Master Cylinder Change

[07sierra8.1]

Hello,

I have a 2007 GMC Sierra 2500HD classic body truck with the 8.1l motor. I need to replace the master cylinder. When I go to order the master cylinder there is two different option cylinders. One for integrated trailer brakes and one for non integrated trailer brake trucks. I do not have the factory integrated trailer brakes but I do have an aftermarket tekonsha controller which is wired into a factory black box and into the factory wire harness behind the brake pedal of the truck that does look like it was made to just be able to plug into for a brake controller. I was told that each truck was factory wired for the integrated brake controller even though not all came equipped with the actual in dash controller, and that I should order the master cylinder for integrated brakes. Is this true??

 

Thank you

[Jsdirt]

Love how GM throws a wrench in what should be a simple process ...

 

You would need to know the differences between each part, and go from there. Not sure if the RPO codes would be of any use here, but I'd look into that as well. My 1500 has completely different braking systems based on the GVWR of the truck - in that case, the RPO code is a must.

 

My line of thinking is that it shouldn't make a lick of difference as to whether or not the truck does, or does not have a brake controller. Can't see how that could possibly affect the master cylinder design, unless they installed some electronic doodad, which wouldn't shock me one bit ...

 

Just a quick look on Autozone's website shows no mention of any of that. Only options are with, or without, the reservoir. I put 4x4, as I don't know what you've got there ...

[Doug_Scott]

Finally, something I actually have first hand knowledge of...

 

Simply put, factory trailer brake controller is not just a brake controller. It includes a different master cylinder, plus wiring and BCM changes. GM will not sell you the factory brake controller if you are thinking of adding it to your truck that did not come with it due to this.

 

All GM half ton trucks come with "roughed in" trailer brake controller hookups for aftermarket controllers. This means that in the case of the OP's truck, he orders the master for a truck without factory brake controller.

[Jsdirt]

Ahh, interesting!

 

Used to be possible to know just about everything about every vehicle made. Not so much anymore. Just when I think I'm getting a grasp, I get a curveball!

 

Friggin modern vehicles. THEY are the cause of high blood pressure! Cholesterol my ass!

[07sierra8.1]

Finally, something I actually have first hand knowledge of...

 

Simply put, factory trailer brake controller is not just a brake controller. It includes a different master cylinder, plus wiring and BCM changes. GM will not sell you the factory brake controller if you are thinking of adding it to your truck that did not come with it due to this.

 

All GM half ton trucks come with "roughed in" trailer brake controller hookups for aftermarket controllers. This means that in the case of the OP's truck, he orders the master for a truck without factory brake controller.

Thank you very much for that info. I got the correct one ordered now! Hauling a load of firewood down to my parents house the week of Thanksgiving and you know, being able to stop is on the list of preferred things I would like to be able to do with all that weight on the truck. ??

[Jsdirt]

I hear that!

 

I hauled 9,600 lbs. of palletized coal (4 pallets) on a 2k lb. trailer to my parent's place 30 miles away, about 3 years ago. Wouldn't you know that on that trip, only ONE of the 4 sets of brakes on the trailer were working! I found all the brake wiring just hanging bare when I got home. Was only 4,100 lbs. over my towing capacity ...

Was wondering why I had to bury the pedal in the floor at every stop.

 

Had to go straight through Worcester too. What a friggin ride that was ...

[07sierra8.1]

I have had a mushy brake pedal in this truck since the day I got it 6 years ago. I have replaced all 4 calipers, caliper brackets/pins, rotors, pads. Rebled the whole system again and alittle better but still mushy. This past spring I had a hard line blow out on me so I bought a Prebent Stainless brake line set from Dorman for $89, it wasn't even worth bending and flaring my own lines at that price, plus it's all stainless. While I was installing the new lines I noticed the master cylinder leaking brake fluid on the bottom between the cylinder and booster so that's why I am replacing it now, I have since bought a vacuum brake bleeder and read up on how air gets trapped inside the abs pump and very hard to get out without a tech 2 scanner that will cycle the abs pump while you bleed the lines. Which the weekend warrior that I am doesn't have this $1000 scanner.

 

Now I am hitting up all my actual mechanic buddies to see if I can borrow their scanner to get he abs pump to cycle. I am determined to get a good pedal finally in this truck. I am about ready to rip the rear disc brakes off and convert it to drums. I have never had good luck with my vehicles that had rear disc.

[Jsdirt]

Just FYI - any bi-directional scan tool can perform that ABS bleeding procedure - doesn't have to be a Tech 2. Most however do cost over $1k - unfortunately, that's the world we live in today.

 

Back in the day, everyone was so glad when cars went to front disk, and even today they rant and rave about how "crappy" drums were. When properly serviced and set up, drums are every bit as good as disc in the automotive realm, IMO. I've never had an issue with inadequate braking with drums. There's a reason most heavy trucks still have drums all the way around on all 3, 4, 5 or 7 axles - they just work.