D100 318 Convert to Automatic Transmission?

[67D100Pickup]

Hello all. I'm rebuilding the motor on my D100 and I want to convert to an automatic transmission while I'm at it.
- because I don't need a truck with a granny gear
- because I don't have any underlying desire to shift gears or operate a manual clutch
- because other family members could/would drive it if it had an automatic transmission

As the subject says, it's a 1967 D100. Currently has a manual tranny with 3 on the tree. I don't know how to tell what gears the rear end has (if that tells you my skill/knowledge level) but I'd say it has a granny gear in it now.

A friend suggested I find a 727 automatic transmission and work from there, using the same rear end.

Is that easy enough to do or am I insane? Can you guys get me started asking the right questions so I can start filling in (correct) answers?

Jeff

[Wildergarten]

Is that easy enough to do or am I insane?

It's a lot of work and a lot of parts. Off the top of my head, besides the trans, you'll need a different dashboard, cable linkage, supporting crossmembers, driveshaft, throttle kickdown linkage, cooling lines to the radiator, starter relay, and transmission hump. There is wiring to do for the neutral safety switch and starter relay. I have the whole thing available as a kit for sale, but unfortunately for both of us, the trans I have fits a big block engine.

[67D100Pickup]

Wow! That is way over my pay grade.

Thank you very much for the feedback but I think I'll go ahead and put the brakes on this now.

Jeff

[PwrWgnDrvr]

Its easy to convert to an auto tranny. Just buy a different truck - its a lot less money and hassle!
And no, u don't have a granny gear with a 3 on the tree.

[Txas2step]

Its easy to convert to an auto tranny. Just buy a different truck - its a lot less money and hassle!
And no, u don't have a granny gear with a 3 on the tree.

[Txas2step]

Hello all. I'm rebuilding the motor on my D100 and I want to convert to an automatic transmission while I'm at it.
- because I don't need a truck with a granny gear
- because I don't have any underlying desire to shift gears or operate a manual clutch
- because other family members could/would drive it if it had an automatic transmission

As the subject says, it's a 1967 D100. Currently has a manual tranny with 3 on the tree. I don't know how to tell what gears the rear end has (if that tells you my skill/knowledge level) but I'd say it has a granny gear in it now.

A friend suggested I find a 727 automatic transmission and work from there, using the same rear end.

Is that easy enough to do or am I insane? Can you guys get me started asking the right questions so I can start filling in (correct) answers?

Jeff

Jeff, it is a lot of work to convert to auto. If you still have the Data plate on the drivers side cab/door frame, it will show what rear axle ratio you have. Being a '67 d100, most likely a 3:91 or 3:55. The 3:91 is the worst for hwy, 3:55 is ok for some hwy driving. The 3:23 would be ideal and fairly easy to swap out.

[67D100Pickup]

Its easy to convert to an auto tranny. Just buy a different truck - its a lot less money and hassle!
And no, u don't have a granny gear with a 3 on the tree.

OK. As I don't want a different truck... I'm seeing talk of swapping out the rear end so I'll chase that down.

[67D100Pickup]

[/quote]
Jeff, it is a lot of work to convert to auto. If you still have the Data plate on the drivers side cab/door frame, it will show what rear axle ratio you have. Being a '67 d100, most likely a 3:91 or 3:55. The 3:91 is the worst for hwy, 3:55 is ok for some hwy driving. The 3:23 would be ideal and fairly easy to swap out.
[/quote]

You are correct. The plate shows 355. For a 9% reduction I'm going to wait and see how the rebuilt engine feels and take it from there.

Thank you very much for the technical guidance.

[67D100Pickup]

Is that easy enough to do or am I insane?

It's a lot of work and a lot of parts. Off the top of my head, besides the trans, you'll need a different dashboard, cable linkage, supporting crossmembers, driveshaft, throttle kickdown linkage, cooling lines to the radiator, starter relay, and transmission hump. There is wiring to do for the neutral safety switch and starter relay. I have the whole thing available as a kit for sale, but unfortunately for both of us, the trans I have fits a big block engine.

Hi Mark, I have a friend who has built cars all his life and he's concerned I'll blow up my stock transmission with my new engine which is being built to deliver quite a bit more horsepower than stock - and he's willing to help with the conversion.

I understand the need for cable linkage, supporting crossmembers, driveshaft, throttle kickdown linkage, cooling lines to the radiator.

I don't understand
- the need for different dashboard
why is this needed?

- transmission hump
can I just cut a hole in my transmission hump and install a floor shifter?

- starter relay
What is different about a starter system for an autmomatic tranny?

- wiring to do for the neutral safety switch and starter relay.
I'm guessing this is to prevent hitting the starter while in gear? (Maybe your kit comes with magic knowledge beans)?

Jeff

[Wildergarten]

I don't understand
- the need for different dashboard
why is this needed?

The stock setup has the cable shifter is incorporated into the dash as a lever mounted feature. Everything just screws in place. Linkages and cables all made up. Etc. That's what I have for sale.

can I just cut a hole in my transmission hump and install a floor shifter?

Don't know if there's room for one. The auto hump has no holes for shifters.

What is different about a starter system for an autmomatic tranny?

The neutral safety switch lockout.

- wiring to do for the neutral safety switch and starter relay.
I'm guessing this is to prevent hitting the starter while in gear? (Maybe your kit comes with magic knowledge beans)?

Yes.

I have the whole setup. Everything from a stock truck. If that's what you want, it's for sale. If you don't want the trans, I can do that too, but I'm not breaking up the conversion kit. And don't forget the driveshaft!

[PwrWgnDrvr]

Long bed uses a different driveshaft than a shortbed.

[Wildergarten]

Long bed uses a different driveshaft than a shortbed.

Having one cut down and balanced is a no-brainer. Finding the yokes is not.

[Wildergarten]

Long bed uses a different driveshaft than a shortbed.

Having one cut down and balanced is a no-brainer. Finding the yokes for 68 and earlier 10-spline diffs is not.

[PwrWgnDrvr]

Long bed uses a different driveshaft than a shortbed.

Having one cut down and balanced is a no-brainer. Finding the yokes is not.

Yup! A $300+ no brainer!
Makes $80 Dolfinite look cheap!

[Wildergarten]

Yup! A $300+ no brainer!

I suggest you find another driveline guy.

The cost to balance a driveshaft, like most car repairs, will depend on the mechanic/dealership you choose and the car you drive. From what we researched via multiple quotes online, the average driveshaft balancing, including professional labor, tends to be in the $120 to $185.

Source: https://www.howmuchisit.org/driveshaft-balance-cost/

[67D100Pickup]

Its easy to convert to an auto tranny. Just buy a different truck - its a lot less money and hassle!
And no, u don't have a granny gear with a 3 on the tree.

I already have different trucks, with automatic transmissions. I want this one to have auto too! :-) But there is only a certain amount of money and pain I'm willing to go through to convert it.

P.S. Thanks for the note that I don't have a granny gear! Yes, it seems a little low to me but I understand.

Jeff

[PwrWgnDrvr]

Granny gears are only on 4-speeds and typically a ratio around 6.6:1
They're prettty much wound up at around 3-5 mph. You can put a truck in granny, let out the clutch and idle along in stopped and go traffic w/o having to use the brakes.

[moore7568]

Jeff,
Don't be scared of the Auto install.
I've got a 68 with a 727 strapped on to a 505 stroker.
A 727 behind the 318 will outlast your grandkids.
There will be some fitting and fabrication and drive shaft work to get it done, but it'll be a big payoff down the road.

That said, with the small block, there's no reason not to go with the 46RH Mechanical or 46RE electronic, which is basically a 727 with overdrive and a locking converter. This will resolve any need to swap the rear end ratio (most likely the 3.91)

I'm having a 46RE built for my 505 now and expect to go from 8 miles/gallon to around 12 or better.

Hit me up if interested in more info and I'll send you pics of what my install looks like.

Some pics of my build at viewtopic.php?f=19&t=40679

[67D100Pickup]

Granny gears are only on 4-speeds and typically a ratio around 6.6:1
They're prettty much wound up at around 3-5 mph. You can put a truck in granny, let out the clutch and idle along in stopped and go traffic w/o having to use the brakes.

Or maybe idle along through a pasture slow enough the hands to load hay :-)

[Hobcobble]

Granny gears are only on 4-speeds and typically a ratio around 6.6:1
They're prettty much wound up at around 3-5 mph. You can put a truck in granny, let out the clutch and idle along in stopped and go traffic w/o having to use the brakes.

Or maybe idle along through a pasture slow enough the hands to load hay :-)

I've walked beside my '68 W200 in an open field [not for too far ]. It has
the 6.68:1 first gear and I had it in 4-Low [4.88 axle gear ratio].

John