C4 transmission leak

[rkmiller73]

OK I know what you are thinking, but this is not the atypical leak at the transmission shift lever.

I got busy this summer and did not drive the white fastback for 4 months. If it sets that long it starts to leak a lot and I got about half a quart in the pan I threw under it. When I started the car and put it in gear it did nothing so I let it run for a few minutes and then it went into gear. I added a quart of type F fluid before driving it.

Now I had the transmission rebuilt by a guy in Fort Worth in 2011 that only does C4 and C6 transmissions. He did a shift kit upgrade and put a deeper oil pan with drain plug - it shifts and runs great. The first 3 months it did not leak at all - I did drive it more the first couple months. Then it started having slow leaks and if let set for a couple months it does as described above.

Soooo.... I am sure I need to pull the transmission and have it checked. I am thinking it is a bad check valve allowing all the fluid to drain out of the torque converter and thus leaking out of the transmission.

I am debating to 1. replace transmission with an AOD, 2. try to repair this transmission and put on a gear vendors.

I really hate pulling off the exhaust and the transmission as I hate doing things over.

Any thoughts or comments?

[Nuts]

Ryan, drainback from the converted is a common problem with the c4. Best advice is to start the car every week.

[Nuts]

One thing to check, is to remove the pan and filter. There is supposed to be an anti drainback check valve under the tab on the filter. it's about 1" long with a spring. These often get lost during filter changes. Hopefully that's your problem. The other possible cause is the check valve in the pump. This valve is not really serviceable and would require pump replacement. Getting hold of a new pump may be an issue.

[hybrid]

The check valve may have been removed for improved flow too.
But where is the actual leak from? Drain back should not really cause a leak unless it's coming out the breather, but that sounds unlikely.

[Nuts]

The check valve may have been removed for improved flow too.
But where is the actual leak from? Drain back should not really cause a leak unless it's coming out the breather, but that sounds unlikely.

seen many do this. With drainback the sump gets a further litre plus and there is no where for it to go. So out the breather and even the dipstick tube it goes.

[hybrid]

Weird.. I would have thought the body of the box would hold that easily before it went out the top.

[nassi]

Weird.. I would have thought the body of the box would hold that easily before it went out the top.

Nope, it vents.

[rkmiller73]

I am pretty sure it is coming from the vent tube, its been too long since I really looked at it. I had the other fastback restoration going, and then with moving and buying/running the clinic I put it on the back burner. I have just been checking the gas and filling the transmission with oil when I want to drive it and it runs great.

I am going to clean it up really good and keep it over at the lift, put it up once a week and check for exactly where it is coming from, will take about 3-4 weeks before it really starts to accumulate.


I called a transmission shop in Olathe that the local small town Napa parts store owner I know recommended and it didn't seem to be sure, but said he could look it over once out of the car. He mentioned some issues at the pump motor, check valve and at the end said he would just run the engine once a week.


I think it is coming from the vent tube and I have a feeling it is a check valve issue - either bad or may have been modified/removed for improved oil flow.

My question is that a 1. pull the transmission and take it to a shop or would it be more of a 2. pull the valve body out and have it checked out for the check valve issue?

It is getting more difficult to find people that know/have work experience with these older transmissions and I keep getting the response of - exchange it with a rebuilt transmission.
That really doesn't work for me either - 1. I spent the money to have it rebuilt and it shifts/runs great ( if I don't get on it the shifts are not too harsh and if I get on it the shift is more crisp and I can even bark the tires on 2nd and 3rd if I want to) 2. even though the engine is not original, the transmission is and if I were to go this route, I might as well put the money toward an AOD.

[rkmiller73]

I called an client of mine who has a body shop up in Olathe and he recommended a transmission shop that has been around 30+ years run by an older guy.
I went by there today while out on farm calls and they suggested a check valve on a transmission cooling line to reduce the torque converter drainage overfilling the transmission.

I am fairly certain the majority of the leak is out the vent tube.

What do you think?

[hybrid]

That would only help with the cooler draining back rather than the converter.

[hybrid]

Weird.. I would have thought the body of the box would hold that easily before it went out the top.

Nope, it vents.

Must be a C4 thing. It's a common AOD mod, but maybe there's more room in the body of the transmission to hold the extra fluid.

[rkmiller73]

OK, so I am going to check with that shop and see if I take the car there can they check under the filter tab for the check valve.

It never leaked this bad until after the last rebuild.

I am afraid of taking the car too far apart and I know myself too well and it will end up like the last project car and I will have it torn in a thousand pieces. When I did this car with my dad, they didn't have the full panels to replace floors and rear quarters and new date coded glass, etc.

The wife was noticing too much on the last car and I barely squeaked by to finish before she started asking about my expenses.

I have to lay low for another year or two.....

(remember my first rule of restoration - you don't want your wife to know what you spent. 2nd rule is I don't want to know what I spent for plausible deniability to my wife. 3rd rule is to save receipts and if I have to sell the car I can prove to the IRS that I lost my shorts on the deal).

[Nuts]

4th rule is it's better to ask for forgiveness than to ask for permission.. Just add to the budget some new jewellery.

[rkmiller73]

So..... I added an extension onto the transmission vent and so far no leaks, but it has only been a month.

[123abc]

my fmx used to weep out the cork gasket if you left it too long between drives