I just pulled a 69 delivery A108 or A120? van out of the weeds, and turned it in to a daily driver, I love it but its gear too low, 50 mph its screaming, it has a /6 w/ 3 speed , the rear end i think is a 8 3/4 geared 3.91 ?? or so the tag says
Is it the rear end or the 3 speed that need taller gears, its hard on the freeway 55mph is pushing her hard , nobody goes 55 anymore. were all the vans geared low like this?

Thanks
Scott

If it's a 8 3/4, it's very easy (compared to most designes) to drop out the center section and replace with different gears.

if it's got 3.91 ratio, that's not really good on the highway. If you won't be towing or racing then you can find a better drop out section and get more favorable highway performance. Switching transmissions might be a better long term solution (better mileage and more ranges for different situations) , but rear end gears are MUCH cheaper and easier. I imagine that 3.21 or even 3.55 gears would make a noticable improvement. I would avoid much lower than 3.21 for a heavy van, but even 2.94 will work if you arn't towing and do lots of highway travel.

I shouldn't be very hard to find a drop out with more favorable gears, and someone might even trade if they are in good condition.

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1980 Aspen 225 super six

I think the tallest gear you could get in those vans was a 3.55, unless it had the V8.
Shift linkage becomes a nightmare because of the distance, so manual tranny swaps aren't fun, but an auto OD might be nice.
I'd love those 3.91s in my 318 car, and I always look for those vans/trucks, but the ones I find are too nice/expensive to cannibalize.
Definitely stay above 3.23 with that little brick.
Tall tires will tame it a little in the meantime.

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O==\=/==O

"A mechanic is Somebody."
- Jim Preston

I've got a 69 A108 slant 6 3 speed and it's got 3.91s. I would think it's to help get that heavy sucker to get moving. I'm looking for a set of 3.23 SG for the van and those 3.91s are coming out

Do like Chrysler did in the late '70s and up vans, and drop an A833OD in there!

As sixinthehead said linkage for an 833OD would be a real bear, especially converting from the 3 on the tree. If I were to do a swap, I'd use the automatic with OD.

Years ago, during Hot Rods van phase, they had an articule on how to put a 4 speed into a mid '60s Ford van. What they did was to mount the shifter firmly to the floor and use sheathed cables to run back to the gear box. They claimed that it worked OK. Maybe you can find a reprint somewhere, since this was from memory.

3.23 is a good mileage gear but not a good get-the-hell-out-of-the-way gear. My truck has 3.25 and it is a dog. I suggest 3.55 gears.

How does it accelerate with those 3.91 gears ?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Where are you located? Ive got a 3.23 section,sure grip...........

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1966 Dart GT
4 spd. OD conversion
8 3/4 - 3.55 SG (Sold)

62 Lancer GT
B Body 8 3/4

Iv got a 74 W100 with a /6, what would be the best gears for me to have in my front and rear end for takin her offroad?

go low, like 5.13 for some serious grunt

depends on how much off road you do, and what type of terrain