[Profish00]

285x75x16 fill up the wells,but dont rub...They say a Goodyear ATS 305 will work as well, I have both and the 305 on my F20 seems just a little wider.

 

[Argo]

*shrug* , 265's just didnt look that big to me when I had them on my Z to begin with. I am sure you are right, 285's look better and have a wider track, that is the size I would say to use.

 

[Freshwaterman]

Hey Fred email me so I can send the picture of the shark. Nice ride by the way.

magy

[email protected]

 

[FS552]

Hey Fred email me so I can send the picture of the shark. Nice ride by the way.

magy

[email protected]

Thanks...you have mail.

 

[bigdav160]

Can you all tell me the when is the best time to use 4HI, 4LO.

Your truck has a real 4WD system meaning you DO NOT want to use 4WD on pavement. It will bind up and if enough traction is available, something will break. Use it only in low traction situations.

Also is the Auto 4WD drive the same thing as the auto track you all were mentioning earlier?

Yes, GM has named their push button 4WD system "Autotrac"

Oh and should I stop before I engage in either 4hi or 4lo? Or can I just push the button while i'm driving. If not, well I already did it once LOL.
.

Unlike other brands, 4Hi can be engaged at any speed. I've engaged mine doing 70mph after encountering snow and ice in the mountains of New Mexico.

4Lo can be engaged at speeds under 3mph. As others have mentioned, it is probably easier on the transfer case if you stop, put the transmission shifter in neutral, then put in 4Lo.

and Auto 4WD

The best part! Normally the transfer case enters 4WD followed by the front axle engaging. Auto 4WD, engages the front axle first and in milliseconds uses clutches to engage the output of the transfer case if a speed difference is encountered between the front and rear wheels. You can drive in Auto 4WD on any surface at the penalty of slightly diminished fuel economy. It really shines when road conditions are changing like rain, snow and ice.

 

[Profish00]

"well said" welcome to the board. I always wondered how the auto works

 

[Argo]

Big Dave, auto trac is not just push button 4x4 it is all time 4x4 that has a computer control telling it which wheel to send the power too when there is slippage including front wheels. I have a similar system on my ford and it is all time 4x4

 

[bigdav160]

Big Dave, auto trac is not just push button 4x4 it is all time 4x4 that has a computer control telling it which wheel to send the power too when there is slippage including front wheels. I have a similar system on my ford and it is all time 4x4

Sorry to politely disagree. I worked for GM up through 1999. I spent two day of training on the autotrac system and it works just as I discribed. GM did offer an "all wheel drive" on the smaller trucks/suvs but not on the full size. Quoting from the training manual:

Auto 4WD: The transfer case control module engages the front axle. The transfer case utilizes a clutch pack similar to an automatic transmission. Under certain conditions the clutch pack is applied, locking the prop shafts together. If the transfer case control module detects a difference in front to rear wheel speed, it reacts within 200 milliseconds to apply the clutch pack.

2HI: The transfer case control module disengages the front axle and operates in 2WD HI only. In this mode the transfer case (NV246) operates exactly like previous 4WD systems in 2WD HI mode. Torque is transmitted to the rear axle only.

4HI: The transfer case control module moves the PWM motor to apply the transfer case clutch pack. It engages a clutch brake to hold the clutch pack in position, then engages the front axle. In this mode it operates exactly lke previous 4WD systems in 4WD HI.

4LO: the transfer case control module reverses the PWM motor. The motor moves the shift sector in th opposite direction into 4WD LO.

Neutral: Disengages both axles for towing.

A mode shift from 2HI to 4HI or Auto 4WD can be cmpleted in any transmission gear position and at any vehicle speed.

2HI, 4HI, or Auto 4WD to 4LO
4LO to 2HI, 4HI, or Auto 4WD can be accomplished only if:

The engine is running
The transmission is in neutral
The vehicle speed is below 3 mph
The transfer case motor/encoder signal is present.

Hope it clears it up.

 

[Argo]

4x4 Systems

http://www.chevrolet.com/pop/blazer/4x4_systems.jspThe standard Insta-Trac 4x4 electric transfer case system (on 4x4 models only) lets you shift on the fly from 2WD to 4WD HI and back with the push of a button. An Autotrac 4x4 system is available on 4x4 models with an automatic transmission. Along with the ability to manually select 2 HI, 4 HI and 4 LO, when AUTO 4WD is engaged, Autotrac automatically transfers power between rear and front wheels whenever rear-wheel slippage is detected.

 

[bigdav160]

Argo, you are quoting the page from the smaller truck. (i.e.Blazer). I think they stopped using the manual lever 4WD in those trucks around '94.

The push button "Insta-trac" was optional then, I believe, standard equipment in '95 4WD Blazers. It used a vacuum motor/cable to engage the front axle. The similar Oldsmobile Bravada (and Astro Van) used a single speed "All wheel Drive" that was a "full time" system.

LOL, http://www.chevrolet.com/pop/blazer/4x4_systems.jsp shows the same control buttons for Instatrac and Autotrac. Only the Autotrac has the "Auto 4WD" feature.

The full size GM trucks have three systems available:

The single speed, full-time AWD in the Denali and Silverado SS.
The manual lever, part-time 4WD that standard when ordering 4x4
The push button, part-time Autotrac that is optional.

 

[Argo]

Tell me then what happens when you push the button to engage the auto trac system? I seem to remember having a Tahoe z71 with this option that I drove a little while and once I pushed the autotrac it put it in an alltime 4x4 mode that controled which tire got what amount of power. This is what my expedition now has except I cant turn off the AWD feature on it like you can on the z71. (BTW-I know ford and gm are two different things)

 

[bigdav160]

Any Ford experts?

Argo, I'm not an expert on the 4WD system Ford is using in the Expeditions (ContolTrac/AdvanceTrac). They appear very similar to the GM system. Both GM and Ford use a planetary geared transfer case that normally divides the torque about 40/60 front to rear. GM uses the clutches in the transfer case to lock it into 4WD. Ford slips the clutches in a way to allow even less torque to reach the front wheels if it is not needed.

It appears the BIG difference is Ford allows the front differential/driveshaft to turn all the time. Without locking/unlocking hubs this system must add friction and wear that would adversely effect fuel economy. GM has an actuator on the front axle that disengages the front axle from the wheels allowing it to act like any 2WD truck.:spineyes:

 

[Argo]

The only thing that I was saying about the chevy auto track is that once you push that Auto 4wd button (autotrac) it is in AWDand the front and rear wheels will be getting power at a computer/traction decided level and this is different from 4HI. Right or wrong? Because of this autotrac feature it adds alot of cost to the lift.

 

[bigdav160]

The only thing that I was saying about the chevy auto track is that once you push that Auto 4wd button (autotrac) it is in AWDand the front and rear wheels will be getting power at a computer/traction decided level and this is different from 4HI.

Yes and No. The Auto 4WD function works by engaging the front axle. At this point it is working like your Ford in 2WD. No power is getting to the front axle but it is turning. Once the Autotrac computer sees a difference in RPM between the front and rear (like 15rpm difference) it know to engage the 4WD transfer case clutches. GM claims the clutches in the transfer case can be locked up in as little as 200 milliseconds. The transfer case module then cycles the clutches ever 50 millisecond to release pressure on the clutches to see if 4WD is needed. If it determines there is no more slip between the front and rear wheels it releases the clutches completely basically returning it to 2WD mode except for the front axle being engaged.

 

[Argo]

BTW my fuel mileage does stink.

 

[FS552]

BTW my fuel mileage does stink.

Tell me about it. It took $44.00 to fill up the suburban yesterday. I ententionaly
let it run close to empty so that I coulld figure out how many miles per gallon I was getting. Turned out to be 13.65 miles per gallon.
Does that sound right bigdav160?

 

[FS552]

bigdav160,

So should I use the Auto 4wd button down the beach or just use 4hi or 4lo
when the conditions require me to use 4wd.

Also is it pretty much safe to say that my suburban is beach worthy just as it is?
Thanks to argo, bigdav160 and everyone else that has supplied their input.

 

[Argo]

I would just the auto 4x4, I never lock my expy into 4hi unless it gets real soft and nasty. And yeah, go hit the beach.

 

[FS552]

Thanks argo,
BTW...how many mpg's are you getting on your expy?

 

[bigdav160]

Tell me about it. It took $44.00 to fill up the suburban yesterday[\quote]

You should have bought a '92-'99 model Suburban. 42 gallons of fuel. It takes about $70 to fill mine up.

Turned out to be 13.65 miles per gallon. Does that sound right bigdav160?[\quote]

Mixed driving with the A/C on? Then yes. Remember those truck are as aerodynamic as a brick and quite heavy. Just for fun check the EPA fuel economy averages for those V6 midsize SUV's. They are the same as your full size V8 powered SUV.