Why do we run vacuum brakes as oppose to hydraulic brakes on our TJs?

Goatman said:
I have to think Jeep might have suspected I might add bigger tires when they built the Rubicon. Upgrades to make it for hard offroad use without thinking larger tires might be involved is unlikely.

A hyrdoboost would be placed in the same spot as a vacuum boost. So the odds of leaking into the cabin is low. Brake fluid is more likely to do that.

Do they at least offer it as an option on those house sized 1 ton pickups? They keep bragging about tow capacity numbers going up every year. The hydroboost would be ideal for them. Plus adding a component on the front of their diesel engines just to produce usable vacuum would save $$. The amount of h.p. vacuum brakes saves compared to the load put on the engine by adding a port on the power steering system would be (in my little brain) minimal. I would think the OEMs would jump on the idea to offer such an upgrade. Adding 10 more cup holders is getting ridiculous.
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Lots of large trucks use hydroboost. Ford has been using it on the diesels since 99. I'm sure it serves the purpose of better braking as well as no longer needing to run a separate vacuum pump.

Cost has to be the biggest driving factor, as well as simplicity. A vacuum booster is cheap and only needs one line. The hydraulic lines, routing, and modified PS pump probably aren't worth the cost.
 
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A hyrdoboost would be placed in the same spot as a vacuum boost. So the odds of leaking into the cabin is low.
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The shaft seal that leaked all the time is the one from the brake pedal to the booster (High Pressure Seal shown below), that seal is holding out the hydraulic pressure from the power steering pump, not the brake fluid. When they leaked, they would screw up wiring and everything else that fluid leaked on. Sometimes when it leaked it sprayed everywhere under the dash, cost GM a lot in warranty work back then.
And nothing like the confusion of a customer wondering why in the hell is there transmission fluid coming from under my dash.

hydro boost.jpg


Of course that was GM in the 80's, everything was pretty crappy so I would imagine that there is much improvement in the "new' hydro boost equipment of today
 
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WallyWest said:
Ok then, I guess it's a luxury feature now, lol.

I haven't worked on every car/truck out there of course, but everything I've owned since the late 90's seemed to be eliminating vacuum powered anything.
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My mini cooper S, a vehicle which by all logic should have had an electric brake booster because they seemed to be in the habit of making everything electronic just because they could, still had a vacuum brake booster, powered by a vacuum pump driven by the end of exhaust camshaft. They have a habit of locking up and breaking the timing chain, taking the whole engine with it. I replaced mine at the first sign of trouble, when extended highway trips would end with a rock hard pedal and no boost from the turbo, since the pump also supplied vacuum to close the wastegate.
 
Goatman said:
A hyrdoboost would be placed in the same spot as a vacuum boost. So the odds of leaking into the cabin is low. Brake fluid is more likely to do that.
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You couldn't be more wrong on this point. Hydro-boost would be 99.9% more likely to leak hydraulic fluid(power steering) into the cab of a vehicle because the cylinder seal is pretty much sitting flush if not inside the firewall. With a Vacuum boost the only way to get any fluid inside the firewall would be if the master cylinder failed and allowed brake fluid to fill up the booster and then it would have to eat its way through the vacuum diaphragm of the booster and fill it up to the level of the piston hole in the firewall... Not completely unheard of but unless the owner of the vehicle is continually topping off the master cylinder and ignoring the fact that he shouldn't be going through that much fluid, it's not very likely.

Goatman said:
Do they at least offer it as an option on those house sized 1 ton pickups? They keep bragging about tow capacity numbers going up every year. The hydroboost would be ideal for them. Plus adding a component on the front of their diesel engines just to produce usable vacuum would save $$. The amount of h.p. vacuum brakes saves compared to the load put on the engine by adding a port on the power steering system would be (in my little brain) minimal. I would think the OEMs would jump on the idea to offer such an upgrade. Adding 10 more cup holders is getting ridiculous.
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Most HD pick-ups at least on the diesel side of things switched over to hydro-boost a long time ago because Turbo diesel engines do not develop vacuum. Early Dodge diesels actually used a vacuum pump to supply the climate controls and vacuum boosters for the brake systems.

Horse power concerns are negligible at best when it comes to running a hydro-boost vs vacuum boost if any at all. The power steering pump is already supplying pressure as soon as the engine is started. The biggest draw back that needed to be addressed was an accumulator system to provide boost in the event the engine died. Vacuum doesn't go away the instant the engine dies hydraulic pressure does unless you have an accumulator to store the energy. GM used to use an electric back-up motor that kicked in any time you stepped on the brake while the engine wasn't running, and that was not the most reliable alternative.
 
reddvltj said:
The power steering pump is already supplying pressure as soon as the engine is started.
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Yes and no, it is supplying flow. The pressure doesn't build until there is demand in the system. You can watch the effect by stepping on the brakes hard with a HB system and seeing the hoses pressurize and then relax when the pedal is released.

The biggest draw back that needed to be addressed was an accumulator system to provide boost in the event the engine died.
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All modern HB have accumulators on them. That is the little gold or blue canister off to the side.
 
mrblaine said:
All modern HB have accumulators on them. That is the little gold or blue canister off to the side.
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Hence the wording used, "needed to be addressed" (y)
mrblaine said:
Yes and no, it is supplying flow. The pressure doesn't build until there is demand in the system. You can watch the effect by stepping on the brakes hard with a HB system and seeing the hoses pressurize and then relax when the pedal is released.
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True, pressure is created by interrupting the flow, effectively, partially blocking what was an open loop.
 
Hey @Goatman. It seems your thread may have gone off track a bit. I don't know why it wasn't stock but, Chevy Astro vans have a very cheap and adaptable hydroboost set up. There is a ton of info out there. I think you have a 1" MC and the Astro has 1 1/8. That should balance the higher pressure nicely. You will have a shorter brake stroke. I am by no means the master of brakes, just wanted to share something I've learned.
 
fixmysix said:
Hey @Goatman. That should balance the higher pressure nicely. You will have a shorter brake stroke.
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Shorter and much harder to push. Kind of annoying really. I run the 1" stock master on the HB set ups we install for anything smaller than about 5 1/2" of piston area and 1 1/16" for over that up to and including 7" of piston area.
 
mrblaine said:
Shorter and much harder to push. Kind of annoying really. I run the 1" stock master on the HB set ups we install for anything smaller than about 5 1/2" of piston area and 1 1/16" for over that up to and including 7" of piston area.
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Or you can listen to the guy that builds the brake systems. Might be a better route.
 
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