GMT 400 Hydroboost swap

L31MaxExpress said:

Good EFI style clamps are what I use. The worm gear style with the exposed gear teeth is terrible.

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L31MaxExpress said:

Good EFI style clamps are what I use. The worm gear style with the exposed gear teeth is terrible.

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Jesse_Wenting said:

Funny you replied to this actually, been meaning to send you a DM but might as well ask here so everyone has access to the info.

Back when you did your -AN Power Steering Hoses, what fittings did you need? I'm looking to do my return lines too

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DRAGGIN95 said:

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).

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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.

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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

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Eric Davis said:

I'm trying to figure out who says on the 98 2dr tahoe the brake pedal is different, I took the pedal off of I believe a c3500 1998 and comparing the two they are both the same, part no. 15732200 for both of them only the bottom 5 are different and I see no difference side by side. Do you guys know how misleading the pedal thing is and the amount of energy it takes to get that out from around all that crap underneath the dash. Wasted a whole Saturday on that pedal when I didn't even need to change it and could have just concentrated on getting the hydroboost unit. You guys should have said 95 back pedals are different cause it is nothing easy about this hopeful upgrade

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