Hydraulic brake booster » FAQ


What is Hydraulic brake booster?
Hydraulic brake booster is a hydraulic brake booster that replaces your vacuum booster, it results in ~2-3x the braking pressure for the same amount of pedal pressure as vacuum operated brakes. It runs off of your power steering pump.


If it runs off my power steering pump and my pump dies, the belt brakes, or the engine quits how do I stop?
Well if you have vacuum brakes and your engine quits how do you stop? On manual brakes, and isn't that a grunt? So, there is an advantage to Hydraulic brake booster in those circumstances because it has an accumulator for residual pressure in the event of losing the pump. The accumulator is the gold cylinder usually seen on the right side of the unit, and it's filled with 1,500 psi of nitrogen and when your pump is running it fills the chamber with power steering fluid and compresses a piston. Provided you have a full charge of nitrogen in your accumulator (yes they can go bad) you will have 2-3 full power brake applications in the event you lose the pump... before you switch to manual brakes.


Will my power steering pump be adequate to run both the brakes and the power steering?
In most cases the answer will be yes. If your pump is already on it's last leg than it will be obvious when you add the additional work load of the Hydraulic brake booster. Because the Hydraulic brake booster requres very little of the pump's pressure typically the only time you might notice a drain on your power steering capacity is while you are applying the brakes and turning at very slow speeds with large tires in an offroad situation. If you encounter that situation you can 1) upgrade to a higher performance power steering pump, 2) swap in a pressure relief valve from a GM dually truck power steering pump that was in a Hydraulic brake boostered system, 3) figure a way to swap on a GM power steering reservoir can that had the additional return line nipple so you can eliminate the barbed hose T-fitting that are included in the kits I sell.


Can I just use my master cylinder or do I need to buy one with the Astro Hydraulic brake booster?
Some of the Jeep master cylinders will not work the Hydraulic brake booster for a couple of different reasons. If you already have an OEM aluminum master cylinder (1981+) it's not going to fit into the Hydraulic brake booster so you will need to either buy one with the Astro Hydraulic brake booster or source your own elsewhere (the stub end of the master cylinder needs to be 1 1/2" to fit into the Hydraulic brake booster, no larger on most Hydraulic brake boosters. The bolt spacing is 3 7/16.). If your master cylinder is iron and installed on a currently vacuum assisted Jeep from 1980 to 1974 you can retain your master cylinder if you like, it will bolt directly to the Astro Hydraulic brake booster and you will have one less hydraulic system to bleed on installation. For Jeeps prior to 1974 I recommend replaceing your OEM master cylinder and most cases will require it (I'm not recommending the modifications it would take to make some of those work). Whatever master cylinder you use with this Hydraulic brake booster it will require a shallow dimple on the piston as pictured.


I need to replace my master cylinder also, how do I bench bleed it so my brakes bleed faster?
The instructions are here.


How much do hoses cost, where do I get them and what are the part numbers?
You will need, at the minimum, two pressure hoses and six feet of return line. Plan to buy six 3/8" hose clamps for the return line as well. You can buy the hoses anywhere you want, I priced them at about $50 for all of it at AutoZone... and that's for the cheaper ones. I'm not going to give you the part numbers because they really aren't that helpful and will even slow you down if you try to use them at AutoZone due to their inventory system.

  1. If you have a 1980+ Jeep and your power steering system is stock then you have metric 0-ring fittings and you can simply ask for power steering hoses for a 1985 GM dually K30 with a 350 engine and Hydraulic brake booster.
  2. If you have a 1979 down Jeep and your power steering system is stock then you have flared hose fittings and those are going to require adapting to the metric 0-ring fittings of the Hydraulic brake booster I sell.
  3. For stainless braided hoses and fittings you can order those through: HydraTech Braking I can provide the part numbers for you and have priced this out at $89.95 for the hoses and $148.02 for fittings required to adapt to 3/8 flare pump/steering box using the barbed hose return Tee fitting, prices will vary with optional fittings. This totals $237.97 and that did not include shipping. (Prices subject to change.)
  4. If you want to source your own 3/8 barbed hose fitting for the return line you can find them at Plumbing Supply.


Are the GM hoses a direct bolt up?
They will bolt straight up to the Hydraulic brake booster. At the pump and power steering box it requires that you bend the hoses to match. Pictures are on the Specs page.


Does it matter how I hook up the T-fitting for the return line?
It is critical that the T-fitting is installed in only one way or you will have trouble with your system. A picture showing the correct installation is on the Specs page.


Can I fit a flared hose fitting to metric o-ring ports?
Yes, Hydratech Braking sells flare adapters that fit in the metric ports. Check out their part # HBS9104 which fit all the HB ports I have come across (unless the HB has been ported for higher flow). Also check out their low profile banjo fittings for increased clearance if required.


Which port goes to where?
The larger port is pressure in from the pump. The smaller port is pressure out to the steering box/rack. Mix these two up and the booster won't power the brakes, the pedal may stay at the floor and pulse. The nipple is the low pressure return line which typically goes to the side leg of the brass Tee fitting. Return from the box/rack must flow straight through the Tee "on run" to the pump. Mix that up and you run constant pressure back the wrong way into the HB.


That reservoir on the Astro/Safari Hydraulic brake booster looks kind of small, is that going to work with the rear disc brakes I plan to use?
The Astro/Safari reservoir is adequate for disc/drum applications, not for disc/disc setups. You can remove and replace the reservoir with one from your Jeep MC if you have the plastic reservoir (1981+) or take one from a GM truck in a parts yard. On occassion I can do the swap for you if you request it. If you do it yourself (some reservoirs will be brittle from heat and shatter) when you go to re-install it place the grommets in the master cylinder first and then plug the reservoir in.


What if my truck has drum brakes all the way around, will this still work?
Not necessarily, but the set up is more involved. You have to source a few more parts and drill two additional 3/8" holes in your firewall.


Will I need to add a residual pressure valve to my brake system to use this with all discs or all drums, and which one would I use?
Yes, if you have all drum brakes you may wish to add a 10Lb. residual pressure valve to the line that serves your front brakes although some who've done this will tell you it's not necessary (the rear port on the Astro master cylinder). If you plan to run all discs you are best off to add a 2Lb. residual pressure valve to the line that serves your rear brakes, but again some will tell you they felt it wasn't required (the front port on the Astro master cylinder serves the rear brakes). These are available from Summit Racing for about $20.00.


What if I have really crappy brakes, my wheel cylinders are crude, shoes are old, hard brake lines are pitted and rubber lines are cracked... this is going to improve my brakes still?
No, it will make your brakes more likely to fail due to the increased pressure. Bring your system up to safe operating standards prior to considering installing a Hydraulic brake booster system.


Can I use cheapo power steering fluid?
I don't advise it. Howe Performance recommends using GM Goodwrench PN: 89020661.


Should I add a filter?
A filter is a great idea. It will keep contaminants from jamming the spool valve inside the HB. You can place it in the return line between the T-fitting and the power steering pump reservoir. Clean fluid is the key to Hydraulic brake booster longevity. Look up Cardone Magna-Pure inline power steering filters for a great, serviceable one that you can inspect and clean out.


Can I run a PS cooler with this?
Certainly. Make sure it is installed down line from the T-fitting in the return line if a T-fitting is used. Do not use a cooler that is more than two pass. Flow tests are being done on the standard two pass as well as the plate type coolers, stay tuned for the flow test results.


Can this be used in combination with steering assist?
My feeling is that with modifications it will work fine in many applications in combination with steering assist. This will be explored more but there are things you can do to improve/hot rod your HB without having it "flowed". Using a smaller (less than 2") steering assist cylinder would benefit in this situation.


How can I get the most out of my low speed performance?
You can get the most out of your HB by eliminating the T-fitting in the return line. In many cases you will never find the need to do this but if you have a doubled transfer case and running some seriious crawl ratio with an auto tranny and you rock crawl then you want all the low rpm performance you can get. Install/braze a second return nipple to the side of your PS reservoir can. Also, if you don't already have a high flow pump then go to the wrecking yard and pull the relief valve and spring out of a similar year range one ton truck that had HB (you want to stay consistent with either 3/8" flare fittings or metric o-ring, depending on what you have in your rig). Install this in your pump and it will boost you from 1,100/1,300 psi to 1,500 psi.


Can you provide a mount kit I can weld up myself if I find my own HB?
Yes, I currently have a CJ/YJ mount kit listed on Ebay and more applications are coming as well as a cheaper tool for removing & replacing the large nut. Check my ebay listings under Sterlingworth16 for updates or to send me a message/ask a question. Realize that in most HB swaps you will need to cut the brake rod, chamfer it 45º and thread it 3/8-24 for a coupler or adjustable rod end you source.


I'm running a big block and need all the room I can get, can I run this thing upside down for more valve cover clearance? -or- I'm running a 6 cylinder with a weber carb and need more clearance at the throttle rod, can I run this thing upside down?
Yes, it can be installed upside down and will operate just fine. You will need to work with the hoses fitting up inverted and it will take a little longer to bleed air from the system but it will work.
Ask me about custom rotations other than 180* if interested.


I want to run disc/disc and understand some guys feel the disc/drum proportioning valve has worked well for them but I would rather use a disc/disc proportioning valve, what options are there for me?
1) BJ's Offroad sells a disc/disc prop valve for ~$105 that replaces your OEM valve. http://www.bjsoffroad.com/CartGenie/prodList.asp?scat=73

2) BJ's Offroad also sells an adjustable valve for $50. http://www.bjsoffroad.com/cartgenie/prodInfo.asp?pid=986&cid=10  

3) For another option on the adjustable valve there is a seller on Ebay that lists one for $70 shipped. See: Classic_Performance_CPP







More pics of installs...


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