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View Full Version : Nothing like the smell of transmission fluid in your hair



Fasttrack
04-30-2006, 09:17 PM
I can't get my th-400 to stop leaking! I don't know what else to do -- i replaced the pan, pan gasket and used gasket maker on it. I got the pan to pretty much stop leaking and about three days later the *slip yoke* started leaking and the dipstick was seeping (around where the tube plugs into the case). So i replaced dipstick o-ring, vacuum modulator and o-ring, replaced rear seal (although it wasn't leaking from here but from the inside of *slip yoke*), replaced the tailshaft / slip yoke bushing and the o-ring that is on the output shaft and rides inside the slip yoke. I figured since it kept leaking it must be a problem w/ pressure, like maybe the breather tube was plugged or something so i drove it around with my dipstick popped slightly off the tube to allow it to breath. I let it sit and it started leaking again from the tailshaft. Its almost like the slip yoke is too far out so under normal operation the o-ring isn't sealing the slip yoke - also it only starts leaking after letting it sit long enough for quite a bit of fluid to drain out of the torque converter. What am i missing / doing wrong / ignorant of?? Any advice would be appreciated!

torker
05-01-2006, 01:54 AM
Fastrack, are you really sure the leak is coming from the tailshaft?
The seal for the torque converter neck (that slips into the pump) can leak. The fluid gets blown to the rear as you drive and may show up as a leak at the rear.
Also...is your slip yoke (the part that fits inside the tail piece) in good condition?

J. Randall
05-01-2006, 01:59 AM
Fasttrack, it has been many yrs. since I messed with a turbo 400 so take this for what it is worth. I seem to remember the tailshaft being a solid splined shaft, I don't recall any being hollow.Could it be leaking out the back of the driveshaft yoke? I think there is supposed to be a plug there. There should be a vent on top of the tranny, be sure it is clear, I am not sure pulling the dip stick up would actually vent the main housing properly. Also you might check that your dipstick is correct for your tranny and you are not ovefilling it. Someone might have stuck the wrong one in before you got it. James

torker
05-01-2006, 03:10 AM
Fastrack...there is a little plastic vent cap on the top of the tranny. Right at the bottom of the bellhousing curve on the right hand side. It is hard to see from the bottom. That is supposed to take care of any venting.
Normally the only time anything will come out of the filler tube is (as was mentioned) if the tranny is overfilled or if your torque converter is hooped or the stall is too high.
Too much torque converter slippage causes the fluid to boil inside the TC and it will spew out the filler/dipstick tube.
I'm thinking that shouldn't be your problem.

Fasttrack
05-01-2006, 05:23 PM
The dipstick is the correct one - actually i broke the one that was original and replaced it with an OEM part. I cracked the top not to let fluid out but rather to allow pressure to equalize. In my mind i assumed any pressure would build from expanding fluid as it heats up or having too much in the case. Previously i have actually filled it a little under the full mark to test this theory and it still leaks. I checked the tube coming from the vent and it seems clear but that was all i could really get to with it sandwiched between the tunnel and top of the transmission.

Also - i was taught (by a shade tree mechanic) that the tailshaft and output shaft were two different things. I guess the correct term for what i was calling the tailshaft is really the slip yoke or driveshaft yoke. Makes sense - afterall it *is* the yoke for the universal :) Thats really where it is leaking from - the slip yoke slides over the output shaft and there is an o-ring on the output shaft that seems like it should seal to the inside of the slip yoke (the splines stop towards the back of the slip yoke to allow this to happen) but it doesnt seem to be quite long enough but i'm not sure about that. Also the output shaft has a tapped hole but nothing is bolted to it - not sure what that is for... Anyway, thanks for the information! Sorry about the confusion - i'll go back and change tailshaft to "slip yoke"!

Oh - for the possible leak at the torque converter neck, what do you mean it would be blown to the back as i drive? Would it be visible from the underside because i have a new chrome pan that has remained nice and shiny - no oil or greasy marks on it and the rest of the transmission i cleaned fairly well (or at least the sides that i could reach w/ some degreaser and towel). Thanks again guys!

dirty old man
05-02-2006, 09:08 AM
Fasttrack, what's happenong here has been the bane of TH 400s since they came out. There is an internal leak that allows the fluid in the torque converter to leak back into the trans case{which is at a lower level} during extended down time. As a consequence, the fluid level in the pan after a period of time of not running is way above the intended level. The seals, gaskets, and O rings weren't designed to hold while submerged in fluid but for splatter and splash.
I had an '85 Chevy truck with a towing package that did this, and a friend has a '57 Nomad with TH400 added that did it. I never found a solution other than driving it more often and I'm not sure if my friend ever cured his Nomad or not. If there is a cure it involves pulling trans and doing internal work, I'm told. I'll try to contact my friend and ask him if he ever fixed his.
Dave

Fasttrack
05-02-2006, 06:41 PM
Thank you so much! I've been wondering about this for awhile - thats why i think i mentioned that it leaks after the torque converter has time to drain. I wasn't sure whether this was supposed to happen or not. That is likely the problem because the fluid level changes alot when you let it sit and if you drain it, a day later there will be like another two quarts in the pan. Thanks again for the information! I don't mind pulling - i've been thinking about that for awhile. With it continually leaking and being 27 years old i really think i should just buy a complete rebuild kit (~80bucks at napa all bushings and seals and etc) and yank the tranny. I think it would be alot of fun but time consuming. Our school has a bunch of old 350's lying around - i think i'll see if i can tear into one of those first to sorta get the hang of it. Otherwise my auto teacher has a good freind who teaches a trans repair class who could give me some help if i hit a wall.

dirty old man
05-02-2006, 08:40 PM
I've called several times to the house of the Nomad owner and gotten his answering machine. Since he and his wife are retired they may well have gone on a trip somewhere. I'll keep trying and let you know here.
Dave

J. Randall
05-02-2006, 10:01 PM
DOM, thats an interesting theory, I don't think I had heard it before. I have seen many different autos that would leak after an extended peroid of sitting idle. My theory on this is that the weight of the torque converter slightly deforms the front pump seal allowing a couple quarts to leak out. When ran again the seal rounds back out and works just fine. James

dirty old man
05-04-2006, 01:00 AM
Finally caught the Nomad owner at home, he never found a way to stop the tc drainback he finally got most of his leak stopped by using extra effort at sealinf things up, like 2 seals on the shift lever shaft where it exits the case.
He tries to remember to crank it up and at least shift it thru the gears every couple of days. The guy I sold my truck to, I told him about the problem, and I still see the truck often around town, he uses it as primary transportation and drives it every day, so no problem.
Dave

Fasttrack
05-04-2006, 06:17 PM
Dave - thanks for all the help! I sure appreciate you going through the trouble to contact the owner of the nomad. I'm not too concerned about the driveability - i'm just getting tired of the stains on the drive way. Its not a small leak either - it looses about two quarts of a week out of the slip yoke. Oh well - i'll drive it for a while and then when i get some time i'll pull the trans and the engine. It needs new main bearings and a rear main seal and it i'd really like a slightly higher compression piston in there. Plus the trans is old - for 80 some odd bucks i dont mind getting a rebuild kit. It's supposed to have all of the friction material, including the band, as well as steel parts, gaskets, seals and bushings. Not too bad in my opinion. Anyway, thanks again!

J. Randall
05-05-2006, 12:04 AM
Fasttrack, have you ever had the u-joint out and looked at the very back of the yoke? I am not sure it has been a long time, but it seems to me there might be a welch plug in the back of the yoke. If there is and its gone fluid would come out the very back of the yoke. Might be worth a look. James

Fasttrack
05-05-2006, 03:07 PM
J. Randall - yeah there is certainly no welch plug in the slip yoke. Whether or not there was supposed to be one there, i haven't been able to figure out. No one at my school new and i haven't found it online. The trans was a junkyard trans and i get the feeling the previous owner had no clue what he was doing, as in even less of a clue than i have! Anyway my point was that it very well may be that there is supposed to be one there and he didn't know or removed it or who knows. Thanks again everybody.