C4 Transmission Issues or Questions

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navyguy66mustang
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C4 Transmission Issues or Questions

Post #1 by navyguy66mustang » Sat Dec 31, 2016 9:00 pm

I am having a few questionable issues with my C4 tranny in my Mustang. So first issue is the transmission pan gasket. It was leaking when I purchased the car so I first replaced the gasket with a new rubber gasket. I checked the surface of the pan for flatness then torqued it to 10 ft lbs. I stopped there because I noticed the gasket bulging significantly. Still leaked as I figured it would. So then I ordered a new pan just in case from CJ pony parts and a cork style gasket. When replacing it I started to torque it again to 10 lbs and the cork gasket started splitting. I stopped torquing it down if I noticed it splitting. Still leaks. So the question I have is would it be safe to replace with another new cork gasket and hand tighten to the point of when it start to bulge slightly but doesnt split. I would say about 7 ft lbs.

Also my shifter has a Drive, Drive 2 and Low. When I put the tranny in Drive 2 it puts me in first gear and wont shift to second until I put it in Drive. I also tried Low and shifted to Drive 2 and it didnt shift from 1st to 2nd. Is this normal or does it need adjusting? It shifts fine once it goes into drive. I also "think" that when I am in Drive it does go into 1st gear but starts me out at 2nd gear. It shift fine though with no rough shifting or slipping when driving. Im guessing a linkage problem if there is such a thing. You guys are wise in your old age and I'm curious to see what ya got. :mrgreen:

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bubba22349
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Re: C4 Transmission Issues or Questions

Post #2 by bubba22349 » Sun Jan 01, 2017 10:10 am

Welcome to the site! The C4 pan bolts are torqued to factory spec of 12 to 16 ft. lbs some of the cheaper cork gaskets are of a poor quality, thin, porous and so can seap as well as split. As a comparison a good one can be found at NAPA. Also don't try to torque the bolts to spec all at once go in steps of say like 3, 7, 12 working slowing back and forth. If you still have trouble you can use some weather strip adhesive (yellow or black) and use it to glue the gasket to the pan then set it on a flat table overnight with weight on it to hold it flat. You may also want to check that the dip stick tube isn't leaking a simple fix with a new O Ring, the other thing that can leak is the Shifter Lever seal in the case is a bigger job requires removing the valve body plus the lever assembly.

On your Duel range trans D is used for normal driving and will start out in Low / 1st and then will shift two times, into second and last into Drive. In D2 the trans starts out in 2nd gear and shifts one time into Drive, this is used when you don't need to use Low / 1st or when street traction is limited like with snow, water etc. The old racers trick to get them to shift all three gears and or hold them in gear longer was is to start out in Low / 1st, move the lever up to Drive and then when it shifts into 2nd pull the leaver into Low this holds it in 2nd until you move it into drive it takes some practice. Better still is to swap in a later model Select Shift C4 valve body (1967 up) and install a good shift kit (TransGo is what I like to use) it will transform and improve the shifting making it so much better with (P, R, N, D, 2, 1) selector pattern. Good luck :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

navyguy66mustang
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Re: C4 Transmission Issues or Questions

Post #3 by navyguy66mustang » Sun Jan 01, 2017 3:34 pm

bubba,

Thanks for the info. Is there a specific brand gasket I should get at NAPA?

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Re: C4 Transmission Issues or Questions

Post #4 by OpelGT+3point3 » Mon Jan 02, 2017 12:16 am

Knock down the holes where they're pooched up. Too far down is better than too far up. I use lacquer thinner to clean the pan rail and case so the gasket doesn't slip. Might even use some sandpaper on both. Watch the gasket edge for distortion.

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bubba22349
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Re: C4 Transmission Issues or Questions

Post #5 by bubba22349 » Mon Jan 02, 2017 7:24 am

navyguy66mustang wrote:bubba,

Thanks for the info. Is there a specific brand gasket I should get at NAPA?


It's in their NAPA line of Filters and Trans parts. Good luck :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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B RON CO
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Re: C4 Transmission Issues or Questions

Post #6 by B RON CO » Tue Jan 03, 2017 10:20 am

Hi, saw your question so I looked at our Mustang, 66 C 4. My selector is labeled P R N , DOT, DOT in a circle, and L. DOT ( first choice after N) will give you second and third. DOT in circle will give you first, second and third. Why is this? Who knows. This is explained in the owners manual, just like Bubba said. Another difference on mine is the kick down is from the linkage, and not from the arm on the carb . On the pan gasket, we used the yellow 3m gasket adhesive, AKA mule snot, or High Tac spray, to hold the gasket in place. I feel the tranny is very thin in the corners and you have to be extra careful. I know I have used gasket maker silicone in the past, sparingly on both sides of the gasket, a little silicone spreads out a long way when squeezed, and some are against that because of the chance that silicone may get into the valve body. I have had good success with quality brand name rubber and cork gaskets ( whatever comes with the filter). As mentioned, flatten the pan rail and tighten it up in the criss cross pattern in a few steps, and then go for the final snug down to make sure you got them all. I don't use a torque wrench, I go for "medium snug". I have been told that Napa type F fluid is the best for these old trannies. Good luck
B RON CO. Still workin' on it!

1933 Ford Pickup - 59A Flathead V8
1966 Ford Bronco - U14 - 170/200 Straight 6
1966 Ford Mustang - 289 V8

navyguy66mustang
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Re: C4 Transmission Issues or Questions

Post #7 by navyguy66mustang » Mon Jan 09, 2017 1:50 am

Thanks for the info. So after further review, I decided to go ahead and replace the O-ring on my shift linkage and it seems to have slowed the leak significantly. I tried to change the dipstick tube O-ring but a large amount of transmission fluid gushed out which I wasnt expecting so I was unable to do it. I believe that when I shoved it back in I may have caused that to start leaking which sucks because I dont think it leaked before due to the place of the leak changing. So, the journey continues with this transmission. Question I have for anyone is when the fluid came out of the dipstick tube it smelled burnt-ish. The fluid in the pan is fresh fluid which is why I was puzzled to smell burnt fluid like that. Any suggestions?

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B RON CO
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Re: C4 Transmission Issues or Questions

Post #8 by B RON CO » Mon Jan 09, 2017 8:06 am

Hi, when you check the fluid on the dipstick smell it. It should not smell burnt. It should be a nice clean red color. You can never get all the old fluid out, now it is mixed. If you change the fluid in like six months the overall quality will improve to much more good and new, and less old. Good luck
B RON CO. Still workin' on it!

1933 Ford Pickup - 59A Flathead V8
1966 Ford Bronco - U14 - 170/200 Straight 6
1966 Ford Mustang - 289 V8

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bubba22349
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Re: C4 Transmission Issues or Questions

Post #9 by bubba22349 » Tue Jan 10, 2017 11:10 am

navyguy66mustang wrote:Thanks for the info. So after further review, I decided to go ahead and replace the O-ring on my shift linkage and it seems to have slowed the leak significantly. I tried to change the dipstick tube O-ring but a large amount of transmission fluid gushed out which I wasnt expecting so I was unable to do it. I believe that when I shoved it back in I may have caused that to start leaking which sucks because I dont think it leaked before due to the place of the leak changing. So, the journey continues with this transmission. Question I have for anyone is when the fluid came out of the dipstick tube it smelled burnt-ish. The fluid in the pan is fresh fluid which is why I was puzzled to smell burnt fluid like that. Any suggestions?


In all likelihood there might of been some dirt or grit around the bottom of dip stick tube & hole in the trans case. This all needs to be cleaned before you install a new O Ring. As far as the burnt trans Fluid if you didn't also drain the fluid out of Torque Converter (it has drain Plugs) at the same time as you did the trans then you will still have some old fluid in the trans. Good luck :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

navyguy66mustang
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Location: San Diego

Re: C4 Transmission Issues or Questions

Post #10 by navyguy66mustang » Tue Jan 10, 2017 11:30 pm

So two days since I replaced the o-ring on the shift-linkage and there is no leak or fluid build up under my transmission. Awesome help from you guys. I am going to give it a few months and then do a fluid change. Luckily when I replaced the the pan, I purchased one with a drain plug. :beer:

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