727 Still Leaking at Output Splines
 

Just to refresh from previous posts, my trans doesn't leak if the truck is run every day or two. I only use it now every couple of months. After about 3 days of sitting the TC drains back enough fluid to place the level above the splines which allows it to leak (it is not the seal leaking). Research shows a lot of ref. to an antidrainback valve in the cooler lines, but I can't find a reference to this particular truck. All cooler connections are above the level of the TC so any TC drainback would have to be a siphoning action. Is there a checkvalve in the cooler lines or has anyone had experience installing one? I am considering changing the valve in the VB to prevent drainback, but I want that to be a last resort. One thing that confuses me on this situation is that I would expect to have delayed engagement after startup when I shift. That isn't the case. I don't hotrod the truck so maybe it refills the converter quickly and I don't see the problem. I did read that the trans level should be an inch or so above the actual check level with the engine off. I checked mine after sitting for a month and it was 5 or 6 inches over with the trans actually 4 quarts low.

Output yoke can leak at a plug in back of sliding yoke. 89 does not have drainback valve in cooler line. You cold install one making sure is installed in correct direction. No drainback valve in VB.

Thanks for the reply Dozer. I wish I had the sliding yoke with a plug. That would cure my problem. My yoke is the open type secured with a nut and washer. Are you saying that the after market manual valve for the valve body won't work on my trans. I had a thought that I might be able to park the truck in neutral. That would keep the manual valve in a position to prevent the exhaust of fluid back to the pan. According to the circuit diagram the TC is pulling air through the cooler discharge and letting the fluid go to the pan from the manual valve in park (same reason that you can't check the fluid in park).

Put a bead of RTV under the washer. Jeep used to have a rubber washer in their setup.
You are making me think now. Bleed down of converter can be two sources.
Typical is through cooler lines. Other is at converter hub, and input shaft area. To describe these leaks, follow this line. Engine turned off, converter is hot and fluid expanded. Fluid cools and shrinks, Pulling air from converter hub area or input shaft. Now the fluild leaks down through cooler lines or input and front pump area. Converter oil glug, glug, glugs down till half empty and stops.
The manual valve you speak of has a internal passage that allows fluid to fill converter feed circuit in park. The larger land keeps fill circuit from leaking. It has been a while since reviewed, but believe cooler check valve would better suit the drainback situation. Yes, the manual valve will keep converter filled in park and provide more positive lube (larger land) and refill converter after drain down. My brain is mushed out. JMHO

Thanks. I appreciate the recommendations. I will try anything except the RTV. I had a rule when I used to rebuild transmissions. That was no RTV even in the same room where a rebuild was going on. I could have cured the problem by removing the yoke nut and applying RTV, but I've had to work to many transmissions where someone used RTV to seal a gasket and let a small particle get to the valve body or clutch. I guess Chrysler must build a good trans because I don't ever remember having to tear one down but I also never saw a trans that allowed pump pressure to dump to the pan when in park. Here is the best info I have found and the reason I think putting it in neutral may work. http://www.asashop.org/autoinc/jan2001/mech.htm I do plan to install a check valve if this doesn't work, but I don't want to do it unnecessarily. Stuck check valves have burned a few transmissions. Again Thanks for the help.

I respectfully disagre with some of your experts statements and assumptions. I also have 40 plus years experience with the 904 plus extended family of trannys. If you don't like rtv, use a O ring. A 1/2 inch bead of rtv will get anybody in trouble. There are too many applications that used rtv at assembly to cast aside it's use. JMHO