07 Silverado ABS and Shifting Problems.

[CollinBailey]

Alright so this is my first time using a forum so hopefully this helps.

I have a 2007 Chevy Silverado 1500 Classic 4.8l LS crew cab with factory 20" wheels; about a year ago I installed a bullydog tuner and not to long after that I started to noticed my brake pedal starting to pulse pretty bad fairly often and since my truck has 125k miles i went ahead and replaced the pads and turned the rotors thinking they were probably getting pretty worn. unfortunately that didnt fixed my problem and realized it was actually an abs problem due to the fact my abs light started to come on along with the abs pump (I realized later that the pump was causing my pedal pulsing) and slowly as the weeks went by it began to get worse and more frequent. It got so bad to the point were everytime you go to stop the pedal sputters and the speedometer goes crazy and my abs and brake lights come on the dash along with "service brake system". It started to drive me crazy so since I work in a shop i started to ask around and everyone kept suggesting to watch it on a scan tool and see which wheel was messing up so i did and the rear wheel speed singal kept dropping out so i put in a speed sensor and it didnt fix it so i returned the sensor. Well now currently... the abs pump activates all the time (even without touching the brake pedal while driving), my speedometer goes in and out and now my transmission is shifting crazy. for example if you're driving down a road crusing between 40 and 50 mph the transmission will randomly shift from 4th to 1st and when you try to accelerate you dont have any gear to grab onto except 1st till it decides to shift to the proper gear (very annoying when you're in traffic and having to slow down so you're not cruising at 6k rpms). Ive replaced the abs control moduel, rewired the wires from the abs control module to the pcm and from pcm to the rear wheel speed sensor, replaced the rear wheel speed sensor, and now the pcm. my truck is pretty basic and doesnt have any kind of traction control and has two abs sensors on the front wheels and one abs sensor (vss) mounted ontop of the transmission. nothing has worked and ive had 3 different crazy good master techs who are also master electrical diag techs and they couldn't figure it out. my truck has 145k miles on it now and doesnt leak a drop of oil ANYWHERE and runs so darn good... i dont want to get rid of it just because of this.

Thanks in advance!!

[Swimmer8366]

Do you have a drums or disk rear?

 

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What codes is it throwing?

 

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[CollinBailey]

it has drums. and i believe if im remembering correctly it throws a c0055 for loss of rear wheel speed signal

[CollinBailey]

I am all out of ideas with this thing. Ive replaced the abs control module, pcm, rear wheel speed sensor, cleaned the front wheel speed sensors like the tsb says to do, ive replaced all related wiring and its still messed up....

[Cameron Jenkins]

I got a truck that is doing the same thing and I was wondering if you ever figure out what was causing the problems.

[CollinBailey]

On 7/31/2020 at 5:07 PM, Cameron Jenkins said:

I got a truck that is doing the same thing and I was wondering if you ever figure out what was causing the problems.

Hey man, Yea i figured it out.  been a while haha  Ive gotten rid of the truck since then.  turns out the transmission needed to be rebuilt because a C clip came out on the output shaft and was allowing the output shaft to slide in and out as I accelerated.  Had to tear the transmission all the way down to access this part so ended up just rebuilding the whole thing.

You can confirm this is your issue but removing your drive shaft and grabbing the output shaft and if it can be pulled out and shoved back in then thats your problem.  The output shaft should be firm in place.  basically whats happening is the output shaft has a reluctor wheel on it that the WSS reads and when you let off the pedal, the pressure in the transmission and is released and the output shaft moves backwards, causing the reluctor wheel to move out of view of the WSS which in turn makes the ABS Module think the back tires have gone to 0 MPH and thinks it sliding.
Best of luck to you.  Hopefully yours isnt this issue but if it is then be prepared for a transmission.