4L85E or Gear Vendors???

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Hi all,

I am building a CUCV M1010 ambulance into an offroad camping rig. I have recently put 35" tires on but with the 4.56 gears, I am still very limited in top speed and keeping the RPM's reasonable. Without a doubt I am going to need to put some sort of overdrive system into my rig.

Here's were it gets a little complicated. We do very remote camping, in many cases 50-100 miles from the nearest anything let alone repair shop. I need to have something that is about as 100% reliable as possible (and needs to stay an auto so my wife can drive if needed). I have been reading so much about both units over the last couple months. I am just as unsure today as I was when I started.

My biggest thing is reliablity and it seems each unit, people have had issues with. Here's seems to be the pros/cons from what I have found.

4L85E
Pro's: Strong, basically same ratios as current T400 with adding OD, can be tuned (depending on controller used) to meet specific needs, serviced by any GM dealer or trans shop, likely not to add any vibes to driveline, all four gears availabe in 4WD Hi/Lo range, one less item in the driveline system
Con's: Cost, more parts to install to get to work (controller, TPS, etc.), need to modify both driveshafts, some people have issues with failed units

Gear Vendors
Pro's: Can gear split, simpler install, only modify one driveshaft, can have auto or manual control, less overall cost
Con's: Can add vibes to driveline, additional lenght off transfer case, can be finicky with smooth shifting, only used in 2WD, less repair shops available, some people have had issues with failed units

I am not looking to something that is going to be towing a trailer so not worried about that but I will be spending a lot of time in the dirt where I might be crawling along at less than 20 MPH for hours on 2-3 rated (out of 5) trails.

What would you choose and why?

[twaddle]

Is it to be powered by the 6.2 non turboed or are you converting to another engine?

Jim

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Is it to be powered by the 6.2 non turboed or are you converting to another engine?

Jim

Will start as non turbo 6.2 but will be install a Bank system (in garage now) at some point down the road.

[Edahall]

Another advantage of the 4L85E over the TH400/Gear Vendors combo is the fact that it has a lockup torque converter which increases fuel economy and furthur lowers the rpm's. However, you could install a low stall torque converter on the TH400 to help this some. That said, I do have a Gear Vendors on my 1990 Suburban. It's behind a NV5600 6-speed manual. I have never had any issues and it works great.

Since reliability is very important to you, I would think you would also want simplicity as well since there's less things to go wrong. In that case, I would probably lean towards the TH400/Gear Vendors combination. I would have the TH400 built up strong and spend some money on a good low stall torque converter to decrease heat and have the fins brazed to strengthen it. On top of that, I would install the largest tranny cooler you can find and have a fan mounted to it so it cools even when driving slow through the outdoors. One advantage of the Gear Vendors is that it can easily be bypassed so you can continue on should something go wrong with it.

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Thanks for the info. I visited GV last week and had a good talk with them. Basically they were able to answer all my concerns and I feel good with the fact that the GV will likely never leave me stranded. It might not work but should not allow the vehicle to move. Worst case, being 4WD, I could run off the front driveline. I am getting a fixed yoke unit so I can remove the driveshaft should I ever need to and not worry about any fluid lost.

I agree with a larger cooler and aux. fan for it. Already have that in my plans.

Biggest thing that has me going GV is the gear splitting. Being able to split between 2nd and 3rd gears will be a major bonus for driving hills. Just can't get that with a normal 4L80E/4L85E.

Thanks agian.