RacerX Thanks for the correction, he did say front.
Like the others that have posted I'm not convinced the tranny fluid would damage the system, thou I certainly could see it causing major issues if it were the other way around....

 

It is the mix of fluids that has caused a reaction and gummed things up.
I would think that the tranny fluid would have no effect on the rubber brake parts. It is the brake fluid that is the wicked stuff compared to tranny fluid.

If the master cylinder seals have swollen to the point of not allowing caliper pressure to be relieved, wouldn't the brake pedal remain in the down position?
Does it remain down?

If only one one rear brake line failed, there should only be tranny fluid from the master cyl. back to the point the line broke.
The fluid in the other lines will go back and forth a couple of inches but not all the way to the ends.

If the brake pedal comes back up but the brakes are still dragging hard, I suspect the balance valve (if it has one) or some ABS valve downstream of the master cyl. that allows caliper fluid to come back is gummed up.

Now that it has been driven 20 miles with the calipers dragging hard, they may now be burnt up along with the rotors warped.

 

Well, he said he pullled the cap off the reservoir and the fluid was syrupy.

Additionally, brake fluid is 0W and trans. fluid is 5W, that could be an issue. Something, a foreign element has been introduced into the system that has the front grabby.

Even more, we dont know what kind of ATF she poured in there, or if was really even ATF.

I 2nd, getting a new girl!

 

Any time a petroleum product comes in contact with brake parts they swell up. Im afraid you will have to rebuild or replace all cyls. to be safe. Then hope you can flush the system good enough to get all the AT fluid out.

 

Hi all, thanks for the many responses. I did take the truck into a local garage today and they flushed the brake system for $95. The guy said it'd be an hour but it took 4 instead...? He also told me most of the tranny fluid was found in the rear brake lines, which makes sense since that's where the broken line was when tranny fluid was poured in. Anyway, I had to work all day and haven't had a chance to try the truck on a long drive but this will be a good first test. If the problem persists, I'll move to checking seals.

Thanks again for the opinions. And no, the girlfriend is not getting the boot I give her credit for even knowing how to pop the hood and find the brake reservoir - that's better than most women out there