Transmission - Hard Shift at low speed

ltp1

My 2005 LeSabre has a "hard or rough shift" when I travel between 20 - 30 mph in "3rd gear", It's very noticeable. I checked the transmission fluid and there are small bubbles on the dipstick. The fluid level is normal. I will the check the fluid level again tonight. The LeSabre has 53,000 miles. Does anybody recognize this problem?

imidazol97

Has the transmission fluid ever been changed? If not, that would be a first step especially if you have someone to change it and NOT do a flush. Be sure to use the GM-recommended Dexron VI fluid, made by several companies.

The problem could be from old oil affecting the controls in the transmission. Changing might help after a few hundred miles.

However, does this problem come and go at times. Is it always shifting better after the car has been restarted and especially when the car has been started after sitting overnight? Does it shift nicely if you accelerate very briskly and just keep the pedal down as you start onto a highway, for instance, where the tachometer shows the engine speeds stay at 2500 or above?

It may be the PCM (pressure control module) that's not able to control the shifts at low speeds. Some of the better box stores, Advance Auto Parts, Autozone, will do a check for codes and their scanner can read the transmission codes, if any.

The PCM can be replaced for a few hundred dollars in labor IF THAT'S THE PROBLEM--the engine cradle has to be dropped slightly to get access easily to the side cover on the transmission on the driver side to replace the PCM.

If you find that driving briskly when accelerating helps, while idling through the shifts causes the long shifts which the PCM has trouble controlling shift times on and sets the trans in protect mode which does quick shifting to protect the clutches from wear, you have your answer. BTW, it takes 2 long shift times that are too gentle for the trans to go into default limp home mode.

ltp1

I bought the car about two years ago, with 37k miles. I don't know if the transmission fluid has been changed. I checked the fluid this morning, the level is fine. The problem does come and go. The hard shifts don't happen when I'm idling, just while driving slowly in 3rd gear. The hard shift occurs when I'm driving slowly in my neighborhood at low speeds in 3rd gear, 20 - 30 mph. When I start it in the morning, after sitting overnight, it shifts nicely when I accelerate very briskly in O/drive. Is Dexron VI fluid recommended? The owners manual lists Dexron - III as the recommended fluid. Thanks for your great advice!

ltp1

Thanks for recommending "not" doing a flush. I was planning on changing the fluid myself. So, simply drain the old fluid, replace the filter and gasket, and add the new Dexron - VI, right?

imidazol97

Nope. You don't change the gasket. The original is good for life unless damaged and is made to help dissipate heat to the pan. The Dexron VI replaces Dexron III and other GM spec fluids.

If I were in your place and you are able to do the pan removal yourself, instead I'd recommend getting a hand suction pump from Harbor Freight if you have a store nearby for $4.99 and put the suction tube down the dipstick tube all the way. Pumping will remove all 6 quarts of fluid that would have dropped out when you removed the bolts on one end of the pan to let it drain.

I'd replace that with 6 quarts of Dexron VI fluid (I just used Walmart's brand of trans fluid Dexron VI (Supertech blue bottle) for $4.27 each). Fill with 5 and and warm up the transmission then use last one to fill to just the full level when trans is hot.

Drive it for 5 K Miles or so. By then you'll know if you have a continuing problem or if clean fluid helped things move better inside the trans after some time to clean with the new chemicals in the Dexron VI.

THEN drop the pan and put a new filter on and replace 6 quarts with Dexron VI fluid. You will have replaced about 75% of the old fluid in the 2 changes with fresh Dexron VI.

Don't put in any additives. The first refill with fresh fluid with fresh cleaners will do any cleaning that additives might do. The old filter will catch any sludge loosened. Then you're replacing a filter that may have caught some goop with a nice fresh one--I use Purolator from Pepboys.

Page on link contains the $4.99 coupon for the pump. Click on print coupon to get actual coupon.
Get on their mailing list and they'll send you coupons--look for the ones where you get something free with any purchase!
Pick up a second hand pump with a duplicate coupon. The first one I had didn't last long. I don't think it liked the warm trans fluid I pumped out. Maybe should have let trans cool.
https://us-mg4.mail.yahoo.com/neo/b/message?sMid=8&fid=Inbox&sort=date&order=down&startMid=0&filterBy=&.rand=1467261453&midIndex=8&mid=2_0_0_1_447301_AEwNiWIAALt6VXYKLwluEPeTrQw&fromId=

Good luck. Please report back to me what happens.

ltp1

Thanks! Harbor Freight is close by. This is a great advice on the 2-step fluid change.

imidazol97

Itp1: I sent you an IM (instant message). Go to your profile and it will tag your icons with your name with a red marker showing you have a message. Click on those and the word "message" to read.