66 GT 350 automatic transmission information

[aboss4tg]

Is there a vin stamped on the automatic transmission housing? I have a 66 Hertz that was converted to a four speed and want to convert back to an automatic. Recently purchased a C4 and noticed a vin or series of numbers stamped on the top side on a flat tab. The one I purchased reads 135920 and not sure if this is a vin number.



Todd

[Bob Gaines]

Is there a vin stamped on the automatic transmission housing? I have a 66 Hertz that was converted to a four speed and want to convert back to an automatic. Recently purchased a C4 and noticed a vin or series of numbers stamped on the top side on a flat tab. The one I purchased reads 135920 and not sure if this is a vin number.



Todd

No vin on 66 auto trans. Be sure you are looking at a 66 production year C4 case .

[J_Speegle]

Sounds like you purchased a C4 originally from a 68 on up car, truck or van depending on how its equipped or if its been modified for floor verses column shift.

[98SVT - was 06GT]

No VIN - however there were differences in the auto trans for the HiPo. The Servo cover is one you can see externally. I think the valve body also had some changes. The "regular" HiPo Mustang and the GT350 used the same trans so nothing Shelby specific to find.
68 up the Feds changed the rules on VINs and where they needed to be stamped. Today you can find the VIN lasered, labeled or stamped into about every part - engine, trans, rear end, fenders, doors, etc. Just about anything a chop shop could sell.

[S7MS427]

No VIN - however there were differences in the auto trans for the HiPo. The Servo cover is one you can see externally. I think the valve body also had some changes. The "regular" HiPo Mustang and the GT350 used the same trans so nothing Shelby specific to find.

+1. The Hi-Po C4 for a 1966 Hi-Po Mustang is a rare beast indeed. If you can find one, expect to pay a substancial premeum over that of a standard C4.

There were three major differences made by Ford between the high performance C4 and the standard unit that was used with all other non-Hi-Po cars:

• Valve Body — The throttle pressure boost valve spring and intermediate servo accumulator spring were lighter and the separator plate had two holes that were enlarged, one from 0.047 inch to 0.070 inch and the other from 0.125 inch to 0.188 inch.
• Intermediate Servo and Cover — The intermediate servo was larger which provided additional area for the piston face and subsequently more force on the intermediate band which resulted in better 1-2 shifts.  This servo is identified by a large cast "C" on the cover rather than the "A" that the standard Mustang C4 used.  The "A" servo piston is 2.84 inches in diameter and the "C" servo piston is 3.13 inches in diameter.
• Governor — Ford changed the secondary valve in the governor by reducing the weight from about 19 grams to 12 grams, 37% lighter.  This moves the wide open throttle shifts points into the 5800 RPM range.  Contrary to what has sometimes been reported, Ford DID NOT install a lighter spring in the governor to achieve higher shift points.

Good luck in your search, if you find more than one, please let me know as I've been looking a long time for one I can aford. I don't htink that is likely to happen, but I have to ask...

[aboss4tg]

TY for all your response to my question. I purchased the transmission from a friend that had it rebuilt and never installed after rebuilding. Should be a good start for the short term until I can find an original.

Can a C4 be built with all the parts that make it a HI PO?

[Steve McDonald Formally known as Mcdonas]

Contact Roy in the posts on this subject he has extremely detailed drawings and modifications to make a c4 for a HiPo

[Bob Gaines]

TY for all your response to my question. I purchased the transmission from a friend that had it rebuilt and never installed after rebuilding. Should be a good start for the short term until I can find an original.

Can a C4 be built with all the parts that make it a HI PO?

Although genuine hipo trans is preferred it is definitely problematic to find. Building a hipo trans out of a generic C4 is the most practical way . Parts, tags etc. are available to make the conversion to similar performance and the look good enough for concours. That is if that is your goal.

[S7MS427]

Contact Roy in the posts on this subject he has extremely detailed drawings and modifications to make a c4 for a HiPo

Thanks, Steve. However, you were also a big help on this project.

Can a C4 be built with all the parts that make it a HI PO?

aboss4tg, Check out the GT350H section of my website for a narative of how I converted a plain jane C4 out of a '67 Mustang to serve duty in my GT350H. Much credit for this information goes to Bob Mannel for his amazing book "Mustang & Ford Small Block V8, 1962-1969" (RPM Press, 2014) as well as others that are listed in my atricle. Link to my website is in my signature.

I would say that a 1966 transmission is the best to start out with as there are some minor differences between that one and the 1967 version I used. If you are using a transmission out of a '65 or '66, the shift kit from Transgo will be different than the one I used. Good luck and please let us know how it goes. You may contact me privatley if you think that will help.

[J_Speegle]

If your going to make one remember there are running changes you should consider since not all Hipo 66 C4's look the same in every detail.  There are threads already on the site that go into depth on these.

[aboss4tg]

A lot of good information everyone has provided. Considering looking for a 66 transmission and will try and update when I get started.

Todd

[warwick]

Bob Mannel also wrote an article specifically on 289 HiPo C4 Automatic in Fairlaner May/June 2007. It offers substantial detail. Bob is prob on this forum.

As an owner of an orig 66 hipo C4 I would say they are different-I would say shift points are above 5800 and they only stay in first if selected, otherwise they shift out of first very very fast.