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Discussion Starter #1
Hello,

I soon have to rebuild my stock C4 transmission (early type, 24 spline). It's a '66 coupe C-code currently built to A-code specs. Engine is fine, but when it needs a rebuild in the future, I will go for K-code specs. I want to prepare the C4 for this future scenario since it's in need for a rebuild anyways. I know that the C4 servo should be a "C" type (rather than the current "A" type), but that's the only difference I have been able to look up.

What other differences are there between the standard C4 (for C-code and A-code cars) and the K-code mustangs?

Any recommendations for suitable kits that will do the conversion from standard C4 to hipo C4?

Will the current A-code engine setup work fine with a hipo upgraded C4?

Kind regards
Anders
 

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Anders, is this a full concourse 'original' sort of thing, or do you just want your transmission to stand up well to more power and torque?


Because that being the case, just get a good shift kit! It should include everything you need to improve your shift quality, and help prevent you from burning things up. If your transmission is old and tired and in need of a rebuild anyway, just go all out and put in new friction materials while you're at it. The C4 is considered a great transmission to learn on, because of its simplicity.


With new friction surfaces and a shift kit, properly adjusted, that transmission will handle more than your 289 could dish out without splitting down the middle.
 

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I'm with Grimbrand on this. The C4 is an excellent transmission! One of the best reprogramming kits for your C4 is the TransGo 45-1. Coupled with a Sonnax "C" intermediate servo & a quality overhaul kit with Red Eagle frictions & bands your C4 will laugh at anything a 331 can throw at it. Pay close attention to clutch clearance & gear train end play & your transmission will live a long & happy life. While your in there & if budget allows upgrade to a torque converter in the 2400 - 2600 rpm stall speed. This will compliment your engine characteristics better than any stock converter.
 

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No such thing as hipo C4. the hi[o came with a 4 spd behind it. That said, the shift kit equipped C4 will be fine for you. LSG
 

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My HiPo C-4 lasted until about 110,000 miles. I rebuilt it myself. A lot of small, but important differences between the HiPo and the regular C-4.

That said, I would not try to replicate the old HiPo C-4. I would get a quality rebuild kit and a looser convertor and run it.
 

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You guys don't recommend upgrading to a larger input shaft from 70 C4? Going from the 24spline to 26 spline? I was curious on this as well if I ever have to rebuild my C4. Knock on wood, hopefully not for awhile.

.
 

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You guys don't recommend upgrading to a larger input shaft from 70 C4? Going from the 24spline to 26 spline? I was curious on this as well if I ever have to rebuild my C4. Knock on wood, hopefully not for awhile.

.
If you are going for big power sure. I had my stock converter rebuild and reflashed and don't plan on more than 325hp so i wasn't concerned and i stuck with the 24 spline. Agree that 24 spline torque converters are starting to get harder to find.
 

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I just had my C4 rebuilt, and like you, it is going behind a 289 built to/like the period "k" code engine power. I ended up doing what everyone stated above, mildhe shift kit, C servo, 2400 - 2600 stall converter, and a B&M oversize oil pan just for better cooling. My builder is a Ford guy that knows his stuff and C4's very very very well and said with what he had just built for me, that it is more than cabable to handle what you are I are putting in front of it. I could have gone with a more aggressive shift kit, but it all has to do with your intended use and mine is a spirited weekend warrior. I wanted it to be agressive, but not overlly agressive goving me whip lash all the time.

As for the older C4, I was told that parts for them are getting harder and harder to find if something needs replacing. If it is a 70 and newer C4, parts are far more readilly availabe for them. I was a bit lucky, my C4 was not origional to the car, it came out of an early 70's Maverick which has the 26 spline shaft.

I was going to rebuild it myself using the Badshoe video, but finding the time for me to do it....it was worth having a builder who knows what he is doing rebuild it correctly the 1st time.

Best of luck, think you will be fine
736058
with a shift kit and c servo.
 

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A shift kit is a good idea, of course, but adding a C servo would be a great upgrade.

736059
 

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Discussion Starter #10
Thanks for the very informative replies guys, this helps a lot. I'll stick with the 24 spline setup as I'm not aiming to go crazy HP wise. Ideally around 300HP when the engines is up for a rebuild (hopefully in some years in the future, was just dyno'ed, [email protected] RPM).

Just to wrap up the above suggestions (and please correct me if I misunderstood), I should go for the following:
  1. "C" servo piston and cover kit: https://calponycars.com/collections/transmission/products/1964-1973-c-servo-piston-cover-kit (@22GT: thanks for the info)
  2. Shift kit, TransGo Performance 45-01: https://www.summitracing.com/parts/trg-45-01/ (@Pony Gaz: Thank for the info)
  3. Rebuild kit (soft components), TCI 528600: https://www.summitracing.com/parts/tci-528600/
  4. Clutch plates, TCI 524000: https://www.summitracing.com/parts/tci-524000/
  5. Intermediate band, TCI 525500: https://www.summitracing.com/parts/tci-525500/
  6. Reverse band, TCI 525505: https://www.summitracing.com/parts/tci-525505/
Will this be overkill for a ~270-300HP build?

@Grimbrand: It's not a concourse correct build, but I'm aiming for an all stock K-code appearance. I'm fine with modern and better internals. However, I would prefer that the car is serviceable as per the old manuals, e.g. not having to rely on modern synthetic tarnsmission fluids and so on. Ideally, I can take out the old shop manual and just follow the instructions in that.

@LSG: Yes, in '66 you could get the K-code with a C4 aut. transmission

@Fly2xs: Which torque converter did your builder go for brand wise?

@66kcar: Which torque converter do you have?

Kind regards
Anders
 

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I'm with Grimbrand on this. The C4 is an excellent transmission! One of the best reprogramming kits for your C4 is the TransGo 45-1. Coupled with a Sonnax "C" intermediate servo & a quality overhaul kit with Red Eagle frictions & bands your C4 will laugh at anything a 331 can throw at it. Pay close attention to clutch clearance & gear train end play & your transmission will live a long & happy life. While your in there & if budget allows upgrade to a torque converter in the 2400 - 2600 rpm stall speed. This will compliment your engine characteristics better than any stock converter.
No such thing as hipo C4. the hi[o came with a 4 spd behind it. That said, the shift kit equipped C4 will be fine for you. LSG
LSG you are way off base. The Hipo C4 was used in 915 '66 GT350H models as well as many non Hertz GT350s. It was also an option on late '65-66 K code Mustangs and Fairlanes, and a different version was made for '67. Tag codes are PCW-BA for '65-66 and PEE=K for the '67 only version.
Randy
 

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My HiPo C-4 lasted until about 110,000 miles. I rebuilt it myself. A lot of small, but important differences between the HiPo and the regular C-4.

That said, I would not try to replicate the old HiPo C-4. I would get a quality rebuild kit and a looser convertor and run it.
You guys don't recommend upgrading to a larger input shaft from 70 C4? Going from the 24spline to 26 spline? I was curious on this as well if I ever have to rebuild my C4. Knock on wood, hopefully not for awhile.

.
my289
While the 26 spline shaft itself is stronger , it rips the splines out of the planetary hub it slips into. I have run the 24 spline input for 45 years of continuous drag racing in my '66 GT350H and never had a failure. It currently runs 10.90s-11.ohs but has been in the 10.70s in the past. 1.48-1.50 60' times has it "leaving" with the wheels in the air. 24 splines are not an issue @ less than 700 hp.
Randy
 
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Great info. Tks Randy.
 

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You guys don't recommend upgrading to a larger input shaft from 70 C4? Going from the 24spline to 26 spline? I was curious on this as well if I ever have to rebuild my C4. Knock on wood, hopefully not for awhile.

.

Yes, upgrade the impute shaft and pump with the later model parts. I did that when I was faced with the same decisions. Also, a transformer shift kit. Back in the day (late 90s) I added the larger modulator and a 2500 stall converter. It was a good tranny. I sold it when I converted to a T5z in 2010.
 

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Bruun,

I went with a B&M Holeshot. Living in NASCAR country, I actually found a custom builder of torque converters, yes.....fram scratch, not rebuilds. If I were racing and or had an unlimited budget, I would have gone with a custom new converter built for my specific car. Since I am not racing and willing to spend about $2,000 for a torque converter, after all the research I did, I went with a B&M and feel as a spirited weekend warrior pushing between 250 and 300 hp estimated, it should fit the bill. I can't recall exactly what I paid, but think it was between 350 and 400. I didn't feel comfortable buying an Autozone part and could not find a builder (not custom, but a rebuilder) who I felt comfortable with so B&M it was. I haven't got my 289 and transmission installed in my car yet to give you an after action report.......but hopefully by Christmas, everything should be in and tuned correctly. Good luck my friend!
 

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Discussion Starter #16
So, here’s an update on the C4 standard to hipo upgrade. I need some troubleshooting advice: C4 trans 64-66 valve body (green-dot).

Freshly rebuilt with new bands, clutches, steel, gaskets etc. TransGo 45-1 just installed + C-servo.

All, except 2-3 shifts works perfect (reverse, 1-2 shift, kickdown have nice crisp shifts).

The 2-3 upshifts are sporadic. They happen, but not always, also an issue after a kickdown shift from 3-2.

What to look for (vacuum and modulator are ok)?

I had a trusted and good old-school mechanic do the job. He has experience in rebuilding the C4’s. But the TransGo requires some minor mods to the seperator plate and check balls needed to be removed, new valve springs also. He said the TransGo instructions were very clear (unlike other shift kits he previously installed).
 

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"No such thing as hipo C4"... You might want to tell that to Carrol Shelby if he was still alive... He put Plenty of Special C4's behind 289 Hi-Po engines starting in 1966 with 900+ Automatic GT-350H Hertz cars...and then again in 1967...

:eek:)

Tony K.
 

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As I recall Shelby had one of his personal Cobras fitted with a C4.
 

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Bruun, this sounds like an internal fluid leak in the circuit to the high/reverse clutch. Also you say the 3-2 down shift is not perfect but sporadic is an indication that the hydraulic circuit to the high/reverse clutch has an issue. This circuit is also for the release side of the intermediate band servo piston. For the 2-3 shift the intermediate band has to release & the high/rev clutch is applied. A possible source of an internal leak to the high/rev clutch are the front 2 steel sealing rings on the stator support at the rear of the pump which may have been unknowingly damaged while refitting the pump into the case. It may not show up in reverse, where the high/rev clutch is also applied because the clutch is applied with about 3 times the pressure it is in high (direct) gear.
Another thing might be excessive gear train end play. Correct end play is critical to proper sealing of both the high/rev & forward clutches.
Cheers. Gaz
 

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Valve body issue for sure. Find another "green dot" valve body and put the shift kit in it. OR before you take out the valve body , take it for a "spirited" drive , in "drive" . Once in second pull the lever back to low ( before the 2-3 shift) and then manually shift to high. If it shifts immediately and firmly it tells you the problem is indeed in the valve body. If it still acts up , you could have a leaking rubber seal on the servo or in the high gear drum.
Randy
 
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