Fixed Wonky Tc Lockup & Shifting Issues

Nanotech Environmental · July 26, 2011

I drive a 2006 Fullsize GMC Sierra Ext cab 4X4 with a 5.3, which I've owned since new. The truck has about 118,500km(~74,000 miles) on it.

Recently the truck would occasionally shudder a bit at highway speeds and it seemed to be shifting a lot from OD to 3rd and back. It would drop down at the smallest of hills etc., which it never used to do.

I typically drive at speeds of 55-65 mph, almost all highway. I don't do a lot of hauling except the occasional small trailer with 2-3 dirtbikes and some gear. Total weight is maybe 1500-2000lbs with riders.

I figured out on Sunday AM that the torque converter was going in and out of lockup at odd times, sometimes several times a minute. That's what was causing the shudder. Add the irregular shifting at highway speeds & I was getting a bit concerned my trans was headed for the shop.

After a search on here and another forum I couldn't find anything conclusive.

The trans had never been serviced since new & GM specs a service at 166,000 km for normal service. So I figured I should still be good.

I thought, well it can't hurt to try some fresh fluid. So, Sunday aft, I flushed out & replaced about 12-13 litres of fluid with new Mobil Dexron VI.

Problem solved. Have put on a couple hundred km since and all seems good.

Just some food for thought if someone finds they have a similar problem.

BJ

Nanotech Environmental · August 11, 2011

After a couple thousand more Km's the problem seems to be resurfacing, but isn't as bad as it was before (yet).

Anyone have any thoughts on what's going on?

I thought I read something about a flaky TPS causing similar issues in a thread somewhere a few weeks ago, but can't seem to find it.........

ybsane · August 12, 2011

After a couple thousand more Km's the problem seems to be resurfacing, but isn't as bad as it was before (yet).

Anyone have any thoughts on what's going on?

I thought I read something about a flaky TPS causing similar issues in a thread somewhere a few weeks ago, but can't seem to find it.........

Sounds like a bad torque converter, if you still are getting the shudder at 55-60 mph and it goes away when you tap the brakes than you need a new converter. While they pull the tranny out to change the converter have them check everything else over to get another 50k out of it.

Rob

joshw1303 · August 13, 2011

I drive a 2006 Fullsize GMC Sierra Ext cab 4X4 with a 5.3, which I've owned since new. The truck has about 118,500km(~74,000 miles) on it.

Recently the truck would occasionally shudder a bit at highway speeds and it seemed to be shifting a lot from OD to 3rd and back. It would drop down at the smallest of hills etc., which it never used to do.

I typically drive at speeds of 55-65 mph, almost all highway. I don't do a lot of hauling except the occasional small trailer with 2-3 dirtbikes and some gear. Total weight is maybe 1500-2000lbs with riders.

I figured out on Sunday AM that the torque converter was going in and out of lockup at odd times, sometimes several times a minute. That's what was causing the shudder. Add the irregular shifting at highway speeds & I was getting a bit concerned my trans was headed for the shop.

After a search on here and another forum I couldn't find anything conclusive.

The trans had never been serviced since new & GM specs a service at 166,000 km for normal service. So I figured I should still be good.

I thought, well it can't hurt to try some fresh fluid. So, Sunday aft, I flushed out & replaced about 12-13 litres of fluid with new Mobil Dexron VI.

Problem solved. Have put on a couple hundred km since and all seems good.

Just some food for thought if someone finds they have a similar problem.

BJ

This shuttering? Is this when its in auto mode on your 4x4 or 2rwd mode?

Nanotech Environmental · August 13, 2011

The shudder was in 2wd on dry/wet pavement. Really it was the TC lockup kicking in and out more than it should.

However, I got the issue solved again. (this one was causing the F word to be uttered more than once....) :

I had checked the tranny fluid level last weekend and it was good. Then this week, the original issue started gradually re-appearing.

Thursday evening I was moving my truck in the driveway to load some stuff in it to go away on Friday & I noticed a small fresh puddle of red fluid on the driveway. Got the flashlight and looked around underneath and what do I see? A drip, drip, drip from one of the POS rusted out trans fluid lines. (barely 5 yrs old) It had been leaking in such a way that it was hard to notice in my daily routine.

Anyways, I re-planned my day Friday to fix the truck instead of doing fun stuff & replaced the POS rusted out stock lines with rubber 3/8" ID trans oil cooler line.

Topped up fluid (truck had lost probably 3 litres from the leak), took it for a 100km test drive to run some errands & all is good.

Glad I caught the leak, or I would have toasted that tranny early Friday AM out on the road somewhere & really ruined my weekend. However, it is frustrating when 2 concurrent problems happen that makes diagnosing the first one more difficult.........

BJ