Hydro Boost Brakes

This is the original system the Scout had, vacuum booster, disc front drum rear master cylinder and proportioning valve along with the added Wilwood unit to compensate for the aftermarket rear disc brakes.	Here is the hydro boost unit getting some paint.  The small cylinder wrapped in blue tape is the gas pressured reservoir that will give you that extra power assist should the engine stall.	All painted and with the custom bracket attached.	Notice this key slot and the threads?  The key slot keeps the unit from rotating while the threads are for a large nut that holds the unit to the bracket that attaches to the firewall.

I also pulled all the hoses, proportioning valve, original mounting bracket and two return steering pump reservoir.  Hydro boost brake systems require two returns to the power steering reservoir, one from the hydro boost unit itself and the other from the power steering box as normal.  An easy and inexpensive way to do this is to just splice a t-fitting into the return line before the reservoir, but since the Scouts use a standard GM style steering pump, I decided to opt for the fancy solution and use a  two return reservoir.  

For proper front to rear brake biasing when going from a disc front and drum rear to 4 wheel disc brakes you need to do one of the following, add an adjustable proportioning valve or pull a stock proportioning valve from a car that was factory equipped with four wheel disc brakes.  Originally I added the adjustable type, but when I found the hydro boost system I decided to make sure I pulled the valve along with it to help clean up the brake line plumbing and under hood aesthetics a bit.  Just a quick note, you cannot buy a proportioning valve from almost all the major chain parts stores, not sure why, but you can't.  Companies such as Stainless Steel Brakes and Inline Tube does sell them however, they are pretty pricey.

I cleaned up the proportioning valve from the '76 Eldorado and painted it with a cast gray paint.  This valve is already set up for front and rear disc brakes so it will eliminate the need for an adjustable aftermarket unit.	It is easier to visualize the two return reservoir than to explain it.  Two low pressure return hoses, one from the hydro boost unit and one from the steering box, attach to the two 3/8" nipples.	Nothing fancy here, just the inside of the reservoir to show how the lines come in.	All nice and painted with 500 degree semi-gloss black paint, same as the rest of the engine type accessories.  Reservoir is a little dinged up and has been brazed in places, price you pay for being cheap and getting it from the junk yard I guess.

The stock bracket that came with the hydro boost almost would bolt into place. It had four studs pressed into it that I had to punch out to give it a trial fitting and the top two holes lined up perfectly with the original Scout holes.  Only problems were that I would have to drill two new holes a little lower as the lower holes did not line up, no biggie, and the master cylinder and boost unit now sat at about a 15 degree angle downwards.  I had seen some people that just used it as is as the master cylinder has rather large reservoirs, but that didn't seem like the ideal solution to me.  In order to get the hydro boost unit to fit the Scout and fit it right, I was going to have to make a custom bracket.  Jim Weed has a great hydro boost information web page and I also did some searching around the net to see what other people have done.  

I used the original bracket as a template for overall dimensions.  I just happen to have a large sheet of 1/4" steel plate lying around (who doesn't right?) and used my plasma cutter to cut out the square bracket.  If you don't have a plasma cutter, a cut off wheel, grinder, cutting torch, sawzall or similar will all do the job just as well.  I them measured the bolt holes in the firewall and drilled four 3/8" holes in the bracket to match.  I then bolted the bracket to the firewall nice and tight and scribed the hole where the nose and brake rod portion of the hydro boost unit must penetrate the firewall.  I took it back to my workbench and used a punch to mark the center.  I then had to make a run to Lowe's.  The hole in the plate needed to be 1 5/8" and I didn't have that size of hole saw.  I thought about using the plasma cutter but once again this is my brakes and I wanted it to be perfect with as little slop as I could.  With the bracket made I bolted everything up and gave it a try, wouldn't fit.  The nut was too big to go through the stock firewall hole and the bracket wouldn't fit flush.  I re-read Jim Weed's information and he cut a bigger hole in the firewall to accommodate the nut.  I measured it and a 2 1/2" hole saw was in order, back to Lowe's.  

I tried and I tried to cut that danged hole but just couldn't do it.  Time for plan B.  I went and cut another bracket, the same size as the one I already made and transferred all the bolt holes to it as well.  In this one I used the 2 1/2" hole saw to cut the big hole.  I bolted everything up and slipped on the new bracket, worked perfect.  I then tried to bolt it to the firewall but somehow the bolts did not line up with the holes anymore.  Plan C, drill out the 3/8" holes in the second spacer bracket to 1/2" and retry - success.  Now paint and put it all together.

I suppose if you look closely you can see the angle of the stock Eldorado bracket.  You will also notice the key nubbin that lines up the hydro boost unit correctly and keeps it from rotating.	The mounting bracket, the spacer bracket (before the 1/2" holes) and the mounting nut.  I used my welder to put that key nubbin on the mounting bracket.	You can see how the nut fits into the 2 1/2" hole of the spacer bracket.  The nut is a little thicker than the 1/4" plate but it didn't matter too much once it was all bolted up.	Here is the mounting bracket installed on the hydro boost unit.  If you look closely you can see a snap ring groove at the edge of the nut.  This helps keep the nut from backing off, but I added some Lock-tite to the threads as well.

When I found the Eldorado and looked under the hood, the master cylinder didn't have a cap on it and was filled with water and rust.  I thought about cleaning it up and getting a rebuild kit but went over to Autozone and asked about a replacement, they had a rebuilt MC for $21 including the core price of $7, so I bought it.  I figure once again, better safe than sorry, so I bought it and brought it home.  It has two big equally sized reservoirs to provide the increase in volume necessary for disc brakes.

I also managed to salvage the drip pan that mounted to the original Eldorado bracket sitting under the hydro boost unit.  To mount it, I drilled two 5/16" holes in the new bracket and cut the heads off of some 1" by 5/16" bolts.  I then welded the bolt thread part into the holes in drilled the mounting bracket and that was that.  I figure the drip pan might be a useful feature to have if everything goes to leaking on me, but hopefully I won't have to use it.

While I was grabbing parts in the junkyard, I also grabbed all the high pressure hoses.  They looked to be in good condition and I brought them home and cleaned the hard piping on the wire wheel and the hoses cleaned up with some Gojo and Armorall.  It looks like I might have to put some bends into the pipe to get the hoses to fit better, but they fit  into the steering box and pump.

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This is the under bracket / drip pan prior to paint.	Not too bad for $14.  This particular master cylinder appears on a large number of GM vehicles so they are pretty plentiful and as I mentioned, relatively cheap.

  I will post some more pictures of the finished installation once I get it all together ... so stay tuned.