P1870 hard shift

[DrFix2Fly]

I have been dealing with this problem for two years on my 99. Turns out that GM knows there is a problem with the valve bodies in 4L60e made in 98 and earlier. Classic symptoms include a hard 1-2 shift after the transmission has gotten warm. This is due to wear in the TCC valve bore which allows a pressure loss and thereby causing the TC to slip. Once it slips senses a couple of slips, the computer takes pressure modulation out of the picture and shifts with full pressure. There's your hard shift. If you allow it to cool or clear the code, it will shift normally. I am tired of carrying my code reader with me. I have my dealer looking at several TSB's to tell me what the fix is. I have already had the TCC valve bore oversized with a Sonnax valve, but the problem hasn't been resolved. Has anyone else been to their dealer with this problem and what have they told you? I don't think we should have to pay for such an expensive repair if GM knows this valve body is faulty and will probably only work for 30K miles before it starts to crap out.

[1 FAST V6]

When I first got this code, I took it to the dealership and they looked at it. They told me that the transmission is slipping and that it needs to be rebuilt or replaced right away. Of course it was for the price of $1300. So I just told them I would be back next week and never went because that is too much money and I was told that if a tranny starts to slip and you take care of it, it will still last you a while. About three days after that, the SES light turned off. Now about 4 months later I got the code again one night and it was on for 1 day. 3 days later, it came on again and for now I am just ignoring it. .........(by the way, I do notice that it slips sometimes when switching from 2nd to 3rd)

[Guardsman]

Superior Transmission sells a a kit that gets rid of the Pulse Width Modulated (PWM) TCC, which is the ultimate cause of the leak (the TCC apply piston being modulated to vary the apply pressure). It converts it to a straight on-off apply.
If this has been going on for a while, my advice would be to get the tranny rebuilt. Superior, and couple of other companies, offer multiple fix kits for known problems with the transmission, problems that won't be fixed if you get it rebuilt or replaced by the dealership.
Also, the heat generated by the slipping tcc causes a lot more damage than you might think. My tc was torched by the time my tranny was taken apart, and the Redline High Temp ATF (racing ATF) that I put in about 11,000 miles before was also torched.
In addition, a good tranny rebuilder can get rid of the excess play in the transmission, which will result in it lasting longer.

Here's what I found and did on my rebuild (from a previous post of mine):
For all of you with A4s, I would highly recommend getting your tranny rebuilt the first chance that you're able. You will be amazed at the difference it makes.
The guy who did my rebuild said that he found almost .004" of play in the pump housing (total of .072" of play with a .068" bushing from the factory), and .100" of play in the clutch housing alone, and said that's what he routinely finds from the factory. He said that they have one standard size of bushing that they use, and they don't bother with shims, they just throw the thing together, regardless of how much play is in it.
As part of the rebuild, I had him install several fix kits, one got rid of the delay going into first and reverse, another one got rid of the pulse width modulated tcc apply and converted it to a straight on-off apply. He also installed corvette servos, a 9-disc clutch pack (stock is 6 disk), a high energy band, and a mild shift kit.
This thing is amazing now. It's noticeably firmer, and accelerates much better. The shifts are not harsh, but sharp and firm. There's no more play in the driveshaft when it's in park (grab your driveshaft, and you can turn it a bit each way). It's beautiful .
In addition to the rebuild, I put a whisper lid and aluminum ds on. Now, I can accelerate at 1/2 throttle as fast as I used to at full throttle. A good rebuild will put you back about $1600, but it's well worth the money if you put a decent number of miles on your car, and plan on keeping it for a while.

[DrFix2Fly]

My dealer quoted me $770 for a rebuilt valve body plus $50 for the core. I also pressured him to answer the question about what GM does for their customers if they are just out of warranty and have a problem like this with a known defective part. All the dealer could tell me is "talk to GM." May God strike me down, but I'm considering a Ford.

[DrFix2Fly]

Now that I am done venting, I would like to thank you for directing me to Superior Transmissions. I have already had a tranny shop install a Sonnix valve, but the problem was not resolved. I will ask them to look into this. By the way, me in a Mustang...not a chance, I'd still rather push my Bird.