Shifting??

[jhgw]

If you put your Envoy in first gear, should it shift out of it as if it were in "D". If I put mine in "1" and go, it will shift on its own to second and so on, not very smooth though. Where would this problem come from, computer or trans??? I beleive it is also part of other issues...:bonk:

[ylab]

With the shifter placed in '1', the truck should stay in first gear unless you exceed a preset maximum rpm. (Its a safety feature to prevent engine damage). If that preset is exceeded, the transmission will shift into 2nd. To my knowledge, there is no preset rpm shift point...but 2nd during a hard acceleration in 'D' is good for something like 50-60 mph. - How high of an rpm are you seeing when it shifts? The 1 & 2 positions are meant for extreme conditions, when 'D' or '3' are inappropriate, such as off-roading, snow/ice, etc, when maximum engine braking is desirable.

What are the 'other' problems, that you feel are related?

[jhgw]

It also has a clatter while coasting at slow speeds(only in overdrive) (there is a thread on this issue started by someone else), has now developed a vibration while in od when you accelerate, like it is stuck between gears? I had a tranny shop look at it a month ago, all they did was pull the pan and change the fluid and filter. Said there were no visible (pile of metal in the pan) signs of anything wrong.

[ylab]

What if you move the selector to '3' (D) as opposed to 'OD'? Do both symptoms go away, or are they still present?

BTW: Don't manually shift the transmission (1, 2, 3) with the shifter, it can damage the transmission. Our transmission wasn't design to be manually shifted and the accumulators don't build pressure to cushion the shifts, when manually shifted. You'll end up having to rebuild it if you do.

[jhgw]

Everything feels good in 3, these problems are only present when it is in "d"

[ylab]

Accelerating shouldn't be any different in 3 or D, other than the transmission wouldn't shift into 4th (OD) gear. I'm wondering if the shifter is physically not fully engaging drive in the 'D' (OD) setting and needs adjusting....which is why I asked if the problem went away in '3'. If the shifter isn't locking into the correct gear, this could also possibly explain the shifting when placed in '1' (first gear). - Other than a shifter issue, the other cause that comes to mind would be a problem in the valve body itself. (Which can be serviced through the oil pan, so no need to pull the tranny - usually not terribly expensive either, I've replaced them on older transmissions). First thing I'd try is adjusting the shift linkage, no parts involved, but I'm sure there's a special procedure to ensure proper engagement.

How many miles are on the truck? (I'm guessing you're beyond the warranty period at this point?). Some friction modifier or additive designed to clean and free sticky valve bodies might not hurt either, should the adjustment not help.

[jhgw]

You may be on to something, I remember the first time I put it in 1st, it didn't go the first try. You had to pull back on it to get it to go. The truck has 75k on it. What type of additive (brand) would you recomend? Without getting ripped, where would be a good place to start for the valve body? I thought the fellas I had look at it the first time would have found something, the only thing they mentioned was some bearings that tend to dry out? The rattle has been there as long as I can remember, the vibration has just started happening.

[SKEETER1978]

every chevy truck i have owned or driven from 1998 to 2005 both 4l60e and 4l80e all will shift on there own when in first it will be a long delayed shift and the throttle has to be under 1/2 and it will shift to second only. (this is most of the time) sometimes it wont do it. pisses me off when i plow snow and want to stay in first

[glfredrick]

What type of additive (brand) would you recomend?

Typically, adding additives to ANY oil is a mistake, as the additives may only serve to mask real symptoms and issues that ought to be solved by properly repairing the unit.

With that being said, there are two additives that seem to be a cut above the rest, and come highly recommended. The first, Lubegard, is widely used by transmission rebuilders. I don't buy their claims that their product will somehow turn one transmission oil into another. I believe that is a misdirected statement by the company, but that being said, the product probably can help with a sticky valve body problem.

http://www.lubegard.com/automotive/index_trans.html

http://www.transmissionpartsusa.com/Lubegard_fluid_additive_s/9154.htm

Then, there are the Lucas products, which a lot of people seem to like. I've used some myself on older vehicles that are on their last legs, in order to squeeze a few more miles out of them. Note that they work mainly by introducing a chlorinated (which makes stuff slippery) and sulfer-laden formula to the oil. That may not be the best for longevity of your transmission, as altering the chemical composition of the oil can create acids that speed up internal damage and clutch wear.

http://www.lucasoil.com/products/display_products.sd?iid=29&catid=2&loc=show

Then, there are high quality synthetic oils that have the proper factory recommended additives already in place that will likely cure most sticking problems, such as Amsoil.

http://www.amsoil.com/storefront/atf.aspx

Below is an interesting article from Fleet Manager Magazine that talks about adding additives.

http://fleetowner.com/equipment/feature/oil_additives_pour_1108/

At the end of the day, I prefer to run Amsoil versus use additives. I have also added external filters to a good many of my transmissions of late, and they do a great job of "un-sticking" stuff. The performance gain, just from adding an external filter, can be amazing. It is the small crud that ends up filling the valve body passageways that makes the VB sticky, and a fine filter that takes this crud out of the oil is the best solution (along with REGULAR flushing). I've seen an external filter plug within the first 500 miles when installed on a transmission. After the second filter change, they run a year or so before needing changing. That is a lot of crud removed from the system.

I use something along these lines (not a recommendation for this particuar unit), tied into the cooler return line, for filtering.
http://cgi.ebay.com/ebaymotors/Automatic-Transmission-Filter-Universal-Crv-Rv-F150_W0QQitemZ200318623477QQcmdZViewItemQQptZOther _Vehicle_Parts?hash=item200318623477&_trksid=p4506.c0.m245&_trkparms=72%3A1171%7C65%3A12%7C39%3A1%7C240%3A131 8

[fiberop1]

It also has a clatter while coasting at slow speeds(only in overdrive) (there is a thread on this issue started by someone else)

http://forums.trailvoy.com/showthread.php?t=26792