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Discussion Starter · #1 ·
I've had transmission fluid leaks on a few of the cars I store but only after letting them sit for several weeks without driving. If I drive them regularly they don't leak. I've read a lot of threads on several forums and a lot of times proper fluid level comes up, sometimes heat, output shaft/tail shaft, gear selector and speedometer cable.

I'm currently working on a TH200-4R but the discussion could be for just about any "old school" transmission. I didn't see a transmission section of the forum and since this particular instance is on a TH200-4R I thought I'd post here.

I recently had the pan off and I intended to measure the bottom of the inside of the pan to the flange and then I planned to try to see how far the "full hot" indication on the stick was relative to the pan flange... I was doing a lot of other work and released I forgot to measure until the pan was bolted back up. So I took a piece of music wire and found the bottom of the pan through the fill tube and I compared the distance from the top of the fill to where the dipstick bottoms on the same surface (end of wire and tape were aligned so I think the slight offset is due to the camera angle).

I do have a PML deep pan so some things will look a bit deeper but I was shocked to see how far up the end of the dip stick was from the bottom of the pan. I had assumed the "Full hot" should be close to the top of the pan.

One other reason I'm asking is I have an aftermarket dipstick and I'm questioning the marking.

Scott

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That's why they leak. The fluid level is above the gasket and the dipstick tube seal. If the car sits for a while, you should be able to determine where the leak is coming from. Mine seems to be leaking under the torque converter when it is parked for a long time. I don't understand how the fluid can leak there while parked. You should try to determine if yours is leaking from the dipstick tube or gasket or torque converter area or rear seal area..
 

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Discussion Starter · #3 ·
al2,
Not all of my cars are this clean underneath so I do need to check the others out more thoroughly so I'm not ruling anything out on those. On the TH200-4R in the photo it looked like the leak was coming from the rear. I took a dry paper towel and I checked the rear seal and it was dry. I checked the gear shifter input and the speedometer cable area and they were dry. I checked the top of the tail area and it was dry. The inspection cover had a little engine oil which ran down from when I did the last oil change so I wiped that off but it wasn't transmission fluid. I also verified that I have the copper bushing in the tail shaft for the yoke (mentioned because it looks like the GM original had a seam down the length where it could leak).

When I changed the gasket I did see that the anti-seize I used, ceramic non metallic white, had bled a bit to the surface of the gasket. It didn't look like fluid was leaking there but hard to say. When I scrapped the old gasket off I also noticed the "old" (less than 4 years old) gasket seemed to have an appearance of being saturated. I was wondering if the fluid could have been wicking through the gasket itself?! I replaced it with an ATP higher-end gasket.

I think my next step in checking the dipstick marking is to compare it to an original one. I have another vehicle with a TH200-4R but not in the same location.

Scott
 

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The pan gasket is the issue-- you're probably filling it correctly. If the trans doesn't slip, you're probably good to go. Easy enough to compare the new deep pan to an oem style.

That pan looks like it's really stout.. need to question the small head allens, though. Not like it's an issue because the pan flange looks to be stout. Though, I'd still use bolts with a broader shoulder.

Goop the heck out of the sealing surface. Even though the gasket is supposed to be "dry"-- I'd still goop it. Warpage from cast pieces is a thing. Very tough to see, even with a straight edge across the surface..
 

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Discussion Starter · #5 ·
Hi Eric,
I did use washers under the heads but the washers were not much larger. I bought those a while ago but as I recall the selection was limited. There isn't a lot of room between the wall of the pan and the edge of the fastener. The ATP gasket I used is much better but you are correct the edge must be submerged when the fluid is cold. Every GM trans I have of this vintage measures a lot higher cold despite fluid expansion when hot so part of the issue is very likely the normal fluid simply drains back into the pan and over the pan edge.

I wanted to compare a stock dipstick to the one I'm using but I haven't had the 2 cars in the same place in a while.

Scott
 

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Sorry, can't help any further because mine is the late 70's TH400.

If you are able to compare dipsticks, I think you're onto something there...

I found a hotrodders retail site that says the ATP TH200 deep pan has an additional 2 quart capacity. However, that's all relative to the trans being wet or dry on the fill (and it's all wet now!)
 
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