TH400 Problem
Thread Starter
Racer
Joined: Jan 2006
Posts: 381
Likes: 24
From: Uxbridge Ontario
TH400 Problem
Well, I think it is a problem. 71 350 270 HP with a Th400. The issue is on long drives the tranny dumps a little bit of Auto fluid out the vent pipe. Now the tranny was drained, new filter and refilled with Royal Purple synetic. No overheating problems etc. The tranny has the right level when warm (half way between full and first line) almost not on the stick when cold. When running on the highway it is fine but when I jump on it anything over 3K RPM I can smell a touch of auto fluid on the exhaust pipes. The tranny works fine, doesn't slip etc. This weekend I am going to check to see that the tranny lines to the rad are fine and free just to see if the tranny fluid is getting to the rad. I was told by a respected mechanic that some Th400's do this until they find their own level. Any ideas?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
The only way tranny fluid can get to the engine [that I know of, anyway] is that the vacuum modulator on your THM400 has a diaphragm that is ruptured and the fluid is getting sucked into the intake manifold via the vacuum line connected to the modulator can. Get under the car and remove the metal vacuum line from the can. If you find any tranny fluid in that line, the modulator is leaking and needs to be replaced. Try to find an exact replacement modulator, if you can; there are lots of substitutes, but they usually don't operate the same [shift points change].
Thread Starter
Racer
Joined: Jan 2006
Posts: 381
Likes: 24
From: Uxbridge Ontario
Sorry if I indicated that fluid is getting to the engine. The TH400 has a overflow pipe out of the top of the tranny, I have attached a hose so that if it does overflow it will drip down below the tranny and not all over it. The fluid is coming out of the overflow hose and is not getting to the engine.
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
Sorry if I indicated that fluid is getting to the engine. The TH400 has a overflow pipe out of the top of the tranny, I have attached a hose so that if it does overflow it will drip down below the tranny and not all over it. The fluid is coming out of the overflow hose and is not getting to the engine.
Sounds like the trans is getting over heated and building presure in side and dumping out the breather.
Thread Starter
Racer
Joined: Jan 2006
Posts: 381
Likes: 24
From: Uxbridge Ontario
Thanks Manuel, that is what I was thinking so this weekend I am going to unplug the lines to the rad and see if fluid is pumping to the rad and it comes out of the rad. If it is clogged I am going to replace it with a trans cooler and see if it changes things. By the way the engine temp is normal.
Melting Slicks
Joined: May 2002
Posts: 2,431
Likes: 52
From: Florida
Are you certain it has the right dipstick & tube? An internal pressure loss could be foaming the fluid if it's not overheating. It could still be working yet have a pressure loss. I've never heard of a TH400 finding it's own fluid level. They hold about 11 quarts when trans. and converter completely empty, 4-5 quarts on a fluid change assuming you don't have the deep sump pan. There are pressure ports for testing pressures but once you're in a trans shop, you're at their mercy. You could buy a manual on rebuilding the trans. and test these pressures yourself. Bottom line is IMO, if the fluid level is right, and it's not overheating and still puking some fluid, something is wrong and it'll need to come out. The TH400 is one of the easiest to rebuild. If it has not been rebuilt in many years, it may be time.
Jim
Jim
Thread Starter
Racer
Joined: Jan 2006
Posts: 381
Likes: 24
From: Uxbridge Ontario
Thanks Jim. The tube and dipstick are the orginal items. Tranny has never been rebuilt. After it has been driving for some 15 or 20 miles I check the fluid and its about on the first line (add fluid) I do check it with the engine still running. Shifts great, no slippage, Fluid shows no sign of foaming on the dip stick. I have heard from two sources three now that some TH400's find their own level. What concerns me is on long summer drives at highway speeds ever now and then you can smell a little bit of tranny fluid on the exhaust and it seems to be coming from the overflow pipe as there are NO leaks anywhere else. The fluid as I said has been changed along with the filter. The issue happened before the change so it is not related to the change. Thanks for the input.
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Drifting
Joined: Mar 2008
Posts: 1,900
Likes: 2
From: Nixa Missouri
I have a question about this problem and I'm wanting to learn about these TH400 tranny's cause I have one in my 70 coupe.
First of all I dont know a dam thing about a auto transmission other then general maintenance.
Mr. Dippold stated that the transmission has never been out for repair, and that it has had ATF fluid in the transmission all it's life from the way I read it.
Mr. Dippold states he changed the fluid from ATF fluid to Royal purple synthetic. Is this fluid or are these fluids compatible with each other, and was he able to remove all the old fluid when being changed out.
The other thing is, and please correct me so I can understand the transmission a bit better, is Mr.jimvette999 states the TH400 holds plus or minus 11 quarts. How does one get the fluid out of the torque converter to drain out. I was told it's a pita or a person has to start drilling holes.
My main question is can the two different fluids be the problem if that the case?
Now I know what that black thing-a-ma-jig is on the passerger side of the transmission, it a modulator.
Thanks.
First of all I dont know a dam thing about a auto transmission other then general maintenance.
Mr. Dippold stated that the transmission has never been out for repair, and that it has had ATF fluid in the transmission all it's life from the way I read it.
Mr. Dippold states he changed the fluid from ATF fluid to Royal purple synthetic. Is this fluid or are these fluids compatible with each other, and was he able to remove all the old fluid when being changed out.
The other thing is, and please correct me so I can understand the transmission a bit better, is Mr.jimvette999 states the TH400 holds plus or minus 11 quarts. How does one get the fluid out of the torque converter to drain out. I was told it's a pita or a person has to start drilling holes.
My main question is can the two different fluids be the problem if that the case?
Now I know what that black thing-a-ma-jig is on the passerger side of the transmission, it a modulator.
Thanks.
Instructor
Joined: May 2004
Posts: 209
Likes: 6
From: Glendale AZ
I had a TH 400 do the same thing. It was getting hot. I put a finned type trans cooler which looks like a radiator in. I do not have it hooked to the radiator at all. Added a deep trans pan and run 1/2 pint low. This fixed the problem.
Thread Starter
Racer
Joined: Jan 2006
Posts: 381
Likes: 24
From: Uxbridge Ontario
The ATF fluid has been changed a number of times under normal maintenance. The only real way to remove all the fluid is to remove the tranny and the converter and let them drain. The other way which I have heard a lot about is to connect the top hose that goes into the rad and start the car and let about a quart of fluid out, stop the car, fill the tranny with another quart then continue the process over and over till the fluid runs clean (pink). It may not get every little bit of old fluid out but it does a good job of it. It is a PITA. My rad has all the shrouds, foam etc that is required and the engine temp never goes about normal. However I think I am going to purchase a AT rad just the same and see if that cures the issue.
