ABS Not Working after Installing new gears.

[Dan Fahey]

Preparing my 1994 Caprice wagon for towing.
Just had 3.08's Installed which originally had 2.56's.
The 3.08's were from my 95 Impala SS.

After installation Re-flashed the PCM for the 3.08's gears.
Now the ABS INOP light is coming on.

Tested the Front Wheel Sensors and Pinion Sensor on the Pinion housing.
They were all working properly. The Car has new 94 ABS Brain.

When starting up the engine ABS light reads the Brain and goes off.
Travel about 30 seconds the ABS INOP Light comes on.

Attached new SnapOn Test tool to check everything out.

Results:
The Speedometer is reading the same speed as the Front Wheels
The Rear Sensor was reading about 5 mph less.

Have TunerCat. How can this be corrected?


Dan

[Ed Wright]

Don't those have the ABS reluctor on the pinion? They are different for different gear ratios.

[bob shirley]

3.08 s need reluctor with 20 openings for abs to function

[ss3011]

If the sensor was on the diff ring gear , it wouldn't matter what ratio you had. I think the ABS sensor reads off the reluctor that is on the transmission output shaft. Try reloading the old ratio and see if the ABS works. This all depends where the signal for the ABS comes from, and where the reprogrammer recalculates it.

[Dan Fahey]

Originally Posted by bob shirley

3.08 s need reluctor with 20 openings for abs to function

YUP..You are right...forgot that.

The PCM measures the Reluctor on the Tail Shaft Housing.
The ABS on the Tail housing.

Looks like they installed the wrong one on the Pinion.


Thanks


D

[Dan Fahey]

Problem solved.

Just spoke to the Mechanics that Installed the Gears.
They though it was a 3.73 gear set instead of 3.08's.
Used a 3.73 Reluctor.

FWIW going through the entire ABS system with another Mechanic.
Learned a lot about them.

Here are some links I used to study and troubleshoot the issue.
I learned to read Engine or ABS Codes without a Scanner.


http://www.troublecodes.net/gm/
http://www.gmtuners.com/OBD1_DTC.htm
http://www.goldsswagon.com/ABS/Bosch...%20Systems.htm


Thank you all for the help..!!

Dan

[ss3011]

Glad you were able to figure it out. Where is the reluctor located, Differential, or Transmission ?

[Dan Fahey]

Originally Posted by ss3011

Glad you were able to figure it out. Where is the reluctor located, Differential, or Transmission ?

There are two Reluctors one for each.
Reluctor on the Pinion Housing used for ABS System for both rear wheels.
Each Gear Ratio has one designed for each set up.

There are Reluctors on the Front Wheels and the Speed on Front and Rear have to match or the ABS triggers on the INOP light.

Reluctor on the Trans is for MPH and Odometer.

D

[Greg Reimer 7376]

Back when all this ABS stuff was new, a new Corvette owner(who else?) was constantly harassing the service department of the local Chevrolet dealer where he got his new plastic fantastic, stating that the ABS light was always coming on. The brake and FE tech was getting ready to hide at the sound of an approaching vette,because this thing had all kinds of erratic intermittant codes and issues in it, just like the driver. One fine day, he offered to take a test ride with the customer driving, a brave offer at that. While on the road test, the driver bragged about the Lingenfelter high horse engine he bought and had installed, and to prove it he entered the freeway at warp eight with both rear tires practically ablaze all the way up a long onramp. The ABS light came on, and the brake tech immediately knew what went on as well. He went back to the dealer, tipped off the service manager about the driver abuse and the non-stock aftermarket engine installation, and the service manager immediately called a zone rep who rather quickly came out to the dealership for a look. They set the driver /owner down, calmly explained that the vast difference in wheel speed between the fronts and the rears caused the ABS to see all kinds of things that were out of the normal spectrum, thereby going into a no ABS mode, and that the modified non stock aftermarket crate engine was in violation of the warranty. He got mad, threatened to sue everybody that moved, screamed, ranted and raved, so the zone rep cancelled his warranty. Now, the story adds up here, because the vast difference in wheel speed data that the ABS saw due to a wrong reluctor being installed in one end of the system would create a scenario to the ABS computer similar to the one in the Vette.I'm sure that the driver of the station wagon wasn't doing that to his car,however. These ABS systems aren't really that hard to understand,actually.