leaky TH 350

[rtm]

my transmission has leaked since day one.
I've tried all sorts of different ways to install the trans pan, (cork gasket, rubber gasket, rtv, no rtv. etc. etc.)
went to the local gearhead garage for advice, his advice.... scrap the trans for a turbo 400.
He says that almost ALL turbo 350's leak. and he refuses to use them.
I am unwilling to take such drastic measures at this time, so any advice would be helpful.
I know alot of guys run TH 350's, there has to be some secret to keeping the fluid in the case where it belongs.
the dipstick tube leaks,the kickdown cable leaks, and the cheap chinese chrome pan that says: 350 TURBO on it, will not seal.
have to remove my exhaust system to access this stuff.
Even then, it's tough, with no service lift, to get at .
car's on jackstands, with a 99 cent turkey basting pan under it, (to catch my expensive synthetic fluid)

enough ranting for now, off to find a suitable replacement pan , (gotta start somewhere)

[cjbiagi]

First thing is to determine exactly all the sources of leak. The dipstick, speedo cable, shift shaft all have "O" ring seals. It could also be that the trans is over filled as the fluid level should be below most of these seals.There is also a possibility that the aluminum casting has some porosity issues. It's possible that some leaks actually come through the case itself. Hopefully that's not the issue. Then, get a good quality trans pan along with a quality gasket. I have always had pretty good lucj with the blue gasket maker (forget the exact name right now). Just a very thin coat on each side of the gasket and then evenly torque down the pan using the correct pattern and torque specs.
I have a friend with a 64 Vette with a powerglide trans that will literally puke 2 qts of fluid over the winter. The issue with those are that the torque converter slowly drains down and overfills the trans by 2 quarts. When the fluid level rises above the O ring seals it will leak past them until the level gets to where it should be.

[rtm]

Exactly my problem clyde.
When the torque converter drains, the fluid level rises above the level of ALL of these seals.
I have procured an aluminum pan from a local speed shop. ($79.00)
The "O" ring gaskets are next, although, I know I did the dipstick one already.
As for being overfilled?, I have the stock dipstick and housing.
Could they provide an errant reading with aftermarket pans?
If the dipstick reads wrong, how do I determine a full level w/ aftermarket parts?
My trans. cooler is mounted in the rear of the car, (where the stock fuel tank used to reside).
The line length/diameter should not matter, if I am checking trans fluid while warm and in park (engine running)?
Thoughts to ponder.

[cjbiagi]

I researched the problem on my friends Vette and found this to be a common problem on Powerglides. It could hold true for other transmissions as well on cars stored for a extended period. Unfortunately I was not able to find a definite solution, most people on the forums pretty much said "yeah, they do that". Other than starting the car periodically during the winter to keep the fluid in the converter I don't know. Is this only a winter time problem when the car is stored? You can try and replace all the O rings and hope that reduces it but these seals are not designed to stop that much fluid. Again, usually the fluid is below the level of these seals. Once it rises above them they are submerged in fluid and just can't stop the seepage. Is your aftermarket pan actually deeper than the original? It would seem to me that the level on the dipstick should remain the same, the extra fluid is just lower in the deeper pan. Same holds true for the pan gasket, I don't think the normal fluid level is above the gasket (like a engine oil pan). Once the level comes up above the gasket it can seep over time. The Blue Permatex gasket maker usually works good in those instances, like on the rearend where the oil is at gasket level.

[chevyart]

rick the synthetic fluids always seem to find a way to leak. maybe thsa is part of the problem. if the fluid all returns to tranny at shutoff time and maybe overfills the tranny, would some sort of residual valve, placed on return line, close to tranny(inlet area) stop the fluid from returning at shutoff, and then just open up when car is restarted and goes. just a thought. is this a good idea. there is probably alot of fluid in rear lines due to location of cooler. art

[rtm]

So, my buddy walks into my garage, and sees how much fluid I have in my drain pan. (more than the trans. pan can hold below gasket level)
and he sez, rememba ,I told you, when you mounted your trans cooler higher than your transmission, that it would drain back and leak?
I don't remember.
ANYWAY HE SEZ, WHY DON'T YOU MOUNT A CHECK VALVE INLINE?
Why didn't I think of that?
becuz I bang on rocks for a living.
Art, your Idea wuz close, but, I would forget to open the valve, and burn up my transmission. lol

[chevyart]

rick a residual valve is a check valve and i would put one on the in and out line. i know this and i pun ounded my head with a hammer for 35 years art

[rtm]

hey art,
sorry for misreading your original post.
musta been that big word (residual ) that threw me off.
anyway, there are valves designed for brake systems online, offered
for 2 psi or 10 psi of pressure.
Can I assume that this is the pressure required to open the valve one way, and that fluid will not flow the other way at all ?
thanx for any help.

found this one too;
http://www.ebay.com/itm/One-way-Check-v ... 65&vxp=mtr

[chevyart]

rick that answer i am no sure of. just guessing the lightest pressure would be the safest to use as it would open quickest, probably someone like cj or one of the guys could tell you best as to tranny pressure. planning on coming up your way next month or so. better get all that tranny fluid off the floor before i get there. art

[rtm]

thanx art,

I better get some snow tires, if I'm gonna take you for a ride in December LOL

[rtm]

O.K. guys, which line is which, coming out of transmission case? (TH 350 )
trying to figure out which way to mount my RESIDUAL valve (learned a new terminology from chevyart ) .
I love this automotive stuff.

[Monza Harry]

Rick, the brake residual valves are designed to hold pressure in the wheel cylinders (10#) to keep the cups (seals) flared so they don't leak/back flow contaminates into the cylinder and the 2#'s are for some rear disc set ups* for similar reasons. So that means that valve will try and keep pressure in the cooler the way you are going to set it up, it isn't supposed to add forward resistance to the system just stop a certain amount of return flow, and if it isn't to restrictive it should do what you want. I have never seen a 5/16" listed (or have I looked) I would be wary of a 3/16" or even 1/4" as brake systems don't usually have huge flow like I would expect from a transmission cooler. Harry * And some track setups up's on the front to try and eliminate pad knockback

[cjbiagi]

I am not convinced your leakage is because of a tranny cooler, from the research i have done it's from the torque converter draining down over a extended period of storage. A trans cooler doesn't really hold that much fluid, a torque converter holds a couple quarts or more.

[rtm]

I am not convinced your leakage is because of a tranny cooler, from the research i have done it's from the torque converter draining down over a extended period of storage. A trans cooler doesn't really hold that much fluid, a torque converter holds a couple quarts or more.

I am having the same thoughts, however, I went from a huge, stock stall speed converter, to a smaller( 8"? ) higher stall speed converter, and the problem is the same, if not worse.
Although I am not enthused at adding check valves to the system, it is a first, and low cost, step towards solving a recurring problem.
I have all winter to hash it out, unless I need the garage bay, and then I would need to have the car operate under it's own power.
Other people are suggesting catch cans, external resirvours, etc.
but, IDK.

[chevyart]

rick didnt realize you had an 8 inch converter. you are gonna catch hell with that thing slipping when driving on the street. i have not believed from the beginning of your post that it was your converter draining back into the tranny. if this was the case, then every converter in every car would do the same.JUST MY WAY OF THINKING THIS OUT). are you sure you have the right dipstick length in there?. a deeper pan would not make the difference in a reading if the correct length dipstick was used as the extra fluid is below the dipstick , but say the dipstick was too short, then you would have to overfIll the tranny to get fluid up to the line on the dipstick( too short of a dipstick). just a thought. with a big cooler and an in and out line, you could maybe have an extra quart of fluid. that would be alot, especially if dipstick was wrong one. after all the fluid leaked onto the floor, did you start it up and see if it leaked again(just start for a few seconds in case the system is low)? this has to be a simple problem with an easy fix. keep us posted. is it possible yoiu have a dipstick for one of the other chevy trannies installed in your car. does anyone know the difference?. maybe a call to jegs could get you this info. art