[Eldon McFarling]

Just thought I'd chime in so another great thread doesn't go up in smoke. I think this is like alot of subjects here, the more you understand about how things work the better. Maybe a bit of history is a good place to start

Originally Posted by Title

Why hydroboost?

The origin of the Hydro-Boost dates back to 1968. It was then that vehicle and brake manufacturers realized new brake systems or improvements to existing vacuum systems would be required to meet future regulations governing stopping distances and pedal effort. Equipment to meet proposed emission regulations also posed a problem for existing vacuum boosters with reduced engine vacuum and higher underhood temps. In 1974 Bendix introduced a hydraulic power brake booster patented under the name "Hydro-Boost". Bendix later developed a similar system for mid sized trucks which is called "Hydro-Max" which is used on many IH & Navistar mid sized trucks and busses. The Hydro-Max system is similar to the Hydro-Boost with the exception of the reserve system which uses a electric pump attached to the booster which is activated when the pressure from the main hydraulic system drops below a preset level.

Originally Posted by Jon

Hi, What is the advantage of adding hydroboost to a scout

The Hydro-Boost has many advantages over vacuum systems, it's compact size allows it to be used where underhood space is at a premium such as with vans, or compact cars, I bet you could even find room in an early Scout. Try that with a vacuum booster. Other important features, a vacuum source is not required so the unit can be used on Diesel, and souped up, blown or turbocharged gas powered vehicles. Higher pressure available with less pedal effort and faster response time with a stored reserve for emergency operation. It works good on them Caddilac boats and on those 1 tons, also works well on a little Astro van. And yeah it does work really well on a Scout II with either gas or Diesel power. An additional benefit with the Diesel is being able to use an alternator without a vacuum pump.

On the safety side less pedal effort is needed which makes the vehicle easier to control. The ability to lock all 4 wheels does not translate to better control or a reasonable safety factor. Quick response and the ability to easily control the brake application are factors that help maintain control in an emergency situation. The Vacuum booster is supposed to store enough vacuum for 1-2 brake applications, but I have rarely found one that works like that, especially after 25 years of use. The Hydro-Boost works like it has 3 modes, power assist, reserve assist, and manual. From expierience with the system on my own '80 Scout the manual application of the brakes is close or equal to the vacuum assisted system. This is the factor that I believe provides the greatest safety margin for rigs that are used on the trail, or with the oversize tires, towing, etc.

The reason for such a difference in engine off performance between the vacuum and hydro systems is simple geometry. Take a look at this pic of the linkage on a Scout II booster.






You can see in the bottom pic the link from the pedal is connects to the center of the pivoting portion. When you mash the pedal the linkage amplifys the movement so the movement of the push rod in the booster travels farther than the input from the pedal. When you have good vacuum and the moon and venus are in perfect alignment and with alot of luck the booster does the work and you get stopped ok before you shorten that VW that stopped suddenly in front of you. The HUGE disadvantage of this arrangement is when there is no vacuum like when you are climbing a steep grade and the engine stalls. You hang on with both hands and put your foot towords the radiator with all you got and you keep rolling backwards faster than you went up. The laws of physics are working against you, when you increase the travel you reduce the force. Lets say for the sake of discussion here that you lose 10% and you can muster 200 lbs. force on the pedal with the adrenaline rush. If your master cylinder piston area is 1 square inch and the caliper piston is 10 square inches you end up with 200 less 10% = 180 lbs x 1 = 180 psi x 10 = 1800 psi effective pressure on the caliper piston. Don't beat me up on these numbers, I just made them up for an easy comparison. you get the idea tho. Here's the Hydro-Boost linkage.



Now apply the same numbers to the Hydro-Boost setup with the straight through link connected to the pedal. with the same 200 lb. force on the pedal you get 2,000 at the caliper, or 200 psi more on each caliper if you have 4 wheel disc brakes. Clearly an advantage I would want for my trail rig. It could mean the difference between changing your shorts or retrieving your rig from the bottom of a ravine.

Originally Posted by Jon

What are the downsides of it?

Ok now for the darkside.... hmm, I can't think of any. But there are lots of myths, and or misunderstandings. I found some ancient info from this very forum that really covers alot of them, I'll just copy it to reduce my typoing load here.



[font=Times New Roman][/font]
(begin ancient archives)

Re: Hydra Boost conversion

Dan McIntyre -- 1/19/2000, 7:25 p.m.

Well From my experience of seeing them on other trucks. I dont like them. The reason why is because they take power away from the steering. I also will make you brakes pull to the left or right. If you run out of P/S fluid then you have no brakes.

They also put a load on the engine. ( at least what I have seen)

Hope this helps!

Dan McIntyre

62 80

69 800a

70 800a

Re: Hydra Boost conversion

Posted By: Eldon McFarling (EldonMcf@aol.com )

Date: 1/23/2000, 11:00 p.m.

Dan,

Just wanted to point out a few things that you may misunderstand about hydro-boost brake systems.

Dan = I dont like them. The reason why is because they take power away from the steering.

The Hydro-boost system uses power steering fluid circulating through the booster, then the steering gear, then back to the pump from the return port of the steering gear. The steering system has priority over the braking system, and the brake system does not use any pressure when the brakes are not applied so it doesn’t take anything away from the steering. In a worst case scenario the brakes would revert to manual after all the stored energy in the reserve is used up To be practical it is unlikely that you would need maximum steering assist, and maximum braking at the same time..

Dan = It also will make you brakes pull to the left or right.

This is impossible regardless of the type of booster. To make the brakes pull there would have to be a problem at one of the wheels, or elsewhere in the system. The pressure to the front or rear wheels is delivered thru the same port on the master cylinder, and then split between each side of the vehicle.

Dan = If you run out of P/S fluid then you have no brakes.

This is incorrect. If you run out of brake fluid you have no brakes. If you run out of P/S fluid you would have the equivalent of manual steering, and manual brakes. Both may require a bit more effort than they do with full assist, but still well within a person’s ability to safely maintain control of the vehicle.

Dan = They also put a load on the engine.

Since the brake booster operates with oil pressure from the steering system it cannot load the engine any more than the steering gear could when it is turned against the steering stop. In some situations the engine idle rpm may be slightly less, like when you are sitting at a stoplight with your foot on the brake for example, but this does not cause any additional stress on the engine, or power steering system. Most of the power to actuate the hydro-boost system comes from the fluid that would normally just be returned to the power steering pump reservoir.

Eldon

(end ancient archives)

Originally Posted by Carl Wiese

One downside to mention that I didn't seem as I skimed the thread. If you lose the belt to your power steering pump your ability to steer and brake are greatly reduced. The ability to brake won't all go away with the proper pressure resevoir, but you'd lose it eventually. It's why the Cummins PS pump is direct drive off the engine on the newer models.

lets think about that one. If you lose the PS belt on your gas rig w vac you still have vacuum so you can stop, but you have armstrong steering. If you lose the PS belt on your Diesel and it gets under the alt belt and breaks it you lose brakes and steering. in that scenario I would sure like to have the Hydro-Boost so I could stop within reason. the vacuum booster is worse than nuthin without vacuum. The best thing to do is keep decent belts on either way. I think the most common problem is loss of all power when the engine dies for whatever reason. In that case you lose all power, and you have the better stopping power with the Hydro-boost.

Originally Posted by Erik VanRenselaar

I don't see any advantage with a hydroboost brake system in a Scout II. I do see more mechanical complexity and added cost. Hydroboost is for big haulers like 1-ton dually trucks.

I'd say there are advantages for just about every use of a Scout II. I have yet to hear from anyone who was not thrilled with the performance of the rig after converting to Hydro-Boost. I don't believe it is complex at all. its all basic stuff. The cost can be about the same or less than replacing the vacuum booster with a rebuilt unit, but it is an UPGRADE much like replacing your points system with electronic, carb with fuel injection, etc. I would not run out and modify my good working brake system for no reason, but I would choose the Hydro-Boost based on the vehicle usage and if repairs are needed:

1. modified or towing needing more braking power
2. Diesel needing alternator upgrade
3. all other stock needing booster replacement or if the vacuum system doesn't work as well as desired like with a tired engine with low vacuum.

Originally Posted by Erik VanRenselaar

Fine, I'll just stay out of commenting on things.

I'm with John on this Erik. You have helped this community alot over the years and your input is always valuable. with as many folks as we have involved these days everyone is going to have different needs and different opinions.

Originally Posted by Bill usn-1

Vanco has been one of the few vendors that takes the time to help the enthusiast.

I'm with you on that Bill. Van has offered to help folks that are not even customers, supports the site, and offers much help in this forum. :::::tipping my hat to ya Van::::: BTW if you all want more tech info check out the VANCO website. Lots of good info there.

I have reproduced an article titled "Hydro-Boost your brakes" that was published in web site # 19, february 2000.

Hydro-Boost Your Brakes

I have done several installations in Scout II's, all have been Diesel powered. I have used boosters from GM Diesel cars with stock unmodified pumps. the linkage from the booster is the exact length needed, and no modifications to the booster are needed.