Hydroboost into a 67-72

[JJorgensen52]

I did some research on this a while back, and it seemed like every thread I found talked about drilling holes in the firewall or other modifications that made this swap difficult to do.
In looking at donor trucks, it seems like only the metric (1980+) trucks had the type of booster I'm working with here.

Anyways, some pictures:

Comparison between an unmodified '87 hydroboost bracket and my '72 power brake booster


Lining up the center holes puts the pushrod in the center of the hole in the firewall. I should note that the hydroboost had two pressed-in studs in the center holes, which I popped out.


Using two snug fitting bolts and a welding clamp, I carefully lined up the two holes and marked for the other holes I needed. It's tough to see here, but there was a stamped bend in the top of the hydroboost, which I pounded flat prior to marking (just below the top holes)


After drilling three new holes and some cutting and grinding, this is what I came up with. The cut on the bottom right was to allow me to bend the bracket out slightly to clear the flange around the steering column on the firewall.

Bracket dry fit on my '72 cab


And here's the donor hydroboost bolted in place



I had to make zero modifications to the firewall, except pulling out the original rubber linkage boot.

The photo doesn't show, but mounted like this the hydroboost pushrod is about 5/8" too short (and offers no adjustment). Unfortunately it's a smaller diameter than the adjuster end on the 67-72 style pushrod, so either I will cut and thread the rod and thread a piece of tubing to make an adjuster of my own, or I'll modify the pedal to move the pivot closer to the firewall.

[Ozzy2013]

Cool thanks for the post i have the booster and am doing this to my 68 !

[70blackfish]

looks good

[68shortfleet]

Very nice, thanks for sharing.

How is the pressure and return line plumbing going? Are you using all the stock lines the the 80+ truck? Are they flare or O-ring lines? What are you doing to get two return lines into your reservoir housing?

[JJorgensen52]

Originally Posted by 68shortfleet

Very nice, thanks for sharing.

How is the pressure and return line plumbing going? Are you using all the stock lines the the 80+ truck? Are they flare or O-ring lines? What are you doing to get two return lines into your reservoir housing?

I have all new lines here for the 80+ setup, and they are all O-ring. I'm using my original PS pump, I'm going to swap in the metric outlet fitting from the later truck. In the early hydroboost trucks, they had a tee in the return line, so the hydroboost and the box both fed into the tee and then one line went back to the reservoir, and that is what I'm doing. The 80+ setup had two return fittings on the reservoir. Fortunately, the return lines are all slip fit with hose clamps so I can monkey with them however I like

This is happening at the same time as my 2wd to 4wd 1 ton swap, so I probably won't get to finalizing the plumbing for a week or so and I will update this thread when I do. More info on the swap here

[JJorgensen52]

Had a few spare hours this afternoon - modified my brake pedal to work with the pushrod for the hydroboost. That way, if the hydroboost ever has to be replaced, it's a bolt-on.


I've put it all together, it works, I've painted the pedal and I will get some pictures once it's dried and I can put it back for good.

[Ozzy2013]

Great this will make my swap easy!

[69moneypit]

I'm new to the power brake / hydra boost swap . What's the difference between them ?

[JJorgensen52]

Originally Posted by 69moneypit

I'm new to the power brake / hydra boost swap . What's the difference between them ?

The biggest difference is that the hydroboost is fed by the power steering pump, rather than engine vacuum. It gives a more consistent, positive pedal feel and works with big cams, turbos or diesels that don't make much vacuum.

The functional difference for us is that the 67-72 came with power brakes, you can just bolt it on, where hydroboost was first available around '74 or '75, that I know of.

So, basically to make a hydroboost work you need new power steering lines, a modified mounting bracket for the firewall, and either a modified push-rod or a modified pedal (as I did in this case)

[69moneypit]

Originally Posted by JJorgensen52

The biggest difference is that the hydroboost is fed by the power steering pump, rather than engine vacuum. It gives a more consistent, positive pedal feel and works with big cams, turbos or diesels that don't make much vacuum.

The functional difference for us is that the 67-72 came with power brakes, you can just bolt it on, where hydroboost was first available around '74 or '75, that I know of.

So, basically to make a hydroboost work you need new power steering lines, a modified mounting bracket for the firewall, and either a modified push-rod or a modified pedal (as I did in this case)

Thanks , you cleared it up for me

[Alan's Classic]

Subscribed

[JJorgensen52]

I don't have any photos yet, but status update:

With the modified pedal, the hydroboost unit fits nicely and is installed for the final time.

The '87 truck brake lines actually fit in the '72 almost like they were meant to go there

I was able to successfully swap the pressure outlet fitting in my PS pump to the later metric unit, and the '87 pressure line fits nicely (they're a tad longer than needed but it is nice to have the extra for neat routing). I had to make a couple small tweaks to the line shape, but it was nearly a bolt on affair.

[JJorgensen52]

Well I am WAY behind on my photo updates, but I finally got a chance to get some photos of how this turned out:

First, overall engine bay shots



These are regular issue 1987 V30 hydroboost lines (Eldelman power steering lines and Inline Tube stainless brake lines)


Detail shots of hoses. I chose to use the '87 steering box on my '72 frame to make the plumbing easier


I also retained the original '72 power steering pump, which required a tee in the return lines


Just a few notes.
1. I did have to tweak the PS lines, and also the inner fender, a bit at the steering box to make everything fit but it all clears and no cutting was required.

2. The original PS pump has a smaller reservoir than the newer style pumps; initially I thought this was an unsolvable issue because I was getting aeration when turning and using the brakes at the same time. However, after some road time and bleeding the system out I've eliminated that and am happy to report no problems.

3. I read a bunch here and elsewhere about not using a "T" in the return line as it would starve the pump. After doing some research, the first years of GM hydroboost trucks (up until about 1980) were designed with a "T" in the system. Provided you use a tee of the appropriate ID, this is NOT a problem at all.

Overall, could not be happier with the swap. Very consistent, solid pedal feel across all different engine and truck loading conditions, and it is so very much cleaner under the hood.

[Bigdav160]

Subscribed also. This is a conversion I'll do eventually. I love the hydroboost in my diesel DD's

[SierraMtns]

Good job on the swap. It really cleans up the firewall.

[El Campo]

Very nice

[boraxman]

Have HB on my truck the previous owner installed...One thing I can say is if I ever need to hit the brakes hard im sure I will be going through the windshield.

[Ozzy2013]

Awesome so a stock power steering pump works with a t on the return!I am going serpentine belt so i will use a pump from the same year i take the set up off of 1996 most likely.

[7dee2]

Great job as usual, subscribed!

[70CHEVYBB]

where did you mount the prop valve?

[JJorgensen52]

Originally Posted by 70CHEVYBB

where did you mount the prop valve?

Since I was using the square body lines, I mounted it on the front cross member just like they do. I used the square body cross member for the sway bar mounts, but the same position will work on a 67-72 cross member no problem




I happened to have a second '67 truck harness laying around, and the harness - prop valve wire is made in two pieces with a connector where it leaves the main harness. By pulling that piece off my spare harness, I was able to plug into the extension already on the '72 and reach the prop valve on the cross member no problem.

[Billyburban]

Originally Posted by JJorgensen52

Since I was using the square body lines, I mounted it on the front cross member just like they do. I used the square body cross member for the sway bar mounts, but the same position will work on a 67-72 cross member no problem




I happened to have a second '67 truck harness laying around, and the harness - prop valve wire is made in two pieces with a connector where it leaves the main harness. By pulling that piece off my spare harness, I was able to plug into the extension already on the '72 and reach the prop valve on the cross member no problem.

First off I'd like to thank you for your part of the write up and all your photos and I have a question what year make and model did you get all your parts from so I know because I see that you wrote 87 but kinda car ?

[Bigdav160]

Hydroboost would have come from a 1 ton truck

[Twisted78SS]

Astro vans are another common source for the hydro-boost unit.

You may already know, but there are some great threads covering the conversion to go along with this one.
http://67-72chevytrucks.com/vboard/s...d.php?t=523502
http://67-72chevytrucks.com/vboard/s...d.php?t=372984
http://67-72chevytrucks.com/vboard/s...d.php?t=539517

And to make things even easier for some, CaptainFab has adapter brackets
http://67-72chevytrucks.com/vboard/s...d.php?t=347480

[chewychevy67]

I have a 78 gmc 1/2 ton that had a diesel in it new but now has a 350 in my shop that im wrecking but the brakes did work. should I take it off before it hits the scrapper? Hoses would all need to be changed if I reused this set up. seems like its going to be a messy situation.