A/T jumps gears when cold; new fluid help?

[jonnythan]

My A/T ('98 Grand Am) gets a little schizophrenic and jumps back and forth between 3rd and OD when the temperature outside is very cold (20F or below) and I'm cruising at highway speeds. When the shifter is in "3" or I'm accelerating it seems just fine.

I don't know much about auto transmissions, so I can't really figure out what might be making it shift back and forth. The shifts themselves are smooth.

Since it's so related to temperature, I was wondering if it's possible this is due to the fluid. It does seem to go away when the car gets fully warmed up. I had the fluid changed at a transmission shop in February, but it was doing it before that as well.

Could getting a flush and switching to a different fluid, maybe a synthetic, help? Any other comments would be appreciated. Thanks.

 

[Bgallagher]

When was the last time it was serviced and what fluid was used? Was the filter changed with it? How many miles are on the vehicle?

GM's transmissions are typically smooth running so it could be old fluid. If it has been over 30k you should considering doing a pan drop (not a flush!) and change the filter. Fill it with Valvoline maxlife (great synthetic fluid with cold weather pumping and a great add pack) and a bottle of lubeguard Red. A lot of the people on BITOG will attest that it is a winning combo for transmissions. Keep in mind that there could be a mechanic issue with the transmission but it is good to rule out that it is just worn out ATF

 

[jonnythan]

I don't know exactly what fluid was used. The transmission has never been opened except to have the fluid changed. The last changes (not flushes) were:

2/3/12 @ 246,600 miles
7/2/08 @ 185,200 miles

Current mileage is about 260,000.

The fluid looks and smells fine on the dipstick, and there are no leaks. I have seen people recommend Lubeguard. Is "Red" the regular or the platinum?

 

[Gotch]

Are you sure it is shifting gears or may it be the torque converter locking and unlocking? GM's older transmissions would hold off lockup until the engine/transmission is warmed up.

 

[jonnythan]

I've been going back and forth on that, actually. I'm pretty sure it's shifting gears, but I'm not 100% sure. It's pretty hard to tell.

 

[Bgallagher]

Originally Posted By: Gotch
Are you sure it is shifting gears or may it be the torque converter locking and unlocking? GM's older transmissions would hold off lockup until the engine/transmission is warmed up.


+1 a 98 with over 250k that makes sense. OT is a gear which explains why it feels like a gear shift. I would also stay away from flushes. Especially at a high mileage like that. Pan drops (including filter changes) are generally the best rule of thumb. Next time you bring it in have them change the filter and only drop/fill.

It sounds like it has been regularly maintained. I would try a bottle of lubeguard red (which is the normal fluid.) Otherwise I would be easy on the transmission until it warms up. My Equinox hard shifts until it is warmed up then is fine. Just got used to driving it in the cold.

 

[Lead Shoes]

My 3.4 v6 grand am did the same thing when it was cold, OD wouldn't engage until it was warmer, I dropped the pan and changed the filter/fluid and it was gone.

 

[jonnythan]

You think some Lubeguard would help with the torque converter unlocking?

Why regular LG and not the platinum?

 

[Bgallagher]

Originally Posted By: jonnythan
You think some Lubeguard would help with the torque converter unlocking?

Why regular LG and not the platinum?


I personally have no experience with Platinum but I can attest to the positives with the regular red. It is under $15 and should make a world of difference. Pour the whole bottle in and shift through the gears for a few minutes then go for a drive. The results should be almost immediate but should set in after it has mixed.

 

[Dave Sherman]

Just a wild thought, but I had this problem on an '88 Pontiac. Check the thermostat. That car would have the torque converter engage and disengage, seemingly at random, on the highway. Turns out the thermostat was either stuck open or opening too early, and a new thermostat fixed it. I finally noticed on a long trip that it would engage going up hills, and a little while after coming down hills it would disengage. I also noticed while I was on this trip that the heater went from comfortable to wickedly hot while sitting in line at the tollbooth, and pulling away the torque converter worked normally - until the heater cooled off again.

 

[jonnythan]

Thanks for the advice everyone. This is great.

I think I'll change the fluid and put in some Max-Life with a bottle of Lubeguard. Considering I don't know what's already in there, and I don't really want to add half a quart of fluid when it's already full, I might as well drop the pan and change it all.

As for the thermostat, it's actually only about 6 months old. I had to replace the water outlet when the old one cracked and went ahead and replaced the thermostat while the system was drained. I'll never understand why they make these important parts that bolt onto the engine block out of plastic.

 

[jorge345]

...

 

[jonnythan]

I think I confirmed that it's the torque converter locking and unlocking. I ended up working 130 hours in the past 12 straight days (!) and obviously haven't had time to change the fluid. I'll be doing it this weekend, weather permitting, and will report back.

 

[jonnythan]

I dare say that the fluid change and Lubeguard has fixed it up, or at least significantly improved it.

I might do another pan drop and refill with Max-life in the spring.

Thanks BITOG!

 

[demarpaint]

Originally Posted By: Bgallagher
When was the last time it was serviced and what fluid was used? Was the filter changed with it? How many miles are on the vehicle?

GM's transmissions are typically smooth running so it could be old fluid. If it has been over 30k you should considering doing a pan drop (not a flush!) and change the filter. Fill it with Valvoline maxlife (great synthetic fluid with cold weather pumping and a great add pack) and a bottle of lubeguard Red. A lot of the people on BITOG will attest that it is a winning combo for transmissions. Keep in mind that there could be a mechanic issue with the transmission but it is good to rule out that it is just worn out ATF


Good advise. I have Maxlife and LG red in my 00 Century and am very pleased with it. After the pan drop and filter change, I extracted with a Miti-Vac a total of 3 additional gallons of fluid, 1 gallon at a time. I did that over a period of a few days, I added LG red at the end.

 

[RF Overlord]

Originally Posted By: Gotch
GM's older transmissions would hold off lockup until the engine/transmission is warmed up.
Define "older". My 2001 GMC work van with the 4L60E also does this.

 

[SteveSRT8]

^^^Virtually any slushbox does this when it's cold outside to aid warmup.

 

[zerosoma]

Originally Posted By: jonnythan
My A/T ('98 Grand Am) gets a little schizophrenic


Fascinating.

 

[jonnythan]

It's not unusual for our more senior members to get a little bit of dementia in their old age..

 

[JHZR2]

Does this AT use a Bowden cable for control?