GMT 400 Hydroboost swap

Discussion in 'Axles + Brakes' started by DRAGGIN95, Sep 6, 2012.

  1. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    Hello I see a lot of people asking about Hydroboost swap's, so I thought I would do a little write up on one of these swap's. The difference between the setup's are, vacuum assist brakes use engine vacuum in a stored chamber to assist the vehicle in stopping, hydroboost uses hydraulic pressure from the power steering pump to the the hydro boost booster to assist in stopping the vehicle. Hydroboost booster's offer almost twice the psi brake force than the vacuum booster does. So first off getting started here is what we are starting with regular 1/2 ton 2wd regular vacuum boost brakes (please not that the ABS was already deleted off of this truck before). DSCN1786.jpg Now on to the swap, first I start by removing the 2 brake lines from the master cylinder as you need to swap to a matching master cylinder that will work with the hydroboost unit as the original master cylinder has to large of a O.D. bore to fit in the hydroboost unit. Next the master cylinder is by removing the 2 15mm nut's that hold the master cylinder on to the original booster. Next the large vacuum line from the engine can be removed from the booster. Now we can move inside. I start by removing the plastic panel underneath the steering column, it is held in place with several 7mm bolt's, you also need to remove the parking brake handle and set the panel aside, next remove the 4 10mm bolt's that hold the steel knee bolster panel in place and set it aside also. Now on 88-94 if your factory radio head unit is still in place above the gas pedal then you need to drop it down out of the way temporarily, on 95+ there is a bracket above the gas pedal that hold's the optional factory keyless entry unit as well as a couple of other relay's, it is held in place by 2 15mm bolt's and one small 7mm bolt, you need to drop it down enough to be able to access the brake pedal bolt, I did this without unplugging anything but it was tight. Next pop the brake switch off of the brake push rod and then remove the brake switch retainer clip. At this point you can remove the original vacuum boost brake pedal bolt, it is located above the gas pedal and it is an 18mm bolt, there is a welded in nut on the other side so there is no need for a wrench on the other side. Now you can pull back the firewall insulator pad to reveal the 4 15mm nut's that hold the booster to the firewall, I use a deep well 15mm socket on a rachet to remove these nut's, yes it is tight in there but it is doable. With the nut's removed you can slide the brake push rod off of the brake pedal and the booster can be removed as well as the brake pedal. Now here was my pile of new part's to be installed. DSCN1790.jpg Now I start my reinstall of part's, first off i install the new hydroboost brake pedal( this has to be changed because the pivot point for the pushrod is at a different height as compared to the vacumm boost pedal, also (note that the hydroboost pedal's are different for 88-94 than they are for 95+) now reinstall the brake pedal bolt and tighten it down. Next install your hydroboost unit itself to the firewall, make sure you slide the brake pushrod back over the pushrod pin on the pedal before you fully tighten the 15mm nut's. Now you can reinstall the brake light switch and brake switch clip. Next you can reinstall the metal bracket that hold's the keyless entry unit, and then reinstall the knee bolster and underdash trim plastic and e brake release handle. Now you should be done inside and you can now move back out under the hood. I like to install the new master cylinder and related bracket's to the hydroboost booster, once again reinstall the previously removed 2 15mm nut's, now you should have this DSCN1792.jpg

    DSCN1786.jpg

    DSCN1790.jpg

    DSCN1792.jpg
     
    Last edited: Sep 6, 2012
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  2. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    Next you need to remove the old vacuum line the fed the original vacuum booster, on a TBI engine it can be removed and an NPT plug installed in the intake or you could plug the line with a bolt and clamp it off, and on a vortec you can plug the line and clamp it off or get the small twist in intake plug that came factory on the factory vortec truck's that came equipped with hydroboost like in this pic. DSCN1791.jpg DSCN1788.jpg Next you can bench bleed your new master cylinder and reinstall the 2 brake lines and bleed the brakes on the truck. Once that is done you can start installing the 3 new hydroboost lines and removing your old existing pressure line that goes between the power steering pump and your steering gear. Leave the return line alone for now. Now start by installing the new pressure feed line from your power steering pump to the hydroboost booster, now you can install the next pressure line that goes between the hydroboost unit and the steering gear (note that these connections are mostly 16mm and 18mm). At this point you can install the return line from the hydroboost unit to the power steering pump. Now on a factory hydroboost truck the pump housing has 2 nipples for both return lines, but obviously the 1/2 ton truck's that came vacuum boost brakes did not have the 2 nipples, they only have 1. So I tee in to the existing return line coming from the steering gear to the pump, I use a simple brass 3/8 tee with 3 gear drive clamp's, this work's very well and I have done this many times. DSCN1794.jpg DSCN1787.jpg Now at this point you are ready to fill the system with power steering fluid, There will be lot's of air in the sysytem so I like to start the engine and rotate the steering wheel lock to lock 10 times while applying the brakes to get rid of all the air in the system, shut the engine off top of the power steering pump with fluid. the retart and check for leak's. It should look like this DSCN1796.jpg DSCN1795.jpg

    DSCN1788.jpg

    DSCN1791.jpg

    DSCN1787.jpg

    DSCN1794.jpg

    DSCN1795.jpg

    DSCN1796.jpg
     
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  3. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    This will work on most GMT 400's but it is written for 95+ and there will be a few difference's especially on the dash part's removal on the 88-94 dash. Here is a link with most of the part number's from Q'reilly Auto Part's [​IMG]Home> Shopping Cart


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    1997 Chevrolet C3500 Pickup RWD Base
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    [h=4] MasterPro® Power Steering - Power Steering Hose [/h] Part Number: 92006
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    [h=4] MasterPro® Power Steering - Power Steering Hose [/h] Part Number: 92004
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    [h=4] MasterPro® Power Steering - Power Steering Hose [/h] Part Number: 91816
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    [h=4] Cardone Remanufactured - Hydraulic Booster [/h] Part Number: 52-7358
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    Last edited: Sep 6, 2012
  4. Darkrider

    Darkrider Dexter

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    Great write up! Now that I see what you ment about Teeing off the line I can forsee doing this mod soon to my k3500! Def sending some rep your way once I get back on the laptop.

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  5. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    Also note that I did this in roughly 3 hour's with basic hand tool's, nothing fancy required.
     
  6. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    Thank's!
     
  7. Darkrider

    Darkrider Dexter

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    No problem man! I def like seeing easy mods like this, Granted in my case I will need to get the bleeding done professionally since I dont really have the tools/time but I can def forsee installing the components. Worse comes to worse I have the complete install done professionally if it comes down totime being a limiting factor.

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  8. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    Yeah I can understand that, either way the Hydroboost swap is so great, it makes these truck stop really quick!
     
  9. Darkrider

    Darkrider Dexter

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    Yup!!!!! My K1500 has it due to being a Diesel and the first time I laid into them in a panic stop I damn near wound up eating the steering wheel lol

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  10. monstar_est87

    monstar_est87 I'm Awesome

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    Finally a REAL Hydro boost write up..! Might I suggest adding part #s... And STICKY this thread..!

    I wonder why ur 3500 isnt already equipped with hydro boost brakes..?

    Would a diesel 1500 power steering unit work in this swap..? Or a 3500 power steering unit wit hyrdo work..? I have heard it might not bolt on but I'm not sure here...
     
    Last edited: Sep 6, 2012

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