Disc brake swap questions PLEASE HELP

[Heath815]

Hey guys! I came here because I have some questions I can’t find any good answers to. I have a 2005 GMC Sierra 4dr 2wd that had drum brakes on the rear. I swapped out the rear end with one from a 2006 that had disc brakes.

Problem: If I pump the brake up it won’t hold pressure on the rear. Has anybody done this swap or know what is needed? Proportioning valve? Master cylinder? Brake booster? ??‍♂️ I’m stuck and don’t want to start spending hundreds if it’s something simple. 

[mikedeezxxx]

Proportioning valve needs to be changed


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[Heath815]

13 minutes ago, mikedeezxxx said:

Proportioning valve needs to be changed


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Do you possibly know where it is located on my vehicle? I followed the line all the way from the master cylinder to the back and couldn’t find it. May have looked over it. ??‍♂️ And thanks for the response 

[davester]

My '04 Sierra (disc brakes all around) doesn't have a standalone proportioning valve.  Just 2 lines from MC to ABS controller, 3 lines out of the ABS controller (2 to the front wheels, 1 to the rear, which splits again at the rear axle to go to each wheel).

[Heath815]

3 hours ago, davester said:

My '04 Sierra (disc brakes all around) doesn't have a standalone proportioning valve.  Just 2 lines from MC to ABS controller, 3 lines out of the ABS controller (2 to the front wheels, 1 to the rear, which splits again at the rear axle to go to each wheel).

Just traced all my lines. Mine is the same. Now back to square one on what needs to be done? Lol

[greatmizzou]

Not to derail, but what was GMs reasoning to do drum brakes on the rear?  

[davester]

maybe get an abs controller/computer from a 4wd disc brake truck?  maybe the MC is different?  or maybe there's still air in the system, if say the reservoir ran dry while you were swapping the axle?

[RivGuy]

Are there sections on this forum for "Write Up's" where someone will do a complete write up of the modification and document it on here with pic's.??

 

I have not been able find anything like that. But I'm new and still learning to navigate the forum as well as trying to learn as much as I can about the subjects that matter to me and my truck.

 

Such as converting the rear drum brakes to disk brakes. If there's an in-depth write up I'd love to read it so I'm not making rookie judgements and mistakes.

Someone that has done this mod and posted all the steps taken and parts needed would be great.

 

Thanks to anyone who can respond with the info needed to do this job using all the correct parts and more importantly What Not To Do.