A thread for Hydroboost (not Hydravac) questions

[1project2many]

Since people kept jacking my thread about Hydravac to ask about Hydroboost, I decided to be the nice guy and start this for anyone who has Hydroboost questions.

This was the question posted by 57taskforce

I'm wondering since you've got hydroboost expierence, how hard do you think it would be to mount to the fire wall? I've already got a firewall mounted pedal assembly from classic parts. Im currently running 7" dual diaphragm booster. It has hard time stopping 35's. I've got hydroboost on my k2500 and it stops 35's without much issue. So I've been contemplating this swap for a while now. Any insight would be awesome.

I work on Hydroboost systems almost daily. Mounting Hydroboost to the firewall is no more difficult than a vacuum booster. The GM version uses the same holes although in some cases the center hole for the pushrod is a different diameter. The pushrod length may need to be modified and the post on the pedal where the pushrod connects is often at a different location bwhich can alter the pedal pressure required to give stopping power. Because Hydroboost units require a very large amount of pedal pressure if the hydraulic assist is not present, I strongly recommend installing a reinforcing plate on the inside of the firewall.

One consideration is the size of the rotors / drums on your vehicle. Many times the brakes for the 2500 / 3500 vehicle are larger in anticipation of larger loads. While switching to Hydroboost my reduce the pressure needed to stop your vehicle, if the brakes are under size for the application you run the risk of generating enough heat during a fast stop that the brakes fade and lose effectiveness.

[57taskforce]

Like I said in your thread. I appreciate the effort but this was unnecessary. I only asked the question in your thread because the topic had been directed to hydroboost a few posts ahead of mine. Thanks for your contribution to my question

In relation to my truck. I'm running a 14 bolt ff rear w/drums and an 8 lug 3/4 ten bolt front. Both with new brake parts. My pedal is pretty stiff and seems to have little assist. The vacuum source is the big port at the back of my 600 cfm edelbrock carb and has plenty of vacuum present. I got the booster/proportioning valve/master cylinder set up that was recommended for disk/drum. The pedal has never felt like it had much assist. Although the pedal feel in my other truck takes some getting used to, it stops that fat pig pretty well. If I had to stop the '57 in a hurry id be in trouble.

[dwcsr]

I have seen many over seas vac booster bad right out of the box.

Make sure the vac line is not collapsing
Make sure you don't hear hissing or whooshing noise when you press on the pedal
Put a Vac gauge on the engine and clamp off the vac line to the booster and see if the vacuum changes.

I suspect you have a bad booster

[1project2many]

Like I said in your thread. I appreciate the effort but this was unnecessary.

Plenty of people ask Hydroboost questions from time to time and in this forum there really isn't a thread for it. It only seemed appropriate. Wasn't trying to come of like an a$$ (though I probably did), just realized there might be a need for an informative thread that wasn't project specific.

In relation to my truck. I'm running a 14 bolt ff rear w/drums and an 8 lug 3/4 ten bolt front. Both with new brake parts. My pedal is pretty stiff and seems to have little assist. The vacuum source is the big port at the back of my 600 cfm edelbrock carb and has plenty of vacuum present. I got the booster/proportioning valve/master cylinder set up that was recommended for disk/drum. The pedal has never felt like it had much assist. Although the pedal feel in my other truck takes some getting used to, it stops that fat pig pretty well. If I had to stop the '57 in a hurry id be in trouble.

Lotsa stuff that can come into play. Without specifics I can only throw out general advice.

If you're using an aluminum master cylinder from a newer vehicle then it's probably designed for "quick takeup" calipers. It's supposed to reduce drag on the rotors but the design really slows pedal application. It seems to take for-ever to apply and then you (well, I) don't feel much assist when they hit. Switching this type master for an older iron version usually makes for better pedal feel but it can increase pedal travel, too.

If your truck has 73-87 front calipers there are a couple of different size pistons available. You want the largest pistons to reduce effort at the pedal. If you accidentally ended up with 1/2 ton calipers (they bolt up) then you've got 2.94" pistons. 3/4 ton calipers are 3.15" diameter and make all the difference.

GM used the same basic rear drum on the 14 bolt 3 1/2" X 13" brakes from about '70 to at least '02. There aren't many variations. Like calipers, larger diameter wheel cylinders make for less effort at the wheel. One ton dualies usually have the largest wheel cylinders so if you're using the 1" or 1 1/16" cylinders you can move up to the 1 3/16" version for better rear braking.

On the master cylinder side you want a smaller bore to create higher pressure and reduce pedal effort. The tradeoff for all of this is in the distance the pedal has to travel before it builds pressure. If you're not careful you'll end up with a system that doesn't build a pedal until it's halfway to the floor when it's fully adjusted. And it gets worse as the brakes wear.

Master cylinder, caliper, and wheel cylinder sizes are published in many brake catalogs although that information is getting harder to find. Sometimes it takes some digging on a manufacturers' site or at the part store to get it. I do have several references at home and am happy to look up dimensions from time to time.

HTH

[57taskforce]

I picked up the calipers Reman at napa for a 3/4 truck. Who knows what get gave me as I didnt measure the piston. It's got a 1" bore iron master cylinder. The rear wheel cylinders are for an 80s hd 3/4 truck. My guess is they are probably 1". This is all good good for thought. My booster doesn't appear to leak but I've not put a vacuum gauge on it to be sure. I'm kind of leaning tward a defective booster myself which is why I'd like to Pursue hdroboost.

[_Ogre]

iirc you have a 7'' vac booster, can you bolt in a bigger oem style vac booster? that would be the easy fix.
the 03 mustang gt used a vac booster, the cobra motor was too big and had to use the hydroboost

i can say that the hydroboost does work well, very well if needed

[57taskforce]

Yes I have a 7" dual diaphragm. While I could probably mount up a factory style booster without too much trouble, my truck does get used as a truck from time to time. Don't get me wrong I cruise around in it as well but, when I am hauling heavy loads having the additional assist to stop the big tires and load is appealing to me. I very well may go this route. I know I need the hydroboost assembly, the lines, hydroboost power steering pump, and likely the master cylinder. Is there anything else I should know/get if I do choose this route?

[1project2many]

Technically, the pump is the same. Some reservoirs have a second connection from the booster return but many don't. Delco and Fenco pumps use a brown, high temp seal on the pump shaft that seems to hold up better than the standard temp seal.

The fittings at the hydroboost can be duplicated using a custom hydraulic flare tool so you're not limited to factory style hoses. Steel lines in and out and inexpensive short hose sections made by a hydraulic shop can provide for a good system that doesn't cost an arm and a leg. You can Tee the booster return into the steering box return line. Get a high quality brass Tee with good barbs. I would definitely add a cooler. Pumps can seize from excessive heat and a cooler is the best insurance I've found against it.

[spreader]

Originally Posted by 1project2many

You can Tee the booster return into the steering box return line. Get a high quality brass Tee with good barbs. I would definitely add a cooler. Pumps can seize from excessive heat and a cooler is the best insurance I've found against it.

I did a lot of searching on hydro-boost mods before installing one on my Scout II. All on the International Harvester sites tho. The consensus was that a 'Y' block from the low pressure side of steering gear box to the PS pump and hydroboost unit was the best way for return lines verses a 'T'. Used a fuel block from Jegs @ about $25.00 for the return lines. Also installed a PS cooler from the mid 80's GMC 3/4 ton I scavenged the parts from. The hydro is pushing an aluminium MC from a 68 Corvette used in either disc/drum or disc/disc. Steering is just fine. The brakes work great on this 4500lb pig. So well in fact that I installed the same set-up in my 48 GMC on a 78 C-20 frame/drivetrain

[1project2many]

LMAO! I figured someone would set me straight with some cabover information,wasn't expecting the Bluebird,lol.

I figured if anything could demonstrate reliability of an under cab master cylinder, it was a bus. But it's not just the Bluebird. Plenty of Type D buses (the snub nose design) are built this way. Some use Electroboost or Hydromax and/or an electric pump to provide boost even if the engine's not running. P6 in the manual below has pictures of the compound pedal linkage including the pull rod and the bellcrank.

http://www.centralstatesbus.com/2010...ulicBrakes.pdf

Steering is just fine. The brakes work great on this 4500lb pig. So well in fact that I installed the same set-up in my 48 GMC on a 78 C-20 frame/drivetrain

Great looking engine compartments! I think HB swaps are one of the few mods that people like so much they'll duplicate again.

Even the factory applications will show what I'm describing in some cases. 97-2002 G vans certainly do. While turning the wheel (not holding it in a turn, but actually rotating it), rapidly apply the brake... panic stop style. If you feel anything like a slight "jerk" in the wheel that's what I'm describing. There seems to be a correlation between steering gear ratio and the likelihood of noticing the symptom.

[57taskforce]

Thanks for the Good info. I was thinking about looking into braided stainless hose with -an fittings. I need to do some research and see if I can find the right fittings to make it all work.(don't anticipate it being an issue) I was contemplating the cooler before this but I will certainly add one if I go this route. I will update this thread with my findings and progress. It may be a few months before I dig into this, but I do want to go this route.

[1project2many]

The early units used inverted flare. Later boosters (GM) use Saginaw fittings (often just called metric). Sizes are 16 and 18mm. They were tough to find years ago but there are apparently adapters today.

http://www.purechoicemotorsports.com...=cat/cat99.htm

http://www.purechoicemotorsports.com...rod/prd347.htm

[CharlieSheen]

Nice write-up thanks for taking the time.Hydroboost was one of those rare things that GM hit a home run with.I have driven several hundred thousand miles in vehicles with it,problem free.And when they go bad...they go bad,not much diagnosis necessary.I think it is a great system.Just have to be careful trying to steer one of these trucks if the hydroboost craps out,they don't turn for squat without the hydraulics.

The drawback to hydroboost,for many of these projects is the aesthetics of the hydroboost unit.They are just plain big and ugly,and take over the engine bay of AD trucks especially.I'm not sure that an AD pickup that is used for around the town cruising and not loaded down or towing really requires that kind of braking power that hydroboost allows.

[_Ogre]

Originally Posted by CharlieSheen

The drawback to hydroboost,for many of these projects is the aesthetics of the hydroboost unit.They are just plain big and ugly,and take over the engine bay of AD trucks especially.

not really

no engine bay take over if you keep the hydroboost under the floor

[CharlieSheen]

Originally Posted by _Ogre

not really

no engine bay take over if you keep the hydroboost under the floor

I've seen your installation,Ogre, and it is a beautiful one.

I kind of have reservations about having a master cylinder down there,but my concerns are probably unfounded.I guess it comes from my weekly safety checks.I have probably splashed more brake fluid around the engine compartment removing the MC cover than I have added to it.But with the remote reservoir type.....

Just wondering,is anyone aware of any modern factory installations of master cylinders mounted undercab,away from firewall?

[yossarian19]

I'm not aware of a single one of them, no.
I used the Speedway under-floor power brake pedal, an Ebay hydroboost mounting plate (supplied without bolt holes, but with the center hole & notch for the boost unit), an Astro Van HB unit & master cylinder with an S10 reservoir. Not as big a pain in the neck as it sounds. Pedal is great, brakes are better than a 1957 has any business with. The steering can't even close to keep up with the speed I'd be comfortable stopping form.

To plumb it, I scoured the junkyard with a small pipe cutter & found the right power steering hoses. Cut the ends off with about a 2" straight section, brought them to a hydraulic shop, had ferrul lock hoses made. Put it together on the truck. $45, plumbed.
The brass "T" seems to work for return lines, as others have said. It's been rumored that you really want the reservoir to have a separate return and I have to think GM designed & manufactured & installed that other reservoir for a reason, but damned if I can see what it is.

[1project2many]

Just wondering,is anyone aware of any modern factory installations of master cylinders mounted undercab,away from firewall?

The brass "T" seems to work for return lines, as others have said. It's been rumored that you really want the reservoir to have a separate return and I have to think GM designed & manufactured & installed that other reservoir for a reason, but damned if I can see what it is.

I believe it affects the steering slightly. Applying brake while turning wheel in my Blazer with "fast turn" steering box resulted in noticeable, but very brief, reduction in power steering. It was nothing more than an annoyance to me.

Many G vans use a remote fill PS reservoir. In these vehicles the primary PS pump reservoir only has one return hose connection. There is a third return line from the HB plumbed to the reservoir. This may handle additional fluid volume or pressure surges caused by HB activating and releasing.

[CharlieSheen]

LMAO! I figured someone would set me straight with some cabover information,wasn't expecting the Bluebird,lol.

Its good to know,and I may well go in that direction.My truck will be dually with discs all around,which makes me feel better,being that calipers seem to be a bit more reliable compared to wheel cylinders,and getting to the master probably won't be necessary for the most part.I'm going to have a 12k GVW,plus towing trailer,so I will be subject to safety checks and road inspections,and those inspectors seem to feel so proud when they find a MC not topped off.So I would have hesitated if they weren't seeing this setup anywhere else.

What kind of pedal setup does the Bluebird have?

[57taskforce]

My 98 k2500 will do something similar if the wheel is about half thru the turning radius one direction or the other and you stab the breaks hard. It's only happened once or twice and I can never seem to reproduce it if it try. So I've got a "universal" gm iron master cylinder 1" bore. Do you think guys I could do the same as above and use the iron master instead of swapping it out?

[1project2many]

Possibly. Check the diameter of the machined alignment ring on the back of the master to make sure it fits in the HB. Make sure the pushrod in the booster is the right length, too. Compare depth of the piston on the old master to the one you want to use. If all is good then you can bolt it up.

[57taskforce]

Ok thanks for the insight. I've been doing a bit of research the last week or two as time permits and I came across this thread on pirate4x4. (I troll that board often but have noticed posting there at times isn't for the faint of heart). Any who, http://www.pirate4x4.com/forum/jeep-...oost-info.html
This has several good links and diagrams for hydroboost newbs and likely veterans alike, so I figured I'd share the wealth.