ABS Issues After 4.56 Swap

[escapepilot]

I posted this on GMTN, but having issues logging in since the move to a new server. Thought you guys may be able to figure this out.

Before switching to 4.56s, everything was fine. Swapped 3.73s for 4.56s (35x12.50s) and started having ABS issues. I could drive for a while then the ABS and BRAKE lights would come on, along w/ the annoying chimes. When slowing down, once I was to walking speed, the ABS would kick in and pulse. This happened after 4.56s AND the shop pulled the engine for some other work (5.3L). I assumed it was due to the rear sensor expecting 3.73s and the EBCM not liking 4.56s and 35s. Superchips has the Flashpaq that allows gear and tire size changes in their programmer for 2003-2004 5.3Ls so I got one and did the reprogram. Semi-success. Now, the light doesn't come on, but the ABS kicks in more frequently unless I brake aggressively. All codes have been cleared and no new codes thrown.

The only clues I have now are:
1) Codes before Flashpaq were Left Front Wheel Sensor and EBCM. Wheel sensor replaced (cheap replacement version).
2) ABS only kicks in when almost stopped - such as easing up to a parking space, etc.
3) Using GPS and DashCommand for verification, DashCommand is 3 mph fast @ 60.
4) Engine was removed during gear swap - no visibly damaged wiring.
5) No unusual noises before ABS engage.

[ErikSS]

Was the transmission speed sensors messed with?

[DirtyBacon04]

I'm guessing your cruise control doesn't work. Is that correct?

Mine was doing that too because of the different readings from the 2 speed sensors after a gear change. After a few miles the Brake and ABS light would come on. I just pulled the J Case fuse for ABS and got my cruise control back. Down side is ABS is completely disabled now and braking hard enough will cause tire lockup. Also, the ABS and Brake light are permanently on now.

[KingBird]

After replacing the engine in my '02 Bravada with one from an '06 Ranier and converting over to a TB transfer case, TCCM, and switch, my ABS kicks in at low speeds when lightly slowing to a stop, no dash lights though. I don't know of any sensors on the engine could cause it but I DO know that the ABS system uses the ground to the frame under the driver's seat. I don't know if this helps any but may help you narrow your problem down.

[Trail X]

Inoperable ABS is a common symptom of a gear change on a 2002-2005 model. There's really no way around it unless you do as a few members here have done put a VSS signal interceptor inline.

Maybe the programming in the V8 models is different though. My understanding is that in the 2002-2005 models, the gear ratio was hard programmed in, and not a variable that could be readily changed by any programmers on the market.

[KingBird]

Ah, then that probably explains why mine isn't working correctly either since my TCCM came from a TB with 3.42 gearing and I have 3.73s.

It's super sensitive in "A4WD" though (we never use it, I just tried it to see if it worked after the swap).

[escapepilot]

To my knowledge, the transmission sensors were not messed with.
The cruise control has continued to work both before the gear swap w/ 35s, after the gear swap, and after the programmer change.
I did check and clean the EBCM grounding point on the chassis.
The Superchips Flashpaq showed it being able to change gear ratio and tire size. Did that and that eliminated the ABS/Brake light coming on, but didn't affect the ABS kicking in at slow speed problem...in fact, made it a little worse. (Flashpaq only available for V8).


I'm leaning towards a failing sensor - not good, but not bad enough to register a code...or a failing hub. Any ideas will be appreciated.

Thanks,

[Trail X]

I believe that as you begin going slower, the hall effect signal strength of the sensors is reduced in strength, so you may be correct. Its worth attempting the following before replacing hubs:

From a TSB on a similar issue:

Condition
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction
Measure AC voltage and clean the wheel speed sensor mounting surfaces.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual (SI Document ID #899664).
Disconnect both the front wheel speed sensor (WSS) connectors at the frame and harness.
Place a Digital Volt Meter (DVM) across the terminals of each WSS connector.
Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual. Plug the WSS bore in order to prevent debris from falling into the hub during service.
Clean the WSS mounting surface on the hub to remove any rust or corrosion using a wire brush, or equivalent.

Important
Make sure that the sensor sits flat on the hub. Check the sensor flange against a straight edge to ensure flatness. If the sensor flange is distorted, replace the sensor.


Apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344.
Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.