Overhauled transmission still slips in drive and whines at slowing down

COOLOLDS85

MEMBER
2010 CHEVROLET AVEO
1.6L
4 CYL
2WD
AUTOMATIC
73,000 MILES

I just had this transmission taken apart and overhauled. Everything inside is brand new. The Aamco I took it to for warranty work had to replace a shaft and nut on one of the internal hard parts. They told me this was the case for the harsh shifting and not moving when in reverse because one of the gears were found meshed. But it’s still slipping when in drive and whines slowing down. He told me that was the issue for the reasons I am having but didn’t change anything. I drove it to heat up the transmission, I checked the level, it’s full and clean, I didn’t smell burning.

What will cause a new overhauled transmission to still slip in drive on occasions? And why is it still whining? I did some research and read a torque converter or brake band would cause slipping, but more often it will slip when a torque converter starts to fail. I never heard of an overhauled transmission slip or whine. But mine still does it, in drive. He said the reason it was doing this was because the part inside the transmission was defective. That was replaced and it’s still doing it.

Can someone tell me what the specs for a stall speed would be at rpm for my torque converter?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Hi,

What is causing the noise is a good question. However, if everything is new, there could be a few things causing it. When the clutch packs were rebuilt, there could be excessive clearance between the plates or even low line pressure not fully engaging the clutch packs. Does it slip in all gears? Has the Aamco rechecked it for you?

Let me know. Also, do you know if line pressure was tested? Was anything done with the valve body?

I have to be honest, when there is a whine, most times it is related to a bearing.

Let me know.
Joe

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Sunday, March 1st, 2020 AT 4:48 PM

COOLOLDS85

MEMBER
173 POSTS

There was an issue with air pockets inside the transmission when they filled the trans before. It wouldn't allow me to even drive down the block with it and when I would put it into reverse it would move backward harshly. I had to take it back and they had to drain the trans and refill it. The valve body has also been serviced. They had a diagram and had told me they put the check balls back in the right place. Now It only slips in drive when I give it gas, but doesn't do it every time, only when I begin to gradually step on the gas slowly at a stop light or in parking lots, usually when I let off the gas it's okay, when I give it gas gradually is when it slips in drives at times. As for the whining, that occurred as soon as the transmission needed to be rebuild. At the time I was told it was doing that because the engine was trying to work harder to keep the transmission working smoothly, after that the sound has never fade ever since, but this time it's just soft, not loud like before it was taken apart. It's tricky with the whining sound. But as for slipping it's there when you drive it. Just doesn't happen all the time.

From doing research, I read the torque converter makes funny noises and slips in any gear when it starts to fail because it doesn't rotate the transmission fluid in a coupling motion if it goes bad. That will than make the torque converter overheat and make the transmission slip in gears. They never even looked at that. They said the slipping condition wasn't the issue of the torque converter causing that. They said it was one of the hard parts causing it to slip. They replaced that part that had a nut on it. I cannot tell you what part that was. All I know they said the part that was causing the slippage was called an intermediate shaft that the gear was meshed and the teeth on it was damaged. So if that's new what else could it be?

That's why I asked to see specs for the torque converter to check at rpm's if the torque converter is failing. They didn't even test my torque converter. So I am thinking that's what is still causing the slipping in drive.

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Sunday, March 1st, 2020 AT 5:30 PM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Interestingly, anytime there is a hard part failure, I replace the converter because anything could be in it. Also, the idea that I mentioned about line pressure sort of mirrors what you are describing. If you accelerate slowly, the RPM's are low which can cause low line pressure to show. As far as the torque converter, my manuals do not show the specs you are requesting.

Also, keep in mind there is a front pump (hydraulic pump) at the front of the transmission that could be failing as well. (See Pic 1) The only way to check these things is by testing line pressure. Based on the hydraulic pressure created by the oil pump, the transmission control module (TCM) sends signals to the solenoid and the hydraulic control system governs the hydraulic pressure acting on the torque converter, planetary gear, clutches, and so on. If pressure is low, it will slip. I think you could be on the right track with the converter or it could be related to the front pump. The only way to be sure is to check pressure. And yes, the pump could make a noise as well.

_____________________________

Here is how that is checked. Pics 2 and 3 correlate with these directions.

____________________________

2010 Chevrolet Aveo L4-1.6L
Line Pressure Check
Vehicle Transmission and Drivetrain Automatic Transmission/Transaxle Testing and Inspection Component Tests and General Diagnostics Aisin 81-40LE - Automatic Transmission Line Pressure Check
LINE PRESSURE CHECK
Line Pressure Check

Tools Required
* J 21867 Pressure Gage
* J-21867-50 Transmission Line Pressure Adapter

The hydraulic test can inspect the working condition inside the automatic transmission (A/T) by measuring line pressure in drive (D)/reverse (R) range and idle/stall condition.

Pic 1

1. Wedge the 4 wheels and apply the parking brake fully. Lock the vehicle in place.
2. Install J 21867 and J-21867-50 to test the hole (1) for line pressure.

Important: Do not continuously run longer than 5 seconds. Extreme increasing of oil temperature may occur.

3. Fully press on the brake pedal with left foot, shift into drive (D) and reverse (R) range and measure the line pressure idle/stall condition.

* The engine idle line pressure in drive (D) is 0.14-0.37 mPa (20.30-53.70 psi).
* The engine idle line pressure in reverse (R) is 0.59-0.68 mPa (85.60-98.62 psi).
* The engine stall line pressure in drive (D) is 1.10-1.23 mPa (159.54-178.40 psi).
* The engine stall line pressure in reverse (R) is 1.58-1.83 mPa (229.16-265.41 psi).

Make sure to keep interval for more than 1 minute between stall tests.

Make sure to check that there is no oil leak after installing J 21867 and J-21867-50.

Pic 2

_____________________________

In the last pic, it explains what low pressure can be caused by. I would find out if they have checked pressure. Stall line pressure is indicated in the above directions.

I hope something here helps.

Let me know,
Joe

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