D100 geared too low

[general]

I have a 1967 D100,slant six 4speed.First gear is what they used to call jumbo-low.When I do 60 on the highway,it revs so high,sounds like it’s going to blow up! What’s the solution? Would I have to change rear-end or transmission? It has a 3.91 rearend and a 435 transmission.

[PwrWgnDrvr]

Change rear end. Tranny is irrelevant at highway speed. They're all 1:1 in 4th gear unless you install an overdrive unit.

[sixpak340]

Taller rear tires can help too if you can find some that work with your combination.

If it has the 8 3/4" differential, you can find a 3.55 or 3.23 chunk and just swap out the whole center section.

The 3.91 is popular with the muscle car crowd, so you may find someone in your area willing to trade a higher set.

Yoke size can come into play as well. The 741 & 742 cases are easy yoke swaps, but the 489 has a crush sleeve that makes a yoke change complicated.

There are two different yoke / pinion spline types too, 10 spline and 29 spline.

Conversion U-joints are also available.

If you have a Sure-Grip in your current set up, you could order a new ring and pinion and get someone to set it up for you to re-use what you have.

I order all my 8 3/4" parts from www.doctordiff.com

[general]

So I changed the 3:91 rear end to 2:94,s.It had a 741 case so couldn’t go with 3:23’s,and I’m glad.Can’t believe it,can pass cars on the highway now.lol

[soopernaut]

Why couldn't you go with 3.23s? The majority of sweptline era D100s had a 741 case and 3.23s were available.

[general]

My rear end guy(for cars),said new 3.23’s won’t fit into the early 741 housing,need a 489 or 742 case.Totally satisfied with the 2.94’s. Great for highway driving.

[martincom]

I would agree. The 2:94 was a great choice. With the "Granny gear" 4-speed, you'll have plenty of dead stop pulling power. My D100 has the 3:23 paired with an automatic. There is also torque multiplication provided by the torque converter. So that first gear combination would be close to your second gear gear combination.

[Hobcobble]

I would agree. The 2:94 was a great choice. With the "Granny gear" 4-speed, you'll have plenty of dead stop pulling power. My D100 has the 3:23 paired with an automatic. There is also torque multiplication provided by the torque converter. So that first gear combination would be close to your second gear gear combination.

This is exactly what I put in my '65 D100 with the LA318/NP435. Its great.

John