Automatic Transmission 300ci Inline 6
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Automatic Transmission 300ci Inline 6
I'm looking to swap the 4-speed manual transmission paired to my 300 to an automatic. I have been researching and not have found much. I think a c6 trans will fit but I would like to know what you guys think. What's the best bolt-on automatic transmission for a 300?
Bonus points if there is an automatic transmission that would support a Hurst shifter (the shifter that goes 1,2,3, drive, reverse, park).
I do not know much about transmissions for these trucks so please let me know if you need more info.
Bonus points if there is an automatic transmission that would support a Hurst shifter (the shifter that goes 1,2,3, drive, reverse, park).
I do not know much about transmissions for these trucks so please let me know if you need more info.
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 965
From: Tri Cities, TN
Last question first. There are aftermarket shifters for about every RWD auto ever made.
A C6 will fit but it has to go in from the front because the integral bell housing won't fit between the center cross member and the cowl.
With a 6 cyl. your best bet is a C4 or C5 they are essentially the same transmission except the C5 has a lock up converter.
A C6 is a big strong transmission that will handle 450 HP easily and can be built to take 1200 HP. But they have a lot of internal friction and will soak up around 40 HP.
A C4 or C5 is much smaller and only soaks up about 20 HP.
You will have to have a new driveshaft made.
Look for any of these transmissions in 1980's trucks.
There is more to it than this.
A C6 will fit but it has to go in from the front because the integral bell housing won't fit between the center cross member and the cowl.
With a 6 cyl. your best bet is a C4 or C5 they are essentially the same transmission except the C5 has a lock up converter.
A C6 is a big strong transmission that will handle 450 HP easily and can be built to take 1200 HP. But they have a lot of internal friction and will soak up around 40 HP.
A C4 or C5 is much smaller and only soaks up about 20 HP.
You will have to have a new driveshaft made.
Look for any of these transmissions in 1980's trucks.
There is more to it than this.
FTE Legend
Joined: Nov 2015
Posts: 30,917
Likes: 4,123
From: Angier, NC
A question not asked that needs to be, what will the truck be used for?
If pulling heavy loads then need a HD auto trans. A cruiser could then use a LD trans.
Crop Duster for the most part (99%) is spot on.
I believe the C4 / C5 (a LD type of trans) was used in the late 70's to think 80 maybe 81 trucks with a 300 six.
About 81 or 82 the C6 a HD trans as CD pointed out, was used in the trucks.
Now dont over look the AOD auto (no computer needed) used in the 80's trucks up to I believe 86 when the EAOD came into play as everything went EFI and a computer would run both the EFI and transmission.
The only thing to know about the AOD trans is it uses a TV cable and if this is not adjusted right the trans can burn up in no time.
Some say the AOD is a weak trans and were when they first came out but like anything has been improved over time.
That also goes for the C4 / C5 trans as I used a C4 behind a vary hot 302 in a 68 Bronco used for sand drags.
Unless I was using the truck for heavy loads I would not look at the C6.
Think I would look into the AOD as it has over drive good for cruising, then the C4 / C5.
BTW if you do go with a C6 Gear Vender makes a over drive that bolts to the back of the trans but its not cheap. They may make for the C4 / C5 but I have never looked.
Oh I have a NP435, (granny 4sp) with Advance Adapter's over drive behind the 300 six in my 81 F100 flare side 4x2
It is a back up to pull my open deck car trailer.
Dave ----
If pulling heavy loads then need a HD auto trans. A cruiser could then use a LD trans.
Crop Duster for the most part (99%) is spot on.
I believe the C4 / C5 (a LD type of trans) was used in the late 70's to think 80 maybe 81 trucks with a 300 six.
About 81 or 82 the C6 a HD trans as CD pointed out, was used in the trucks.
Now dont over look the AOD auto (no computer needed) used in the 80's trucks up to I believe 86 when the EAOD came into play as everything went EFI and a computer would run both the EFI and transmission.
The only thing to know about the AOD trans is it uses a TV cable and if this is not adjusted right the trans can burn up in no time.
Some say the AOD is a weak trans and were when they first came out but like anything has been improved over time.
That also goes for the C4 / C5 trans as I used a C4 behind a vary hot 302 in a 68 Bronco used for sand drags.
Unless I was using the truck for heavy loads I would not look at the C6.
Think I would look into the AOD as it has over drive good for cruising, then the C4 / C5.
BTW if you do go with a C6 Gear Vender makes a over drive that bolts to the back of the trans but its not cheap. They may make for the C4 / C5 but I have never looked.
Oh I have a NP435, (granny 4sp) with Advance Adapter's over drive behind the 300 six in my 81 F100 flare side 4x2
It is a back up to pull my open deck car trailer.
Dave ----
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