[vidguy]

I finally got some time to work on the Firebird. I need to finish my hydroboost retrofit, put the new suspension on, the new brakes and get the car back down on wheels.. Then I am going to put the motor and tranny in. Here's a rundown on the modifications I did to get the booster in my 75 Formula as well as a few things I figured out that were an issue in my case anyhow.

I got the hydroboost with a flat bracket.
I had pulled my booster and master.
the assumed plan, based on what I had read and seen, was that I would mount the hydroboost on the new brackets and then extend the pedal rod. So I bought some real nice parts at a great price from Piratejack.net (nice people)


Nice parts. After looking at this arrangement, I realized the bracket was interfering with my steering column...bummer....


I figured I could grind it but, then I also noticed it would stick the hydroboost out quite far. I looked at it in the engine bay and saw that the new rear to front brake line I had bought and installed was not going to meet up with the combo valve if I mounted the hydro on the brackets due to the added length of the hydro compared to the original booster.


So next I wanted to compare the firewall to rod end length of the old booster with the new Hydroboost and rod.


Here is the Hydroboost pedal pin hole measured from the bracket:



Below is the old Booster rod measured from the bracket:


So I saw that the Hydroboost was a bit longer and the hole was a bit larger. The Hydroboost rod was about 1/2 inch longer.

I thought I'd proceed assuming I would first try to use the hydroboost's existing bracket, re-drilled, and see how I could adjust the mounting of the Hydroboost bracket away from the firewall to move the rod forward (effectively to make it 1/2 inch shorter as needed) I had originally "planned" on cutting the rod, rethreading it with a die and using the rod and connectors and rod end I bought from piratejack's to set the length. But now I wanted to see if I could make the unit work with less modification.

Looking at the mounting area I knew I was going to want to seal it, so I bought some foam as a sealer to seal the mounting. I bought some .365 I.D. plastic bushings at the hardware store, that slid over the 4 studs very tightly. I pushed them on and secured the foam.




I removed the snap-ring and the large nut from the Hydroboost. I put the unit facing up in a large vise and secured the bracket widthwise on it's edges in the jaws, and used a pipe wrench and hammer to knock the nut loose.

Then I used some thick art paper pressed against the stud ends to make a "pattern" that I then placed on the bracket and made marks.


You can see my paper template pieces there..I was going to be able to use the two bottom holes, but 1 more new holes were needed.

This is where I kinda got sloppy but it all worked out..
I drilled the holes to .420 ..the studs are .380, and checked the bracket fit. It was good. I mounted the bracket back on the hydroboost and checked the fit. I couldnt get the HB to push up flush against the firewall.. ???

I figured it was the angle the HB was entering the firewall was making the holes a bit too tight. So since I had gone through the trouble of remounting the bracket, nut and snap ring. I just took a uni bit and elongated the new holes I drilled.
I test fitted again and widened the holes a bit more...
A third test had me figuring it was something else..

I then took the time to remove the snap ring, nut and bracket again.. and when I test fitted the hydroboost aginst the firewall without the bracket on, it was clear the issue was the nut. It is not going to fit in the firewall hole.


So now my bracket was kinda ugly where I had elongated the holes but it was still gonna work.


So now I put the bracket back on and concentrated on putting the HB on. I was now thinking of a few things:
1) Backing it off the firewall enough to get the nut to not be interfering with the firewall
2) Getting the angle of the rod as straight as I could in-line with the pin on the brake pedal
3) Get the length of the rod hole to match up with the pin on the brake pedal
4) Checking the diameter of the rod hole and pin.

I bought some 15 mm nuts as the studs on my 75 are metric using 15 mm bolts.


I threaded those nuts on all the way down then tried a few test fits of the HB against them.
After a number of tests I ended up with the nuts being threaded about .800 from the end of the upper studs, and about .650 from the end of the bottom studs.


This gave me an excellent straight rod and amazingly the length was dead on. But the hole was too large on the rod..
So now I was back to thinking I'd use the rod end I bought. But when I tried to test fit it it, the hole was too small, and it was too thick.. to get the clip back on the pin.

I figured I at least see if I could get it to work. So I ground it down to the same thickness as the original rod end. and got it to slide on after some more grinding to get it to not interfere on the pedal.

But I really didn't want to cut my rod if I didnt have to I figured there was a way to bush the hole..

I took the HB to the Hardware store and found a hard plastic bushing that was .750 diameter and .385 I.D.
It was a bit too thick and the I.D. was a bit too small. But it fit perfectly tight in the rod hole.

So i took that bushing and drilled it to fit the pedal pin. I matched a drill bit to the original booster rod hole:


And pushed the bushing into the HB rod hole and then drilled it with that bit:


And sanded it flatter to match the thickness of the rod.

Here it is after I modified it compared to the new rod end I had ground and drilled:



And here it is installed in the Hydroboost rod


I then mounted the HB and the length, angle and fit of the rod is excellent! (I'll take pics of the interior pedal fit and post them soon)

After I looked at the mounting I figured I'd try to add a bit of extra stability to the stud mounting on the elongated holes I had made.. I devised a means of bending a washer to sit flat on the flat part of the bracket and tilt up on the inside formed part of the bracket:


I then put lock washers above those. Everything was super tight but I didn't like the angle.. So I then modified that tactic to "Cut" the washers" so they only sit on the flat part of the bracket covering the elongated holes.



I then also put metric sized flat washers behind the bracket on top of the "standoff nuts" turning the nuts in to compensate for the thickness of the washers. In my case it was about .060.

Again putting lock washers above that. I then managed to tighten everything down nicely with a little holding of the cut washers in place with a pair of pliers.. The grip looked good.
So I mounted my master cylinder as a test. I was a bit concerned about teh height of the master.. I couldn't recall if my original sat that high. So I temporarily removed the HB and put my old booster on with the Master cylinder.. It looked about the same.. I took the original off, and remounted the HB and master. I ran a String across the hood to get a sense of a relative location..







And compared that tot he underside of my hood that I have hanging on the fence. Kinda a bad shot but I could see there was clearance at that location which I measured from the rear of the hood.


So that's as far as I got. I wanted to share this info since it is a popular mod. More to come.

[Ollie]

Thanks for the update on Your Hydro boost install. Using the foam pad as a firewall seal is a good idea, I was wondering what to use as the boot is no longer available from GM.
I do have a couple of questions. What is the vertical distance between the fire wall bolts and what is the diameter of the booster rod hole?

Sorry for the extra hassle You had with the mounting brackets but those are the incorrect brackets. You have the 651A, not the 650. See attached photos. The 650 bracket is the top and left.

[vidguy]

Ollie-
That other bracket does look smaller. As it turned out not using the brackets worked perfectly as I didn't have to change the rod and my fore/aft location in relation to my brake line was very close.

Piratejack does have nice cheap stuff.
If you look at my pics you'll see one that has the distance marked for drilling center to center on the bracket.
I beleive the booster rod hole on MY Hydroboost was approximately .750. The original (the pin on the pedal) was about .405, (I think that was the drill bit I used to drill my bushing). I cant say if other hydoboosts would have the same rod.

The end eye piece I bought from Piratejack had an even smaller hole. I didnt measure it before I drilled it, but it was too small to fit over my pedal pin.

[Joel Koontz]

Vidguy, your living up to your handle. Great photos and explanation of your install.

Your install is similar to how I installed mine, but different, probably primarily due to the diference in vehicles (mine is 68 LeMmans) In my final (so far) install, I deliberately tilted my HB and MC by spacing the bottom of the HB plate out further than the top.

It looks like yours has significant tilt to it, and if I understand what you did, it looks like you have mounted it with the HB plate evenly spaced away from the firewall.

Is this correct? If so, your firewall apparently already has tilt "built into it".

Does your brake pedal have 2 holes for the pushrod to attach to? And if so, which one did you use?

It appears you are using the original MC. If so, I suspect you will find the brakes are more powerful than you will like and you may want to get a MC with a larger bore.

I used the MC from the 92 Astro (1 1/4" bore) When I tilted my HB, it was putting the reservoir close to the hood (but probably would have cleared) and IMO "it did not look right". I bought a reservoir off of a 96 Caprice. I was able to install it on the 92 Astro MC and IMO, it looks great, the top is very close to parallel with the ground.

Sorry, I'm not a Vidguy so I don't have any photos.

[Ollie]

If You look closely at photos 1,5,10, and 11 it appears the Astrvan plate is not flat. There is a tilt built into the plate.

[vidguy]

Joel-
I would really like to try a new low profile plastic master! That's something I need some advise with. Which should I try to buy? Do they all more or less fit as long as the mountings are the same? I had read that 78 was the year the master changed somehow.
Any help?
I bought a re manufactured original for this.

My plate had a slight tilt built into it. You can see the rounded area where I put the bent washer. That shape mounts the nut and held the booster tilited as compared to the stud hole plane of the bracket.

My firewall is pretty vertical, not real sure as its up on jacks not level. but that my impression. In your case you probobly ended up with the same slight downward tilt as I did.

This plate was designed to tilt downward towards the rear a bit if mounted flat with the accumulator on the drivers side. On my car it would tilt UP if you had the accumulator on the passenger side. I toyed with both mountings but felt the more stuff I could move away from my valve covers the better.

Aside from better brakes, 2 things Im hoping to deal with by installing the HB are, Valve Cover Clearance with my taller valve covers and no vacuum issues with a bigger cam I trying out.

So in my case I compensated for that to make it more vertical by having the lower nuts closer to the firewall by about 1/8". I kept checking this and the angle to the pedal pin till I got it real close.

The angle to my pedal rod isn't perfectly horizontal so some tilt worked well.

On my car there was only one pin / no second hole on the pedal. Likely since there was no manual brake option in 75?

Glad you like the photos!

[Socrates]

Ollie,

How'd you get the actuator rod out of the HB??? Does the new ball/socket rod just pop back in?

[Joel Koontz]

I did not realize your HB plate had tilt to it, but now that I have looked at the photos closer, I see that it does. My HB plate was flat, and I deliberately tilted it (front up) to get the rod to align with the lower hole in the brake pedal.

I think that MOST MCs will bolt up to HB, but there may be some that don't have the correct bolt spacing, and/or diameter may be too large. The main thing to be aware is the depth of the pushrod hole. As far as I know, there are 2 different styles, a deep and a shallow hole, pretty sure all HBs MCs have the shallow hole and I think they were typically used with power brakes.

[Ollie]

The Hydroboost unit I got did not have a push rod installed, I have not attempted to install one as I dont know if I could get it back out.. My plan is to remove the vacuum boost and measure the rod lenght from the mounting bracket to the pin hole, like vidguy did and set up the hydroboost rod to the same length. With the three ball end rods and the threaded rod I got from Pirate Jack I should not have any trouble getting the rod to the correct length. If all else fails I will cut and thread the vacuum boost rod and use that.

[GS470]

Great info here. I'm starting to size up my situation (Astro HB w/ flat plate into a '72 LeMans) and was planning on using the 650 brackets (from Pirate Jack) to mount it. I got my old booster pulled off now and tried holding things in place approximately where they'll go and got a little concerned about hood clearance. The HB is quite a bit longer and pushes the MC up there. I think I'll still order the 650s and just be prepared to modify them if I need to.

Ollie - What kind of car are you installing in? It would be great to see how things fit with the 650 brackets. Sounds like you haven't started your install yet? Or did I miss something?

[Ollie]

The Hydroboost is going on a 79 TA. No I have not started to install the Hydroboost yet. Compairing Viguy's # 5 photo and every thing I have been able to measure and eyeball the 650 brackes are identcal to the brackes on his vacuum booster. I dont know, yet about the tilt angle on a 79 TA I think it needs some. If it sets level it appears that master cylinder and the break lines will interfear with the inner fender panel.
In these photos it appears the brackes are gaped slighty away from the flat hydroboost plate. This is because the shoulder of the studs are slightly longer than the thickness of the plate. I added washers to take up the extre length. The brackes now sit flat against the plate.

[vidguy]

Joel-
Is this the 92 Astro master you used? (Pictured on the right) Dorman M39961
And then you put one of the single piece slanted reservoirs on? Like on the Left?
Also were the fittings on the Master from the Astro Metric?? Or SAE.

[67cruiser]

vIDGUY!! SUPER JOB ON THE PICTURES AND EXPLANATION!! A+A+

[GS470]

Originally Posted by Ollie

The Hydroboost is going on a 79 TA. No I have not started to install the Hydroboost yet. Compairing Viguy's # 5 photo and every thing I have been able to measure and eyeball the 650 brackes are identcal to the brackes on his vacuum booster. I dont know, yet about the tilt angle on a 79 TA I think it needs some. If it sets level it appears that master cylinder and the break lines will interfear with the inner fender panel.
In these photos it appears the brackes are gaped slighty away from the flat hydroboost plate. This is because the shoulder of the studs are slightly longer than the thickness of the plate. I added washers to take up the extre length. The brackes now sit flat against the plate.

Thanks for the info, Ollie.

[Joel Koontz]

Vidguy, that does LOOK LIKE the Astro MC that I used, and the reservoir that I used.

I took the MC off the Astro with the HB when I got it.

I ordered the reservoir, Fenco R26212, from AutoZone. It came with cap and gasket, but not grommets, had to reuse grommets from MC.

NOTE: I had to pull REALLY hard on the Astro reservoir, to get it off of the MC. I was pulling so hard I was afraid I might break it, getting it off, but it finally came without breaking.

I reused my original brake lines so I assume the fittings are SAE.

[vidguy]

Joel - Thanks for the info!
I'll order that Master today. I'm anxious to try that.
67 Thanks!
I'll take a few more this evening.

[vidguy]

Well I got the new 92 Astro master cylinder. $30.00 shipped from a dealer on Ebay.
I have a few shots here. I checked the fit on the Hydroboost. Mainly to see how the Actuating Rod fit on this new master vs. my stock iron master. I put Dykem on the the rod end then installed both masters. The old iron master had a very small amount of free space. probably .070 - .100 thousandth. No transfer.
The new master actually touched the rod and had about .040 thousandth before it pulled flat. I based that measurement on how thick of a washer on the studs had to be to allow me to mount it without any dykem transfer.
What is preferable?

I also compared the sizes of the 2 masters.


You can see the new master is about the same height at the "Rear most" of the 2 reservoirs.


I was more concerned about the forward part of the old master as it tilted up towards the hood. On the new master, that resevoir is much smaller so I dont anticipate any issue.
I also compared the bore sizes. On the old master it measured right about 1.100



On the new master it measured 1.240 there abouts. So that larger bore is supposed to soften the response a tad?



I also have a shot of the rod after I bushed it and mounted the unit standing off the appropriate distance from the firewall..




I used the rod that came with the Hydroboost. As you can see if fit perfectly. You can see the combo Valve I got from Pirate Jack.


The line I got from Classic Industries. I was down visiting my son at college a few months back so I took time to go by their place in Huntington Beach. That line fit perfectly.

I also made a lot of other progress on the "Might as Well" driveway resto, that started after pulling the knocking motor, of which the Hydroboost install is a major part.

I also put back in my new heater core....... and the Refinished AC box


new fan. I cleaned my evaporator and put new sealant all around it.




I repainted the Front Bumper too. Over the last few weekends, Snd filler, primer then paint primer paint. Seems to look pretty good.

I cleaned and repainted the frame in the engine bay some.

It was pretty clean already having been a mid level resto when I bought it.

The firewall is really clean so I didn't touch that.



I also put in a new front to rear brake line.



I had also taken the 2 fuel vapor and return lines off and steel wooled them and then dusted them with Cast Iron and lacquer.




I bought 2 new clip sets from Inline Tube. I am making the 2 brake lines to the front calipers. I'm using my originals as a pattern.

I also replaced the body mounts.





I installed the Energy Suspension Motor Mount mod,


As well as my control arms with all new bushings (Original Rubber style here). I mocked them up without the springs just to get everything setup. I may cut my springs yet. I don't know. My car sat higher then I liked..
When I took out the old body mounts off they had a number of flat washers on them and the radiator core support bushings were about 3/4 inch taller then the Energy Suspension set I put in.



So Im thinking I already lowered the body about 1 inch..

That's it thanks!

[Joel Koontz]

James, it looks like things are coming along pretty well.

Are you going to run the reservoir that came with the Astro MC or swap to the slanted one? I am amazed at tiny capacity of the front section of the Astro MC, it only holds a few ounces, and I would be hesitant to use it, even if I liked the appearance (which I don't) I would be afraid that losing just a few ounces of fluid would result in no brakes.

In the picture with this caption,
"I cleaned and repainted the frame in the engine bay some"
above it, it looks like the plate and MC are tilted somewhat. My MC was tilted some when I initally installed and I was able to level it by turning it slightly. The "alignment nub" keeps it from turning a lot, but there is still a few degrees of rotation that can be had to "fine tune" it. My out of level condition was not very obvious, UNTIL I put fluid in the MC reservoir. It was then very apparent. If I see, what I think I see in the photo, just rotating the MC may not work for you as it appears that the plate is also tilted. If so, you will need to do some modifications to the plate if you want it to be level.

[vidguy]

Joel, I think I'm OK with the tilt. All of the masters/ boosters on my old GM cars have been tilted. The original is at a similar angle as well as my GTO.
We'll wait on that one.. I wonder what the capacity of the slanted one you have is in the front. Maybe we can measure them. I'll check mine. you check yours?
I kinda like the plastic modern reservoirs on this.

I'm not sure about the fluid amount there but I'm thinking that with the minimal travel of the Hydroboost system that not much fluid is required?
And if I lose fluid the diagonal braking setup comes into play, I think... I hope i DONT lost fluid, havent yet...

[Joel Koontz]

In case I wasn't clear, I'm not talking about the front up tilt, it is tilt (passenger side higher than the drivers side) as viewed from the front of the car that I am referring to in this question. As I said, if it is tilted, it will become more apparent when you put fluid in the reservoir and see the fluid line.

I think both chambers on my slanted reservoir have about the same capacity and probably about the same as the capacity as the rear chamber on the Astro MC.

I also prefer the appearance of the aluminum/plastic MCs. They weigh about 1/2 as much and from what I have read, they last a lot longer(usually forever)