transmission leak

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transmission leak

Post by pila on Fri Apr 10, 2015 3:10 pm

I have the TH400 ready to come out of my Elco project. It's been leaking a while, but don't really know where the leak is yet, so, out it comes.
Luckily my exhaust system is band-clamped together & no U bolts on it. Comes apart very easy, and I had to remove the down pipes to get the cross member out.
Early on, I thought the OEM steel pan was leaking at the gasket flange, but after putting a cast aluminum pan on it, it still leaks the same way.. Head Bang
Maybe I'll have it out this weekend.......

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Re: transmission leak

Post by Joe73 on Fri Apr 10, 2015 4:21 pm

Id like to run the ribbed rubber one with steel center. Theyre reuseable and cant overtightened.
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Re: transmission leak

Post by thatfnthing on Fri Apr 10, 2015 4:37 pm

Leaks were the bane of my existence when I had the TH350, so I feel for you.
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Re: transmission leak

Post by pila on Fri Apr 10, 2015 5:55 pm

Never had any leak problems with all the TH350s I rebuilt. I thought early on that the front seal was leaking, but that is kinda high-up to leak that much fluid. I'll get a better look when it's out & on the bench.
There's some oil in the bottom cover on the flex plate also, so it's hard to pin down while the trans is in the vehicle.....

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Re: transmission leak

Post by BBMALIBU on Fri Apr 10, 2015 9:38 pm

Wait, you took the trans out to find a leak?

TH400 pan gaskets are known to leak.

If the pan is leaking, try a Fel-Pro TOS18621 gasket with a very very thin coat of that brown Permatex aviation sealant.
I know you are not suppose to use sealant on the gasket, but I don't think a very very thin coat, allow to dry before adding trans fluid, will hurt the trans. I did it, no leaks, trans still works.

Also, check the selector shaft seal, very common, can look like the pan gasket is leaking.
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Re: transmission leak

Post by pila on Sat Apr 11, 2015 12:22 am

Yeah, I went through all that, and went to a cast pan for a better gasket surface etc, but I know what you mean.
Thanks for that gasket part number !! And I'm not against using a skin coat of sealant ! Smile

Bill

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Re: transmission leak

Post by bracketchev1221 on Mon Apr 13, 2015 6:37 am

As a test, run a hose from the vent to a soda can tied up under the car. Take it out for a good drive and see how much fluid winds up in the can. You may be blowing fluid out the vent and it running down the trans. I chased leaks all over on my race trans. Started collecting the vent gases (and fluid)and the leak stopped.
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Re: transmission leak

Post by pila on Tue Apr 14, 2015 12:26 am

Well, it's ready to drop out. And the vent thing crossed my mind too Ray !! It does kinda look like fluid is coming from up top someplace. I may find out tomorrow when I have it out.

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Re: transmission leak

Post by 77mali on Tue Apr 14, 2015 6:02 pm

Darn leaks! Hope you find it Bill (I'm sure you will).

Going through some leak BS too w/ my truck. I think its the end seals on the front axles. UGH...I'm gonna have to drop it to replace them & the gasket too. Not fun.
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Re: transmission leak

Post by pila on Tue Apr 14, 2015 6:42 pm

Today I have it off of the engine, sitting on the trans jack. I have to raise the body more in order to get it out from under it., or maybe slide it off of the jack & slide it out from under.....that kinda sucks also...
I will have to jack the engine along with the body if I raise it...

The transmissions get heavier as I get older !! Very Happy

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Re: transmission leak

Post by bracketchev1221 on Tue Apr 14, 2015 6:52 pm

Yes a t-400 sucks. They are heavy as hell. I can't get mine high enough. I get it off the jack and slide it out. You have to see me get it back on the jack under the car when I put it back in.
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Re: transmission leak

Post by chevellelaguna on Tue Apr 14, 2015 8:43 pm

That's never fun... I'd rather take the motor and trans out than just the trans. Done it in the middle of winter after I fragged a torque converter on my daily driver 75 four door. That was.....well....sucky.
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Re: transmission leak

Post by pila on Wed Apr 15, 2015 1:03 am

I always slid the TH350s off & on , but this one ....... Head Bang
Just have to see how it goes...

And the little vent tube is dry, and I have the converter wired to the case yet, so it didn't fall off. Wednesday I'll pull that & get a better look at the front of the case.

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Re: transmission leak

Post by pila on Sat Apr 18, 2015 7:22 pm

Today my son helped me remove the converter from the trans, while it was still under the car, so I could look for the leak source.
It was just as I first suspected, the big diameter O-ring on the pump, where it sits in the case.
So, we wrestled the trans off of the trans jack & out on the floor. I have to check & see if I can move the pump forward enough to replace the O ring, without tearing into the "guts" !
Time to dig into the books .....or maybe talk to a local trans shop that sold me parts occasionally They may know...

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Re: transmission leak

Post by ant7377 on Sun Apr 19, 2015 7:53 am

I have the same leak on my 73. Its not that bad, and when I pull it im just going to get it rebuilt which Im not doing anytime soon I dont think. P.i.t.a....
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Re: transmission leak

Post by pila on Sun Apr 19, 2015 8:30 pm

I rebuilt this one myself, but it was the first TH400 I've done. If the leak is the only thing wrong with it, I'll be happy Very Happy

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Re: transmission leak

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