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1999 chevy 5.7 liter, Z-71 pickup knocking

Posted by timdstone (My Page) on
Sat, Sep 7, 13 at 23:52

I have a puzzle I'm hoping someone can help me with. My son was driving my 1999 Chevy Z-71 5.7 liter auto transmission. He said that it got to where the transmission would not shift, as in when in drive from 1st to 2nd. He got it home and parked it. When I got in from work, I started it up, the motor sounded good as always, but when I tried to shift into drive, I could feel it shift, but it wouldn't move and made the sound of gears slipping, put it in reverse and it seemed to back up. With no money to have the truck looked at, it sat for around 3 months before I started it. It started just fine and the motor sounded good. I didn't try the transmission. 3 months later I started it again, and it sounded like someone was inside of the motor with a hammer on the passenger side trying to beat their way out. I let it run for several minutes but it didn't get any better. Today, about 4 months from the last time I started it, it started just fine, with the same knock. I let it sit and run for about 30 minutes. The engine smoked for a few minutes then cleared up. I put the transmission in reverse and it again wouldn't try to back up and sounded like gears slipping. I placed it in 1st and it went forward. I drove it around the yard for about 5 minutes. I stopped, held my foot on the brake and gave it some gas, the knocking stopped and I didn't feel any slippage in the transmission, soon as I took the load off, the knocking started again.
The truck has around 200K miles on it. The transmission was rebuilt at 100K miles.

The questions I have are: What would make the trans not shift from 1st, 2nd, 3rd ect? What could be making the slipping noise in reverse? Is it a rod or main knocking? and why would it start knocking after setting for a long time? All help is very much appericated.

Follow-Up Postings:

RE: 1999 chevy 5.7 liter, Z-71 pickup knocking

Check the oil level in the engine.

Check the fluid level in the transmission. (Refer to the owner's manual for the procedure for checking the fluid level. It varies from model to model.)

Let us know what you find.

New transmission fluid has a pinkish color. Used fluid will darken some but should appear clean. If the fluid is very dark or has a burned smell, the clutches in the transmission may be worn out.

You had the transmission rebuilt at 100,000 miles, but more important, how many miles are on the rebuild?

Check your owner's manual. Does it recommend a transmission fluid and filter change at a specified interval? If so, has this been done?

From what you described, my fear is that the truck was continued to be driven with slipping clutches and the transmission needs a rebuild or replacement. The knocking sound could be either the engine or transmission. Get some help. Have a mechanic or a driver who does his own maintence and is familar with similar products listen and test drive your truck to get an opinion.

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