I tow a 6' X 10' single axle utility trailer with 2' sides over 120 miles with it loaded with 24" firewood cut and split and stacked. Anyone that knows PA from Lebanon county to Bradford county can atest to the hills and mountains on I 81 , PA901 and 42 north. I tow with the M1009 stock. A few hills it goes into first gear and it works hard. I have done it 10-15 times a year for the past 10 years and never had any problems. I never even thought about it till I put all the gauges in my Blazer. I kept the idiot lights hooked up and never had them come on but the water temp goes up high on the climb and comes down directly after the climb. Even in July it never over heated.I never saw the temp light on and it does work. The vehicle works as designed and gets the 15 mpg when I tow loaded. I only get 16mpg with a new fulsize truck empty. No complaints. This M1009 I have still has the original injection pump on it. So the stock set up is slow but it will get you there. I towed an M1028 from Georgia with my M1009 one time and the temp light blinked on when I was climbing a long mountain from NC into VA. That gave the M1009 with the 3:08's a work out on that trip. I think that mountain is on I 77. It's been 5 years. Anyway you can get by with the stock gears if you are a patient man. But lower gears are nice at times. Anyway good luck with your project. I was always budget minded and spent my money on housing not toys. To each his own.

 

[ODFever]

Tinman - Welcome to the Green Iron Laughing Academy!! Congratulations on your recent acquisition.

I've owned my M1009 for 8 years. It is my daily driver. I have a stock 6.2L and TH400 with 3.08 gears and 31" tires. I have absolutely no problem cruising at 70-75 MPH on the interstate. I don't like to run much faster than that because the engine starts screaming. Pulling my 1700 lb 18' double axle flatbed trailer with a load is a different story. I run about 55-60 MPH on the interstate to save fuel. I also don't like pushing my truck past it's limits. If I were you, save the $2000+ on a transmission swap. Don't think about spending another $2000+ to install a turbo. Get to know every inch of your truck. Spend countless hours drilling through the TM's. Read all the stickies. Read every thread in the CUCV Forum. Make friends with the local parts houses so they know who you are when you call up asking for parts for a 30 year old K5 Blazer. Do a thorough PM check on your truck. Check everything. Do the Doghead Mod. Make it a safe, reliable daily driver. If you are unhappy with the performance of the truck down the road, then reconsider modifications.

In numerous other threads, Recovry4x4 refers to the 6.2L as a fuel miser that was never meant to be a powerhouse. I personally couldn't agree more. I refuse to install a turbo on mine because Detroit Diesel never designed the 6.2L engine for a turbo. I enjoy driving my truck the way it is, and the way it was designed. My TH400 works great the way it is. I get 20 MPG city if I keep my foot out of it. I do not need nor want overdrive in my truck.

My + tax.

 

[Skinny]

I do not need nor want overdrive in my truck.

Spoken by someone with 3.08's and not 4.56's

 

[Recovry4x4]

With all this said, I would agree that the OD in conjunction with the 3.08 axle gears would be all but useless. There is one other consideration though. The 700R4 has a 3.06 first gear which would help get the truck rolling a little easier if loaded. Not advocating the swap, just dispensing info for consumption.

 

[Skinny]

Don't forget the lockup converter. Not helping as it lowers rpm into the bad zone but certainly helps with efficiency and fuel economy.

 

[Tinman84]

Thanks for all the input so far guys. As several have pointed out, I have not managed to get through all the CUCV stuff on the site yet. I find myself getting lost in the sheer volume of info and discussions, and I can burn hours without noticing the passing time, or running across what I was looking for. Sometimes it feels like looking for a needle in a haystack, so I appreciate the guidance.
Whether it was smart or not, I bought my M1009 and then sold my other two vehicles, so it's my daily driver. I love the vehicle, but since it is my only rig, it puts some extra constraints on my tinkering. At this point, I'm focused on making sure it's ready to go for winter, but I've been mulling over my fuel economy and power questions ever since I bought it. I try to keep my foot out of the throttle and I'm getting about 16mpg, assuming that my odometer is semi accurate. Mine came with 33" tires on it, and they are a bit wide, so if I compensate for the extra 2" of tire (increase distance traveled by 6.06%) when I figure mileage, it bumps it up by a little over 1mpg. This is why I was wondering about the gearing and turbo options. I don't need a huge powerhouse, but I've heard of turbos increasing mpg as well as power. I've also had some folks caution me that turboing some diesels that aren't beefy enough for it can cause them to meet an early demise, but it sounds like the 6.2 handles it.
One last question: is there a good discussion of IP issues on here? I've searched with the site search engine for info on an IP rebuild and have yet to find it. Thanks again, and happy tinkering.

 

[61sleepercab]

I have driven and hauled heavy loads with automatic and manual transmissions with 3.08 (gutless airplane gear) and 4.10 (pull a redwood tree stump but wound tighter than a banjo string at 60mph) . I found that 3.73 gears were a happy medium with direct drive, overdrive when truck empty would be fine. I ran 6 cylinder or 350 V8 in 1/2, 3/4 and 1 ton Jeep and Chevy trucks and hauled loads up to 4000lb of rock and towed a flat trailer hauling a tractor or grist mill and engine.

 

[rsh4364]

I would love to see some mpg #s for a turbo conversion on a 6.2 with th400 with 323,342 gears And also a N/A 6.2 with a 700R4 with 373,390 and 410 gears.With 33 inch tires.

 

[Cleptomaniac]

M1009
6.2 with turbo
4L80e tranny
NP208 with slip yoke eliminator
Dana 60 and 14bolt with 4.56 gears
37" hummer tires and wheels
13mpg in town
16 mpg on the highway at 70-75 mph.