Transmission change

[Gumpy]

I have an '85 van with a C6 transmission 4.1 rear end.

-I want more torque at the wheels from a stop (7000# trailer on a steep mountain dirt road; this would only happen a couple times a year)
-I want better fuel mileage (overdrive)
-I want to be able to haul a heavy load over a mountain pass without the transmission overheating (I haven't done this yet).
-More engine braking ability for steep mountain passes with a heavy trailer.
-It would be nice to have an automatic for the sake of others who may drive the van but not necessary.

These are the options I've thought of so far:

4x4 C6 w/ transfer case. Regear rear end to 3.? I would like it geared higher than 3.5. Is 3.0-3.3 an option? Can I get a limited slip or locking differential this gear range?
Question: If I have it geared at 3.? and I need to go over a mountain pass and 1st gear isn't cutting it will it damage the transfer case to run it in 4 low for 40 miles?
Question: Will a transfer case fit under the van without major modifications? I don't mind moving a crossmember but would rather not modify the floor too much.

4x4 Zf5 w/ transfer case. I can get two parts trucks both with 4x4 zf5's in them for $600. The downside is trying to modify the van to have a floor shifter with a bench seat in the front. The other downside is it will be less drivable for my wife and mother-in-law (they still can).

Medium duty manual or automatic transmission. This has the additional downside of many unknowns. I can mount up a zf5 and I know the clutch and flywheel will work. I don't know what I'm getting into if I go the medium duty route.
Question:Is it possible to get the gear spread I want?

C6 with aux transmission. Possibly regear rear end if I can't get an overdrive of 0.7-0.8.

Budget and time are a concern here

How much does a budget conscious limited slip or locking differential cost with 3.? gears on it?

Any thoughts? Is is even worth looking into a medium duty automatic transmission? If I'm going to go that route I would want a lock-up Torque Converter with overdrive and a big gear spread.

How much do aux transmissions cost?

 

[franklin2]

You do not want to get rid of your 4.10 or whatever you have rearend. If you go lower it will kill it for towing. Just follow what the the factory did; They kept the 4.10 rearend to keep what towing ability you have, and started installing the E4OD to tame the 4.10 gear for better fuel mileage and highway driving. I believe the E4OD also gives you a better 1st gear. 2.71 to 1 instead of the 2.46 to 1 that the c6 has. The automatics also give you better take off power with the slip of the torque converter.

 

[david85]

Not many low cost options here, unfortunately.

I don't know what it would take to get a 5-speed into an econoline chassis but with enough work, anything's possible. One option to get "slightly" more torque out of the hole is to rebuild your C6 automatic with E4OD gears. This will have the wider ratios Franklin mentioned.

Another option is to turbocharge the van, since that would also result in more torque at the rear wheels.

There is a member here that converted his 80s econoline to 4wd and also swapped to the E4OD transmission. From what I remember, he had to modify one of the floor supports to fit the larger transmission. I can't imagine a HD truck transmission fitting any easier under there, but I'm not a van expert.

 

[u2slow]

I would go all-in on the ZF5 swap with tcase. I have less than $500 total tied up in 2 sets.

I never felt a NA diesel with a manual trans was lacking in grunt. (Unlike with a 3spd auto.) Probably don't need to change the axle ratio, but decide that later.

If I hadn't been able to unload my 97 E350 work van, it would most likely been a 5speed campervan by now.

 

[71 Highboy]

I have an '85 van with a C6 transmission 4.1 rear end.

-I want more torque at the wheels from a stop (7000# trailer on a steep mountain dirt road; this would only happen a couple times a year)
-I want better fuel mileage (overdrive)
-I want to be able to haul a heavy load over a mountain pass without the transmission overheating (I haven't done this yet).
-More engine braking ability for steep mountain passes with a heavy trailer.
-It would be nice to have an automatic for the sake of others who may drive the van but not necessary.

These are the options I've thought of so far:

4x4 C6 w/ transfer case. Regear rear end to 3.? I would like it geared higher than 3.5. Is 3.0-3.3 an option? Can I get a limited slip or locking differential this gear range?
Question: If I have it geared at 3.? and I need to go over a mountain pass and 1st gear isn't cutting it will it damage the transfer case to run it in 4 low for 40 miles?
Question: Will a transfer case fit under the van without major modifications? I don't mind moving a crossmember but would rather not modify the floor too much.

4x4 Zf5 w/ transfer case. I can get two parts trucks both with 4x4 zf5's in them for $600. The downside is trying to modify the van to have a floor shifter with a bench seat in the front. The other downside is it will be less drivable for my wife and mother-in-law (they still can).

Medium duty manual or automatic transmission. This has the additional downside of many unknowns. I can mount up a zf5 and I know the clutch and flywheel will work. I don't know what I'm getting into if I go the medium duty route.
Question:Is it possible to get the gear spread I want?

C6 with aux transmission. Possibly regear rear end if I can't get an overdrive of 0.7-0.8.

Budget and time are a concern here

How much does a budget conscious limited slip or locking differential cost with 3.? gears on it?

Any thoughts? Is is even worth looking into a medium duty automatic transmission? If I'm going to go that route I would want a lock-up Torque Converter with overdrive and a big gear spread.

How much do aux transmissions cost?

Thats alotta questions! I can speak to some of them from truck chassis experience nut not a van chassis.
Years ago, the C6 was all that was available, and as Franklin mentioned, a good tranny shop can install those E4OD parts in your C6 with a new converter to match your engine torque peak. Electronic lock ups are available now, but I have no experience with them. Keeping your C6 trans will aid in easy driving for your ladies. Simplicity.
To the gearing question, My truck WAS 4:10's front and rear. I switched to 3:54's. If I was to do over. I would use 3:73's. I tow loaded horses and race trailers regularly. To the question of using low range for added pulling power. Yes, as long as you don't lock the hubs, it will work fine on hard surfaces for 40 miles. Consider an aftermarket OD unit mounted to the back of the trans, but in front of the t case. This allows use of the OD unit in low and high range. Yes, you will have to move a cross member or make new ones. My T case moved rearward about 2 1/2", and the OD connects directly to the front of it without a jack shaft. I'm not sure what T case you are considering, but NP 205 was what was used later on remote mounts, while Dana 24 was used earlier. Choose the NP if you can. All of this is to keep it simple.
To the question of medium duty trans, there were some allisons offered in small buses using 6.9 idi's. I recall they were direct in top gear. Not worth the effort.
To the question of braking, use Total Seal rings on the second land of the piston. Prolly as close to a jake as you'll get with these antiques. Zero blow by. I use second gear as needed on a downgrade, usually under light throttle, if third won't slow with no throttle. See what US gear has to offer for OD. My GV unit has not been without problems. Let us know how you proceed.

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[david85]

Lockup for a C6? I found talk about it, but did anyone actually build one?

 

[IDIBRONCO]

It would be awesome if someone did. That would take away the main weak link (to me) in the C6, the built in slippage.

 

[david85]

I'm not saying it can't be done, but for the cost involved in custom machining new internals, you're better off building up the E4OD/4R100. I would even consider the 5R110, now that they are so common in wrecking yards (with an adapter plate, of course). Depreciation is a wonderful thing.

Although, I would be more curious to see a 5-speed stick in an Econoline. The kind of fabrication involved to make a 5-speed work would be far easier and cheaper than just about any auto-box solution.