[GS470]

I'm looking into doing a hydroboost conversion and have been reading different threads. The Astro van hydroboost appears to be a good match for these cars, so that's what I'm probably going to look for.

I got a new master cylinder with my Baer brakes kit fairly recently. Can I use it with an Astro van hydroboost? If I need a different master cylinder, what do I need?

[Joel Koontz]

GS470 - Your MC will PROBABLY bolt up and function, but it is probably not the ideal bore size for using with HB. The Astro HB puts out much more pressure than a vacuum booster with the same size MC bore so you will probably want a larger bore MC.

From what I have read, a lot of people use a 1 1/8" bore MCs, but I am using the HB and MC from 92 Astro (1 1/4" bore) on my 68 and I would prefer for it to require more pedal pressure. If I could find one that fit for a reasonable price, I would get a MC with a bore larger than 1 1/4".

If I were to do it over again, I would consder using a late model Mustang HB and MC instead.

The Mustang HB puts out less pressure than the Astro HB, but still more than a typical vacuum booster unit and I think it may be a better option.

[GS470]

Thanks for the reply, Joel. I'm no expert in this area, so I've got a couple more questions.

So I assumed the bore diameter was more a function of physically getting things to match up. But in actuality, it impacts the braking characteristics. Interesting. So is there a particular MC that has the bore diameter larger than 1 1/4"? In other words, what vehicles run this size/type of MC? Because I have 4-wheel disc brakes, does that impact the MC choice?

If I went the Mustang HB and MC route, are you aware of any specific challenges mounting and hooking it up on a GM A-body?

[Socrates]

GS470,

Joel is referring to the bore inside the MC, the size of the internal piston(s) diameter, not the size of the MC mounting flange. Finding the perfect MC for your setup is going to be an exercise. Lots of trials and errors may be required here. You're not likely to find someone with the exact same car and brake setup as you, so, just like a woman, you should plan on trying out a few different MC's before settling on the "right one."

The mustang HB is an interesting option, though a road less traveled and will not be as simple as the "Astro Van HB" setup used by many in the GMC world. Checkout www.pro-touring.com for great info on these types of conversions for great, if not mind-numbing, reads.

I have to ask: Why is it that you think you need the HB setup? Are you using the suggested MC for your setup now from Baer and not happy with it? Manual brakes or vacuum booster currently? Do you not get enough vacuum to run the booster or not like the feel of manual brakes? In other words, do you need the HB or just want the HB?

A HB is cool, for sure (I have used a few in the past and have 2 sitting on my workbench ready to use now!) though as I think Joel may agree, maybe not "right" for every application. I have 13"/12" f/r PBR brakes for one of my cars and I have a hunch that manual brakes may be the hot ticket over the HB. I'm going to run both and see what has the best feel and performance for my needs. FWIW, I have a MC from a 90's Safari Van HB setup that was disc/disc that I think might workout. We shall see shortly...

[GS470]

I appreciate the clarification, Socrates.

I was leaning towards a HB for a couple reasons. First and foremost, I want more clamping pressure on the discs. I do have power brakes now and since I installed the Baer brake kit, I can't even lock up the brakes (front or rear) if I try with a controlled "panic stop". I have an adjustable proportioning valve for the rear brakes and it's opened up all the way. I think I'm getting enough vacuum for the booster because my HVAC vents seem to work OK and under normal braking the feel is good. IMO, it just doesn't stop as well as it should when I hit the pedal hard.

I had read an article a while back and the symptoms were exactly the same as mine (one of those tech support articles in Car Craft or Hot Rod). I think the person writing in had even installed the same front and rear brakes that I have. A HB conversion was the recommended best option to resolve it.

I'm also considering a larger cam and I'm not sure what that might do to my vacuum, so a secondary benefit of the HB is to eliminate the dependency on vacuum for brake boost.

I've never considered converting to manual brakes. The disc/caliper combination you mention sounds very similar to what I have. Why do you think manual brakes might be a good fit for that application? My dad's '67 Chevelle convert had manual drum/drum brakes and personally, I never liked the feel of the manual brakes. Granted, the drums may have something to do with it, but it seems like you have to lean on them pretty hard to get decent braking under just normal conditions. We're currently doing a full restoration on that car and converting it to front discs and power brakes.

I'm assuming since the MC came with the brake kit, it must be a decent match up for the brakes. If I move forward with the HB conversion, it sounds like there may be some trial and error, so I may as well start with my current MC as long as it physically hooks up to the HB (please speak up if it won't). And if the Astro van HB is an easier overall conversion, I'm leaning that direction. I want to try to keep this relatively "easy".

Does this all sound reasonable? Is the HB a good plan, or should I be considering another route?

I'll also check out the pro-touring forum, to get some thoughts, but I'm expecting to be overwhelmed...

[Old Goat 67]

Only thing I added was the Hydroboost unit and I'd NEVER go back.

[Joel Koontz]

GS470, I have not yet found a suitable MC over 1 1/4" that is reasonably priced. There are some on late model GM Pickups W/HB, that have a 37 mm bore, but they have a tall MC Reservoir. They are fairly expensive and I think they might cause a hood clearance issue with my current mounting arrangement.

Have you spoken with Baer about how your brakes currently function? I can't remember a car that I have driven that I could not lock up the tires. Unless your running full on race slicks or something like that, I would think you should be able to lock up the tires. I would suspect something is not working as it should with your system.

If your system is working properly, the fact that your current MC requires a lot of pedal force MIGHT make it suitable for use with HB. I think the Astro HB roughly doubles the force that you get from typical vac booster so even with a very large MC bore it would probably apply pleanty of pressure.

As a general rule, power brakes use a larger MC bore than manual brakes. The smaller the MC bore the more pressure it puts out. If a small enough bore is used you CAN get manual brakes that will lock up the tires, the issue is that the small bore requires a lot of pedal travel, IE it may go to/near the floor before if moves enough fluid to lock the brakes up.

Another general rule is that if all other things are equal, drum brakes will take less pedal pressure than disc brakes, most manual brakes are referred to a partially self actuting. I can't explain exactly how this works, but basically, when you apply the brakes it sort of automatically pushes the shoes against the drums. No such feature with disc brakes. The down side of drum brakes is that they overheat and fade much more easily under heavy/aggressive use.

Another thing you might consider, is which hole you are using in the brake pedal. On most cars there are 2 different holes in the brake pedal that you can use, depending on what MC/Booster you are using. Using the upper hole is like using a smaller bore MC, more pressure, but more pedal travel. Using the lower hole, less pressure, but less pedal travel. Depending on the parts you are working with, you might want to see if you can move the rod to the other hole. If you are currently using the lower hole and CAN use the upper hole you might want to try it to see if that improves your brakes. You may not be able do move it. Depending on the specific parts involved, you may or may not be able to get the rod/hole to line up properly.

I am in the process of relocating my MC rod to the lower hole of my brake pedal. When I originally installed the HB, I put it at a slight tilt(front of MC higher than the rear) but it was not enough to let the rod line up properly with the lower hole on my brake pedal. I drilled a hole midway between the two factory holes on my brake pedal and used it. I have now modified my homemade mount to create more tilt, which should let me use the lower factory hole. I am hoping (but not confident) that this will increase the required pedal effort to where I am satisfied with it. I have the motor partially torn down so it will be a while before I can test function with it in the lower hole. When I added the tilt, I decided that a tilted MC Reservior would be a good thing (look better and increase hood clearance) so I have ordered (but don't have yet) a MC Reservoir from a 96 Caprice. I am not sure it will fit, the the holes look like they are in the same location and same diameter so I am hoping it will. If it fits, I think it will fuction well and hopefully look good too.

MUSTANG HB - this is a link to info from a guy that installed on on 68 Camaro

http://www.geocities.com/casanoc/

and as Socrates said there is some info on them at ProTouring.com

[Joel Koontz]

Another detail on MCs.

At least in GM products, they use 2 (that I know of) different "depths of holes" in the back of the MC where the rod from the Brake Pedal/Booster goes in the back. One is fairly shallow and the other deeper. You will need to use a MC with the appropriate hole depth. On my 92 Astro MC that came with the HB, it is the shallow hole. I have not looked at it recently, but I would guess it is about 3/8" deep, no deeper than 1/2".

I think the shallow hole design is normally used with power brakes, so if you have a MC for power brakes the hole depth will probably be OK.

[GS470]

Old Goat 67 - Sounds like you kept it simple and got good results. That's nice to hear. I've tried to do a fair amount of searching on this subject on this forum, but can't remember who used what combination of parts. What HB unit did you use for your conversion? And it sounds like you must have used the MC that you already had.

Joel - Thanks again for the info. Lots to digest.

I haven't spoken with Baer. That's a good idea, I'll follow up to see if they can shed some light on this. And while my Ecsta MX tires are somewhat sticky, it's not them preventing the skids, it's the brakes not clamping down. I don't feel like I'm about to be tossed through the windshield when I jam on the brakes, it's just slow to stop. Not that it's the hardest braking car on the planet, but when I nail the brakes on my Vette, you want the seat belt on. To give you a comparison, I honestly don't think my LeMans stops much faster than my 7000# diesel pickup at this point. Yet they feel good and work well under normal driving conditions.

If I get a chance over the weekend, I'll take a look at my brake pedal to see what my options are. Unfortunately, it's not fun car season yet in Minnesota, so I probably won't be able to test anything out for a few weeks.

Unless I'm really missing something or discover a physical incompatibility, if I do end up doing the HB conversion, I think an Astro Van HB along with my current MC is a reasonable place to start. There's a decent chance it may work well for me and I can control costs at the same time.

[Socrates]

Originally Posted by GS470

And while my Ecsta MX tires are somewhat sticky, it's not them preventing the skids, it's the brakes not clamping down. I don't feel like I'm about to be tossed through the windshield when I jam on the brakes, it's just slow to stop. Not that it's the hardest braking car on the planet, but when I nail the brakes on my Vette, you want the seat belt on. To give you a comparison, I honestly don't think my LeMans stops much faster than my 7000# diesel pickup at this point. Yet they feel good and work well under normal driving conditions.

Sounds to me like you need to bleed your brakes or fix a leaking line or fitting somewhere in your system. Did you bench bleed the MC exhaustively? I'd go back and bleed everything. Try Gravity Bleeding. Then Vacuum. Then pressure. Whatever it takes.

Another thought, are you running racing brake pads on your fancy pants brakes? They take a LOT of heating up before they grip. Try a series of rapid 50-10mph slow downs on a back road then try a hard panic stop and see if the car stops better then. You just may need a real street pad not a track pad. Just a thought...

[bobzdar]

Originally Posted by Socrates

Sounds to me like you need to bleed your brakes or fix a leaking line or fitting somewhere in your system. Did you bench bleed the MC exhaustively? I'd go back and bleed everything. Try Gravity Bleeding. Then Vacuum. Then pressure. Whatever it takes.

Another thought, are you running racing brake pads on your fancy pants brakes? They take a LOT of heating up before they grip. Try a series of rapid 50-10mph slow downs on a back road then try a hard panic stop and see if the car stops better then. You just may need a real street pad not a track pad. Just a thought...

What he said, I have hydroboost on my 3500 p/u and when I replaced the rear brake hose and didn't have anyone to help me bleed it, the brakes felt the same way when I moved it around the driveway - air in the line or in your case some other part may be badly mismatched. If you already have a power booster and can't lock the brakes, the hydroboost is going to just be more money for no improvement. I'm not a big fan of the hydroboost, they're big and heavy, don't particularly like the feel and when something goes wrong the rebuild kit costs the same as a new vacuum booster. They make sense in a boosted or low vacuum situation, but other than that I don't know that I'd use one. Plus side is they aren't difficult to rebuild and it can be done in the car (or in the truck in my case).

If I needed more assist I'd use a dual diaphragm vacuum unit, but the hydroboost isn't even an option unless I put power steering back in my car .

[Old Goat 67]

GS470,

I used a hydroboost from an early 80's GM truck. Reused the MC I had on there which is a 79 Firebird one that I put on there when I installed front disks 20 something years ago. The improvement was dramatic, just what I was looking for without having to break open the brake hydraulics at all. Gave me a good benchmark, but I wish I would have had a G meter to document the results.

Charles

[Silverbird]

Im looking to replace my vacuum booster for valve cover clearance

just when I was about to buy the $600+ hydBoost,I find this thread.

Did you buy a rebuilt one? salvage yard? how much for the complete conversion.
or
should I just replace booster with a smaller one?

.

[GS470]

Socrates / bobzdar - I'm pretty sure I bench bled the MC, but I installed this stuff in '04, so it's been a while now. I just went back and quickly reviewed the install instructions and didn't find anything about bench bleeding, but I thought I had done it for this install. If I did, I just went until the bubbles stopped. I always thought that if things weren't bled properly, the system would have a "spongy" feel from the air in the lines. But I don't feel that at all. I've also checked the system for leaks and haven't found anything anywhere and the level isn't dropping in the MC. I have purchased some "speed bleeders" for the car. So I may as well install them and re-bleed things.

And I would hope there's nothing badly mismatched in the system, that's the main reason I bought a system from what I consider (and hope) to be a reputable company rather than gathering the components on my own.

There's also nothing "fancy pants" about what I installed, pretty basic stuff. I don't remember what the pad composition is, but they're the standard pads that came with the system. 99% sure they're not ceramic pads or anything like that. I also followed Baer's "bedding in" process.

Old Goat 67 - Thanks for the additional details. Sounds like your conversion was about as painless as it gets.

[bobzdar]

Originally Posted by Silverbird

Im looking to replace my vacuum booster for valve cover clearance

just when I was about to buy the $600+ hydBoost,I find this thread.

Did you buy a rebuilt one? salvage yard? how much for the complete conversion.
or
should I just replace booster with a smaller one?

.

You may want to try the '81 t/a dual diaphragm unit, it's smaller in diameter and also has more assist, it runs 95.99 at advance auto. If you can find a hydroboost in a salvage yard make sure to look for one that isn't all crudded up as that usually indicates it leaks and needs a rebuild. Kits are available to rebuild but as I mentioned they cost almost the same as a new vacuum booster ($50-70 iirc). Rebuilding one yourself is very simple as it's just a bunch of rubber o-rings.

http://shop.advanceautoparts.com/web...S_677078623___

[vidguy]

Do any of you guys have a flat Hydroboost bracket you'd want to sell? The unit I got has a weird angled, rounded center bracket that I just cant drill...

[Joel Koontz]

Just an update to something I posted earlier.
In post # 7 I mentioned that I was going to try tilting my Astro MC more and use the lower hole in the brake pedal and also try to use a MC reservoir from a 96 Caprice.

It was a bit of work to get it tilted the additional amount, but I have completed this "modification". I originally tilted my MC by putting nuts on the lower studs(that run through the firewall) under the plate on the HB. This created a small amount of tilt, but I could not get additional tilt using the stock lower studs, because I ran out of threads on the lower studs. I knocked out the lower studs and replaced them with bolts.

I initially could not figure out an easy way of removing the studs, but I eventually figured out a way that worked well. I backed off the nuts that were under the HB plate (on the lower studs) so that there was some space between the nuts and the firewall. I then tightened up the nuts on top of the HB plate on the upper 2 studs and this put pressure on the lower studs trying to push them out(back through the firewall) The pressure alone (I did not really torque on it) was not enough to push the studs out, but when I hit the bracket beside the stud head(from the dash side of the firewall) with a hammer/punch the studs came loose and I was able to remove them. I then put the bolts through, put nuts on them to hold them to the bracket/firewall and put washers over the nuts to create additional tilt.

I don't have the car running to check function, but it seems like it is going to work out very well. I was able to tilt it enough to use the lower hole of the brake pedal and the reservoir from the 96 Caprice worked out very well. It is designed to be tilted and with it installed the lid of the reservoir is very close to level and has good hood clearance. It also has more capacity than the Astro reservoir and IMO looks much better.

[GS470]

I've got an update, too. I finally called Baer to get their thoughts on my poor brake performance. I was told the symptoms were the result of
1.) The MC bore size being too big
or
2.) Inadequate engine vacuum

The first question he asked was whether or not I had used the MC that came with the brake kit. When I told him I had, that ruled out #1.

It's been a while since I measured my vacuum so I don't remember the exact value, but I think it pulled somewhere around 10-12" at idle. Since I'm considering a bigger cam, my vacuum isn't going to get any better. He said most boosters require somewhere in the 14" to 16" range to operate properly. He also said that booster performance can drop off sharply if you don't generate the minimum required vacuum. In a nutshell, to resolve #2, he suggested either some sort of vacuum pump/boost system, converting to manual brakes, or his preferred solution, a hydroboost. He said I'd be amazed at the increase in stopping power if I went with a hydroboost.

[Joel Koontz]

GS470, did Baer tell you what your MC bore size is?

Did they recommend it for use with Hydroboost?

[GS470]

Originally Posted by Joel Koontz

GS470, did Baer tell you what your MC bore size is?

Did they recommend it for use with Hydroboost?

They didn't say what the bore size was and I didn't think to ask until I was off the phone. The guy did say that my master is designed for my brakes and would work well with a hydroboost.