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Drivetrain - 2001 - 2010 Discuss front and rear axle, transfer case, brakes, etc. Transmission questions belong in the appropriate transmission forum below. First through fourth generation...

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Old 11-12-2016, 10:02 PM   #1 (permalink)
gdoro1
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hydrobooster/ master cylinder leak

I have a 2003 3500 with the lb7. My brakes were weak last week, so I started searching for a bad brakeline. The puddle of fluid after a few days led me to look up front. I removed the drivers side inner fender to make it easier, and the bottom side of the booster and master cylinder are wet. My power steering fluid is low. It looks as though it is leaking where the two meet. How do I tell if its the booster or master cylinder leaking?

Thank you for any help

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Old 11-13-2016, 01:09 AM   #2 (permalink)
OkDually
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The Hydroboost uses Power Steering Fluid and helps with Steering and Braking functions

The Hydroboost is well known to lose a seal or two and go bad..

You can have someone sit in the cab and turn the steering wheel and push the brake pedal with the engine running to try and hunt the leak down but it may be too small to notice..

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Last edited by OkDually; 11-13-2016 at 01:10 AM.
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Old 11-13-2016, 02:43 AM   #3 (permalink)
davester
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There is a rebuild kit available (basically new seals) for the hydroboost part if that turns out to be the problem.
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Old 11-17-2016, 06:16 PM   #4 (permalink)
w1ngsmk
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Second on the Hydroboost... common issue with our trucks....top off PS fluid and watch to see if Master or Hydroboost levels go down.....amount of time and loss of fluid is the giveaway....New Hydroboost W/O core is a couple of hundred dollars from RockAuto or amazon...or if you are near a reputable rebuilder pull the hydroboost and have them rebuild it with a kit There are you tube video's on this subject matter
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Old 04-22-2017, 05:38 AM   #5 (permalink)
jblather
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My symptoms same as yours - bottom side of the booster and master cylinder are wet. My power steering fluid is low.

Replaced the hydroboost this week. You don't have to crack the brake lines. Two hours to replace it. Easy to bleed the power steering system, just rock the steering wheel lock to lock several times.
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Old 04-23-2017, 10:59 PM   #6 (permalink)
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it must be that time if the year cause just today my 03 LB7 hydroboost is leaking too. lol i am just going to rebuild the hydro, buy a new master, and a new power steering pump with new lines. its cheap enough and then you wont be chasing any problems. my $.02
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Old 04-24-2017, 12:45 AM   #7 (permalink)
jblather
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Quote:
Originally Posted by Hetkehog View Post
it must be that time if the year cause just today my 03 LB7 hydroboost is leaking too. lol i am just going to rebuild the hydro, buy a new master, and a new power steering pump with new lines. its cheap enough and then you wont be chasing any problems. my $.02
Good idea. The power steering lines are pretty cheap.
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2003 2500HD LS CC/LB 4x4 Duramax/Allison Completely Stock
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Replaced instrument cluster stepper motors.
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Old 12-31-2019, 09:15 PM   #8 (permalink)
srodster
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I know this thread is a little dated, but after putting on new fuel lines and brake lines this month, I discovered some "wetness" and a small drip at the hydroboost. See photo. For those that have tackled this job, would the "3 seal" rebuild be enough, or should I do a "full seal" rebuild. And of course, just get a remanf one and swap it out. Just curious as it looks like a "main" seal is only leaking in the photo.

For those that have swapped it out with a new one, any thoughts on brand?
Pondering my options......
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File Type: jpg Master Cylinder leak.jpg (106.1 KB, 13 views)
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Old 12-31-2019, 09:49 PM   #9 (permalink)
srodster
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I should also add, that on occasion when I push the brake pedal, sometimes I get a "fading" pedal as it gets to the bottom. Would that go beyond a "3 seal" change?
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Old 12-31-2019, 09:54 PM   #10 (permalink)
OkDually
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Quote:
Originally Posted by srodster View Post
I know this thread is a little dated, but after putting on new fuel lines and brake lines this month, I discovered some "wetness" and a small drip at the hydroboost. See photo. For those that have tackled this job, would the "3 seal" rebuild be enough, or should I do a "full seal" rebuild. And of course, just get a remanf one and swap it out. Just curious as it looks like a "main" seal is only leaking in the photo.

For those that have swapped it out with a new one, any thoughts on brand?
Pondering my options......
If I was going to rebuild it I would do a full rebuild and be done with it.
When I replaced my Hydroboost about 4 years ago I just used a Cardone Reman unit from OReillys and it has been fine.

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1996 K3500 6.5L,( "F" Eng #141 cast block) 5 speed manual, crewcab, dually longbed: 208,000mi.
Diamond Eye 4" Turbo Back Exhaust w/2.5" Flo-Pro Crossover
AirDog II DF165 w/ tank sock delete - XDP
TD-Max boost controller - Kennedy Diesel
OPS extension hose - Leroy Diesel
Glow Plug Harness- PT Wiring Solutions
Glowshift Maxtow EGT,Boost, Fuel gauges
Boost & Fuel Pressure Bolts - Leroy Diesel
2/0 Battery Cable Upgrade - PT Wiring Solutions
PMD w/#9 resistor and Re-Location Kit, mounted to bumper - Leroy Diesel
GM-5 Turbocharger
4.10 gear ratio
OptiLube Winter Formula


Proud member #1039 of The 3500 Dually Club

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