Hill Assist - HAC

[dancojgl]

But honestly, would you drive in 4lo for a prolong period on the asphalt?

When I first got my '04, I drove it in 4LO around the block on dry pavement (there wasn't any snow yet...)

Btw, dancojgl... our 4wd system has a transfer case (w/o we wouldn't be able to switch to 4lo).

I beg to differ...the Torsen Locking Center Differential is not the same thing as a transfer case (which I did have on my '96 4Runner). When locked, the center differential performs the same function of a transfer case (50-50 torque split), but it's not an old-fashioned "transfer case."

See: http://www.torsen.com/products/T-3.htm

—Dan

 

[Good Times]

I beg to differ...the Torsen Locking Center Differential is not the same thing as a transfer case (which I did have on my '96 4Runner). When locked, the center differential performs the same function of a transfer case (50-50 torque split), but it's not an old-fashioned "transfer case."

See: http://www.torsen.com/products/T-3.htm

—Dan

Dan, so you're telling me the 4th gen does not have a transfer case? I'm confused...

The 4th Gen's have a center differential, not a transfer case. A transfer case operates like the locked center differential.

 

[c44me]

Hey, isn't it kinda ironic that dcampen tried to get a pure thread going on HAC and here we go debating some completely off-topic subject

My two cents on HAC and DAC, is:

HAC is totally bogus. It's a Marketing Department invention. In my '03, it does not in any way slow down the vehicle's backward motion, it just makes a horrendous commotion of beeping, flashing, and electronic busy-work noise. I find it amusing to set it off by stopping and letting off the brake on our driveway. It's kind of cool to see all the fireworks while you're rolling back towards the neigbor's car. Whatever happened to common sense, you know we ALL have auto trannies and a left foot, just keep the left foot on the brake as you apply throttle and rolling backwards is a complete non-issue. It's not even hard to do, works first time and every time.

DAC is totally bogus. It's a Marketing Department invention. The one time I was in an actual 4WD situation and tried it, in 4LO (not on asphalt ) the truck took off like a bat out of hell (at least a couple of miles an hour) and by the time I got it stopped I had the privilege of setting off all the other BS VSC and Trac stuff as well, not to mention getting a bit sideways in the gravelly, rocky track which I could have done without. So I find it way too fast for 4WD situations, way too slow for anything else. Again, where's common sense, just use the brake pedal if you need to go slow, eh?

Which leads me to another question that is also off topic - has anyone ever experienced a beneficial effect from VSC or Trac, or just a lot of alarming flashing, beeping, brappping, and loss of control in a real emergecny situation?

 

[dcampen]

Which leads me to another question that is also off topic - has anyone ever experienced a beneficial effect from VSC or Trac,

I can't speak with any experience about VSC but with ATRAC, yes I have experienced the beneficial effects of ATRAC.

ATRAC is a traction control system that takes the place of having locking front and rear differentials. As I mentioned in another thread, recently I was traveling with a couple of other trucks on some dirt backroads in Arizona. As we went up one steep hill that was rutted and covered in loose gravel I saw the Nissan Xterra ahead of me loose traction and slide backwards down the hill. When I went up the hill, at the point where the Xterra had lost traction, I heard and felt the ATRAC system become active and I made it to the top of the hill without loosing traction.

More recently, on a dirt backroad at the North Rim of the Grand Canyon, I was going up a steep hill where I had to move to the far right into ruts and debris to partially avoid a large rock to the left, I felt the truck slow and then the ATRAC become active. I am convinced that without the ATRAC I would have lost traction and begun to slide backwards. It would have been a very bad place to lose traction as the large rock obstacle was right at a sharp turn in the road, if I had started sliding backwards I might have gotten the truck turned even further sideways.

I am a bit surprised though at how infrequently I have needed the ATRAC, usually just having the center differential locked is enough. But the few times that I did need ATRAC I really did need it and might have been in big trouble without it.

 

[c44me]

Thanks for the report on ATRAC. It sounds like a very good asset to have in reserve!

 

[Mr. Lambdebois]

Yup. Without atrac you just have two open differential in the front and rear.

Atrac is good. HAC is a joke. DAC works if you engage it properly.

 

[c44me]

Well, Mr. Lambdebois, now that you have revived a thread from the past, I thought I'd relate an experience I had test-driving a Porsche Cayenne. I had completed my little circuit with the salesman (who complemented me on never turning on the stereo during the test drive) when I told him about the bogus HAC on my 4Runner. To my surprise, he said the Porsche HAC was a big selling point for the socker-mom crowd, and he'd be pleased to show me how it worked. He took me to a place where there was asphalt between the upper parking lot and the street, with a sewer grate in the steep slope. He had me stop with the vehicle at about a 30 degree angle, with one wheel over the sewer, so we're sitting there on three wheels. He says let off the gas and brake, which I did. To my surprise, nothing, and I mean absolutely nothing, happened. No noise, no lights, no boing-boing, or any motion whatsoever. It just sat there idling and dead still until I put on the brakes and reversed down the slope. So it is actually possible to engineer HAC that works!

I still don't understand why you would want HAC...

 

[Koz]

All these system have been designed and engineered to work in the best way possible with the technology available. There is a reason why they work the way they do. You may not see it but there is a good reason. It's amazing how some people think Toyota is so stupid as to make a system that does not work the way they think it should.

There is no reason why you can't use 4wd low on pavement, now the center lock is a different story.

Koz

 

[OUTRNNR]

Wow,

I'm way confused now. First we got all this talk about how the 4Runner doesn't have a transfer case. Does it, or does it not? How would you be able to "transfer" torque to the lower gear without a transfer case? How could the Torsen center diff multiply torque (lower gear ratio)?

Also, I've driven with the center dif locked on pavement, even while turning, and just feld a mild bind. If you think about it, why would any binding even take place? All you are doing when you lock the center dif is splitting the torque 50/50 front and rear. Its not like the front wheels move at different speed than the rear wheels (as for the outside vs. inside wheels, wouldn't the front and rear differentials take care of this? So why would there be binding?). I don't think this would cause any damage because the torsen (unlike many center difs) locks mechanically rather than using clutch packs and hydraulic fluid. Am I correct here?

I am a little dissappointed about the way HAC works, I wish it would just stop the car still, but it does seem to kick on more aggressively on steeper grades. Never tried the DAC, but I imagine it would be the same way, more aggressive intervention on steeper grades. I've also read that it modulates the brakes to keep the vehicle on its intened path (i.e. straight down), something you can't do with the brake pedal on your own.

 

[JB.]

First we got all this talk about how the 4Runner doesn't have a transfer case. Does it, or does it not?...

...Also, I've driven with the center dif locked on pavement, even while turning, and just feld a mild bind.. ..So why would there be binding?)..

Never tried the DAC, but I imagine it would be the same way, more aggressive intervention on steeper grades.

4Runner does have a transfer case.

There can be binding with the center diff locked because all 4 wheels
follow a seperate path on turns. The difference is subtle on a mild turn but will become very evident on a sharp one.

The manual says DAC targets a 2-4 (might be 3-4) mph speed so, yes, it would be more agressive on steeper slopes 'cause it doesn't want to let the vehicle go faster than 4mph.

 

[OUTRNNR]

4Runner does have a transfer case.

There can be binding with the center diff locked because all 4 wheels
follow a seperate path on turns. The difference is subtle on a mild turn but will become very evident on a sharp one.

The manual says DAC targets a 2-4 (might be 3-4) mph speed so, yes, it would be more agressive on steeper slopes 'cause it doesn't want to let the vehicle go faster than 4mph.

Thanks for clearing that up

 

[Koz]

Transfer case (Assembly) is the unit bolted to the rear of the trans.

 

[oua]

Hey, isn't it kinda ironic that dcampen tried to get a pure thread going on HAC and here we go debating some completely off-topic subject

My two cents on HAC and DAC, is:

HAC is totally bogus.

DAC is totally bogus.

Which leads me to another question that is also off topic - has anyone ever experienced a beneficial effect from VSC or Trac, or just a lot of alarming flashing, beeping, brappping, and loss of control in a real emergecny situation?

DAC is legit - Great for doing down hills.

VSC is legit - Saved my family from a major fatal accident.

HAC - how do you get this thing to work again???

 

[Koz]

The "Hill Start Assist Control" works exactly the way it was designed to work. It was designed to assist you on starting on a hill, not hold you there. The 10 sec of pulsing the brakes is more then enough time to move your foot from the brake to the throttle. If you are on dirt or a slippery slop you would not want the brakes to lock, you would slide back or to the side. That

 

[oua]

I have always though

HAC was suppose to be like "hill brakes"


After I bought the vehicle I find that HAC is the same damm thing as DAC.

DAC = rolling down hill slowly going forward regardless of shift position.

HAC = rolling down hill slowly going reverse regardless of shift position.

 

[Koz]

I have always though

HAC was suppose to be like "hill brakes"


After I bought the vehicle I find that HAC is the same damm thing as DAC.

DAC = rolling down hill slowly going forward regardless of shift position.

HAC = rolling down hill slowly going reverse regardless of shift position.

NOT! The DAC controls the throttle and brakes to maintain 3/5 mph downhill. All you have to do is steer and it works great. The HAC simply pulses the brakes to HELP keep the vehicle from rolling back on hill.

Koz

Koz

 

[cdoyle]

The thing I find annoying about the HAC is, Every morning I have to stop on this hill at a light.

So when the light turns green, I take my foot off the brake (I start rolling backwards) and put my foot on the gas to move forward. That's when it starts beeping a clunking, as I'm trying to accelerate?

Isn't it too late by then?

does it almost every time, it's never actually kicked in before I put my foot on the gas.

 

[Koz]

Mine kicks in as soon as the vehicle starts to roll back. Maybe the Stealer needs to look at yours.

Koz

 

[khaug]

Several issues here:

-Center Diff/transfer case: '99 and later 4WD 4Runners include a transfer case which incorporates a center differential. Do NOT lock the center diff on dry pavement, as you will force the front and rear wheels to slip while following different paths. This must occur through tire slip, which enormously stresses the drive train (binding). This option is intended only for slippery surfaces where tire slip can occur naturally/easliy. On my '03, choosing 4-L is independent of choosing to lock the center diff.

-HAC: An ineffective substitute for left-foot braking when stopped on an upslope. If you don't have the skill to do left-foot braking, what are you doing driving, anyway??? This appears to have been designed by marketing personnel! It doesn't work worth diddly!

-HDC: Hill Descent Control. This lets the ABS system brake individual wheels to descend a slope slowly. You cannot do this yourself, as there's no way to brake individual wheels manually. Good stuff, but only available in 4L, at least on my truck!

-Enjoy!!!

 

[jharris2]

The thing I find annoying about the HAC is, Every morning I have to stop on this hill at a light.

So when the light turns green, I take my foot off the brake (I start rolling backwards) and put my foot on the gas to move forward. That's when it starts beeping a clunking, as I'm trying to accelerate?

Isn't it too late by then?

does it almost every time, it's never actually kicked in before I put my foot on the gas.

While you're stopped at the red light, you could move your left foot to the brake and right foot over the accelerator. When the light turns green, you begin accelerating before taking your left foot off the brake pedal.