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Looking for some opinions regarding a an issue I'm having with a 65 C4 Transmission in my 289 Mustang fastback. The transmission was supposedly "gone through" a couple of years ago but it's always had an issue where when you start it and put it in any gear after it has been sitting a week or two there is usually a no engagement (no drive condition). The longer you let the car sit between startups the worse the problem. I'd put the trans is park and let the car run for a bit (5-10 minutes) and it would usually engage but would occasionally drop out of gear. After the initial 5-15 minutes of idle time in the driveway I would put it in gear, go for a drive and not have any issues. I thought it may be related to some sort of fluid drain back because the car usually sat a week or 2 between cruises but one time after the typical 5-10 warm up and a couple of mile drive, it dropped out of gear (shifter still on the green dot) when I stopped hard at a stop light. I gave it a little gas a couple of times and it went back into gear. No problems for the rest of the 30 mile cruise. Fluid level is good. Any ideas? I picked up a 66 C4 that I may try to rebuild myself but was wondering if there may be something simple i'm missing like a band or some other adjustment.
 

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Does it go into reverse at all? Have you adjusted both bands? Doe it have the proper filter on it?

If also no reverse, could indicate pump issue or converter.

If reverse but no forward, that indicates the rear band or servo piston, iirc.

There's also the center band and servo piston, accessed from inside the pan, again iirc

Improper filter or clogged filter not picking up fluid.

There are external ports for measuring pressure on the transmission. A service manual or Google search will net you the pressure check procedures.

Sent from my SM-N960U using Tapatalk
 

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Are you checking the fluid with the engine hit, idling in park on level ground, by pulling the stick then wiping it, reinserting it then pulling it to read? Any excessive bubbles? The torque convertor should have an anti-drain back feature, but if it was draining back, it seems it would be excessively high to begin with in the pan. Maybe a sticking servo or valve body. How about that connection from the intake to vacuum tube and the small connection from the tube to the modulator valve?
 

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Discussion Starter #4
Does it go into reverse at all? Have you adjusted both bands? Doe it have the proper filter on it?

If also no reverse, could indicate pump issue or converter.

If reverse but no forward, that indicates the rear band or servo piston, iirc.

There's also the center band and servo piston, accessed from inside the pan, again iirc

Improper filter or clogged filter not picking up fluid.

There are external ports for measuring pressure on the transmission. A service manual or Google search will net you the pressure check procedures.

Sent from my SM-N960U using Tapatalk
When the problem of not going into gear happens, it affects all gear selections including reverse. I have not done any band adjustments. Transmission seems to work fine (drives and shifts with no slippage) when driving. Yes, as far as I know the proper filteris installed with clean Motorcraft Type F trans fluid.

I saw the procedures in the Ford shop manual for doing air and pressure checks. I was wondering if the issues I'm encountering would point to a "most likely" problem.

Are you checking the fluid with the engine hit, idling in park on level ground, by pulling the stick then wiping it, reinserting it then pulling it to read? Any excessive bubbles? The torque convertor should have an anti-drain back feature, but if it was draining back, it seems it would be excessively high to begin with in the pan. Maybe a sticking servo or valve body. How about that connection from the intake to vacuum tube and the small connection from the tube to the modulator valve?
I'm following the correct procedures for checking the trans fluid. The level checks out okay and there is no excessive bubbling on the dipstick. The fluid level is very high if I check the fluid level before I start the car but I did not think much of it because you have to bring the fluid up to operating temperature and run it through the gears before checking. I did a visual inspection of the vacuum line from the intake manifold to the vacuum diaphragm on the transmission and it looked okay. I'll have to check the vacuum at the diaphragm to make sure it's within spec.
 

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Discussion Starter #6
Talked to a local transmission shop that is known locally as the "go to" transmission shop. They are used by local shops and dealerships. They basically said it could be a couple of different issues and the transmission would need to be taken apart and examined. I decided to have the 66 C4 rebuilt by them while I pull the 65 C4 out of the car. $750 plus hard parts (if needed) for a bench rebuild. I can recommend them If anybody needs a good transmission shop in the South Jersey area. They have done work for me on my daily drivers.

Precision Transmissions - Pennsauken, NJ
 

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Most of the time, a slow to engage time lag is due to fluid drain back. Start it up and drive it for a bit. Shut it off, let it sit for a few minutes and check the fluid level. After it sits for a week, check the fluid level again before your start it. You'll probably see a much higher fluid level due to drain back from the converter. I have the same issues with the C6 in my 67 Cougar.
 

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Whenever I have had this issue it has been low regardless of what the dipstick says. Id add a half quart and see if it improves.
 

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Rebuilding the C4 can be done on your kitchen counter, it is not difficult. Recommend a seal + clutch rebuild kit and along with your YouTube Certification, it should be easy enough.

This is a good DIY (1 of 3) on the C4 rebuild
(he has a lot of other cool DIY videos Deome's Workshop)

You can rebuild your C4 in the time it takes to go down to the shop, pay and later pick it up.
 

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A lot of transmissions at the phone company were that way on vehicles did not move for a long time. The fluid drains out of the torque converter and the car will not move until the pump fills it backup. Not all of the same model transmissions did it so you knew that was not normal. Once you started them and then somebody started driving them daily it was never a problem.

If you want to know for sure, check the fluid level when you shut it off and then check the fluid level again in a few days and you will see that the tide level inside the pan has risen. Full moon or leaking drain back valve? I've heard that some faulty front pumps can cause it too?

I saw a previous post by Woodchuck where he showed the valve location from inside the pan. He said the valve could fall out during a filter change.. I'd start with making sure its there, clean and moves and makes a good seal. It wouldn't hurt to pull the pan change the filter and train torque converter anyway.

That does not explain what happen at the traffic light, unless the fluid could drain out of the torque convertor faster than the pump can put it back in at idle. When you raised the rpm the pump could keep up with the loss from a stuck drain back valve. You could always have more than one problem.

When a shop says they are going to go "through" a trans that could mean a lot of different things. They might just put new bands and clutch plates in there. They should install a new torque convertor too and check all the wear on bushings, the pump, gears, all the parts they call "hard parts" which are not worn are not replaced. A rebuilt trans is not a new trans. Not all the parts get replaced.

If a part failed like a band, clutch pack, disc servo, it would be broke all of the time not just occasionally. Your dealing with a fluid volume, pressure problem or both. Low pump volume, stuck check valve...

This video will explain to you what is going on inside your torque converter and why it cannot move the car with out fluid in there. If you want to learn about transmission you learn about one section at a time starting with the torque converter.

 

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Out in the garage in storage somewhere??? I have the most beautiful factory C-4 trans rebuilding binder with lots of photos and beautiful color diagrams of the fluid circuits. Its neat. It had to have been from a factory Ford dealer training class.
 

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Discussion Starter #12
I looked at a bunch of videos on torque converters and that one is excellent. Thanks for the link. I figured that I had some sort of drain back issue happening because when I checked the trans fluid after the car sat for a while, it was very high on the dipstick. I was going to just live with it until the trans dropped out of gear after driving for a while.

I believe the drain back valve in the early C4 can't fall out when you remove the filter. The 64 1/2, 65 and 66 valve body is different than later C4s.

I'm always worried when I have to deal with a shop. That's why I do as much as I can myself. I have used this transmission shop before with good results and they have a good reputation. They already disassembled, cleaned, replaced wear items and reassembled the transmission. They back their work and said to contact them if I have any issues. Keeping my fingers crossed..
 

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They should warranty the trans. They might even know how to fix it without pulling the trans. I would definitely go talk to them. They will probably be amazed you already know as mush as you do. Because 99.9% of people would not have a clue what's going on in there.
 
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