Duramax Diesels Forum Truck of the Week
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Old 08-09-2018, 06:06 PM
19jake91 19jake91 is offline
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Default Brake light issues after LML hydro boost upgrade

I just installed the 2011 LML hydroboost in my 07 LBZ due to my factory one leaking. The install was straightforward but a problem I have had right away is intermittent brake lights, trailer brake controller and sometimes it will not shift out of park. All symptoms of the brake light switch not getting complete contact. Has anyone else done this swap and experienced these problems? If so, how did you fix the situation? Thanks in advance.
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Old 08-09-2018, 06:16 PM
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Did the exact same swap with no problems. You might of accidentally messed with a wire(s) in the process.
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Old 08-10-2018, 06:42 AM
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When I swapped mine I noticed the LML booster had a smaller diameter hole where it connects to the brake pedal/mounts the brake switch. Yours may be a bit tighter than other vehicles causing the push rod to not travel far enough to contact the brake switch. Drill it slightly larger.
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Old 08-10-2018, 07:05 AM
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Quote:
Originally Posted by chevyburnout1 View Post
When I swapped mine I noticed the LML booster had a smaller diameter hole where it connects to the brake pedal/mounts the brake switch. Yours may be a bit tighter than other vehicles causing the push rod to not travel far enough to contact the brake switch. Drill it slightly larger.
What he said is correct. You need to drill the hole out on the booster rod where it goes onto the pedal with a 41/64" drill bit. The first one I did (on my truck), I used a step bit and drilled it out to 11/16" which worked, but 41/64" is almost exactly the same size as the factory booster.
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Old 08-10-2018, 09:48 AM
19jake91 19jake91 is offline
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Quote:
Originally Posted by JoshH View Post
What he said is correct. You need to drill the hole out on the booster rod where it goes onto the pedal with a 41/64" drill bit. The first one I did (on my truck), I used a step bit and drilled it out to 11/16" which worked, but 41/64" is almost exactly the same size as the factory booster.
Thanks for the info. Iíll borrow a drill bit from work and hopefully Iíll have the same problem you guys did as well.
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Old 08-10-2018, 10:44 AM
CarolinaHD CarolinaHD is offline
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Good info this should be added to the other hydroboost thread. I hope I don't have this issue, really don't wanna remove it again.
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Old 08-10-2018, 11:39 AM
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Quote:
Originally Posted by CarolinaHD View Post
Good info this should be added to the other hydroboost thread. I hope I don't have this issue, really don't wanna remove it again.
You don't have to remove it. Just unhook the rod from the brake pedal and hold it with a pair of vice grips. It can be drilled in the truck.
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Old 08-10-2018, 01:27 PM
CarolinaHD CarolinaHD is offline
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Good call, I love this forum.
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Old 08-10-2018, 07:36 PM
19jake91 19jake91 is offline
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Quote:
Originally Posted by JoshH View Post
What he said is correct. You need to drill the hole out on the booster rod where it goes onto the pedal with a 41/64" drill bit. The first one I did (on my truck), I used a step bit and drilled it out to 11/16" which worked, but 41/64" is almost exactly the same size as the factory booster.
Quote:
Originally Posted by JoshH View Post
You don't have to remove it. Just unhook the rod from the brake pedal and hold it with a pair of vice grips. It can be drilled in the truck.
Thanks for the great info JoshH. I was able to drill out the rod to a 21/32Ē(closest size I had readily available) with it still in the truck and the brake light problem is fixed. I would definitely recommend drilling out the new rod before it is installed.

As for the swap, I am happy with the improvement in braking. Iím not sure if it was because of the new design or just because my old one was leaking.

Either way, thanks again for the great info and time saved!
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Old 08-11-2018, 04:25 AM
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I need to do this to my regular cab so it stops better...
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Old 08-11-2018, 08:22 AM
19jake91 19jake91 is offline
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I know the info is out there but just to confirm other posts, I went with GM part number 178-0853. It was less than $200 to my door with no core charge.
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