hydroboost and Power Steering Conversion 1955 Chevy install

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This is based on research around the web for two months, including posts from ChevyNut and Rick L. Please do not hesitate to add to this post or correct me if I seem to be headed down a wrong path. I will summarize each post at end with cost and part number to help anyone who is going to try and attempt this.

So I am starting a thread on a Hydroboost conversion in the 55 wagon with zero offset disc brakes, with a CPP 500 steering box and a shortened steering column. I will post plenty of pics and include part numbers so that anyone reading this thread and wishing to duplicate the install will know what the part is and where to get it.

I think this thread will have three pieces; Hydro boost install, followed by the CPP box, then the shortened column, wrapping up with the disc brake install. Normally I would deal with a complete system first, but the car is sitting on the lift and isnt in the way. I think the sequence install is basically correct to make it easier to access things.

Currently the 55 Wagon has drum brakes with an after market booster, a 67 Chevelle drum/drum MC and a Wilwood combination/proportioning valve. It has stock power steering.

Here is a picture of the booster and the spacer at firewall. The spacer is going along with the booster

Attachment 10332

Part I - Hydroboost

Most recommendations from 55 Chevy people making this mod is 1995 Chevy Astro. The problem is that they are picked over in the bone yards and seem to be a premium online. I was looking used. You can buy remanufactured but they usually want a core so the cost gets high. If you go to a specialist expect to pay about $475. The Astro part usually is about $150. Then there are all of the others that fall in between. My read on this is that the casting is the same though I am not expert.

I can say:

Astro=Pontiac safari=Chevy pickup=Chevy Van. (I believe these are all interchangeable though weight might vary though I cant see why)

First recommendation is stay Chevy. I believe there are differences with the Fords. I chose a 90 Chevy Truck.

Note that the accumulator coloring is different. I believe gold is disc/drum, and blue disc/disc. Plain aluminum I think is early and would also be disc/drum.

Additonally, the hydroboost can be rotated 180 degrees.

Here is the specimen I am working with:

90s chevy truck/van

Attachment 10333

Pay attention to the mounting plate. It wont work with the 55 Chevy firewall. So it needs to be replaced. Chevynut makes the plate that fits and its reversable to allow you to flip the booster so the accumulator is on fender side rather than valve cover.

Here is CN's plate:

Attachment 10334

So to pull the mounting plate, there is a snap ring and a 1 7/8th retaining nut. The nut is serated on the back side and is torqued at 110 ft pounts. To remove the plate you can use the proper Kent-Moore J29192 socket, try and use a crow-foot, buy the socket that a guy sells on Ebay for $65 or make your own. The Kent Moore socket is pricey but I found one for $75. Making your own is a PIA in my opinion. Buy the socket.

Here is the stuff you need:

Attachment 10335

And the Kent-Moore Socket which is offset to clear the actuator rod.

Attachment 10336

See it attached here:

Attachment 10337

Here is the serrated nut removed:

Attachment 10338

Here is the hydroboost with plate removed and CN's plate installed resting on old plate:

Attachment 10339

This is all in mock up phase. Everything will be painted shortly.

The hydro will have new fitings installed to take -6an fittings. I dont have sizes yet except for the return. So I will get to that later.

You will need to cut the actuator rod and thread it at 3/8th fine thread. The rod is stepped, so you will cut on the big end. It comes in at slightly under 3/8ths diameter which makes it thread exactly how you will want. There is a rod adapter that we will get to shortly and that will screw on the rod and run to your pedal bracket.

Here is a measurement of the rod and you can see how it is stepped:

Attachment 10340

My next post we will measure and cut the rod, cut the threads, look at the adapter rod, and adapt to pedal.

Summary:

You need a Hydro-boost unit- Dont be scared, the world is broader than 95 astrovan-Cost $95 +/- (about a midpoint on Ebay)
You should choose a booster with a gold accumulator if you are running/disc drum
You need snap ring pliers and the Kent-Moore socket or Ebay repop - Cost $65-$150
You need CN's Plate - Cost $39.95 shipped (but be sure to check with him)

All for now.

I made a socket for that big nut using a piece of square tubing.

I think the color of the accumulator is an indicator of the internal piston size. Used to be a chart on the internet that said what was what but unfortunately I didn't copy it and it doesn't turn up in a search anymore. Doesn't have anything to do with disc/drum. Whatever brakes you use in back depends on what your front brakes are and you probably need a proportioning valve of some sort. What you need to do for rear brakes is get them proportionally correct for the fronts, and for the vehicle.

You can use a Ford or other hydroboost unit but both pushrods are going to be different. Pushrod to master cylinder is no big deal because you have to modify the Chevy ones anyway, at least the ones I've found.

Quote:

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Originally Posted by Rick_L

I made a socket for that big nut using a piece of square tubing.

I think the color of the accumulator is an indicator of the internal piston size. Used to be a chart on the internet that said what was what but unfortunately I didn't copy it and it doesn't turn up in a search anymore.

You can use a Ford or other hydroboost unit but both pushrods are going to be different. Pushrod to master cylinder is no big deal because you have to modify the Chevy ones anyway, at least the ones I've found.

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Makes sense on the accumulators. Didnt find a chart but did get PSI and supposed color to brake orientation. I read there was another difference between Ford and Chevy but it wasnt specific so I figure you eliminate that possible variable by staying with Chevy- but its good if they interchange because I see Ford boosters on local Craigslists often. Never Chevy for some reason.

Rick, excellent point on the MC. I forgot to mention there is a long rod versus short rod from the Hydroboost to the MC. I have a short rod which marries best with an MC with a dimpled piston (as I have been told). I have read but havent tested yet, that a 77-81 Corvette MC works best with the short rod hydro. I have one in my parts hoard and when I get to MC fitment will see what works. In all the packages sold by the parts specialists thats the MC. They dont discuss the rods though so it may be a mod.

When you check the books, the Corvette MC's were all disc/dic applications. However I checked with a hydroboost guy who said that the disc/disc MC will not have real impact on the boost set up. I expect that I can dial it back with the adjustable proportioning valve.

Also, if you buy a reman hydroboost, the rod/retainer/spring are often if not always missing. You can buy long/short replacements on Ebay that go for $45, if you know what you need and arent modifying.

I did quite a bit of internet searching trying to find the correct pushrod to use with my hydroboost and master cylinder. Looked for either dimensions or a source/part number for one. Nothing turned up (I'm sure some of the hydroboost specialists have them but at a cost, and none listed one online). I did find one article saying that the Astro pushrod ends up with preload when using a standard shallow cup GM master cylinder - which is something you DON'T want. What I ended up doing was figuring out a way to measure preload/clearance, then I used a corner rounding end mill bit in my lathe to cut the pushrod to length. I used a Wilwood master cylinder with a plug in it to emulate a shallow cup GM master cylinder (the plug comes with the Wilwood cylinder). There are commercial tools for measuring preload/clearance but my method didn't use them, it used measuring tools I already had. I did have to buy the corner rounding end mill, but at least it's a tool I might use for a totally unrelated project.

I would suggest to seek a smaller diameter and shorter profile power brake booster. Also one that can be mounted flush against the firewall with out a bracket. Yes it will take a lot more work but the real estate taken up will be far less. Not to speak of the better appearance. The one I obtained on line is also constructed of polished stainless. It is for disc/drums to suit my application. If I recall the price was in the $100 range.

But those tiny boosters aren't worth the trouble - they lack boost.

So I pulled the factory master cylinder and did a direct compare to the late 70's Corvette master cylinder. I used the depth gauge on my digital caliper to get the depth.

Here is the stock MC:

Attachment 10342

And the Corvette:

Attachment 10343

I took a depth reading and its just about 1/16th of an inch or a shade less. I believe the Corvette MC should work. That would correlate with the info I got from a hydroboost guy.

FYI the clearance spec on the pushrod needs to be 0.015"-0.030" or 1/64"-1/32".

Quote:

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Originally Posted by Rick_L

But those tiny boosters aren't worth the trouble - they lack boost.

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For not worth the trouble and lacks boost it sure is working great in my BBC ‘57. Brakes are super great. Just because one’s exposure to cheap units sucks does not mean they all do. Understand one needs to have an engine with some reasonable amount of vacuum. A full race camshaft is not gonna be reasonable vacuum for street application with this brake booster.