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Replaced hydroboost, brake light switch not working.

39K views 10 replies 7 participants last post by  Hjalmar  
#1 ·
2007 2500HD Classic 6.6. My hydroboost was leaking so I replaced it with a rebuild unit from rockauto. Its a cordone I believe. I went with the 2011 version many have suggested here. During install I had to use the push rod and star retainer from my old unit as instructions said to do. It all installed beautifully. Just dropped right in. Flushed the system and bled it. The next morning I drove to work no problems. So happy.
After work I could not shift out of park. I dropped it into neutral to crank it and made it home. No joy.
I purchased a new brake switch but it didn't help. When I have my wife hold the brake after cranking it, I can have the switch in my hand and activate it by pressing it with a screwdriver it works fine, shifts out of park and brakes lights will shine.
I've reinstalled without the clip and with the clip but can't make it work like it should. What am I missing?
Thanks in advance for any help.
 
#2 ·
Possible you lost the washer that sits in the end of the mastercylinder-- that guides the Hydro push rod so it will sit in the MC piston pocket. Without the washer it depresses the MC piston and may not allow the brake pedal to return to the up position. That can also block the MC piston return port-- and when the brakes get hot- the fluid expands and will start applying the brakes while you drive-and may even lock the brakes.
 
#5 ·
Followup...
I was bit confused by the instructions because someone had said to drill out the booster rod to make it fit on the brake pedal. When I installed the booster the rod fit on the pedal with no problems. I didn't think i needed to do anything else.

The hole in the booster rod has to be drilled out enough to create movement in the rod. The brake switch fits on the brake pedal very well with little or no play. As you press the brake pedal the booster rod has to have enough room to move backwards and activate the switch. In it's stock form it will just barely work inconsistently, just to drive you crazy.

I borrowed a 17mm (about 43/64) drill bit from work, and enlarged the hole. The shoulders were rounded and not very deep on the end of the rod so I used a die grander to make the area that contacts the switch a little smaller and deepen the shoulders to make sure it would fully engage the switch. Works like a charm!!! I forgot to take and after photo, so this is before.

Thanks 01silvyz71 for the help.
 

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#8 ·
Followup... I was bit confused by the instructions because someone had said to drill out the booster rod to make it fit on the brake pedal. When I installed the booster the rod fit on the pedal with no problems. I didn't think i needed to do anything else. The hole in the booster rod has to be drilled out enough to create movement in the rod. The brake switch fits on the brake pedal very well with little or no play. As you press the brake pedal the booster rod has to have enough room to move backwards and activate the switch. In it's stock form it will just barely work inconsistently, just to drive you crazy. I borrowed a 17mm (about 43/64) drill bit from work, and enlarged the hole. The shoulders were rounded and not very deep on the end of the rod so I used a die grander to make the area that contacts the switch a little smaller and deepen the shoulders to make sure it would fully engage the switch. Works like a charm!!! I forgot to take and after photo, so this is before. Thanks 01silvyz71 for the help.
Did you drill out the rod in place or did you take it out. If you took it out how do you do that?
 
#7 ·
Just bought a 2007 GMC LBZ about 4 months ago to be my dedicated race truck. I am having a hard time holding the truck while boosting at the line. Plan to do this upgrade real soon, just picked up the 2011 LML hydroboost today.
 
#10 ·
I believe it has to be drilled out to 11/32, might search for it on here. There is info on it on here.