D100 geared too low
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- Sweptline.ORG Member
- Posts: 8
- Joined: Tue Dec 25, 2018 1:40 pm
- City: Calgary
- State: Foreign
- Location: calgary
D100 geared too low
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.
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- Sweptline.ORG Pioneer
- Posts: 7364
- Joined: Wed Dec 31, 1969 6:00 pm
- Location: Walnut Creek, CA
Re: D100 geared too low
Change rear end. Tranny is irrelevant at highway speed. They're all 1:1 in 4th gear unless you install an overdrive unit.
Re: D100 geared too low
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
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
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- Sweptline.ORG Member
- Posts: 8
- Joined: Tue Dec 25, 2018 1:40 pm
- City: Calgary
- State: Foreign
- Location: calgary
Re: D100 geared too low
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
- Sweptline.ORG Pioneer
- Posts: 8931
- Joined: Wed Dec 31, 1969 6:00 pm
- Location: Des Moines,IA
Re: D100 geared too low
Why couldn't you go with 3.23s? The majority of sweptline era D100s had a 741 case and 3.23s were available.
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- Sweptline.ORG Member
- Posts: 8
- Joined: Tue Dec 25, 2018 1:40 pm
- City: Calgary
- State: Foreign
- Location: calgary
Re: D100 geared too low
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
- Sweptline.ORG Member
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Re: D100 geared too low
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.
1*1971 D100 318 A/T
1*1970 Charger R/T 440-6PK A/T
2*1969 Daytona Charger 440 A/T
1*1969 Coronet R/T awaiting restoration
1*1969 Torino Talladega awaiting restoration
1*1970 Charger R/T 440-6PK A/T
2*1969 Daytona Charger 440 A/T
1*1969 Coronet R/T awaiting restoration
1*1969 Torino Talladega awaiting restoration
Re: D100 geared too low
This is exactly what I put in my '65 D100 with the LA318/NP435. Its great.martincom wrote: ↑Sun Jun 06, 2021 6:48 amI 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.
John