Transmission bucks, 1998 GMC Jimmy

transmissions
#1

I am a 2nd owner of this vehicle, 1st owners only used the vechicle to tow a boat and was garaged most of the time. I bought it in 2001 with 30K miles it, now it has 105K, somewhere around 70-80K I noticed that when it shifts (auto transmission) from 1st to 2nd gear when accelorating it bucks into 2nd gear, meaning that there is not a smooth transition- however, if I let up on the gas petal just as it begins to shift it will go into 2nd without any trouble. I have had the trans fluid and filter changed, my mechanic also put in a conditioner, no change.

#2

Were you given any bad news after the Trans Techs had a chance to look at the material (if any) in the trans pan, did they cut the filter open looking for pieces that don’t belong there?

I wonder how big that boat was (was the rated tow capacity exceeded)?

Before I turn this over to the Trans experts on this Forum I will ask is all good at your battery connections (no acid leakage causing poor contacts)? Anything look odd with the harness that plugs into the transmission? or damage to the harness?

I wonder if this could be a software issue and a program update is called for.

#3

This is a very common problem in this transmission. The harsh 1-2 is most likely going to be a result of the computer increasing line pressure because it has found a problem with the transmission. The full line command from the computer is there to protect the transmission from destroying itself. What you need to do first is to take the vehicle to one of your nearest auto parts stores who offers free scanning of the computer. Have them scan it and post the codes/s they get to us here on the board and we’ll go from there. I’m anticipating a P-1870 code just because it is way too common. Let me know what you find out.

transman

#4

I actually dont know what the actual size of the boat was, however the saleman told me the SUV belonged to his dealership’s secretary & it held only four people, he told me the boat was rather small and they wanted a bigger boat, therefore a bigger SUV and thats why they traded it in. However I had this SUV for approx 4-5 years before this bucking started.

When I first purchased the SUV, I had the trans fluid changed, mostly due to the pulling of the boat issue-backing up in water thing. I had it changed again years later when this bucking first started which is around the first of '06 and then again the end of 07, however in 07 I had the filter changed as well, hopeing this would stop the bucking- it didnt. And no there were no bad news when it was changed, my mechanic told me there were some particles/dirt in the pan but nothing to worry about.

The battery question- I replaced the battery in '03 and again first of '08, both times I was not informed there were issues with the cable-

I dont know about the harness issue, as I have used the same mechanic for the past 20 years for both of my vehicles he believe he would tell me if there were an issue with the harness, he recommended using a conditioner, it seems to help alittle initially as it didnt buck quite as much but that was short lived.

I often wonder if it was a software/computer/sensor issue… I guess see below…thanks for your comments.

#5

common problem- eh? hum thats a relief… I have a 92 Ford Ranger that ‘slips’ into 2nd gear has been doing that for approx 7 years now and was wondering why both of my vehicles had 2nd gear issues- my truck is old so I thought it was due to that, but when my Jimmy starting having issues I often wondered if it had anything to do with the fact I park on a severe inclined driveway… in winter my Jimmy has trouble climbing this thing (& sometimes dont make it- I land in my neighbors yard) but my truck has no trouble-although I carry 500 lbs of weight in the bed…

I will check into what you suggested about having the computer scanned and will let you know what I find out-- what does P 1970 code tell you?

#6

I had an auto parts store check for ‘codes’… it came back with Zero codes available… so whats next to check?