Yeah so my 99 Blazer had a CEL on it so took it over to Autozone and it was P1870. So he checked the trans oil and it wasn't in the greatest of states. It was damn near black and smelled burnt. So I bought all the stuff to change the oil out and I wanted to do this weekend. I have been reading up on the internet and most places say if you have a high mileage trans that hasn't been taken care of you don't want to flush it before an oil change. That is fine, I wasn't going to anyways... I also came up to one that said don't even change the oil because the new slick oil will make the clutches slip. Just take it to a shop and have it looked at.

So now Im thinking of what I should do. Should I go ahead with the oil change? Should I take it to a shop to have it looked at? I dont have a warranty on it so if the trans is really fried I'm out of pocket. Im also thinking about getting a warranty from my bank then taking it in.

The trans is not really doing anything out of the ordinary. It does hard shift once in a great while from 1 - 2.

If I do need a new trans, How hard is it to change out one of these transmissions? Ive done a few manual transmissions on like Nissan Silvia's and Mitsubishi Evos.

Any advice would be nice and appreciated. Thanks for the help guys

 

My suggestion...

start calling around to the various tranny shops for a place that is extemely knowledgable on the 4L60E. Plan on a rebuild sometime in the next year or so.

That being said, I would go ahead and change the fluid a couple of times. Having all that crap running around inside there sure isn't helping anything and is more than likely causing more damage. Changing it out may help prolong the life.

The 1870 code is kind of generic, as it just means you are having some slippage of some kind somewhere in your transmission.

 

Check out this thread:
Tranny shifts hard when at operating temp.

 

you could change the oil and add some lucas transmission fix and see if that would help.