1973 k10 hydroboost conversion questions

[Mike_The_Grad]

Hey everyone, I'm in the middle of doing an LS swap on my buddies 73 k10. We decided to do a hydroboost conversion at the same time because the cam he picked doesn't make enough vacuum for power brakes. I already have the hydroboost unit with matching master cylinder that also matches the power steering pump. I already got the hoses and adapters for the original stock steering gearbox. The hydroboost unit is already mounted to the firewall with a anti rotation bracket that I picked up on ebay. I also found a hydroboost brake pedal assembly on ebay from a squarebody truck. That's all installed. Came with all of the required small parts, I think. Plus a weird bracket that I honestly have no idea where it goes. So my question is, as I try bolting up the little plate bracket for the brake light stop switch, I have to apply pressure to the pedal in order to get the bracket bolted to the pedal. When I do this the little switch stop plate is pressing up against the bracket that holds the actual stop lamp switch. Which is already preloading the hydroboost unit. I don't even have the master cylinder attached to the hydroboost unit yet. And I feel like it will be preloading the unit. Also, I don't even have the switch mounted to the bracket. But I feel like if I try and thread the switch into the bracket the plate attached to the pedal won't let it go very far and might even have enough pressure already to pop the switch back but of the bracket. And in it's current position with the plate attached at the pedal rested on the bracket, the brake pedal is really high in comparison to the accelerator pedal.
This is on 73 k10 with lm7 5.3 and 4l60e and np205 transfer case. Any help or guidance is greatly appreciated as it's one of the last few things before I can get it back on the road.

[v30crewcab]

what is your hydroboost out of? they have specific length pushrods depending on what they were in. the 2000's truck ones won't just bolt in without modifying the pushrod length. you can either cut and modify it, or get one from a 81-87 truck with the correct length.

also, you might need to post a pic of whats going on with your brakelight switch.

[Mike_The_Grad]

The hydrobosst unit is from a 1986 1 ton pick up. And so is the master cylinder.

[Mike_The_Grad]

Here are some pictures. Sorry if it's difficult to make out what parts are what. I'm wondering if I need to use a bracket to space the hydroboost unit off of the firewall to bring the pedal height down closer to level with accelerator pedal. And to not have the unit preloaded. Anybody have a picture of what 1986 1 ton hydroboost unit attached to fire wall looks like?

[Mike_The_Grad]

Well after some pretzel twisting I was able to take a few measurements. From the inside firewall surface to the loop of the hydroboost push rod I have 8" to center. If I attach the push rod to the brake pedal stud at this point it puts the brake pedal pad about 12" from the floorboard and about 12" from the front of the bench seat. While the accelerator pedal is about 5" off the floorboard. And the brake pedal stop switch contact plate will not even fit the brake pedal arm at this height. BUT, if I were to add about 5/8" inch thick spacers in between the hydro boost mounting plate and firewall on the engine side, this would put the brake pedal pad height about an inch or 2 above accelerator pedal height and would allow enough room for the brake switch contact plate to bolt to the arm assembly and the brake switch to thread into place on the brake pedal pivot housing. I'm wondering if there is supposed to be a spacer plate on the firewall side of the factory hydroboost truck application for 1987 1 ton. Only one way to find out. Here's a question, any reason why I couldn't use spacer bushings on each of the 4 bolts/studs going through the firewall VS. A solid plate to fill the space? Obviously taking stud length into account room permitting for the added spacing. Thanks again.

[Mike_The_Grad]

Frayed knot my friends. Looks like it's time to get custom. Like we all knew that wasn't going to be the end result anyways. Ha ha. Looks like I'm going to have to cut and shorten the pushrod from the hydro boost unit. I'm thinking of adding a sleeve around the rod to give me some material to bite into with the welder. Plus it'll help with make sure the rod is straight afterwards. I'll be back in a little while to share the end result. Wish me luck. Ha ha.

[Mike_The_Grad]

Well I cut and shortened the pushrod on the hydroboost unit. Ran out of daylight though. So I'll check the fitment tomorrow. Looks like it should work. I took 9/16" out of the push rod length.

[Getter-Done]

Nice work.

I hope this works for you.

[v30crewcab]

I'm wondering if that little piece is different betweeen vac and hydroboost? maybe different spacing.

[Mike_The_Grad]

The reason why I think it wasn't a direct bolt on process was because the factory equipped hydroboost squarebody trucks had a different firewall mounting area for the hydroboost vs. The vacuum assist booster trucks. In all of the somewhat limited pictures I found online of a hydroboost squarebody equipped truck or a unit pulled from one that still had the firewall plate attached to the unit, they look like they have a raised area or recessed area where they mount to the firewall so that there's room for the big square serrated brass locknut. After I actually looked at what was going on and how I needed to move the unit away from the firewall if I was not going to cut the unit pushrod is when I realized I needed a stepped bracket or plate. Because the lower mounting studs that secure the unit to the firewall are factory pressed in studs and are only so long. Sure I could have taken the whole brake pedal assembly back out, cut and punched out those studs and used longer bolts with washers and nuts, I figured just cutting a small section from the pushrod and welding it back together with a sleeve to have more material to bite into was faster and easier. Which is exactly what happened. It worked perfectly. Pedal is about an inch or inch and half higher in relation to the accelerator pedal. This allowed everything to bolt up just like it should. It doesn't preload the unit, has room for the brake switch to thread in and function like normal. No interference, the pedal works just like it should. It's a big hurdle I've been avoiding for the last couple of weeks. And it finally came time to figure it all out. And I did. I feel like there's not much left in the way of completing this ls swap. Have to get both driveshafts modified. But that's not my job. I just need to get correct measurements and send them off to the driveshaft shop. I already have my hydroboost hoses matching master cylinder, and my adapter fittings for the stock inverted flare power steering box. Connect power steering cooler, fill up all the fluids connect exhaust and fire this bad boy up. here's a couple pictures of the swap. The last picture is what it looked like when it showed up at my house at the end of june.

[v30crewcab]

on the 81-87 trucks the studs are part of the steering column brace/pedal hanger. guess I need to look at my 79 and see what it has. never had an issue with the hydroboost on the 81 up's. they're basically plug and play.

[Mike_The_Grad]

Yeah I seen that on other guys conversions for the later year sqiarebody trucks. I'm not sure if hydroboost was offered in 73 though.