What would cause tranny leak?

[seschev3]

My 700r4 started leaking a couple of days ago. So I pulled the inspection cover last night and started her up this morning and she started dumping from behind the torque converter. I understand that the front seal needs to be replaced now, but what would cause it to go out? The tranny is built hardcore because I tow 27' trailer that weighs around 6000 lbs. It only has 13000 miles on it since the rebuild. Could it be the pump? Any help would be great. Thanks in advance.

 

[big83chevy4x4]

had this same problem last weekend on a truck, first check the vent to make sure its not clogged, second do you have a locking dipstick?

 

[seschev3]

Yes I do have a locking dipstick. This also began shortly after I took the trailer camping last weekend. Tranny stayed pretty cool except a couple of hill climbs got up to 210* for a couple of minutes. Wonder if my setup can not handle the towing. I have 1 ton running gear and 4.88 gears with 38s. This is my first 700r4 that has been built.

 

[mikey_d05]

Could definitely be the pump, I had a 700 blow the front seal after the pump screwed up a couple of years ago.

 

[seschev3]

Do you think manually locking up the converter would cause any damage. When in 3rd at a higher rpm on hills I would lock it up manually with a switch I installed to take some strain off of the tranny. This is because at higher rpms my vacuum switch would not engage the lock up automatically.

 

[seschev3]

Okay, I just checked it again. After sitting and then starting the tranny dumps a little and then stops. Could this be fluid draining back from the torque converter and just be a bad seal.

 

[big83chevy4x4]

im guessing that the vent is plugged and with a locking dip stick the pressure built up will blow pump seal out. you can sometimes push it back in with a long screw driver or prybar, but usually don;t last long. it keeps from dumping the fluid out though.

 

[Jagged]

im guessing that the vent is plugged

Where is this said vent? Both of my diff breathers sucked up some water today, and my tranny has spooged all over the aluminum bell housing cover plate (whatever it's called) and the u-joints on the front driveshaft near the output from the tcase

 

[big83chevy4x4]

the vent on the tranny is on the right side on the top of the tranny near where the bellhousing ends and the main tranny body starts.

 

[85mudblazin]

Its the bushing inside the pump, had the exact same thing happen. Thought it was the seal and after replacing it it still poored fluid. Another thing to look for when you pull the tranny is just look at the seal, 700's are bad about that seal poping out, so if it is get a new one and loc-tite it back in. But I would almost bet the bushing inside the pump went out.

 

[mikey_d05]

Its the bushing inside the pump, had the exact same thing happen. Thought it was the seal and after replacing it it still poored fluid. Another thing to look for when you pull the tranny is just look at the seal, 700's are bad about that seal poping out, so if it is get a new one and loc-tite it back in. But I would almost bet the bushing inside the pump went out.

'tis what happened to me...pain in the arse

 

[seschev3]

I am taking it into the shop that built it tomarrow to see if they will warranty any of it. Doubt they will, but it is worth a shot. I have taken this tranny in and out 4 times already and it looks like I will be doing it again. That is what I get for trying to save a buck and have them build it out of the rig. Last time it was my freshly built double lined torque converter that blew up and sent pieces of kevlar through the tranny. Never had these problems with my th400 in my old truck. Beginning to wonder if overdrive is really worth it anymore. My vent was not clogged. I have it running up the firewall with a stock breather cap on it. Thanks for the info guys. I will keep ya posted on how it turns out and what the problem is.

 

[seschev3]

Okay this is the low down on the tranny. Front seal toast, bearing toast, pump toast,and torque converter hub toast. I can't win. Something is out of alignment. There is no wear at the crankshaft end. I think it is in the tranny somewhere. Any suggestions are welcome. Flexplate and motor are brand new with this setup.

 

[dyeager535]

How did the pump become "toast".

I had a TH400 (newly rebuilt by me) that all of a sudden quit propelling my vehicle. Ran maybe 1000 miles before it stopped working.

After I completely tore it back down, I realized that the drive tangs in the pump were halfway ground off, and the drive slots in the converter hub had rounded enges. The *only* way that new seal and the drive tangs/hub could be worn down were because the converter wasn't seated deep enough.

Talked to a friend that owns a tranny shop, he said since almost all converters are rebuilt, when they are machined, they can be machined too "thin", which means the pump and drive don't seat far enough. During re-install (I was broke) I re-used that converter, but added washers under the bolts to the flex plate. After a few miles, the front seal started leaking, which made me pull the converter again, replace the seal, and remove one of the washers between the converter and flexplate, to keep the converter hub weld from hitting that seal. Problem solved after that.

I know on the TH2004R's (at least) they had a problem with the front seal being pushed out. One of the fluid return passages in the pump was designed too small from GM, and builds pressure behind the seal, which eventually forces it out. I would find out if there is a similar problem with certain 700R4's and/or the pumps.

If either the pump or converter were "bad" from the get-go in your case, I'd expect the shop to pay for it, but 13,000 miles is probably outside most places warranty. However, if they installed a shoddy product, I'd still talk with them. 13,000 miles is a pretty long time for it to run then fail though. If something internal were out of alignment, *I'd* expect a seal (at least) to fail long before that, if not bushings, etc.