LML Hydroboost pedal Issue

[MAXX IT OUT]

Looking for some help, but I swapped a cummins into my 67 c30 and used the duramax new lml hydroboost with a LBZ master cylinder instead of going with a vacuum booster. Its using the cummins power steering pump and a 80s power steering box. Currently have a issue with the pedal sticking after pushing the pedal, but it will pop back up after shutting the truck off. I added a second return line to the power steering pump to remove the tee I originally used, but didn't make a difference. Have adjusted the pedal to make sure there is no pressure on it, looking for any suggestions. I am half temped to put a pedal return spring on it, but I don't think that should be needed.

 

[Mikey52]

The size of the rod is different between the lml and lbz. Which rod did you use. Not saying that's your problem, but I remember them talking about having to enlarge the master rod piston end on some variations.

 

[MAXX IT OUT]

I don't remember swapping the rod when I did the same hydroboost upgraded on my LB7, if I remember right it a direct swap other then the hole size in the end of the rod for the pedal.

 

[Bdsankey]

The size of the rod is different between the lml and lbz. Which rod did you use. Not saying that's your problem, but I remember them talking about having to enlarge the master rod piston end on some variations.

It's the pedal end that needs to be enlarged, nothing between the master and booster connection.

 

[JoshH]

It's hard to follow the lines in your pictures. Are you sure you have everything hooked up correctly?

 

[MAXX IT OUT]

It's hard to follow the lines in your pictures. Are you sure you have everything hooked up correctly?

Should be, the high pressure line from the power steering pump goes to the engine side port, fender side rear port goes to the steering box, fender side front port returns to the pump reservoir.

 

[JoshH]

Sounds correct. I have seen some bad boosters act similarly. I know you said it was new, but it could be defective out of the box. Did you use a genuine GM part or aftermarket?

 

[MAXX IT OUT]

Sounds correct. I have seen some bad boosters act similarly. I know you said it was new, but it could be defective out of the box. Did you use a genuine GM part or aftermarket?

Gm #19371361 from Amazon came in a AC Delco box. The only thing I can think of left to check is the connection at the pedal. I cut the eye off the factory shaft, added a bolt with a heim joint to make up the added 2.5 inchs of length, so that I adjust the rod length. It's all in line, but could be to stiff. The pedal and shaft in my 2001 is really sloppy, so I don't know if it's putting a slight bit of pressure on it.

 

[MAXX IT OUT]

Also did some research on the powersteering pump, supposedly hydro boost system wants 1450-1550PSI at 3.0-3.5GPM vs 1150-1250psi at 3.0-3.5GPM. I have original dodge powersteering that was a non hydroboost truck. From my understanding of hydraulics, increasing the pressure will only give you more braking force and shouldn't be a issue with getting pedel to return. If anyone knows more about it, please comment.

 

[2004LB7]

You can shim the relief valve. But do it a little at a time as it's easy to over do it. Apparently one #4 washer is enough to make a big difference

 

[MAXX IT OUT]

Got it sorted out finally after getting rid of the heim joint for a sloppier fitment, spacing out the master cylinder, trying a longer and shorter push rod. Ended up finding out that pedal pivot was way to sticky and stiff. There's a factory return spring that would get it most of the way back, but run out of tension. So pulled the pedal set apart and machined down the pivot rod a bit, greased it up good and now it works great.