Shifting into reverse jolts

[Steve]

Last year I had my A/C compressor replaced, there were no stock ones available so an aftermarket unit was installed. It seems to be a bit more demanding unit than what the engine is used to. This is on a 96 Accord, 2.2L/4cyl, no VTEC, auto.

Since it was installed I've noticed that with it on, when I come to a stop and shift into reverse (to parallel park, usually), the transmission waits a second then comes into reverse with a jarring jolt. Usually, this didn't happen if I turned the A/C off first but lately it's happening even after I turn it off. Not only that, but I can hear a clunking 'thud' noise. How much life does this thing have left? I have no money

 

[steppinthrax]

Originally posted by: Steve
Last year I had my A/C compressor replaced, there were no stock ones available so an aftermarket unit was installed. It seems to be a bit more demanding unit than what the engine is used to. This is on a 96 Accord, 2.2L/4cyl, no VTEC, auto.

Since it was installed I've noticed that with it on, when I come to a stop and shift into reverse (to parallel park, usually), the transmission waits a second then comes into reverse with a jarring jolt. Usually, this didn't happen if I turned the A/C off first but lately it's happening even after I turn it off. Not only that, but I can hear a clunking 'thud' noise. How much life does this thing have left? I have no money

This is known as a "Reverse Slam" a.k.a rough engaement this could be due to a lot of things but the main reason is because the hydrolic plungers inside of the valve body of the automatic taransmission work on the principle of pressure. When you shift into reverse the solonoids that divert fluid into different passages force a piston to engage. Unfortuntalty some dirt or maybe a broken spring is not causing the transmission to engage properly. By this time the engine revs in response to thinking it's already engage and increases the hydrolic pressure forcing the piston to engage creating a thud like or slam sound. In some situations you may need to do a total overhaul of the transmission. But how have you taken care of the transmission have you don't regular fluid changes. You need to do a system flush where your system is totally flushed out. If you have the same problem it may reqire servce.

 

[Steve]

I'm about due for an oil change, I'll ask for a system flush too.

 

[steppinthrax]

Originally posted by: Steve
I'm about due for an oil change, I'll ask for a system flush too.

You can do a system flush yourself. You simply need two buckets and a gallon or more of tranny fluid. Drive the car till it gets hot. I mean street driving. Disconnect the AT coolant lines. Ones that run from the transmission to the radiator. One line is for suction while the other line takes. Put both lines in each bucket. Have an assistant start the engine. If you see fluid come out of one line like a steady flow. You know the other line is the suction. So pour transimssion fluid into the bucket with the suction line. Start your engine and let the transmssion suck the good fluid and spit out the bad. You will notice the different in color (dark red and clear red). When the color starts to get clear you can cut it off and reconnect the lines. The other thing is that while the car is ideling you want to switch the transmission though all the gears P, N, R, D 2, 1. This will clean out the valve body. That is your problem.

 

[natto fire]

To me, it seems like the two problems just coincidentally happened at the same time. Unless this new compressor is making the engine lose too much power at idle and lowering the revs to the point that the transmission does not have enough pressure to engage reverse. There is a pump in the transmission that is driven through the torque converter, which provides hydraulic pressure to engage the clutch bands on the planetary gears in the transmission.

However, there is an EACV (Electronic Air Control Valve) that is supposed to increase the idle when the A/C is on. Is it doing this? You should be able to see the RPM's increase when the A/C is switched on. This can get clogged with carbon, especially on a car that old, or if the PCV system malfunctioned and dumped loads of carbon into the intake tract.

So, check if your RPMs increase when you switch the A/C on, when the compressor is cycling. If not, the EACV might need checked/cleaned. You can use carb cleaner, as the EACV is just a solenoid with a plunger that lets air by. If the RPMs are going up, then I would think there is some sort of transmission malfunction. Have you checked the fluid level? Remember to check it while the car is running, after you have cycled through drive and reverse, in Park.

Originally posted by: steppinthrax
You can do a system flush yourself. You simply need two buckets and a gallon or more of tranny fluid. Drive the car till it gets hot. I mean street driving. Disconnect the AT coolant lines. Ones that run from the transmission to the radiator. One line is for suction while the other line takes. Put both lines in each bucket. Have an assistant start the engine. If you see fluid come out of one line like a steady flow. You know the other line is the suction. So pour transimssion fluid into the bucket with the suction line. Start your engine and let the transmssion suck the good fluid and spit out the bad. You will notice the different in color (dark red and clear red). When the color starts to get clear you can cut it off and reconnect the lines. The other thing is that while the car is ideling you want to switch the transmission though all the gears P, N, R, D 2, 1. This will clean out the valve body. That is your problem.

Haven't tried that, just make sure the bucket you use is really clean, and watch out, those transmission lines can be under quite a bit of pressure. Also, an easy way to tell which side will be high pressure, it will usually be the top, unless you have an external oil cooler, then YMMV.

 

[Rogeee]

If the jarring shift only occurs when the A/C is on the compressor is putting a large load on the engine at idle causing the ECM to open the idle solenoid valve farther to maintain the correct idle RPM thus causing the harsh shifting.
Have a A/C tech check the charge status of the system, it may have inadvertanly been overcharged thus causing high turning resistance in the compressor.

 

[steppinthrax]

Originally posted by: Captain Howdy
To me, it seems like the two problems just coincidentally happened at the same time. Unless this new compressor is making the engine lose too much power at idle and lowering the revs to the point that the transmission does not have enough pressure to engage reverse. There is a pump in the transmission that is driven through the torque converter, which provides hydraulic pressure to engage the clutch bands on the planetary gears in the transmission.

However, there is an EACV (Electronic Air Control Valve) that is supposed to increase the idle when the A/C is on. Is it doing this? You should be able to see the RPM's increase when the A/C is switched on. This can get clogged with carbon, especially on a car that old, or if the PCV system malfunctioned and dumped loads of carbon into the intake tract.

So, check if your RPMs increase when you switch the A/C on, when the compressor is cycling. If not, the EACV might need checked/cleaned. You can use carb cleaner, as the EACV is just a solenoid with a plunger that lets air by. If the RPMs are going up, then I would think there is some sort of transmission malfunction. Have you checked the fluid level? Remember to check it while the car is running, after you have cycled through drive and reverse, in Park.

Originally posted by: steppinthrax
You can do a system flush yourself. You simply need two buckets and a gallon or more of tranny fluid. Drive the car till it gets hot. I mean street driving. Disconnect the AT coolant lines. Ones that run from the transmission to the radiator. One line is for suction while the other line takes. Put both lines in each bucket. Have an assistant start the engine. If you see fluid come out of one line like a steady flow. You know the other line is the suction. So pour transimssion fluid into the bucket with the suction line. Start your engine and let the transmssion suck the good fluid and spit out the bad. You will notice the different in color (dark red and clear red). When the color starts to get clear you can cut it off and reconnect the lines. The other thing is that while the car is ideling you want to switch the transmission though all the gears P, N, R, D 2, 1. This will clean out the valve body. That is your problem.

Haven't tried that, just make sure the bucket you use is really clean, and watch out, those transmission lines can be under quite a bit of pressure. Also, an easy way to tell which side will be high pressure, it will usually be the top, unless you have an external oil cooler, then YMMV.

I did this with my saturn after having to once pay 180 for a transmission flush for a car. It's better because the system they use for a flush only dose a single fluid exchange you can keep on pouring fluid until you get everything out. I think most FWD transmissions are 9 - 12 quarts.