Tranmission flush on a Chevy ... and a major leak
 

One of my good friends has a Trailblazer (go ahead, take your shots) which she loves very much with about 70,000 miles on it. Two months ago the dealership, where she gets it serviced, told her she needed a transmission flush as part of regular maintenance, so she had it done. Everything was fine, until two days ago. The car just started pouring out transmission fluid on the highway, and fortunately went into limp mode and she was able to get it towed to the dealer. I thought maybe it would end up being a stripped drain plug that had popped out, but it turned out it's "at least" a bad front seal. She showed me a picture, and man, this thing was just dumping fluid. She's waiting for an estimate.

Now ... I'm not an expert, but am I out of line to think that the flush may have had a lot to do with the sudden failure of the seal(s)? I know once a transmission reaches higher mileage, if it's never had the fluid changed, you don't change it ... although hers only had 70k and I'm assuming is using synthetic ATF. But I've also heard flushing a transmission isn't a good idea at all. I'd think the internal pressure, plus solvents in the new fluid, might knock loose some of what was holding the seals together and also put extra strain on the seals.

I'm just curious what the thought is on flushes. I never flush my 87, just drain pan and TC for a long time and fill it back up, every 30k.

Hopefully the repair won't cost her too much anyway ... she just lost her job and this is the last thing she needs.

I think you are. That has been an old wives tail that has been going on and on with not a shred of scientific proof behind it. We were just talking to a Ford factory tech who worked in the R&D dept for transmissions and he doesn't even see how it could hurt. Usually, when the person has left it that long and the fluid is bad, they blame the flush.

No way to know now , but could it be possible that some bone head over filled it and it blew out the seal? Guess the answer doesn't really matter now unless ofcouse that even after it spilled out a bunch of fluid it is still full on the dipstick.

I am no expert, but I think it is entirely possible.

Find out the model of the transmission flushing machine, or just have her pay for parts... Front seal isnt much... Their labor is...

If it's a bladder type, it's a low pressure unit
If it's a hydrolic pump type, it's a high pressure unit... And they blow seals out unless throttled way down...

What year TB?

~Nate

An over-fill of flush fluid or ATF most likely caused the seal to fail. In either case, this is too much of a coincidence for the dealer to refuse to take responsibility.

That's why I asked. That was the interval the dealer recommended, though (70K), and they did say the fluid that came out looked fine. So it wasn't a case of her neglecting to have it changed in time. Probably just a coincidence in timing. I was just curious.

To start with, the vehicle was driven for about two months and who knows how many miles since the transmission flush was performed. I would think if the flush were the cause of the leak, it would have occured much sooner (at least that's been my experience up to now). That converter seal may or may not have continued to hold up if the flush were not done. Overfilling a transmission can cause the fluid to come out of the vent hole, but will not "blow out" a converter seal. After all, there is about 100PSI fluid pressure at that seal under normal conditions, and that pressure is regulated by a valve inside the transmission. A transmission flush should not cause a transmission to fail by itself. If the only thing that is "keeping the seals together" as someone stated above, is crud, then the transmission is headed for the repair bench in any case.

With regard to flushers, the older diaphragm type was replaced by the units using pumps because so many late model transmissions have thermostats in the cooler circuit that can be difficult to get to open, and sometimes can close again during flushing as the cool, new fluid cools the thermostat. The pump tends to force the thermostat open for proper flushing.

All in all, it was most likely a coincidence, or was a seal that was on its way out to start with. Not everything that goes wrong after a repair is due to the repair that was performed.

It happens, but those GM gear tranny's are usualy pretty solid. What year?

I just had it changed in my truck. Since their are no drain plugs on anything from 05 on they hook it up to a machine and suck it out.

I agree with loepke72 above.
No way that fresh fluid hurts anything. Since fresh fluid will have its full additive package, it might even soften older seals, maybe not, but no way it hurts anything.
It is an old wives's tale from 20-30 years ago that you never put fresh fluid in old trannys. It was untrue then; its untrue now. As was said before, if new fluid ruins an old tranny--it was already shot before the fresh fluid was put in.

70k...wow. When I was at the trans shop having my dad's 314k trans re-sealed prior to swapping in a new motor, I saw someone's 2003 Trailblazer invoice on the counter...$5400....for a complete removal, replacement, and reinstall. On a 2003! It was only 5 years old!! And probably just out of warranty.

Thanks for all the input. Like I said, I'm not an expert, so a lot of times I fall for old wives tales.:o It also never occurred to me that the car wouldn't have a drain plug. Heh.

Her truck is an '04, I think, but I'd have to double check. It looks brand new; she keeps it in pretty good condition and has always done the scheduled maintenance. Hopefully it won't set her back that much ... kinda of a "when it rains it pours" situation for her.

Turns out her torque converter was toast, burned fluid, game over. But, the dealer is giving her a better price to install a rebuilt trans than AMMCO, and her pension is about to kick in. Bummer, but guess it could be worse.

What kind of things might cause this at 70,000 miles? Low'high on fluid? Dirty fluid? Or just fluke?

Sounds like a fluke, GM usualy makes pretty good auto transmissions, its one of the few things they do right.

Probably a manufacturing defect I'd think.