I have an 85 D100 with a 225, 4 speed OD, and I think a 3.08 axle. Obviously not the best set up for towing, but it's what I have. I was thinking about putting a super six set up on the truck, feather duster exhaust, and a steeper rear gear (say 3.91). Any better ideas? What do you think the maximum short distance (less than 50 mile) trailer capacity would be?

3.91s are the minimum I'd use. Power may not be your biggest issue. If the trailer weighs more than 40% of the truck the trailer needs it's own brakes. For handling heavy trailers you'll want a weight distributing receiver hitch. 2 1/4" exhaust will help power and mileage. A good 2bbl carb will also help, but it will need tuning.

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Joshua

I have towed with my '84 D100. I went 2100 miles a few months ago to pick up a '68 V100. My truck is 225/833od/3.21. I have upgraded to 2.25" exh, standard Mopar ignition, and a super six 2bbl.
My biggest problem is getting it moving with the load from a dead stop with the 3.21 gear, especially on an incline. It does Ok once I get it rolling.
Right now I have the 3.21 geared 8.25 rear out and just need to make brake lines for a 3.91 geared Sure Grip 8.75 (from a '72 D100) that's going back in. My '82 D150, 225/833od/3.91 already had this same swap done.
Here's a pic from several years ago when I sold and delivered my '67 Charger. The trailer is about 2000lbs, the Charger, Hemi/833/Dana, has to be 4000+lbs, not a light weight load.

I also have towed my John Deere 5203, 4600lbs, on the same trailer. I have brakes on BOTH axles. I would never try to pull anything more than my 5'x10' utility trailer without brakes.

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Slant Cecil

Your posts have inspired some confidence in me that my lilttle short bed will be up to the task I need it to do. I need to tow my Massey Ferguson tractor, and had always guessed that it and the trailer weighs 5500 pounds. Also tow a parts car or felled trees once in a while.

Question ---- I have a number of e body 8 3/4s' laying around from scrapping out cars over the years, and I have a 4.10 SG carrier. I imagine the spring perches are wider on a truck, but I don't know the width. Does anyone have that information? Early 70's trucks with 8 3/4s can't easily be found in junkyards around here anymore, but I could do a thorough search if that's a better idea. Either idea seems less expensive that buying a new ring, pinion, and sure grip for the 8 1/4.

I have the 4 speed overdrive transmission and 225 slant in my truck too. The first three gears are like a 3 speed transmission in a car. I think you and I would be better off getting a 5 speed transmission instead of different rear gears. With a 5 speed we'd have a lower first gear which would help takeoff from a stop. 2nd and 3rd are also lower which would help acceleration and then the fifth gear is overdrive. If you want to check out what 4th gear would be like with a 4.10 rearend , leave your truck in 3rd gear the next time you drive it. Its real close to being the same. The same thing can be said for the five speed by leaving it in 4th which might help towing up long grades. I think with a 5 speed you would have all the advantages of switching to a 3.90 gear with the 4 speed but the 5 speed would give you one more gear for better mileage on the highway.

Where would the 5 speed come from --- a later model truck? How complicated would the swap be?

I remember reading on here somewhere that if you have the A833OD transmission in a truck, you can't really switch to the 'truck' transmission as the shifter nob would sit around the rear view mirror. I know there were various incarnations of the A833 with slightly different gearing. But I think it's considered to be a car transmission overall. I also think after it is all said and done, the rear end swap would be cheaper and easier.

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The Old Goat '83 D150 225-2

AKA Ice Titan

I got as much "into" tranny swapping as I did carbs. In my D100 I took out a A745 3 speed, put in a 833OD,Then NP 435, then the T5, now putting in a 727. Next I want to try the 518 using Matt's adapter plate I got a while pback.

having had modes experience thus with tranny swaps into a d100, I didn't find any very difficult. The T5 just used the group buy adapter, the 833 took the most work because i wanted to use a hydro TOB to start with and finally moved to a Wilwood pull slave ond drive side using old brake MC, the NP was a bolt in, and the 727 is mainly a kickdown problem. I pulled a 6,000 lb load with the T5 on a 18 foot two axle trailer (3.91) and pulled it with the NP,the T5 and the 833. All worked fine. I used a shift lever I bent in my shop press because I like my hand at knee level, about 19 inches. Not really at mirror level,

Basically, put in any , they all work fine.
rock
64d100

I think the rearend swap would be easier too but swapping the transmission would be better in my opinion. I was told that the input bearing retaining ring on an nv2500 as the same size as the 4 speed , that the lower transmission mounting bolt holes lined up with the holes for the 4 speed on the bell housing but the upper bolts required some heli-arc welding and tapping on the bell housing. The nv2500 is a light duty 5 speed though and I'm not sure how the nv3500 or nv4500 trans would work with a slant 4 speed bell housing. It sure would be nice to find some diagrams showing all these measurements for all these transmissions. I have an nv2500 transmission that I'm eventually going to try to use in my truck but I'm not throwing away the 4 speed just in case the 5 speed comes apart on me.