The Hollister Road Company


Firewall Mount Hydraboost and swing pedal install



This conversion is on a 58 3100 chevy but is generic enough to be done on most any truck either placed on the firewall or underneth on the frame rail. One of the reasons to use a Hydroboost unit is to overcome a low vacuum condition and with some of the radical cams running on the street today low vacuum is a common problem. Some rodders have used canisters to store vacuum and vacuum assist pumps to over come this problem but GM has one available solution on most all it late model trucks, Hydroboost it runs off the power steering pump and creates almost twice the braking power that a vacuum assisted brake system will apply to the wheels. These units are not without some issues but they are minimal compared to the early 80's iteration in the diesel powered cars and trucks. Leaks and noises are the most common complaint but these can be reduced or eliminated buy purchasing a new or quality rebuilt unit.

I decided to use a late model hydro-boost brake system on my truck and in my research I found that a 2001 Chevy Silverado 1500 with 4 wheel disc had hydro-boost and since I had 4 wheel discs this seemed like a good match. I had previously installed 1975 C10 front end with discs and 89 Explorer rear disc kit.

The booster unit is an A1-Cardone # 52-7359 this comes with a diagram to connect the hoses correctly. Brake Master Cylinder is Raybestos # MC390542 it’s new and comes complete with reservoir and cap, don’t get the MC390541 its for a vacuum booster. Don’t ask me the difference I didn’t see it but Raybestos says the 542 is the one. You will need to get the push rod, pushrod spring and the spring retainer that goes between the master and the booster does not come with a rebuilt the unit or at least not my Cardone unit. I got a complete unit from a junk yard with master for $75.00 and took out the push rod, spring and retainer and used the junk yard unit for my $50 core charge.

The other items are hoses for the P/S lines going to the booster unit and P/S unit. For pump to booster hose you can use an Edelman 92082 if you don't want the expense of AN type fittings and lines. Russell or Aeroquip –AN P/S fittings, -6AN x M16x1.5 O-ring fitting for the pressure-out side of the booster going to the rack, -6AN M18x1.5 fits the pressure-in side of the booster. I ended up using some Aeroquip AN -6 to metric adapters M18x1.5 and two M16x1.5 with O-rings which were made of steel rather than aluminum. The Aeroquip fittings also had a taper on the end to help keep the O ring in place which the Russell ones didn't. This may not be a problem for some but the O-ring on the Russell kept getting stuck in the bore or falling out completely when I was test fitting all this. The advantage to the Russell is it was half the cost of Aeroquip. I also used -6AN fittings and hose to plumb the pressure side of the install.


We need to install a Heidt’s adjustable P/S valve (PS-114) so we can have full pressure to the GM booster but reduced pressure to the Ford rackwhich uses 600-800 PSI. If we run the full 1200 - 1500 PSI from the GM pump to the Ford rack it will eventually blow out the seals and leak it would also be very touchy steering at higher speeds, so we put the Heidt's valve in the lines to reroute some of the full pressure back to the return side of the system lowering the pressure before it gets to the rack. If you’re not using a Ford rack you don’t need the Heitd’s pressure valve. You go straight to the P/S box from the pressure-out on the booster and straight to the return on the P/S pump. This modification on an older P/S equipped car may require that you use a new P/S pump. Some of the older pumps didn’t put out the needed pressure. You may aslo create leaks in the old P/S Box so its best to use rebuilt or new parts.

valveWe need a proportioning valve for 4 wheel discs or an adjustable. I used a Wilwood adjustable valve with an LBS (Lock Resistant Brake) valve from Larsen Racing it helps keep the fat tires on the back from locking up and spinning you around on wet or damp pavement.

You’ll need some metric nuts M10x1.5 to bolt on the master cylinder and bolt the booster to the firewall. I used some fender washers on the inside for the booster to firewall nuts.

I used a 3/16" copper/nickel alloy brake line that is D.O.T approved and very easy to work with, you honestly can’t screw up a flare with this stuff unless you forget to put the nut on first. It flares very well, it bends nicely without kinking and you can give it a polish to a golden color. is the US supplier. It is a little more expensive but the advantages make up for the cost. I think I've wrecked more dollars worth of steel tube trying to flare it than it cost for the roll copper/nickle tube. To straigthen out the coil you just find a flat surface like a counter hold or tack down the end and roll it out flat against the counter.

At the same time I ’m doing the booster I am also fabricating a brake pedal. Below is the boost unit and as you can see the mounting plate is heavy enough to use without modifying it for our installation.


The output pushrod, retainer and spring is for some reason is not available through GM, in fact if you go looking for it they will undoubtedly tell you that either Gm has not used Hydroboost since the early nineties or that they never put it in a 1500 Sierra. They may even ask for a vin # because they can’t do anything without a vin #. Call the junk yards and say “you gata hydraboost for a 2000 silveraada” they say “yup” you say “ow much” they say “75” you say “yank it I’ll be over”. Now that’s a transaction, nobody wasted time and we both got what we wanted. I got the spring retainer, spring and rod out of the junk booster. I’m sending the old booster back for a $50 core charge so I really paid $25 for a used master and the rod and spring assembly.

The spring and rod are an important part in the system; the spring puts tension on the booster piston so it releases the pressure on the rod and doesn’t stay engaged to the master and drag the brakes when you let off the brakes. The disc on the inner end keeps the rod centered in the booster rear cup and the retainer of course keeps the spring in but also centers the rod to line up with the master cylinder indent. If the rod were to drop out on either end it could cause your brakes to apply and not release in a panic stop of just plain fail. So if you’re fabricating these pieces remember these dimensions are for a 2001 Silverado 1500 with 4 wheel disc brakes, the Hydroboost and master cylinder are for the same truck. I have no idea if the rod and spring is the same for any other year or model truck. What I have found is that the rod should be 0.020" shorter than he distance between the two cups. If its longer it puts a little preload on the master and may create a drag on the brakes.

Rod diameter 0.34” with a length of 3.16” it appears to be as hard as a grade 8 bolt. The rear spring seat disc is .970” diameter with a thickness of .040” and placed .25” from the inner end and it is made of plastic. The spring is 4” long and .945 diameter. The wire thickness is .073. It feels like a 20 – 25 Lbs. spring tension.

I lined up the mounting point between the brackets on the dash support and started to drill the bolt holes in the firewall and then used a cutter for the center hole. I used the fender washers and nuts to secure it to the firewall. You need to have it close to center of the dash support and far enough away from the engine.        



Swing Pedal


The Dash support bracket needs to have some way of hanging the pedal. So I cut out 2 side panels so the pedal has a mount point. I tacked in the plates and drilled a hole for the pedal pivot. I temporarily used a piece of copper tube to hang the pedal. You may have to fabricate a pedal or you could get lucky and just use one that is close to the dimensions you need. Because I have a recessed firewall I had to make some bends to mine and decided to fabricate one complete. The pedal is from a 77 and it gives me a rough idea of where the new pedal has to go and what bends I need to put into it. We also need to put in some bracing because as it’s just to flimsy for the stresses of a brake pedal.    



I ordered some steel from the list is below.

1018 - FLAT BAR COLD FINISH 3/8" x 1-3/4" CF FLAT
4130 - ALLOY TUBE ROUND 3/4" OD x .1875" WALL
A36 - HOT ROLL SHEET / PLATE 0.1875" A36 Hot Roll Plate
A513 - TYPE 5 STEEL TUBE DOM 1.25" x 0.188" Wall DOM

The following is the pivot and swing arm being made. I drilled out the outer shaft to accept the brass bushing and then drilled out the brass bushing to accept the center rod then tapped the rod so it will bolt in the dash support.



The outer shaft welded and hung for mockup. Where it’s close to the dash support I needed to put a bend. The Hydroboost only has a 3” through so I don’t need to worry about bottoming out against the firewall and running out of brake pedal. Next on the list to do is to make a drop down arm on the pivot to connect the booster push rod. You will have to place it according to your dimensions on your installation.

While I'm waiting on the rest of the P/S fittings and hoses to arrive I braced the dash support and its as done as it get before I install it. It just needs to be wire brushed, smoothed out and painted. I put some bends in the back brace to make it more ridged and the right side brace is very close to the pedal arm so I may have to give the pedal arm a bend. Once in the new cab I will weld on the arm for the booster rod. One note of interest is that after the back bracing is welded in you either have to remove the booster or the light switch and choke cable to be able to swing pedal and bracket in and out.


Just some notes I researched while waiting on parts. The rear brake line port on master cylinders are not the same through a maker or style, some will have different size thread and some have the same size threads. Some have rear port to the rear brakes and some have front port to the rear brakes. I must have searched 400 sites before I saw a pattern. The easiest way to tell visually is the size of the bowls. If it’s a Disc/Drum system the larger bowl goes to the front Disc and in the event of same size bowls (vette style) the rear brake port may have a residual valve in it and a larger brake line.The master cylinder ports on most late model cylinders have a built-in residual valve in the drum side. Early drum/drum had one in each port. It needs to be removed on a Disc/Disc system. Disc/Disc corvette master cylinder is rear port to rear brakes. It seems that falls true for all GM disc/disc systems but I can't say for sure.

On the drum side there needs to be a residual pressure on the wheel cylinder pistons so they don’t return completely as you let off the pedal and sucking the pistons back into the wheel cylinder bores away from the shoe push rods. This would make for a low or slow responding brake application because it has to push the wheel cylinders piston out to contact the push rods and then engage the drum and then build line pressure to engage the front discs. The residual valve keeps the wheel cylinder pistons extended and in contact with the push rods to the point that 10 psi of back pressure is needed to retract them and they will not be sucked back in when letting off the brakes as the fluid moves backward into the line. Disc/Disc does not have this problem because the resistance of the big o-ring against the caliper piston is greater than the vacuum created by letting off the pedal this O ring helps pull back the piston and the disc not being perfectly true actually helps push the piston back in as well. There is one exception and that is with GM low drag calipers which retract further than normal. They were on early 80's cars and possibly some trucks.So if you have a chronic low pedal it maybe that you have those low drag calipers.



The pressure circuit goes from the pump high pressure outlet to the Hydroboost high pressure inlet which is next to the gas cylinder unit from there it comes out of the high pressure oulet to the Heidt's pressure bypass which is the rear port on the left side and to a return line that also goes to the bypass valve which is a smaller push on hose type nipple.. It comes out of the pressure side of the bypass valve and goes to the rack and the return comes out of the bypass to the "T" connector then to the Power steering cooler and to the reservior return. The rack return also goes to the"T" return. I put a gage into the rack side of the bypass so I can dial down the pressure to the right PSI and not blow out the rack seals. This gage can also be used to test brake pressure when they are applied. It came with several adapters for brake cylinders and disc's and is a 3500 PSI gage.

You can use the pump to booster line for a 2001 Silverado Edelman 92082 it will fit perfectly. You'll have to tweak the pump end a bit but not very much at all. This is what the fitting end looks like. It’s called a "standard O-ring Flare".



I needed some line separators for the P/S hoses and the prices for the ones I wanted were $25 each and I wanted 4. I had some aluminum stock and this is the result. $2.00 in metal and 3 hrs time. I drilled the sizes I needed and cross drilled and tapped a 10-32 hole for a stainless steel screw to hold the halves together, and then cut each off the stock, then cut them down the center. I used a mill file to shape them and sand paper to smooth the out. Once they are polished on the buffer they will look just like the ones I wanted. If you make these just remember to drill a larger hole in the top half so the screw will slide in and screw into the bottom. You could save some work by not cutting the center for the screw out and just counter sink it for an allen head screw


 I decided to change the fitting on the return line from the booster unit from the straight up nipple to n -6 AN fitting. For those who didn't know JIC 37 degree fittings is the equivalent to -AN 37 degree fitting flare. JIC also has a 45 degree flare so be carefull not to get the wrong ones. A BOSS fitting is one that has an O ring boss with a nut that tightens the fitting I used it on the return from the unit to the reservoir. It is picture #4 above which is a BOSS on one end and JIC on the other with a -6AN adaptor. One other point to remember is that you have to torque -AN fittings or they will leak. To tight is as bad as to loose, to loose is obvious why it will leak but to tight will distort the seats. Below is a general chart. There are different torques for steel and aluminum below is for steel. -AN fittings are measured in 1/16 increments. -6AN is 6/16" and -4AN is 4/16" and a  -20AN is 20/16" or 1-1/4”. Most -AN hose and fittings are measured by ID, -8AN is 1/2" hose.

Teflon lined Stainless Steel hose seems to be measured by OD so a -6AN, Stainless Steel Teflon lined hose is actually 5/16" ID hose and a 3/8" OD so remember to get hose ends for Teflon if your using Teflon lined Stainless Steel P/S hoses. These Teflon hose end assemblies are tightened as per MFG reccomendation and each is different. You should always lubricate the threads with something like oil or Russells thread sealer.

Dash Size
1.5 - 2.0
0.75 - 1.0
0.75 - 1.0
0.5 - 0.75

This chart is for Steel AN or JIC fittings


1. Finger tighten the hose end on the fitting until it bottoms on the seat.

2. Mark a line on the flat of the nut down to and on to the fitting.

3. Trun the nut the number of flats as stated below.




Fitting Size
Max Torque in Ft./lbs.


This chart is for aluminum AN or JIC fittings.






Part numbers and where you can get them are as follows:


Male JIC x Male BOSS 90 Degree adaptor
6801-04-02-FG - $4.80 this is the adaptor that screws into the return line threads in the booster unit. It needs to be drilled out to the size of the stock straight nipple. I suggest you buy 2 the drill is most likely to break and you will have to dig it out if you can. It’s a forged fitting so use a good bit. If you don't drill it out it may create back pressure and make you system unstable. Other option are a pushon type fitting.

Female JIC x Male JIC adaptor 2406-04-06 $2.45 this adaptor make the above fitting into a -6 AN fitting so you can run the -6 hose and fittings back to your reservoir.

090-6B Brass ferrule $2.70 each. these are for the reusable Teflon 90 series fittings -6 AN
20090-6 -6 AN Nut for the -6AN line $4.87 Steel.

06-SS $2.55 /ft 5/16 ID 3/8 OD Teflon lined stainless hose. This hose is a bargain same hose as Jegs and Summit at 1/3 the cost.

Various Vendors

Russell performance

620411 Endura hose end 45 degree -6 hose for Teflon.

648060 -6 to M16 x 1.5 w/O ring This is the adapter that goes into the pressure side near the return on the booster.

648080 -6 to M18 x 1.5 w/ O ring This goes on the pressure side coming from the pump on the right side of the unit

Aeroquip - for Teflon hose - steel fittings

FCM2608 -6 AN to metric for the P/S pump on metric pumps it has a better o ring retainer that the Russell and is steel not aluminum.

FCM1122 -6 AN 90 degree steel swivel.

FCM1103 -6 AN straight steel swivel.

FCM2521 -6 AN to 3/8 pipe, steel

FCM2517 -6 AN to 1/4" pipe, steel


For those who have asked about making the rod for a different year master. When the rod is seated and is the correct length, the master mounting flange will not be flush with the Booster unit flange when not bolted up. The master will sit against the rod, when not bolted in place, and leave a gap of approximately 0.065" which will close up when you tighten the nuts. This should take a lot of the guess work out of measuring the parts and trying to see if it’s the right length. Polish up the ends of the new rod so it doesn't gall the rod cups on each end. Picture below is of my boost unit with a used matching master of the same year and model showing the gap.

You do need to have all the original parts, except the rod, so it seats properly into the unit and the retainer centers the front of the rod correctly. If you can't get the plastic disc off the rear of the old rod or it breaks. You need to tack weld a washer of the same dimensions in its place on the new rod. You still need the spring and retainer. The retainer when laid on a flat surface looks either like a spider or an upside down spider. It has all the legs bent in the same direction. To remove it from the unit gently grab a leg with some needle nose pliers on one side and hold it, Then push inward on the opposite side, then with a little twist pull the retainer out with the pliers. It installs by just pushing it into place in the bore groove with the bent legs pointing outward toward the master cylinder. If you don’t want a firewall mount, this setup will mount just like a frame mount master and vacuum booster same parts as the firewall mount just longer lines and of course the frame mount and pedal. You would need to make a bracket/plate for the booster unit to attach to the frame mount but that’s the easy part.

Hope this helps. If you find any thing here thats not right or want to add what you have done on you install contact me at