Kingmeow

[Just trying to gatter additional data points for an issue in the Problems and Fixes forum and my education.]

Obviously this applies to the SH-AWD model. So how is the design of Acura's AWD? If I'm driving on the highway at highway speeds and I gently let go of the accelerator and put the car in Neutral, does the draft shaft to the rear still spins?

I guess it depends on where the disengage point is and I'm guessing that's in the transmission. But the other end of the draft shaft connects to the rear axle through the transfer case and the haft is still spinning/coasting so I would imagine the drive shaft still spins?

George Knighton

I'd be interested in knowing this for sure, too.

I would guess that the drive shaft would have to constantly spin, since the minimum ratio of torque to the rear is 30%, right?

Kingmeow

George, 30% even when the car is coasting in neutral? I noticed that in off ramps when I slow down by letting go of the gas the "AWD" display on the console drops to zero bars. Now I know that it's only a graphical display and there could be something going to the back and it's too small to register.

The reason I'm asking this is the pulsing problem that I seem to be conquering with very small but positive steps. To make a long story short, I did ask my service advisor (not mechanic) and he said w/o hesitation that it stops spinning. But when I think about it logically, I would think it should still spin but I don't know a damn thing about Honda's AWD system.

George Knighton

If the minimum torque going to the rear is 30%, then it seems to me that there would be no reason to disconnect the driveshaft to the rear even when coasting and even when you are applying no power at all.

It would just introduce more mechanical parts, an extra electronic routine and complicate things that don't need to be complicated if we wanted to keep the driveshaft from doing what it would otherwise naturally continue doing.

Does that make sense?

I cannot claim to know what I am talking about but it does not make sense to me to stop it rotating just because you're not applying power at any given time.

If there were a set of conditions that had to be satisfied before *any* power went to the rear, then perhaps it would make more sense stopping it spinning when it is freewheeling. Since they say that the minimum torque to the rear is 30%, then it seems to make sense just to let it spin on its own when you're not applying power.

Am I right that the minimum to the rear is 30%?

Kingmeow

I have no idea George. Just having a thinking out loud discussion with you. I'm going to let the experts chime in.

I don't know about the 30% minimum to the rear under normal driving condition but I don't have the sales brochure with me to check.

big1128z

Im not sure what is going on with your car. Driveline vibration is very difficult to diagnose, and, can be very expensive. Cars NVH is designed for the 85% of the customers to be satisfied. Perhaps your in the 15% that are more sensitive to NVH. To answer your question, there is an electromagnetic clutch in the rear diff, one on each side for each wheel. You can theoretically get 0% torque applied to the rear wheels when the clutches are disengaged. Now as for the propelling drive shift itself, I am not sure if it still spins when in neutral. Im gessing it would.

big1128z

The answer for the propelling shaft is yes. it is a true 4WD setup up until the rear differential. So if the front wheels are spinning the drive shaft is too.

George Knighton

But...we always have some torque going to the rear wheels, right?

I was wrong about the 30&.

The minimum power going to the rear is 10%. The maximum is 70%.

I thought the car varied from 70/30 to 30/70.

But it varies from 30/70 to 90/10.

Kingmeow

What does NVH mean? Yeah, i don't know either what's going on with my car. It's going back after the holidays to see if they can figure out the remaining little noise. I suspect it's the rear tires since they replaced the front two and there was a dramatic reduction. There's still a smidgeon left. The propeller shaft is also a possibility, thus my question.

chaiwala

NVH=Noise Vibration Harshness.

If you have a Pepboys where you are, get a bottle of Redline SI1 fuel cleaner and dump it in an empty tank of gas and fill up. This is very common in the winter time since they use a winter gasoline and it retards the timing a bit.

If there is no Pepboys go to Walmart and get a bottle of Chevron Techron and use that instead.

Another good thing to do is to never let the tank of gas go down to a point where the car reminds you to fill up. Always fuel up around a quarter tank of gas left so the gunk on the bottom does not get sucked into the injectors.

big1128z

If the SH-AWD ECU located in the trunk determines that there is a problem with the rear diff, i.e. temperature or DTC, then it will place all available torque to the front wheels. I can still not find any information regarding the transfer case and its ability to vector torque between the front wheels. The propeller shaft should always spin if there is not clutch in the transfer case, and I have yet to see one.

Yes NVH is noise vibration and harshness. All manufacturers try to reduce it or increase it depending on what type of customer they are trying to make a product apeal to. The 2010 mustang has increase noise from the engine bay to make the car sound more ballsy. The gas in your tank has nothing to do with it. It is mostly gear whine and driveline vibrations such as yours. The rear tires could be the culprit. Also a misadjusted driveshaft could be to blame. The universal joint is not aligned to exact precision. This will cause some vibration. What speeds are the vibrations at and does the whole car shake or just the front or the rear or both? That make a huge difference. Right now since they changed the front tires, did they replace them with OEM. Some tires are more susceptible to cupping in cold weater. I bought some expensive goodyear eagle F1's and they suck in the winter for cupping but once they warm up the cupping is gone.

Kingmeow

It's not George's car but mine. My response in bold.

The gas in your tank has nothing to do with it.

Yep, I know that but it was not my suggestion. I've been using Sunoco Ultra 93 with a splash of Shell V-Power.

It is mostly gear whine and driveline vibrations such as yours. The rear tires could be the culprit. Also a misadjusted driveshaft could be to blame. The universal joint is not aligned to exact precision. This will cause some vibration. What speeds are the vibrations at and does the whole car shake or just the front or the rear or both?

Starting speed can vary depending on road condition. Can be as slow as 50MPH. The car shaking was resolved by replacing the front tires. They did not replace the rear tires. What is happening now is more audio than sensory.

That make a huge difference. Right now since they changed the front tires, did they replace them with OEM.

Yes, exact identical.

Some tires are more susceptible to cupping in cold weater. I bought some expensive goodyear eagle F1's and they suck in the winter for cupping but once they warm up the cupping is gone.

This started in not so cold weather unlike now. Some time around October but it feels like forever.

Another thought to test the drive shaft. If the drive shaft constantly spins, then why can't I rev the engine to around the same RPM as when the car is doing, say 70MPH, but do it in Park? This will rule out road noise and more importantly tire noise/defect. If I hear the pulsing then it's the drive shaft. If not, then most likely the rear tires as the front new ones eliminated the vibration completely and reduced the noise significantly.