Question about 1999 Chevrolet Suburban

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Torque converter lock up problems

1999 Chevy Suburban C1500, 5.7L. 118000 mi At steady state cruising speed the torque converter seems to go in and out of lock up. I'll be doing a steady 65mph on flat ground and the engine RPM will go from 1700 to 2000 and back again. It's like its hunting between gears, but the transmission is in top gear. Any thoughts?

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  • angierob75 May 06, 2009

    How do I know if my problem is
    my transmission or my torque converter?



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  • 7 Answers

Yeah i know exactly what it is its one of the transmission solenoids i beleive its called the torque converter circuit

Posted on Apr 13, 2009


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1 Answer

What causes a Chevy Suburban to develop a RPM pulsate at 2000 RPM in overdrive?

you might not have a problem . TCC solenoid.torque converter is Inside the torque converter there is a clutch to stop the slip about 500rpm . you can check it by like 90kmh steady then with other foot just touch the brake pedal no braking just a little bit you will feel release and push again this is the tcc applied and it,s normal behavior

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How do i know if its my tcc solenoid and not the torque converter its self and will it affect the reverse

If the solenoid is stuck so the torque converter remains locked, the transmission will not be able to shift down and the engine may stall when you slow down from highway speed. This seems to be the most common problem with this part, and it shows up primarily in prolonged high-temperature running.

If you can get the vehicle into reverse with a locked torque converter, you may have to maintain a minimum speed to keep from stalling the engine - not a safe situation.

My experience with hanging TCC solenoids is that they usually release the clutch if they are allowed to cool for a few minutes, if they don't release when the engine stalls.

If the TCC is not locking the torque converter, there will be no difference in high-speed performance when you disconnect the TCC solenoid. If the TCC is working to this extent, disconnecting it will cause a lag in acceleration and loss of gas mileage in high gear. Unfortunately, this is not a completely definitive test; it does not rule out a malfunction in the torque converter clutch mechanism.

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What does the torque converter solenoid do

the torque converter clutch solenoid is kind of like the clutch in a manual transmission. automatic transmissions inherently have a little slip in the transfer of power between the engine and transmission, since the transfer of power is done with fluid instead of a mechanical clutch. however, when the car is in overdrive and cruising, the TCC solenoid acts like a clutch and locks up the torque converter, making a mechanical connection and eliminating the slippage. when you accelerate or downshift, it turns off. if this switch hangs up, when you come to a stop, the car will bog down just like a manual trans would if you don't push in the clutch pedal

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If vibration appears to happen just as you get to a steady cruising speed on highway, it sounds like a problem with your torque converter and/or lock up circuit. A good transmission place, or dealer should be able to diagnose properly and advise you of fix.

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TCC solenoid operation depends on signals provided by the Engine Coolant Temperature (ECT) sensor, brake switch, Throttle Position (TP) sensor, Vehicle Speed Sensor (VSS) and gear position.

The lockup is the last 'shift' feeling when you get to a steady cruising speed. It basically turns the torque converter into a regular (manual type) clutch until you make a significant change in speed or throttle position, at which point it 'unlocks' and turns back into a regular torque converter. Not locking the TC will hurt your highway gas mileage, and may cause you to fail emissions testing (if you need emissions testing).

A simple loose/corroded connection can cause the error, but unless you have had work done, drivern through high water, or something along those lines, it's not hugely likely. On the other hand, it's simple, fairly quick, and the absolute cheapest thing to check for. :)

Most likely, it's either the TCC solenoid itself, or your torque converter is going bad.
Without the exact code (number) it's hard to be more exact.

There is a large chart that includes your model located at:
Your model starts a little over halfway down the page.

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Sounds like the lock up torque converter is slipping based on your description of the problem. i estimate roughly 1,250 dollars based on 400 dollars for a torque converter and fluids, and 10 hours labor at 85 an hour.

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