I had to go back and look at the original post. The c-6 is a horsepower hog, but for what you are doing, it doesn't really matter. Does the guy have receipts for the rebuild on the C-6? It is going in a truck that is most likely a "cruiser" right? 3 tenths one way or the other doesn't likely matter, and the trans will be strong enough, I'd say go for it. You could hunt for a good C-4 or C-5 for a while, in this case, I don't think the performance disadvantage matters.
Looks as though there is some missinfomation being stated here. First of all, 4 & 6 cylinders C4s can easily be upgraded by replacing the forward and direct clutch packs with units that have the 4 and 5 clutch packs. Second, the C5 is a C4 with a lock up clutch the valve body and case are different to allow porting for fluid to lock up the converter. I have used C5 internals in many C4 builds and they worked just fine. I have a C4 out there in an old Mustang that 2 brothers bracket race. I built the trans for them during their Christmas break in 1994. I made them go through it with me so they would know how it worked. Through college and families they have kept the car and raced it. Somehow the trans has lasted all this time and abuse. They have blown 3 engine in that time but that old C4 keeps hanging on. So yes you can build a tough C4 and not break the bank. I am proud of the one lasting so long but have no idea why. But when a guy argues that he HAS to have a C6 behind his street use 302, I refer him to the two brothers and their Mustang.
I had a 55 F-100 with a warmed over 302 and a 65 Mustang C4. The trans was in that truck for over 30 years that I knew of with No Issues what so ever. I occasionally carried a motorcycle in the back and towed a small trailer. No problems. The lady I sold it to pulled a small trailer for her Pool Cleaning business and didn't have any issues either. On a stock or mild 302 I really wouldn't want to give up the 25-30 HP difference between a C4 and C6 - that's about 10% of your power and Yeah I reckon you could tell the difference on a street car (truck). As for what to look for - this isn't all that complicated really. There is no difference between car and truck C-4's. The 71-81 are the best ones to start with. The 1970 only version is a bastard child - 26 spline input and output shaft, one year only. 71 and later are 26 spline input and 24 spline output. 64-66 are the Dual Range or Green Dots, leave those to the restorers. 67-70 are normal pattern but with the 24 spline input shaft. If you're going with the larger 26-spline input shaft in an earlier C4 (prior to 1970), you will need to change the reverse/high clutch drum (forward most clutch), forward clutch cylinder, #3 thrust washer, and front pump. If you can find a 71-81 that is the smartest choice and there are MILLIONS of them out there. The C5 is an improved C4 with locking torque converter and slightly differnt valve body programming for better fuel economy. Otherwise they are the same as a C4. The C5 case is easily identified by casting numbers that begin D2, D3, D4, D5, and D6. There were two bellhousing sizes for V-8 C4 transmissions - 157-tooth flex plate and 164-tooth flex plate.There was also a pan-fill C4 designed for trucks with a 164-tooth flex plate.It doesn't really matter which you use as long as you have the correct motor to trans plate for the bellhousing you choose. There is also the C3 - Pinto's, Mustang II's , and Fox Boides with the 4 cylinder and Euro V6 got their own C4 with a smaller bellhousing and 143-tooth flex plate to clear smaller transmission tunnels. They also had a unique valve body. Stay away from these.
So many statements about how much horsepower a C6 wastes, but under what conditions? I assume high RPM, where you're pumping a lot of fluid and friction losses are greater. HP doing no work (ie, wasted) does nothing but generate heat. 40HP worth of heat is 101,777 BTU. How big is your transmission cooler?
Man, I just cant win, gotta wonder if there is some kinda secret communist plot against me on here... For years I preached about how stupid it was to leave 20hp on the table, and everyone and their dog would jump on my ass, so now I finally give in and say "f*ck it, for the typical HAMB cruiser, it just doesn't matter" and now I get it from the other side! Just kidding guys, its not a declaration of war, just a little ironic humour. Would I PERSONALLY run a C-6 behind a small-block ford? HELL no! I am putting a built C-4 behind the cleveland I am putting in my falcon, and I have a small-block C-6 for sale, and I am spending big $$ to mate one with my FE, so that should be obvious. Then again, I wouldn't run a 2.79-3.08 rear gear with a 30" tall tire, and its the HAMB "house" combo...Would I use an Edelbrock 625? Not on a bet, but again, that's the carb of choice on here. I have to adjust my suggestions to what these guys wants and expectations are, and over the time I have been here, I have come to accept that to 90% of the guys here, performance just doesn't enter into the equation, and I have to adjust my suggestions accordingly. Plenty of mis-information all right. There are more differences between the C-4 and C-5 than just the lock-up valve body. Rather than spend 20 minutes typing, I will just copy and paste. C4 vs C5 comparison,differences,improvements... I was lucky enough today to score a c5 trans out of an F100.I have pulled it down to do a real comparison of the improvements + differences. It even has a 'H' servo,the first i have ever seen. The way to pick a c5 from the outside is Deep pan(2.5"deep) Fine thread on fr band adjuster Large cooler fittings(1/4" thread) E2 casting code Starting at the back ,the #9 thrust washer has the normal 2 locate tangs but also has 2 cutouts to line up with an additional lube hole discussed in the c4 build post.The hole is drilled through the case to meet up withthe cooler return passage.The hole is 9/64". The cooler return passage is also drilled to 13/64" which is larger than a c4(5/32" The rear roller clutch spring retainer has the wafer springs clipped to it instead of being loose like a c4. The front pump has no checkball in the stator support cooler passage and this passage is drilled to 1/4".A c4 has the passage at 3/16" and a ball fitted. The ball can be removed on c4's to improve the oil flow in the cooler circuit. Now moving inside, the sun gear where it fits into the front + rear planetaries has lube holes drilled to get the oil from the output shaft lube circuit to the gearsets.The C5 has 4 holes each end @.094" .The c4 only has 3 holes each end @ .040". The forward hub has 5 clutches.It has a different bevel plate in the bottom of the clutchpack Which is .310"overall with a .110" step. The c4 bevel plate is .265" with a .125"step. The hi/rev hub has 4 clutches @.078",All steels @.090" with a dished cushion plate on top. Both the fwd + hi/rev clutches have a thin .140" pressure plates. The hi/rev hub has the circlip grooved machined higher also as has been mentioned before that the c5 hub has the capacity for more clutches. The top edge of the groove is down 1.020" where a c4 is bown 1.082". This trans is a case fill type and the input shaft has a recess about half way along it and it seems to be hardened. I hope this info is useful as there has been a lot of discussion on the differences .These mods could be done to a c4 to improve the oiling to c5 specs. So, again, like I laid out very clearly in my previous posts, 1)you can expect a C-6 to hurt performance to somewhere in the range of 3 tenths in the 1/4 mile, which I would feel as long as I was conscious, but anyone who cares so little about performance that they choose to run a 3.08 gear would probably be oblivious to, and 2) the internal differences between the C-4 and C-5 relate to improved hydraulic circuitry. All accurate, all correct. I know better by now and usually ignore these bullshit fests, but I have direct first hand experience wiith the transmissions in question here, figured I would speak up.
Ford was aware of the frictional losses in the C6, that's one reason they kept the more-complex FMX in production so long; it was more efficient compared to the C6 and that translated into better fuel economy. Running a C6 will cost you anywhere from 1-3 MPG in 'normal' use compared to a C4 or FMX..
My knowledge of the C4/C6 is limited to swapping a few in and out. Sounds like good info on this thread, I'm in for future reference. Thanks to all that posted.
Not trying to be a wise ass here, just shaking my head and wondering. Where is all this resistance coming from that costs 40 horsepower and why is it so much more than the C-4 or FMX? A logical explanation would help me to understand. I don't see how the resistance from unapplied clutches would be much different, the difference in resistance from loaded gears meshing together doesn't seem like it would be substantial The C-4 has a smaller pump than the C-6, but they both constantly run against a pressure relief valve, so where is the big difference? I remember reading an interview with Joe Hunt talking about Scintilla mags in the 80's. He said that sometime somewhere someone turned the shaft on a Scintilla mag with their fingers and noticed that the magnets caused resistance to rotation. They then pulled a number out of thin air and claimed that at 6000 RPM that mag would cost 20 horsepower to run, for some reason everyone just assumed it was fact. He then stated that his test bench that he had been using for more than 20 years was powered by a 1/4 horse electric motor. He then said that the resistance from the magnets is the same at 6000 as it is when turning with your fingers. Just sayin'.
From the tranny builders who are a lot smarter than me on this, I am told it has to do with much heavier components - the drums etc. so it is rotating weight that causes the majority of the HP losses
HP loss as published by CarCraft about 20 years ago. These were stock transmissions measured for hp loss from input to output with no real comment on whether is was due to rotating weight, drag or anything else. Powerglide_____18 hp TH-350________36 hp TH-400________44 hp Ford_C-6______55-60 hp Ford_C-4______28 hp Ford_FMX______25 hp Chrysler_A904__25 hp Chrysler_727___45 hp
I wasn't gonna say anything more, but I do probably have a better handle than most posting here as to why the C-6 is such a power hog, having built a couple, and made some fairly race oriented mods to them. I think its a mixture of several different factors, or more accurately, I surmise that from some of the mods that show an et gain at the track. Changing the #9 thrust washer to a needle roller bearing is worth roughly .12 according to most sources, and changing #5, #7 and #8 is supposed to be worth somewhere in the range of an additional .05-.07, so I surmise from that that the stock heavy internals are stacking up against the back of the case under hard acceleration, so that's one factor. Another factor is that the original C-6 design relies on the intermediate band holding the drum in second, so when you shift into third, the mass of the drum has to instantly accelerate up to engine speed, this is a big hp hog, just like it is in the 727, and the fix is the same, to switch to a non-band apply manual valve body like the Turbo Action. I had the #9 roller bearing in my trans, as well as the TA valve body. The third factor is probably the weight of the internals, and the helical cut planetarys, I know from gains I have seen using straight cut planetaries in a TF, the helical cut planetary gears are also a hp hog, but these are used in all trans, and using straight cut planetaries in a street car are REALLY LOUD. The C-6 planetaries look like they are cut on a higher angle than most, and I know Ford had a "thing" about their cars being quiet inside. My WAG is the big difference in the C-6 between some other designs is that the slightly higher helical angle planetaries have a two fold effect, 1) they take more power to turn, and 2) the high helical angle is pushing the trans internals back against the rear thrust washer with more force than other designs. I am just reasoning this out, I don't know it to be a fact, and if Paul Forte or Jim Paquet shows up and tells me I am all wet, I'll accept that. With the exception of the needle bearing thrust washers, most of these mods are not what most people would consider "streetable", the TA valve body is EXTREMELY harsh at part throttle, and most people would find the lack of low gear braking unacceptable.
Should also mention, the needle bearing thrust washers are not a bolt-in they require machining in each position, so it is not cheap, and the guy that does the machine work has to have solid skills. Its not a simple mod.
See Olskool34, I knew there was in depth info to be had on this subject, just gotta get the attention of the right HAMBers. I've never had a C6 apart but I can sure visualize how the larger internals could eat up some power just as falcongeorge said with inertial and thrust loads much higher than it's smaller C4 counterpart. Great info in this thread. In the everyday world, my '55 F100 is doing just fine with the cheesy early C4, hauling, towing, doing everything a good ol' truck should do. But when it does finally give up, the whole power train will be replaced with Chevy stuff, ha, ha, ha........
Lots of info here! Thanks guys. At 400 for the C6 I think I am going to wait. This is a truck I am putting together for my wife to take to the farmers market, grocery, etc. I just like the idea of the C4 more now because of this thread.
All this makes me glad I'm a GM/Chevy guy when it comes to building HP. Don't forget to see which phase the moon was in when your trans was manufactured as that might require a different bolt pattern or convertor or... Ok, just ball busting the Ford guys a little. A C4 in Motown should be an easy find. Joel's Trans Service in Plymouth (I think) might have rebuilt units on the shelf for exchange. It was indicated to me when my associate needed built a C4 for his racer. I don't think there's a better trans guy this side of the Mississippi. Don't forget "Parts Galore" yards which are you-pull-it places. Good luck.
These days you will find as many, if not More, C-4's in newer built automatic drag cars then you will TH350/40 trans! They have become the drag racer tranny of choice!
So we now know more than we ever wanted to about C-4's and C-6's and the answer to the OP Question is a C4 will be perfect for your Effie
.................................I run a Rubber band & 2 sticks....................................... works Great No Problem with it in over100,000 miles just my 3.5 cents or when the Cows come home!
I can agree with this as well. I'm of the opinion that for a typical HAMB cruiser, it doesn't matter very much if you use a C-4 or C-6, However, for the reasons I stated above regarding input shafts and valve bodies, I would avoid a pre-'71 Core. Its not really relevant as long as you follow my advice, but I will also mention that there was valve body bolt pattern change in '71, early and late valve bodies do not interchange. FWIW, I am using a '67 case-fill C-4 core for the trans behind my Cleveland, because I have it, but I have been building C-4s for 3 decades, so I am knowledgable about doing the input shaft swap, the valve body variations, and so on. If I didn't already have this trans, and had to shop for a core, I would look for a case fill C-5 core, for the improved hydraulic circuitry and the fact that pan fill cases don't easily fit sixties compact trans tunnels, its going in a '67 Falcon. I haven't addressed the difference in pan fill or case fill cases, its not relevant if you are putting the trans in a pick-up. Aftermarket support is better for the '71-up trans, KISS.
Something about a Ford slush box in a GM drag racer, and then the word "tranny", well there's one helluva good joke in there somewhere but it escapes me at the moment.
Couple days ago, my daughter and I were walking past my neighbours house, and he was out front with a different truck than usual. I said "didja buy a new truck Larry?" so he says "no, its a loaner, mine is in getting the tranny worked on" so I grinned real big and said "so did you blow a tranny??" He looked at me kinda funny and said "well, uh no, it just needed servicing". I bet he thinks I'm a little odd now...on second thought, hes probably thought that for a while now...
Crusty Nut, 1-Shot and others are steering you right to consider an AOD. The transmission is bulkier than a C-6, but the overdrive is just what you want for a truck so you can use a higher number rear end ratio and pull some loads from a dead stop without cooking your torque converter and bands. The OD gets you cruising on the highway without the engine screaming. Get the later AOD with a stamped steel drum, and change out for bigger pistons, more and better steels and frictions. You'll like spending a little more, having your cake and eating it, too.
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