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3 speed manual transmission question

Darryl M

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What is the difference in V8 and 6 cyl 3 speed transmissions? I’m not asking about adapters or transfer cases. I’m asking for info from someone who really knows the difference in the way they are built, and if the 6 cyl Tranny will be ok behind a 302 for normal driving. Thanks
 

jamesroney

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Hello, I can try to help. But you are asking a very open ended question, and there are a LOT of assumptions.

That being said, they are both of a very similar design. The RAN has a 9-3/16 case and the RAT has a 9-11/16 inch case. The V8 RAN has a 9-3/8 adapter, and the RAT has a 8-7/8 adapter. When used behind a 6 cyl, the RAN has a 6-1/2 inch adapter and corresponding tailshaft. The RAN has ratios of 3.41 and 1.86 and the RAT has gear ratios of 2.99, 1.46.

Case length is important, because three fundamental design constraints for strength on a countershaft type manual transmission is centerline distance, gear ratio, and gear width. The RAT case got LONGER, the gears got WIDER(?), the ratios got CLOSER, and the synchros improved. The end result is that the RAT is stronger. But it also means that there are almost no parts that will interchange between the two.

Do you have a specific question?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
33,057
Can the I6 transmission take V8 HP, yes it can.
Does the I6 transmission fit well behind the V8, no the lengths are all wonky.
There are some different ratios, just enough to make driving less enjoyable but not enough to make any meaningful performance gains.
 

thegreatjustino

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The 6-cyl transmission has a shorter output shaft and corresponding adapter to the Dana 20 to account for the longer block length of the engine. If you attempt to use a 6-cyl transmission behind a V8, the stock mounting points and by extension, driveshafts will not work.
 

Speedrdr

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Nov 27, 2017
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Not trying to hijack the thread, but how do you tell the difference between the RAT and RAN 3-speed? I’ve got a 3 on the tree behind a V-8 in my ‘77.

Randy
 

jamesroney

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Not trying to hijack the thread, but how do you tell the difference between the RAT and RAN 3-speed? I’ve got a 3 on the tree behind a V-8 in my ‘77.

Randy
Measure the main case from the bell housing to the transfer case adapter. RAT is 9-11/16 long and is 1/2 inch longer than RAN at 9-3/16.
 

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Speedrdr

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Measure the main case from the bell housing to the transfer case adapter. RAT is 9-11/16 long and is 1/2 inch longer than RAN at 9-3/16.
Many thanks! Will have to get under it and measure in the daylight.

Randy
 
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Darryl M

Darryl M

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Joined
Apr 21, 2020
Messages
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Hello, I can try to help. But you are asking a very open ended question, and there are a LOT of assumptions.

That being said, they are both of a very similar design. The RAN has a 9-3/16 case and the RAT has a 9-11/16 inch case. The V8 RAN has a 9-3/8 adapter, and the RAT has a 8-7/8 adapter. When used behind a 6 cyl, the RAN has a 6-1/2 inch adapter and corresponding tailshaft. The RAN has ratios of 3.41 and 1.86 and the RAT has gear ratios of 2.99, 1.46.

Case length is important, because three fundamental design constraints for strength on a countershaft type manual transmission is centerline distance, gear ratio, and gear width. The RAT case got LONGER, the gears got WIDER(?), the ratios got CLOSER, and the synchros improved. The end result is that the RAT is stronger. But it also means that there are almost no parts that will interchange between the two.

Do you have a specific question?
Thank you so much. Did the RAT come with the V8 and the RAN with the 6 cyl from the factory?
 
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Darryl M

Darryl M

Jr. Member
Joined
Apr 21, 2020
Messages
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Loc.
Angie
Measure the main case from the bell housing to the transfer case adapter. RAT is 9-11/16 long and is 1/2 inch longer than RAN at 9-3/16.
There is a tag on the right side of the transmission that says RAN or RAT
 

DirtDonk

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Bronco Guru
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Nov 3, 2003
Messages
42,670
And theoretically found only on’72 and’73 models as part of the “ambient sensor“ system I think.

Those so equipped would also have a roughly disc-shaped thingy screwed to the driver’s A-pillar above the top hinge.
 

jamesroney

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Thank you so much. Did the RAT come with the V8 and the RAN with the 6 cyl from the factory?
Well, here we go again. Specific questions get specific answers. General questions get vague and incomplete answers.

No, the RAT did not always come with a V8. If you ordered the 240 cubic inch 6 cyl in a 1970 Ford Torino Police Deputy...you got a RAT 3 speed.
If you ordered a 6 cyl or V8 Bronco in 1967, you got a RAN transmission.

So in general, the answer to your question is "yes." But there are exceptions to the rule. Any statement that is generally true, but has a single exception is by definition false. So the correct (and wrong...) answer to your question is "no." (hey! I just invented Fake News!!!)

But this is an early bronco forum...so it's pretty straightforward. But I need more of the transmission ID. Do you consider the HEH 3 speed the same as a RAN? Because all 1966 Bronco 3 speeds are HEH. and the HEH is identical to the RAN. I have no clue why Ford changed the nomenclature in 1967.

1966 Bronco 6 cyl = HEH-DA
1966 Bronco V8 = HEH-DB
1967-71 Bronco 6 cyl = RAN-N
1967-68 Bronco 289 = RAN-R
1969-71 Bronco 302 = RAT

After 71, you are on your own...For some real confusion, this same discussion when it pertains to the toploader 4 speed gets beyond silly. There's HEH, and RUG, and big block, and small block, and big in and short, intermediate and long output. and close ratio vs wide ratio. The DavidKee Toploader ID chart is great...but missing a few here and there. My 67 Shelby 428 is a RUG-S but it uses the C5AR case, and it's big in / big out...but short. I have trouble keeping it all straight. The people think that the 390 is a big block, but it is not a big block toploader. ugh.
 

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