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Ford Bronco Parts - Classic Vintage Early Bronco Parts

Hydroboost Brakes

Tech article by TOFIC and filed under - Hydroboost, Brakes

Tech article by TOFIC

Wandering the wild country one day, I stopped in a small town to acquire some fuel and liquid refreshment, and discovered the scrap metal dump just outside town. In amongst the derelict refrigerators and lawn mowers was a 1976 Mercury Grande Marquis Station Wagon. Ah Ha says I, maybe a source of some useful parts. Lift hood and voila! A stock FORD hydro boost unit intact. Being resourceful and always carrying a tool box with me (the wife calls it the ‘steal and strip kit’) the unit did not reside in the station wagon for long.

I removed from the station wagon the Hydro boost unit, the master cylinder, the power steering pump (A Saginaw with dual returns!) and the Power Steering pump brackets.

Retiring back to the town office, I enquired as to who I would reimburse for the parts I acquired. All I got was a funny look, and “There yours now, don’t bother us with it”. Price every Bronco owner likes, FREE!!

Home I go with my new goodies and stop at the car wash to give them a bath. They look brand new. Disassembled the hydroboost unit and discover it is virtually new. The Master Cylinder is in average condition and the power steering pump is in above average condition, what a score!

Got on the internet and discovered that Ford did put hydroboost units into some of their cars back in the 70’s. The big Mercury cars got them and some of the Mercury Monarch Ghia vehicles got them in the 74 to 79 time frame. A lot of browsing showed that no one has installed any of this particular unit in any other vehicle and only one site knew that Ford installed these in the above cars. Interesting fact.

Talked to the wrench benders at work, and discovered I did not need HP hose to install it, simple brake line is more than sufficient. The only connections that need flexible hose connections were the 2 connections to the power steering pump. This project is really beginning to make me happy.

Removed the old vacuum boost unit off the firewall. What a large piece of metal that disappeared. A quick test fit of the hydroboost unit showed I would have to install it turned 180 degrees. Not an issue, says the mechanics, some installs are that way from the factories.

Now to the installation, some quick looks and some calculations showed I needed some 3/8” line some 5/16” line, unions for both, and some brass fittings to adapt this to the Bronco. Here is what I bought.

  1. 4 lengths of 3/8 inch brake line 30” long 5.23 each total 20.93
  2. 4 lengths of 5/16 inch brake line 30” long 4.86 each total 19.44
  3. 2 brass unions 3/8 in size 2.09 each total 4.18
  4. 1 brass union 5/16 in size 2.29 each total 2.29
  5. 1 90 degree 5/16 inv. Flare to 1/8 pipe fitting 1.89 each total 1.89
  6. 1 90 degree 3/8 inv. Flare to 1/8 brass fitting 2.29 each total 2.29
  7. 1 package of 3/8” inverted flare nuts 1.99 each total 1.99
  8. 1 brass 3/8” tee fitting 5.16 each total 5.16
  9. 1 5/16 threaded rod connecting nut .49 each total .49

Total 58.66

Took hydroboost unit apart, cleaned all the accumulate dirt out of it and painted the unit and made a couple of gaskets out of some spare gasket material I had using the old ones as patterns.

Promptly lost the LP (low pressure) fitting to the unit. Rats, hate it when that happens. No great thing, it was a straight fitting and I needed a 90 degree unit to clear my valve covers anyway. Soon discovered that the threads were different in the unit as compared to my brass fitting I was using. A quick talk with the mechanics and I was told to tap the unit for the pipe threads and ensure that the filings were all out of boost unit.

Did this, took several minutes to get the filings out of unit. Free hint, if you are doing this with yours, put a clean rag in the bore of the unit and then thread it. Saves a lot of work!

Now, I needed a 90 degree fitting for the HP (high pressure) line to the power steering pump. Made this by taking one of the 3/8 inverted flare nuts and the 90 degree 3/8 fitting and threading the nut to 1/8 pipe threads. Clamp the nut into a vice, thread the inside of the nut for pipe thread, clean both the nut and fitting thoroughly with alcohol, put a little JB weld on the threads of the 90 degree fitting and thread them together. Set the aside to allow the weld to set then thread this into the boost unit aligning it to point straight across the unit like the LP fitting. At this point, told the guy at work what I was doing and he gave me a Number 2 lecture about JB Weld and Brass. It will leak. He took my spare two fittings and brazed them together. Tossed them at me and said “ There, that won’t leak, and don’t you ever do a backyard two bit job again or I will take away your birthday” Could not argue with him, smiled sheepishly and said “yes master, please forgive your lowly student for his blundering” We parted ways laughing like hell.

Went to bolt in the hydroboost unit and discovered that the bracing plate on the firewall appeared to be a little loose. Man do I love previous owners; pictures show the butcher job done to the firewall behind the old boost unit. One look at this mess and I promptly went for a beer and a day off this job to think about it. The next day, took some scrap plate I had, made a new bracing plate and drilled it to fit on the firewall. Painted it and pop riveted the plate in place while it redrilled all the holes in the plate to match the firewall. I had some unique language for the PO and his mechanics skills at that point.

Oh well, a small setback the job had been going too well at this point. Also gave me a firmer mounting for the boost unit as it has 4 holes for mounting and the original only has 2 holes for mounting. And, of course, not one of them lines up.

Bolted up the hydroboost unit, fit like glove, put on my old master cylinder, and bolted it up. Man this is going too smoothly, something is wrong!

Crawled under the dash to connect the brake rod to the boost unit and found out what was wrong. The rod was too short. Out came the unit and I cut the push rod and lengthened it with the threaded rod coupler in the parts list. Pictures of this, we have all done it and if you haven’t it is a straight cut and thread operation. Back the unit and MC went and it connected up perfectly and the brake light switch. The brake light switch even works. Yahoo, bonus, no screwing around with a brake switch. Took the time to service the pivot point for the brake arm and paint the bracket.

Back under the hood, and started with the LP line to the power steering box. Using a tubing bender (Most important, do not bend brake line without one.) I bent up the line from the boost unit to where I was going to tee into PS pump. This involved three bends and several extremely descriptive words to get right. Double flared the connection to the boost unit and connected it up. Next was the LP line from the steering box to the tee fitting. Again, three bends and a lot of words and test fit to get right. Double flared the connection to the box and connected it to the box. Connected everything up with a tee fitting and some 3/8 rubber line that was on the truck that originally returned the fluid from the pump and box.

Next was the high pressure line to the power steering pump. Being frugal (read, cheap) I reused the HP line that was in the truck. Took the original HP line straightened out the 2 ends, inserted new nuts on the line, and double flared these ends. Connected one end to the pump and started work on the other end. A few simple bends in the line, cut to length I needed and a new nut and double flaring got this line done. Connected everything with a 3/8 union and voila that line was done.

A similar method was used with the HP line to the steering box from the hydroboost unit, just simple bends and connecting with the union nut completed this job.

GREAT this is going real smoothly filled the PS pump with fluid and left it for the night to work it way into the system as per instruction for installing hydroboost I got from the 76 Mercury manual. (Murphy’s Law is about to strike.) Return the next day after work to find about 2 pints of PS fluid all over the floor. WTF? I forgot to tighten the low pressure fitting to the steering box. Tightened that cleaned up the mess refilled the pump. Time for the bleeding sequence following the shop manual instructions. Jacked up the Bronco and put the front axle on stands. Followed the instructions to the letter and had no problems getting this system working. Felt a little “soft” so I left it to come back to it the next day. Did the brake bleed for the brakes because I am cautious and every time I work on the brakes I bleed them.

While at work on a break, called Paul Clarke at Hydroboost and talked to him about my installation. A finer gentleman does not walk this earth. Was more than helpful gave me a bunch of tips about this install. He was a little amazed that I got a unit off a stock Ford but did not doubt they did it. Told me that the softness was normal and after some driving would disappear. Was really interested in my install and asked for some pictures of it. Also sent me the install instructions for his units so I could ensure mine would work for me. People in business like Paul are rare and you do not hesitate to deal with them. Many Thanks Paul!!

Took the Bronco off the stands, backed it out of the garage and started down the back alley to the street. Got to the street and applied the normal foot pressure to the pedal to stop. BIG mistake. Kissed the windshield with the power of the boost. Man this is too good to be true. Drove it for a few miles and was really amazed at the stopping power of this unit. Another call to Paul to ensure I had done things right and after chuckling a little he says “Welcome to the world of really good braking, no, your unit is working correctly”

I have driven this system for about 1200 miles and it is great. One of the best modifications I have made to the truck. I highly recommend anyone get this system.

Another big thank you to the mechanics at Canadian Forces Base Suffield for keeping me on the straight and narrow.

Special Thanks to Glen Bowers for all his help and patience for educating me on how to do this modification correctly and safely. Another mechanic that took the time to teach this computer geek the right way to do mechanical work, a true teacher and instructor.

Tech article by TOFIC

7 Responses to “Hydroboost Brakes”

  1. hfdco4 Says:

    TOFIC, I am looking at a Hydroboost on a 1978 Lincoln. The only difference appears to be a metering block btween the Power Steering and Hydroboost unit. Was this in place on the Mecury that you removed your unit from? The Power Steering Pump has two pressure lines and one return line. I have a chance to get two complete units, but wanted to know what this other part was, and if I need it.

    Thanks Paul C.

  2. TOFIC Says:

    Paul the one in the mercury had the block also but I left it. all I took was the hboost unit the PS pump and the brackets. I also took the lines but they did not work. on the deal you have, a piece of sage “old fart” advice if some one is going to give you something, take it, you can always throw it away if you dont need it.

  3. Save-A-Horse Says:

    Do you have a proportional valve?

  4. TOFIC Says:

    NO and you do not need one technically
    Hydroboost is a boosting system for your brakes, not a braking system per SE.
    You usually only need a prop valve if you have 4 wheel discs and the system has in balance in the brakes. I have had to use a proportioning valve once of all the systems I have done. Strangely enough it was on a ASTRO system with ford disc’s. the HB overdrove the rear discs and I had to turn the rear discs down a bit.
    to answer your question, NO, I use the Broncos H block and it has worked well.

  5. El Kabong Says:

    What are the brakes like if the engine stalls? Are you able to still stop with added foot pressure as you would with a vacuum booster?

  6. bronco t Says:

    TOFIC, nice write up. I am just starting a HB install on my 77. What PS pump and MC did you use, or better yet, what would you use today in a stock 302

  7. 76'Baller Says:


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