umair

Well I found a solution for anybody having 1-2 hardshift. There is GM service bulletin for it and can be read here:
http://www.trutechtrans.com/Topic-1-00-04.html
Any car model 2000 or below having the 4l60e will have this problem. So if you have a 2001 or 2002 then you are safe. Its the old TCC regulator valve making the bore size bigger and not sealing properly. Fix is simple. You need to open the transmission and remove the valve body. Then remove the old TCC regulator valve and put a A74741Q 4L60E Transmission TCC PWM Valve thats already oversized. After the fix it will shift like brand new.

A74741Q 4L60E Transmission TCC PWM Valve here:
http://www.transmissionpartsusa.com/...its_s/6698.htm

Instructions:
http://www.teckpak-fitzall.com/datas...CC%20valve.PDF

Other option is to buy a reconditioned valve body on ebay.

72blownvert

This is only one fix out of several to take care of an 1870 code especially on transmissions with high miles.

mrvedit

This is only relevant if the "Check Engine Light" is on due to a 1870 code which causes the PCM to command maximum line pressure resulting in harsh shifts.

In other words, if you have a harsh 1-2 shift, but there are no codes, then this is not the problem.

Thanks for the info umair; I didn't know such an inexpensive part was available to help with the common 1870 problem.

BTW - The Transgo HD2 kinda "solves" this problem by replacing the stock valve with a simple on/off valve which doesn't do the soft (PWM) engagement.
(The stock valve does a gradual engagement of the TCC so as not to jar your grandmother in the back seat of the Caddy. If the converter
slips too much during this gradual engagement, you get a 1870 code. I think most of us are happier with an on/off TCC; hence the simple
on/off valve which "solves" the 1870 problem.)

umair

Yea I am going to do mine soon. I am happy with this part. Sonnax also makes this part but is like 50 dollars plus you have to drill a hole with a special reamer that costs 160 dollars. So total is 210 dollars. Plus a specialist needed to precise drill the hole.
Advantage with A74741Q part is its like ten dollars and no need for drilling a hole. It just fits right in. The only bad point is you have to tap it in because its a tight fit. But much cheaper and you can do it yourself.
Correct me if I am wrong, p1870 is code for transmission slipping but you can still have the problem without the code.

maddoglou454

sonnax 1870 fix, The part number is 77754-04K we do this to all our 4L60E and 4L65E transmissions, no matter what level it is, it will definitely fix the common problem 1870 code.

Not A Z

iTrader: (1)

This really isn't true, the reamer is self centering and has a self stop on it for the depth. Once you get the reamer you can just use a tap handle from a tap and die set to turn the reamer.

umair

Thanks I did not know that, good forum.

Not A Z

iTrader: (1)

No problem, and in the directions they have for the reamer, you can see how it's designed:

http://www.sonnax.com/system/instruc...754-04K-IN.pdf