Transman, some long-term feedback

[billr]

About three or four years ago I got the P1870 on my '97 Chev Express (1500 series) van, with about 77K miles.  I pulled the pan and didn't find anything terrible, so I changed the filter and filled with full-synthetic fluid and a dose of Lube Guard "Red", per your suggestion.  I now have about 106K on it and it is generally fine still.  It does occasionally (once or twice a year) set the P1870 and boast pressure to max; and this seems to be unpredictable.  Sometimes it was understandable, we had been charging hard up a windy mountain grade with lots of shifting and load... other times we had just been calmly going to get groceries!  At any rate, I clear the code and all is well again for many months.  I have avoided doing any towing, though.  Soo... P1870 is worrisome, but not always instantly fatal!  Of course, I expect I will have to put money into this trans someday, but hope to push it out a few more years.

[Transman]

WOW! Thanks for the update! This is probably the longest term feedback I have ever received.
As to the 1870 code, PIA that it is, I think when you think about it that more sense will come of it. This is a lockup code that comes from leakage inside the trans or the clutch is not holding well enough. I have found the main source, contrary to accepted thinking, comes from worn bushings inside the pump stator. The leakage by these points cause the valve body to wear as it tries to make up the fluid volume lost by the bushings. 80% of the time, replacing these bushings will FIX the problem without having to replace the valve body. Many factors will affect when the code pops as in your case. Obviously, heavy loads in conjunction with hills and heat will make the leakage by the bushings greater and Bing comes the code. I "think" the unknown times you get the code will directly corespond to "Steady" speed and heat, like a long steady drive when the computer has plenty of time to notice the converter clutch is slipping. The heat is your enemy here as is simple old age & miles. The replacement bushings we use are "beefier", wider to handle the load better and last much longer then the original bushings. Make sure when you deal with this trans, if you are paying someone to fix it for you, that they replace both the stator bushings when they do the overhaul or you will be back in the same boat within a few months. Most builders I have spoken to feel the valve body is the only needed component and that will repair the problem. I have several long term customers with 100k + miles on our trannys with no return of the dreaded 1870 code which was part of what they came in originally. Of those, better than 75% received little or no valve body work besides a basic cleaning with the overhaul. Keep the updates coming, Transman
P.S. If it has been several years since the lubegard, chuck another bottle at it.

[billr]

OK, I'll treat it to some more Lube Guard; cheap insurance for sure!  What you say about the PCM having enough time to "learn" of the slippage makes sense, as a couple of the times have been after several hours of easy driving on the freeway, but in hot (100 F) weather.  I hesitated to make my original posting, as I didn't want to give the impression to others that it is OK to ignore the P1870 (or any other) code; but I appreciate all the good advice you give and thought the least I could return is some feedback "from the field".

[Transman]

This code in particular is common. Understanding (and very simplified) what sets it is important to dealing with the problem. This code sets when it sees lockup is on and the torque converter slippage rpm is 130 or greater. That's not a lot of difference in speed. This is why sometimes a bottle of lubegard can be your best friend, certainly I am not recommending ignoring this code or filling your trans with lubegard but one bottle COULD make the difference between serious trans repairs now and some time to save up the money, as in your case even years. Transman

[billr]

Well, this is going to have all you pros shaking your heads...

In preparation for treating my trans with more lubeguard, I checked the fluid level to see if there was any real danger of over-filling it.  There was barely any fluid showing on the stick, just up to the little loop at the bottom.  Yeah, idling in park with trans at least warm.  Do you suppose the low fluid level could contribute to occasional P1870 in hot weather or hard driving???  Obviously, checking the fluid every few years isn't often enough!  The only defense I can offer (and tribute to Chevy) is that the engine goes 7500 miles on 1/2 qt. of oil at 107K on the speedo, so I have gotten out of the habit of checking under the hood.

[Transman]

Positively! Low fluid is a PROBLEM! Not just the pia code but the fluid is the coolant, lubricant, and it does ALL the movement inside the trans. A few quarts low can cook a trans in no time. After you fill it back up, start searching for the leak. Post back, Transman

[billr]

It's a very slight leak, just a spot or two on the garage floor.  The outside of trans and its pan are still dry after all these years, so I think it is a cooler line.  I'll look some more for it, but will try to be more diligent in checking the fluid in the meantime!  At least now I know how to spell "lubegard" correctly...

[Transman]

LOL!
Monitor the atf loss, you are correct, a little loss adds up over years. Careful with the cooler line leak, they tend to leak while driving rather than sitting AND can turn into a gusher in a moments notice. Post results, Transman