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Discussion Starter · #1 ·
My 69 c4 auto keeps pushing the oil out of gearbox. Seals have been replaced but oil is coming out tailshaft bearing losing at least 2 litres onto ground. It’s as if the box is getting pressurised and forcing it out. Won’t get out of 1st gear. Only thing mechanic said was there were steel ball bearings in the valve body and he thought they should be rubber. Could this be causing the issue? Cheers
 

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Phoenix, AZ 85008
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Welcome to the FFO!

No up shift from first to second.
There is a vacuum modulator towards the rear of the transmission. (It has been awhile since I worked on a C4, so not sure which side)
Follow that metal vacuum line from the engine area to the rear of the transmission. The last part will be a rubber hose.
Lift/raise vehicle
Get under and remove the rubber vacuum line and install a vacuum gauge
Start engine and measure the vacuum signal. Should be the same as intake manifold vacuum. If not there is a restriction or blockage.

If you have a good vacuum signal, turn off engine.
Apply vacuum to the modulator and see if it holds vacuum. If it does not, replace the modulator
If it does then reinstall the vacuum line to the modulator

Make sure transmission fluid is checked with transmission and engine fully warmed up.
Vehicle on level ground
Engine running and gear shifter in park.
Fill to the full mark. Do not over fill

The rear seal on the tail shaft does not seal against pressure. Fluid should NOT be under pressure in that area. The seal is more of a dust shield to keep out dust and dirt.

The transmission will build up pressure when running and the internals heats up.
That internal pressure is vented. There are generally two places the vent is located.
At the top of the tail shaft housing. It will look like a little button
Or out the side of the case as a tube bent across the top of a servo cover.
Either way those vents have to be open or yes fluid will be pushed out of the case at the weakest spot. Tail shaft seal would be one

From memory of the last C4 overhaul I did all of the balls were steel
That can vary and a very hard rubber could work too
This is provided it is installed in the correct location.

Action
 

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Phoenix, AZ 85008
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Vent examples
First is out the case and across the servo cover
The second is on top of the tail shaft housing. (I believe this one is broken)
(Not my transmission)

Action

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Discussion Starter · #4 ·
Welcome to the FFO!

No up shift from first to second.
There is a vacuum modulator towards the rear of the transmission. (It has been awhile since I worked on a C4, so not sure which side)
Follow that metal vacuum line from the engine area to the rear of the transmission. The last part will be a rubber hose.
Lift/raise vehicle
Get under and remove the rubber vacuum line and install a vacuum gauge
Start engine and measure the vacuum signal. Should be the same as intake manifold vacuum. If not there is a restriction or blockage.

If you have a good vacuum signal, turn off engine.
Apply vacuum to the modulator and see if it holds vacuum. If it does not, replace the modulator
If it does then reinstall the vacuum line to the modulator

Make sure transmission fluid is checked with transmission and engine fully warmed up.
Vehicle on level ground
Engine running and gear shifter in park.
Fill to the full mark. Do not over fill

The rear seal on the tail shaft does not seal against pressure. Fluid should NOT be under pressure in that area. The seal is more of a dust shield to keep out dust and dirt.

The transmission will build up pressure when running and the internal heats up.
That internal pressure is vented. There are generally two places the vent is located.
At the top of the tail shaft housing. It will look like a little button
Or out the side of the case as a tube bent across the top of a servo cover.
Either way those vents have to be open or yes fluid will be pushed out of the case at the weakest spot. Tail shaft seal would be one

From memory of the last C4 overhaul I did all of the balls were steel
That can vary and a very hard rubber could work too
This is provided it is installed in the correct location.

Action
Hi action many thanks for your reply and advice. I replaced the vacuum module already. I was not aware of the vent pipe so I will check it out sounds like it could be the issue. Definitely pressure forcing oil out. Too much for a seal. If not I’ll take valve body out and check ball position maybe replace stop balls as well. Many thanks for your help. Sounds like a positive lead cheers
 

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My 69 c4 auto keeps pushing the oil out of gearbox. Seals have been replaced but oil is coming out tailshaft bearing losing at least 2 litres onto ground. It’s as if the box is getting pressurised and forcing it out. Won’t get out of 1st gear. Only thing mechanic said was there were steel ball bearings in the valve body and he thought they should be rubber. Could this be causing the issue? Cheers
Hello Smokit,

When you first start the engine (cold) does the transmission work for a short while and doesn't leak or is it right away? When the fluid is being pushed out have you checked the fluid to see if it's aerated? If it's aerated, that points to a bad/worn out pump as it's sucking in air along with fluid and making the fluid frothy and that will push the fluid out the vent as well as interrupt the shifts because of low line pressure. I would also check the line pressure with the engine running (there is a tap on the case of the transmission to do so).

Automatic transmissions, even old ones, are still very complex and it doesn't pay to guess, rather diagnose.

Cheers
 

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Discussion Starter · #6 ·
Hello Smokit,

When you first start the engine (cold) does the transmission work for a short while and doesn't leak or is it right away? When the fluid is being pushed out have you checked the fluid to see if it's aerated? If it's aerated, that points to a bad/worn out pump as it's sucking in air along with fluid and making the fluid frothy and that will push the fluid out the vent as well as interrupt the shifts because of low line pressure. I would also check the line pressure with the engine running (there is a tap on the case of the transmission to do so).

Automatic transmissions, even old ones, are still very complex and it doesn't pay to guess, rather diagnose.

Cheers
Hi DesertXL I don't believe the oil was aerated although we didnt really look as the oil was just constantly dripping out under the car. and there was a lot of it.
History
The box is out of my 69 mustang. during the rebuild (20yrs ago) A friend of mine rebuilt the box for me, when I eventually put it in to use it it had a problem, I think it was only finding 1st and reverse can't really remember as it was a long time ago and I'm old :0) I took it out and didn't use it. At the time someone told me it was probably missing the two check balls. Some time later I pulled the valve body out and checked and they were missing. I did insert two ball bearings that fit the tracks as per a diagram I found on line. Recently my son had required a box and had it put into his Lincoln towncar lo rider to get it to a show. It drove around in Drive for a few hours and seemed ok. When he bought it home the next day the oil was all over his drive. We trailered it to our mechanic who found the oil was coming out of the selector area and numerous other spots. he replaced seals and things and had it working in reverse and drive he didn't test run it because of what it is (lo rider) which are illegal out here. My son when he drove it home couldn't get out of 1st or 2nd gear couldnt get it over 25-30mph. and when we go it home the oil started running out again and was dropping two drips a sec from the tail shaft seal and kept running for quite a few hours. So that's it sorry for the long diatribe.

I wouldn't have though that the build up a pressure would last so long as to push the amount of oil out that it has. It seems like it empties the whole pan.
Could the check balls be causing any of this, I have ordered a new set of balls and gasket just in case.
Will get it back to mechanic to check the vents as advised by Action. He can pull it out and we'll get it to a box mechanic but a C4 repairer is proving hard to find where we are situated.
Any info given here will be passed on. Many thanks guys much appreciated.
 

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Phoenix, AZ 85008
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The first question asked by DesertXL is rather important.
You have kind of answered that with the statement of, "It drove around in Drive for a few hours and seemed ok. "
My guess (after you have given the rest of the story, is you have multiple issues.

Part of the issue
The C4 you are using was meant for a Mustang. Even though C4 was used in light trucks, there differences are in clutches, servos and planetary gear sets. I am going through an old C6. The intermediate shift servo and band are a lot larger or smaller depending on application. I think the Town Car the transmission is in may be too heavy for the current arrangement. The transmission fluid may have been over heated.

If the modulator is working correctly, the intermediate band may not be adjusted correctly. It is too loose and does not hold the drum. May now be glazed. Or was too tight and has gotten burned.

Overall the transmission may be struggling to handle the load

I have looked for a C4 valve body diagram. I only found this 1970 and later. Shows a plastic ball. The 69 valve body may use metal.

Just some thoughts

Action

Product Font Parallel Pattern Design
 

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Discussion Starter · #8 ·
Hi
The box is out of a 351 V8

Yes the 67-69 valve body is different to 70up. the gasket oem no is C9AZ-7D100-A
I will take all the info here down to him so he can have another look. Still to investigate the relief valves etc.
I think I'm going to have to pull the box out and take it to a professional c4 repairer if I can find one.
Whilst I can rebuild the engines I have no clue on gearboxes unfortunately.
Thank you for your time and advise appreciated.
Font Circle Pattern Rectangle Art

this is the correct gasket
Font Automotive tire Auto part Metal Pattern

1968 valve body.

It mentions 2 balls and a puck whatever that is I definitely didn't put a puck in just the balls.
would a missing cause what its doing?.
 

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Phoenix, AZ 85008
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The attachment in post #9 came from here
TransGo
I used their shift kit on a 74 E-100. I had good results

A puck is about the size of a ball, however it is flat on two sides.

I do not think the pucks or a ball is causing the issue with the fluid getting out of the transmission.
However, the lack of those or placed incorrectly they will definitely cause shift issues

As to doing the work, if you can pull the transmission and install it in a Town Car you have the necessary skill to assemble a valve body. You just have to take your time and follow directions.
That data is in the shop manual.
Or you can get a shift kit from Trans GO

Action
 

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One thing on the vacuum modulator, there is a very small pin that is easily missed when installing a new one. The pin goes on the back of the modulator and without it the transmission will not shift. It's a common mistake for the first timer, if you don't have the pin one can be made from a peace of wire from a coat hanger. Sometimes they come out with the modulator and sometimes they lay in the transmission.
Good luck
 

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Phoenix, AZ 85008
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That throttle control valve rod (pin) is 1 11/16" long and 1/8" diameter wire for modulators that screw in. (Not press in modulators)
C4AZ 7A380 A

Action
 
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