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Discussion Starter · #1 ·
Hey guys so I just replaced my steering gearbox with a redhead one and replaced my burnt up ps pump and after that my power steering was great but my brakes were pretty bad still.. so I did some reading on the forums and decided to replace the hydroboost with the LML one. Just got it all back together and bled the PS the same way i did when i changed the gearbox (jacked it up turned the wheels etc.) the fluid level isn’t dropping but my brakes just go straight to the floor I can hardly feel any pressure. The pedal does come back up. I didn’t drill out the plunger hole because I compared it to old hb unit and they looked exactly the same size and my brake switch fit on fine with no problems, brake lights work just fine too. I’m all out of ideas.. I don’t want to resort to getting a remanned lmm hb but it’s starting to look like that’s my best option. Also i didn’t open any brake lines for any reason so I don’t think there would be air in the brake lines. Oh and i don’t know if this is normal but when i press the brake pedal all the way down with the engine running I can hear what sounds like air being released in the engine bay, I don’t know if that’s normal or possibly the cause of my problem. Please any help is very appreciated.
 

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My first inclination is that you have air in the lines. I’d get a power bleeder and open each of the 4 lines one at a time putting new fluid through. Similar thing happened to me when I changed my fluid due to caliper work. Apparently it takes very little air to make the system not work at all.
 

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My first inclination is that you have air in the lines. I’d get a power bleeder and open each of the 4 lines one at a time putting new fluid through. Similar thing happened to me when I changed my fluid due to caliper work. Apparently it takes very little air to make the system not work at all.
He didn’t take the brake lines off the master cylinder.

To the OP, I don’t know if it’s possible but check to make sure that the hydro boot apply pushrod is in place. I thought there were a few hydro boosts that didn’t come with that pushrod in them so you had to use the one out of your old hydro boost.
 

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Agreed on the pushrod. It may also require adjustment correct?
 

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Discussion Starter · #5 ·
He didn’t take the brake lines off the master cylinder.

To the OP, I don’t know if it’s possible but check to make sure that the hydro boot apply pushrod is in place. I thought there were a few hydro boosts that didn’t come with that pushrod in them so you had to use the one out of your old hydro boost.
How could it get out of place, and if it is how do I put it back? I can get pics here in a bit, everything looks like its in place
 

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Agreed on the pushrod. It may also require adjustment correct?
Some of the older cars had adjustable ones but I haven’t seen one in a long time.

How could it get out of place, and if it is how do I put it back? I can get pics here in a bit, everything looks like its in place
It would have had to have fallen out. Again, not saying yours did but it seems like I had one do that once.

While you have the master off the booster, put a flat piece of stock against the booster mounting flange and measure into the pushrod to see how deep it is back in there. Then, do that same measurement on your factory booster.
 

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Pushrod looks to be in place. Make sure it’s the same depth between the two boosters. I’ve never interchanged a booster before so I don’t have specific knowledge of what may, or may not, be different between the two. Hell, I’m still in the dark as to why everyone here seems to be infatuated with putting LML boosters on everything.
 

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Discussion Starter · #12 ·
Pushrod looks to be in place. Make sure it’s the same depth between the two boosters. I’ve never interchanged a booster before so I don’t have specific knowledge of what may, or may not, be different between the two. Hell, I’m still in the dark as to why everyone here seems to be infatuated with putting LML boosters on everything.
I’m starting to agree with you. I’m gonna mess with it a little while longer and if I can’t figure it out I’m gonna but a stock booster
 

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Discussion Starter · #13 ·
Pushrod looks to be in place. Make sure it’s the same depth between the two boosters. I’ve never interchanged a booster before so I don’t have specific knowledge of what may, or may not, be different between the two. Hell, I’m still in the dark as to why everyone here seems to be infatuated with putting LML boosters on everything.
With someone in the truck pushing the brake I can see the master cylinder moving like half an inch and hen the brake is fully depress, that doesn’t seem right to me
 

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Discussion Starter · #14 ·
I think I'm gonna try to swap the rods and see if that works. I don't have high hopes because as you can see in the pics, the cylinder around the rod is much deeper in the old one, but I'll give that a shot and see if it works. If not I guess I'm out of ideas.
 

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Before you do more crazy work, take some time to do some research. I recall someone posting something about the pushrod being too long, and then when brake is released it didn't fully go back to where it should have been. Can't remember exactly, but the gist was that the length of the rod when released covered up a passageway in the master cylinder that should have been uncovered when the brakes are released. Don't quote me,what I said might not be exactly correct, but do the research either on this forum or Dieslplace or DuramaxDiesels.
 

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Discussion Starter · #16 ·
Before you do more crazy work, take some time to do some research. I recall someone posting something about the pushrod being too long, and then when brake is released it didn't fully go back to where it should have been. Can't remember exactly, but the gist was that the length of the rod when released covered up a passageway in the master cylinder that should have been uncovered when the brakes are released. Don't quote me,what I said might not be exactly correct, but do the research either on this forum or Dieslplace or DuramaxDiesels.
Believe me I've searched everywhere for a solution. I think my last resort is to switch the rod that goes into the mastercylinder, but it doesnt look easy to replace without damaging things or taking the whole unit apart. and I'm not super excited about taking it apart because I want to be able to send it back
 

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Discussion Starter · #17 ·
Before you do more crazy work, take some time to do some research. I recall someone posting something about the pushrod being too long, and then when brake is released it didn't fully go back to where it should have been. Can't remember exactly, but the gist was that the length of the rod when released covered up a passageway in the master cylinder that should have been uncovered when the brakes are released. Don't quote me,what I said might not be exactly correct, but do the research either on this forum or Dieslplace or DuramaxDiesels.
what if I put an LML mastercylinder on there? would that make the rod work?
 

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Well, when someone presents the same problem in 2 different threads... This is how I answered in the other thread...
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If it doesn't work, you probably need to ream out the eyelet just a little. Check that when the brake pedal returns all the way, that the rod to the hydroboost is out completely, or has a little slop of the pin in the eyelet. There needs to be a little slop so the brake light switch works.

I don't remember where I read it (another forum, I think, probably by heymccall), but I think he described how the hydroboost doesn't work (and the pedal goes to the floor?) if the rod doesn't retract all the way.
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I think I'm going on the same info as Ron above (post #15). However, I see a lot of the other posts talk about the rod from the hydroboost to the master cylinder. We are talking the other end to the brake pedal. (added on edit: Oh, and I think Ron has it right, and I described it wrong above, and really the slight pressure messes up the master cylinder. I guess that could also happen as others describe that the rod on the master cylinder side is too long, and presses on the master cylinder just a little too much.)

Also, the reason some of us changed to 2011 LML booster on our LLY trucks is that the power assist action for the brakes actually work now. Before, with just a 2500 lb. camper in the bed, I totally depended on using T/H to come to a normal stop. Yes, I could stand on the pedal, but that gets old. After the booster change, I tend to (are you ready for this?) just use the brakes. If it was just me, you could think that it was just my truck, but there are many others with the same experience.
 
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