2009 Sierra 1500 questions

kevin79 · February 27, 2017

I purchased a 2009 GMC Sierra 1500 with 155,000 miles on it. I have some questions I'm hoping you can answer.

Shifting from neutral to drive when the engine is cold results in a jerk forward. I also noticed that when I shift into neutral, the RPM's jump up to around 1500. It doesn't do this when the engine is warm. Any thoughts as to what this could be? I just changed the transmission fluid and also had a mechanic look at the U-joints, he said those are fine.
The shop that did the transmission fluid change, just did the standard pan drop, drain fluid, put a new filter in, etc. Will this be enough or should I have a shop do a complete change? I do plan to tow a 6500# camper with the truck if it matters.
I had the brake fluid and power steering fluid changed at the same time as the transmission fluid. Should I have the coolant, differentials (front and rear) and transfer case changed as well?
What else should I have done to it for service? Can I take it to my regular mechanic or should I take it to a GMC dealer?

intheburbs · February 27, 2017

Axle fluids should be changed, especially if you're planning to tow. IMHO, the rear axle is the weakest point on these half tons. My '01 Suburban is on rear end #4.

When the truck is started cold, the engine will rev above 1000 rpm for about 10-20 seconds. After that, it should drop down to 600-700. Are you waiting for that drop before shifting out of park?

Coby7 · February 27, 2017

Also if you were holding on to the steering and you moved it a bit while pulling the lever the ECM will detect the power steering pump load an throttle up to compensate. Try shifting without holding on to the steering to see if it still goes up in RPM. Or maybe by coincidence the A/C came on at the same time and that provoked a throttle up signal. This should be normal and worse when engine is cold. Also expect a good jerk in drive when cold if engine is turning faster than 700 RPM and the oil in the converter is as thick as molasses.

kevin79 · February 28, 2017

I'm only waiting for the RPMs to drop to about 900.

Is it normal for RPMs to jump in neutral though?

I'll try it without my hands on the steering wheel tomorrow. Will the jerk hurt my engine or transmission?

Intheburbs - when you say axle fluids, are you referring to the transfer case, differential, both or something else?

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intheburbs · February 28, 2017

Front and rear axle/differential fluids. Especially the rear.

kevin79 · March 1, 2017

Ok. On another note, I let the RPMs go low this morning but it still jerked when I put it in drive.

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kevin79 · March 7, 2017

Front and rear axle/differential fluids. Especially the rear.

Assuming I can only do two for now, would it be better to:

Change front differential fluid

Change rear differential fluid

Change transfer case fluid

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intheburbs · March 7, 2017

Assuming I can only do two for now, would it be better to:

Change front differential fluid

Change rear differential fluid

Change transfer case fluid

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When were these fluids last changed? I'd replace the oldest fluid first, though I'd probably give the axles priority of the transfer case. You won't be using the t-case while you're towing.

kevin79 · March 7, 2017

When were these fluids last changed? I'd replace the oldest fluid first, though I'd probably give the axles priority of the transfer case. You won't be using the t-case while you're towing.

I'm not sure when they were changed last. I just purchased the truck and it didn't come with any maintenance records.

What exactly does the transfer case do?

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intheburbs · March 8, 2017

Then I would replace all fluids. Cheap insurance.

The transfer case is bolted to the output shaft of the transmission, and both driveshafts are connected to it. It sends power to both front and rear driveshafts. In 2wd operation, it's simply passing the power through to the rear driveshaft.

When you shift into 4x4 mode, the transfer case engages a clutch and starts sending power to the front driveshaft as well. In older trucks, there was a special blue fluid for the transfer case. In the GMT900 trucks, they just use regular Dexron VI automatic transmission fluid.