Can someone explain hydroboost systems?
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Cross-Country
Joined: Apr 2011
Posts: 93
Likes: 3
From: Chandler, AZ
Can someone explain hydroboost systems?
Can someone tell me the theory behind hydroboost systems on brakes?
My 1995 F350 hydroboost (not hydromax) is leaking just maybe a drip every one minute or so, if that. Power steering feels maybe barely stiffer, and power braking maybe just barely harder.
If this leak got bad, could the thing fail all together where I have manual steering and manual brakes? OR would that only happen is the power steering reservoir got low?
Trying to see what type of timing I need to get on this repair.
My 1995 F350 hydroboost (not hydromax) is leaking just maybe a drip every one minute or so, if that. Power steering feels maybe barely stiffer, and power braking maybe just barely harder.
If this leak got bad, could the thing fail all together where I have manual steering and manual brakes? OR would that only happen is the power steering reservoir got low?
Trying to see what type of timing I need to get on this repair.
Super Moderator
Joined: Apr 2004
Posts: 34,466
Likes: 2,798
I lost the belts on a GMC rental once. No belt driven pump made it rely on the electric backup. So it felt like you could have brakes OR steering, but not both at the same time.
If you lose the belt driven pump AND the electric backup, you will be able to steer with some effort. The slower you go and the tighter the turn the harder it will be. As to brakes, you'll need both legs plus one from a passenger to get anything close to standard braking power.
Your timing should be ASAP with a close watch on the fluid level. No long trips.
As to theory the hydraulic pressure from the pump is used to assist the pressure applied by the driver on the brake pedal. There is a mechanical linkage between the systems. The brake fluid is separate from the hydraulic fluid.
If you lose the belt driven pump AND the electric backup, you will be able to steer with some effort. The slower you go and the tighter the turn the harder it will be. As to brakes, you'll need both legs plus one from a passenger to get anything close to standard braking power.
Your timing should be ASAP with a close watch on the fluid level. No long trips.
As to theory the hydraulic pressure from the pump is used to assist the pressure applied by the driver on the brake pedal. There is a mechanical linkage between the systems. The brake fluid is separate from the hydraulic fluid.
Fleet Owner
Joined: Jul 2006
Posts: 20,322
Likes: 789
From: Mi'kma'ki
The power steering pump will whine while you turn the wheel or press on the brakes, when the ATF gets low enough. You'll have plenty of time to pull over safely and top up the PS pump.
Like stated, rather than having vacuum assist you, the power steering pump ("hydro" as in hydraulics) is what's assisting "boosting" you. This is why it's sooooooooo much more powerful over vacuum. There's a built in saftey feature as well; you'll have a good, solid, one time stop, in the event the PS pump goes out/ blows a line. Don't do anything silly to count on using it, but it's good it's there haha. Of course, with your F350, you have an emergency brake to use also; pull the handle out and use it as a brake pedal, while holding the handle it so it can't lock (they used to teach this in drivers ed and we used to have to demonstrate using it and coming to a stop with it too.) That will mechanically engage your rear brake shoes.
The F450's of which most hyrdroboost conversions used to come from (and what I use in my F250 dually) ironically, don't have an emergency brake; only a driveline park brake. I always wished someone would make some calipers (the F450's are 4 wheel disc brakes) with an emergency brake cable for the Dana 80's in these, but the trucks are so old now and becoming fewer and fewer on the road, I doubt anyone would bother now. I'd like to install a t-case for low range (the driveline brake is bolted on a 4wd trans, even though the trucks are 2wd) and have a real emergency brake.
Like stated, rather than having vacuum assist you, the power steering pump ("hydro" as in hydraulics) is what's assisting "boosting" you. This is why it's sooooooooo much more powerful over vacuum. There's a built in saftey feature as well; you'll have a good, solid, one time stop, in the event the PS pump goes out/ blows a line. Don't do anything silly to count on using it, but it's good it's there haha. Of course, with your F350, you have an emergency brake to use also; pull the handle out and use it as a brake pedal, while holding the handle it so it can't lock (they used to teach this in drivers ed and we used to have to demonstrate using it and coming to a stop with it too.) That will mechanically engage your rear brake shoes.
The F450's of which most hyrdroboost conversions used to come from (and what I use in my F250 dually) ironically, don't have an emergency brake; only a driveline park brake. I always wished someone would make some calipers (the F450's are 4 wheel disc brakes) with an emergency brake cable for the Dana 80's in these, but the trucks are so old now and becoming fewer and fewer on the road, I doubt anyone would bother now. I'd like to install a t-case for low range (the driveline brake is bolted on a 4wd trans, even though the trucks are 2wd) and have a real emergency brake.
Tuned
Joined: Jan 2007
Posts: 330
Likes: 99
From: Salkum
I lost the belts on a GMC rental once. No belt driven pump made it rely on the electric backup. So it felt like you could have brakes OR steering, but not both at the same time.
If you lose the belt driven pump AND the electric backup, you will be able to steer with some effort. The slower you go and the tighter the turn the harder it will be. As to brakes, you'll need both legs plus one from a passenger to get anything close to standard braking power.
Your timing should be ASAP with a close watch on the fluid level. No long trips.
As to theory the hydraulic pressure from the pump is used to assist the pressure applied by the driver on the brake pedal. There is a mechanical linkage between the systems. The brake fluid is separate from the hydraulic fluid.
If you lose the belt driven pump AND the electric backup, you will be able to steer with some effort. The slower you go and the tighter the turn the harder it will be. As to brakes, you'll need both legs plus one from a passenger to get anything close to standard braking power.
Your timing should be ASAP with a close watch on the fluid level. No long trips.
As to theory the hydraulic pressure from the pump is used to assist the pressure applied by the driver on the brake pedal. There is a mechanical linkage between the systems. The brake fluid is separate from the hydraulic fluid.
Hotshot
Joined: Jul 2020
Posts: 10,268
Likes: 2,563
From: Near Salt Lake City
Your pedal will get hard as the Hydro Boost continues to fail
The power steering pump will not enjoy the leaking hydro boost at all (will also fail)
Once they start leaking you are done, replace the unit
Right, they are a bit expensive from Ford
The time will be to save up dough for the new part
The power steering pump will not enjoy the leaking hydro boost at all (will also fail)
Once they start leaking you are done, replace the unit
Right, they are a bit expensive from Ford
The time will be to save up dough for the new part
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