EDIT: Photobucket turned into a scam and lost my linked photos. Trying imgur.com as of 11/6/2017 for linking these photos.
Do you have power steering fluid leaking from the weep hole where the hydroboost unit bolts to the brake master cylinder?
If so, you have a worn piston seal that is allowing fluid to escape. This seal is Bendix part number 129484. If you have a local hydraulic repair shop or some other place that sells oil seals, you may first try to see if someone local can get you a replacement. Your other option is to purchase the repair kit from Piratejack.net
"2771004X Hydro-Boost Repair Kit" for $33. Unfortunately you can't just buy the 1 or 2 seals you need, you get the whole kit of 25 or so seals. I only used the 129484 and 2770532 seals. But it beats purchasing a whole new hydroboost unit!
Here is what arrives from Piratejack:
A copy of their instructions and a pack of seals.
(EDIT: Picture lost due to photobucket turning into a scam)
The instructions are also available in PDF format from their website.
Before you begin unbolting anything from the hydroboost, with your truck turned off, apply the brake pedal fully a few times. This depletes any reserve pressure from the accumulator.
Disconnect the brake master cylinder from the hydroboost unit by removing these two nuts. I use a 15mm wrench:
Here you can either just crack these connections loose, or completely disconnect them. The steel lines can be tight if they have never been removed before. You'll want some rags/paper towels as these three lines will leak some fluid when they're disconnected.
Now move into the cab and look where the brake pedal connects to the hydroboost. There are 4 nuts to remove. The threaded stems are long so you'll need a 15mm deep socket.
Look straight up at the end of the brake pedal and find the metal clip to remove. I use a flathead screwdriver to to pry it over top of the pin, then slide it off.
Once that clip is off, you can simultaneously slide the electrical connector and the hydroboost rod off of the brake pedal.
Now from the engine bay, you can pull the hydroboost unit away from the firewall. You'll have to push the brake master cylinder out of the way. I pulled up on it slightly and pushed it towards the fuse box, while pushing the hydroboost towards the engine and pulling away from the firewall. Once the threaded studs were out of the firewall, twisting the hydroboost counter-clockwise 90 degrees helped to get around the other obstacles in the engine bay. It should come out without too much hassle.
Take the unit somewhere decently clean to work on. You're dealing with hydraulics and parts that have tight machining tolerances. You don't want dirt/debris getting into the unit. I chose my dirty garage floor.
If you have the appropriate Torx socket, use it. Otherwise, use a 12-point 3/8" box end wrench to remove the 5 "star-shaped" bolts. These can be fairly snug. I had to tap on my wrench with a hammer to crack them loose.
Once it starts opening up, a good bit of fluid trapped inside the unit will spill out. So prepare with paper towels or whatever you use to soak up the mess.
Be cautious of any parts springing out.
Here is the unit in halves:
Take the half on the right, and look into this hole. About 2 inches in is the bad seal and all you can see is the inside lip of it.
I use two small flathead screwdrivers to get the seal out. You dont need to be gentle on the seal since you have a new one, but be gentle on the housing as to not scratch or ding it up.
Just to check, I slid both old and new seals onto the piston to see if I could feel a difference. The new one thankfully fit much more snug and felt solid!
Install the new seal into the housing. Be sure you put it in the correct direction with the lips facing the piston!
NEW ADDITION TO THE WRITE UP AS OF 11/6/2017 - Thanks to Silverado364 for the added info. See his post: https://www.duramaxforum.com/forum/di...ml#post7296618
It can be tricky getting the seal fully seated. Just be sure when you have it in that it is all even and smooth. You should be able to see about 1/16" of the lip all around.
Once the new seal is in, you can start re-assembling. If any parts sprung out, be sure to put them back correctly. The yellow spring goes into this small hole. There is also a small valve that can dislodge itself - My middle finger is covering some of it up. If it fell out, be sure to put it back in the correct way with the three dots facing out.
Continued in next post due to limit of 20 images per post!