ABS and Auto 4wd

[Big T]

When I bought the '99 the ABS was disconnected. Tried connecting the plugs and the ABS light came on at the dash and the ABS did not work. After doing all the work on the front end, including new bearing hubs with ABS sensors, curiosity got to me and I decided to plug it in. No light. So I took it around for a spin up here in Big Bear Lake. Temp is in the low 20s and there's intermittant sheets of packed snow/ice on the road around the point we're on. Sure enough I hear the ABS pump working. Little too much, but then the section of road in front of us is pretty much ice. Finally tried them on dry pavement before a sheet of ice and no pump, then it comes on when I hit the ice. Tried them several times on long sections of ice and I gotta they're working pretty darn good. Lucky me!

I've got the push button transfer case switches. Knock on wood, they've been working just fine. Never had the Auto 4wd option before and decided to try it this trip. Have to say it works quite well. Definitely applies power to where it's needed and definitely provides better control than straight 4wd. A big thumbs up :thumbsup: on that system and another welcomed surprise.:agreed::agreed:

 

[great white]

My ABS came on for the first time yesterday in a snow storm.

Holy mutha that thing is loud!

Pedal had one heck of a "pump" to tit too.

All in all, probably the most obtrusive ABS system I've ever driven.

Worked just fine though.

Just a note:

"Push button" 4x4 is a different beast than auto 4x4. Pushbutton puts it into 4x4 when you select it (no real difference than a GMT400 with a floor lever), auto units are in 2wd until they sense slip and then shift into 4x4.

I have to admit, I didn't think I would like pushbutton 4x4 as all my trucks have been floor lever. But after usign it for a couple months, I prefer the push button. Shifts quick, no "graunching" on shifts like a lever case and it's nearly instant traction when I need it.

Just hope I never have to repair it, the rotary encoder on the xfer case (motor that shifts it) is 500 bucks!

 

[Big T]

My ABS came on for the first time yesterday in a snow storm.

Holy mutha that thing is loud!

Pedal had one heck of a "pump" to tit too.

All in all, probably the most obtrusive ABS system I've ever driven.

Worked just fine though.

Just a note:

"Push button" 4x4 is a different beast than auto 4x4. Pushbutton puts it into 4x4 when you select it (no real difference than a GMT400 with a floor lever), auto units are in 2wd until they sense slip and then shift into 4x4.

I have to admit, I didn't think I would like pushbutton 4x4 as all my trucks have been floor lever. But after usign it for a couple months, I prefer the push button. Shifts quick, no "graunching" on shifts like a lever case and it's nearly instant traction when I need it.

Just hope I never have to repair it, the rotary encoder on the xfer case (motor that shifts it) is 500 bucks!

Yep it is loud. Sort of a groan like when constipated and needing a fork

I also prefer the push button 4x4 and hope it never goes out. Then again, it probably will knowing my luck.

 

[Mudbath]

I have had the push button on some previous vehicles and they work quite well. The only parts I have had to replace are the push button selector itself (cheap and very easy to change) and the actuator on the front diff. Mine being a 95 has the thermo actuator which are slow to apply and tend to fail more frequently. Last time around I needed 4 wheel pronto and all I could get quickly was the thermo unit again so that what I went with. It is still slow to apply when really cold, but I usually engage it before I get my self into trouble. They can be converted to the new style fairly easily, but is a bit more expensive to do, but then last longer and is quicker to apply.

 

[Big T]

I have had the push button on some previous vehicles and they work quite well. The only parts I have had to replace are the push button selector itself (cheap and very easy to change) and the actuator on the front diff. Mine being a 95 has the thermo actuator which are slow to apply and tend to fail more frequently. Last time around I needed 4 wheel pronto and all I could get quickly was the thermo unit again so that what I went with. It is still slow to apply when really cold, but I usually engage it before I get my self into trouble. They can be converted to the new style fairly easily, but is a bit more expensive to do, but then last longer and is quicker to apply.

When I had my son's '95, the thermo actuator failed 3x. Each time it failed was when I needed it most. One time was on a logging road from Willetts to Ft. Bragg, leaving me stuck nearly 20 miles in on the road, rear wheels high centered and front wheels inoperative in a deep mud bog. That was a $300 tow. Other times were during snow storms in the local San Bernadino Mountains with only my experience allowing me to get unstuck.

I went with the electrical upgrade actuator. Took several times to get right. One site recommended splicing the work around harness into the brown wire running along the transmission tunnel on the inside of the truck. The argument was that it kept the splice out of the weather, but it required the wire running underneath the base of the shifter. I had all sorts of unexplained failures with that. The brown wire there along the transmission tunnel finally went unexplainably dead. Ultimately, I traced the brown wire from the tr0ansmission to the plug behind the fuel manager. I spliced the harness in the the brown wire there and it's out of the weather and has worked perfectly ever since.

I've seen several guys here replace the thermo actuator with a thermo actuator, because that's what was availalbe. Based on my (terrible) thermo actuator experience, I'd highly recommend a preventative replacement with the electrical. If you don't, the thermo will fail when you most need it. Last time I priced it, the actuator was like $70 and the harness was like $40 on ebay motors.

 

[great white]

When I had my son's '95, the thermo actuator failed 3x. Each time it failed was when I needed it most. One time was on a logging road from Willetts to Ft. Bragg, leaving me stuck nearly 20 miles in on the road, rear wheels high centered and front wheels inoperative in a deep mud bog. That was a $300 tow. Other times were during snow storms in the local San Bernadino Mountains with only my experience allowing me to get unstuck.

I went with the electrical upgrade actuator. Took several times to get right. One site recommended splicing the work around harness into the brown wire running along the transmission tunnel on the inside of the truck. The argument was that it kept the splice out of the weather, but it required the wire running underneath the base of the shifter. I had all sorts of unexplained failures with that. The brown wire there along the transmission tunnel finally went unexplainably dead. Ultimately, I traced the brown wire from the tr0ansmission to the plug behind the fuel manager. I spliced the harness in the the brown wire there and it's out of the weather and has worked perfectly ever since.

I've seen several guys here replace the thermo actuator with a thermo actuator, because that's what was availalbe. Based on my (terrible) thermo actuator experience, I'd highly recommend a preventative replacement with the electrical. If you don't, the thermo will fail when you most need it. Last time I priced it, the actuator was like $70 and the harness was like $40 on ebay motors.

Ditto on that.

My 98 came with the servo actuator instead of the TLA and it's a night and day comparison.

Immediate engagement (and you can actually hear it instead of waiting for a light) and dead nuts reliable every time. completely unaffected by ambient temperatures too.

I've had my TLA disegage before when plowing snow (burried in a drift and it goes cold) or traversing throught deeper water crossings, no such problems with the servo.

I highly recommend swapping one in if you have the means.

 

[THEFERMANATOR]

Put on stainless braided brake lines and then try out the ABS. Then if it's a BURB add in the updated proprtioning valve that increases the rear line pressure and HANG ON. Even on dry clean pavement I can get the ABS to kick in. I will agree though that on ice it was VERY loud, but worked awesome. Kept me out of an accident coming down a hillside when I was driving on snow and ice covered roads for teh first time in my life earlier this year.

And not all push button 4X4 systems are autotracs. I don't believe they ever offered teh AUTOTRAC full time unit behind a 6.5 as the autotrac cases were fairly light duty by design.

 

[mangus580]

If by Autotrac you mean the 'auto 4x4' they did. 98 and 99 both. My 99 has it...

 

[THEFERMANATOR]

If by Autotrac you mean the 'auto 4x4' they did. 98 and 99 both. My 99 has it...

Wonder what transfer case they used then as I thought the auto 4X4 used the 246 which only has about a 1400(?) foot pound torque rating to it which is quite a bit lower than that of a 241(about 1800-2200 depending upon year and spec). I know gassers had em in 98+, never heard of a diesel with it though.

 

[mangus580]

Wonder what transfer case they used then as I thought the auto 4X4 used the 246 which only has about a 1400(?) foot pound torque rating to it which is quite a bit lower than that of a 241(about 1800-2200 depending upon year and spec). I know gassers had em in 98+, never heard of a diesel with it though.

If I recall properly, its a 241.... Whats the RPO for the 241?

 

[GM Guy]

My ABS came on for the first time yesterday in a snow storm.

Holy mutha that thing is loud!

Pedal had one heck of a "pump" to tit too.

All in all, probably the most obtrusive ABS system I've ever driven.

Worked just fine though.

Just a note:

"Push button" 4x4 is a different beast than auto 4x4. Pushbutton puts it into 4x4 when you select it (no real difference than a GMT400 with a floor lever), auto units are in 2wd until they sense slip and then shift into 4x4.

I have to admit, I didn't think I would like pushbutton 4x4 as all my trucks have been floor lever. But after usign it for a couple months, I prefer the push button. Shifts quick, no "graunching" on shifts like a lever case and it's nearly instant traction when I need it.

Just hope I never have to repair it, the rotary encoder on the xfer case (motor that shifts it) is 500 bucks!

Highly agree on the loud factor, but she works great. on my old mans 98 Chassis cab, it will dim the lights, but she holds the rig straight. IMHO, this is a good ABS System, others probably will not agree with that statement, but I havent had any issues yet.

 

[mangus580]

If I recall properly, its a 241.... Whats the RPO for the 241?

Ok, so I stand corrected, it is the 246. RPO NP8.

I dont really understand why it was considered 'weaker' though. I thought it was the same case as the 241, with a modification to allow the 'auto/full time' For the record, our 99 is a 3/4 ton as well. A 'heavy' 3/4 at that, as it has the full floater rear axle and everything. I can understand not using the 246 behind a duramax or something, as I would presume it could mess things up pretty fast with high torque in 'auto' mode.

Now the real question I have (which is why I started following this thread) the ABS sensors have nothing to do with the Auto 4x4, right? (since our ABS system is down for the count.....)

 

[Big T]

"Now the real question I have (which is why I started following this thread) the ABS sensors have nothing to do with the Auto 4x4, right? (since our ABS system is down for the count.....)"

Good question and I have no idea.

 

[Chevylover]

@ Big T :

YES ! The ABS and auto 4WD are complete different things and the sensors don't "interact" with each other.


Cu,
Sven

 

[THEFERMANATOR]

@ Big T :

YES ! The ABS and auto 4WD are complete different things and the sensors don't "interact" with each other.


Cu,
Sven

Not completely correct unfortunately. The ABS changes it's operation when 4X4 is activated, as well as the full time autotrac unit works slightly different as well in some years. The AUTOTRAC unit that GM used is a unique transfer case by most accounts. MOST full time units use some sort of viscous coupling or differential in the transfer case to distribute the power from the front to rear in a full time unit. They did have a drawback to this style though where if one tire came off the ground and the vehicle didn't have a locker in it of some sort, the vehicle came to a complete stop as almost all of the power would go to the one tire off the ground. This was later combatted with a hydraulic type limited slip where it would lock-out the diff in the transfer case via a hydraulic clutch application. GM went a different direction in the full size trucks and made there transfer case with just a hydraulic apply for the front axle when it was in full time 4X4. Basically it will not engage the front axle at all(except for the axle disconnect) until slippage was present at which time a hydraulic pump would engage and lock up the clutch packs for the front driveshaft. Some of these AUTOTRAC systems used an electronic solonoid to engage the front wheels as wheels that was controlled via the TCCM that worked in conjunction with the ABS system.

With all that goes on in these full time units, I am sure glad I have a 261 in mine with no electrical input to it except for the front axle disconnect.

 

[Matt Bachand]

Just don't blow a rear brake line.

Once that happens, and the ABS kicks on, you lose your front brakes all together, and WILL SLAM into whatever is in front of you. The brake pedal will go right to the floor, with ZERO braking.

Ask me how I know.

I guess one shouldn't be driving with a blown rear brake line though. But still, if she runs and moves, I'm driving it home.

 

[Chevylover]

Not completely correct unfortunately. The ABS changes it's operation when 4X4 is activated, as well as the full time autotrac unit works slightly different as well in some years. The AUTOTRAC unit that GM used is a unique transfer case by most accounts. MOST full time units use some sort of viscous coupling or differential in the transfer case to distribute the power from the front to rear in a full time unit. They did have a drawback to this style though where if one tire came off the ground and the vehicle didn't have a locker in it of some sort, the vehicle came to a complete stop as almost all of the power would go to the one tire off the ground. This was later combatted with a hydraulic type limited slip where it would lock-out the diff in the transfer case via a hydraulic clutch application. GM went a different direction in the full size trucks and made there transfer case with just a hydraulic apply for the front axle when it was in full time 4X4. Basically it will not engage the front axle at all(except for the axle disconnect) until slippage was present at which time a hydraulic pump would engage and lock up the clutch packs for the front driveshaft. Some of these AUTOTRAC systems used an electronic solonoid to engage the front wheels as wheels that was controlled via the TCCM that worked in conjunction with the ABS system.

With all that goes on in these full time units, I am sure glad I have a 261 in mine with no electrical input to it except for the front axle disconnect.

Okay, you got me, but I didnt wanted to explain every detail ! I think, that is the job of the people which got english as their "mother language". Have fun !



Cu,
Sven