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351C.....C-4 or C-6

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changinlatitudes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote changinlatitudes Quote  Post ReplyReply Direct Link To This Post Topic: 351C.....C-4 or C-6
    Posted: 07-September-2017 at 6:18AM
Have a 351c with a C-4 in my Montego at the moment. Gonna need a rebuild. I have a 351c/C-6 sitting in my garage (also have the C-6 driveshaft).  I know most of the pros and cons about C-4 vs. C-6 (weight difference, etc.). I'll not be racing it at the track, nor will I be taking a thousand mile trip on it. My car is a basic street car/turnpike cruiser. Gas mileage doesn't bother me. The Cleveland won't be modified much beyond what it already is...maybe putting a little better camshaft and headers on it later.

My question is this: Can I take the C-6 off my "spare" motor and install it in my Montego in place of the C-4? Like I said, I have the driveshaft. I know I'll have to move the trans crossmember back a hole, and get a different trans kickdown rod.....but is it a direct bolt on swap with what I have, or are the bellhousings different, even though they both are off a Cleveland.

Both will need rebuilt, but is one "cheaper" to rebuild than the other?  I won't be rebuilding, of course. I'll find a reputable shop for that. Transmissions scare me to death.

On the same note, I'll be putting my spare 351c into the Montego this winter, but I need a transmission now and really can't wait for the cold weather project.

Thanks
Matt

1969 Mercury Marauder 390
1972 Montego MX
2003 Mercury Marauder 300A
1994 F-150 5.8
2016 Ford Fusion Titanium
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dave302 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dave302 Quote  Post ReplyReply Direct Link To This Post Posted: 07-September-2017 at 6:43AM
The Transmission Bell housings should be exactly the same.
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Big Bird View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Big Bird Quote  Post ReplyReply Direct Link To This Post Posted: 07-September-2017 at 11:41AM
Bell housing bolt patterns are the same.
Torque converter is trans-specific, and "may" also affect flex plate (flywheel) use.
(Supposed to be different, but, Ford....)
Use the flexplate and torque converter that are from the trans you use and it should bolt in.
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Rockatansky View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 09-September-2017 at 3:49AM
first consider the manual linkage arm on the C6, will it work with the linkage system in the car? look for cable mount bosses on the bell housing if your C4 has them, are they there on the C6?
 
like Randy says the flex stays with the trans, C4 & C6 are different. AOD & C6 are usually the same
 
C4 is more header friendly while the C6 should hopefully be a lifetime trans. labor should be the same for both but parts may be a little more for the C6
 
output speedo tooth count can be a deal breaker with some C6's going into small diameter tire cars but figure yours is on a Cleveland? so the output shaft ~should~ be right for a car
 
everything else being equal i'd leave the car with the original trans, save the C6 for when you think you need it. you may not realize it now but you will see less power to the wheels and more fuel consumption with the C6
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changinlatitudes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote changinlatitudes Quote  Post ReplyReply Direct Link To This Post Posted: 15-September-2017 at 1:04AM
Sounds fair enough. C4 it is for now. In regards to shops, do they charge the same for a rebuild whether it's in the car or drop it myself and take it to them in my pickup. Since show season is pretty much over around here, I'm inclined to just take the whole car to them and let them get trans fluid everywhere, but maybe not if they charge a bunch more for the for labor. Appreciate the input!
Matt

1969 Mercury Marauder 390
1972 Montego MX
2003 Mercury Marauder 300A
1994 F-150 5.8
2016 Ford Fusion Titanium
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MrSmog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrSmog Quote  Post ReplyReply Direct Link To This Post Posted: 15-September-2017 at 1:24AM
Yea a c6 uses like 20-30 hp more the c4.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Don V. Quote  Post ReplyReply Direct Link To This Post Posted: 15-September-2017 at 3:55AM
Neither trans is all that complicated. Try rebuilding it yourself. There are some good manuals for doing your own rebuild and a really good rebuild kit should be less than $250.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 15-September-2017 at 2:16PM
a 'bench job' where you bring the trans removed from the car in the bed of your pick-up should be a lot less than a drive / tow in complete R&R  for the obvious reason of the R&R labor isn't there but you may not get much of a warranty with a bench job because the trans builder / shop owner can't control & isn't responsible for the install. flushing the cooler lines is pretty important & often majorly overlooked by shadetree trans installers. debris from a failed trans left in the cooler & lines can stick up a valve body in a heartbeat & the builder isn't on the hook. hopefully a good shop will have a flusher that heats the solvent & pumps it through the cooler line circuit. modern trans coolers are so dense that you can't clean them sufficiently, the only way to obtain the warranty is to replace the entire radiator
 
it may be well worth the transbucks to let the shop do the install, they'll run a test on the lift as soon as the unit's oiled and a road test. you'd be surprised what you might not notice right away
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changinlatitudes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote changinlatitudes Quote  Post ReplyReply Direct Link To This Post Posted: 21-September-2017 at 1:40AM
Thanks for all the advice. Might as well let the shop handle it all, and I'll teach myself how to rebuild one using the spare C6 later down the line. Now comes the hard part....finding a reputable shop in my area....
Matt

1969 Mercury Marauder 390
1972 Montego MX
2003 Mercury Marauder 300A
1994 F-150 5.8
2016 Ford Fusion Titanium
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 22-September-2017 at 2:21PM
72 GT Ute
   
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changinlatitudes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote changinlatitudes Quote  Post ReplyReply Direct Link To This Post Posted: 23-September-2017 at 12:06AM
Holy Moly that's a LOT of information! I'll definitely take a look at that - Thanks!
Matt

1969 Mercury Marauder 390
1972 Montego MX
2003 Mercury Marauder 300A
1994 F-150 5.8
2016 Ford Fusion Titanium
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rivercrest Quote  Post ReplyReply Direct Link To This Post Posted: 07-August-2020 at 4:49PM
After reading these old posts I did not find the answer to my question; I want to swap out a C4 tranny to a C6 tranny. Both are early 70 ish transmissions and both are currently attached to 351C engines. To do the swap I have to keep the mated flex plates ( bolt pattern ) and my question is : should I be concerned about external engine balance as the flex plates are both weighted but are probably not matching. Thanks for your replies.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Notmikeb Quote  Post ReplyReply Direct Link To This Post Posted: 07-August-2020 at 5:16PM
both should be 28oz imbalance and should be interchangeable as far as balance is concerned. 
-1973 Gran Torino Sport 351C 2V
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 08-August-2020 at 2:52AM
yes flexplates and harmonic balancers are standardized for replacement purposes,

crack a flex and rebalance the engine? no, just swap in a new flex.

351C's are technically called external because there is a weight on the harmonic and flex but these external weights are all the same, standardized to 28.2 oz-in imbalance IIRC. the unique engine specific balancing is done internally, if you were to change the rods or pistons then you'd want to get the internal assy balanced, and the external weights still stay the same.

if you have everything from the flex to the drive shaft, the only thing you need to worry about is the linkage system compatibility to the car. it can be a PITA to source a correct linkage arm, and as i mentioned back when some bells have shift cable mount bosses and some don't. if you're going to use an aftermarket floor shifter no worries

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rivercrest Quote  Post ReplyReply Direct Link To This Post Posted: 08-August-2020 at 5:22AM
I really appreciate the expertise of all of you on this forum and say THANKS.
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