HydroBoost to Manual Brake Conversion on Ford Mod Motor Car

[jslindst]

After searching the forums I could not find anyone who has some tech on removing the factory hydroboost to install a manual brake kit such as the one from Maximum Motorsports. It looks like I can make their kit for the 94-95 cars work on my 98 AI Cobra if I get a different MC, modify the brake light switch, and reconfigure, re-route, and/or shorten the power steering lines. My concern is the power steering pump, will it cause the steering to feel overboosted without the hydroboost in the loop? Just curious if anyone has attempted something similar and what pitfalls, if any, they overcame.

TIA

[snaproll]

Originally Posted by jslindst

After searching the forums I could not find anyone who has some tech on removing the factory hydroboost to install a manual brake kit such as the one from Maximum Motorsports. It looks like I can make their kit for the 94-95 cars work on my 98 AI Cobra if I get a different MC, modify the brake light switch, and reconfigure, re-route, and/or shorten the power steering lines. My concern is the power steering pump, will it cause the steering to feel overboosted without the hydroboost in the loop? Just curious if anyone has attempted something similar and what pitfalls, if any, they overcame.

TIA

Jeff, sounds like a great idea! Put me down for all of your ABS stuff

Bruce

[jslindst]

Sorry Numb Nutz, I'm keepin' the ABS, just losing the hydroboost power brakes in favor of the better feel(and slightly lower weight) of the manual brakes. Looks like I'm gonna be the test dummy to see if this mod is viable. Can't seem to find any info on the www. Surely someone has done this before.

[blackbolt9]

Originally Posted by jslindst

Sorry Numb Nutz, I'm keepin' the ABS, just losing the hydroboost power brakes in favor of the better feel(and slightly lower weight) of the manual brakes. Looks like I'm gonna be the test dummy to see if this mod is viable. Can't seem to find any info on the www. Surely someone has done this before.

I know of an S197 car that lost the ABS and power booster for "better brake feel and lower weight". After driving a car that still had a power booster they got rid of manual brakes. I don't know alot about the manual system that was used, so it may have been poorly designed though. I'm not saying you shouldn't do it, but I'm not sure it's really worth the time or money or there would be alot more of them out there and information more readily available.

JMO from what I've seen someone else go through.

[snaproll]

Originally Posted by jslindst

Sorry Numb Nutz, I'm keepin' the ABS, just losing the hydroboost power brakes in favor of the better feel(and slightly lower weight) of the manual brakes. Looks like I'm gonna be the test dummy to see if this mod is viable. Can't seem to find any info on the www. Surely someone has done this before.

Maybe it's me, but isn't "feel" an oxymoron when you're driving a fairmont with ABS?

[jslindst]

I'm just looking for "better" feel, realizing its all relative. They are never going to feel as good as the brakes on my 996 street car. I was hoping to get two for one, lose a little weight & improve my braking performance. Only keeping the ABS for now because I do not like the "feel" of square tires, and it helps a little when we run in the rain.

[Mattj]

FWIW, I'm running ABS with manual brakes and I love the feel. I wont go back to power assist.

[FRANK THE TANK]

Hey Jeff, why wouldn't we be able to put the MM manual brake conversion for the 94-95 cars on your car with a larger master cylinder?

[cgrant26]

Jeff, if you need anyone to take that hydroboost stuff off your hands once you finish the conversion...

[jslindst]

Originally Posted by FRANK THE TANK

Hey Jeff, why wouldn't we be able to put the MM manual brake conversion for the 94-95 cars on your car with a larger master cylinder?

Its not the master cylinder I'm concerned with, its the power steering pump output. I'm curious if the steering will feel over-boosted after having new power steering hoses made to complete the circuit without the hydroboost unit. Jason's response from MM was:

"You can install the 1994-95 manual brake conversion on your 1998 Mustang.
Some minor changes will be required, such as the brake light switch.
Eliminating the hydroboost typically requires an aftermarket power or manual
steering system."

In my e-mail question to MM I asked if the pump would provide too much pressure without the hydroboost unit in the circuit, but his response was simply that I needed an entire aftermarket power or manual steering system. I sent him an e-mail to clarify his response, I'm sure he will get me a better answer shortly. The part #s for the racks from 94-95 are definitely different from 96-04. Just a guess, but is it likely that the valving in the 96-04 racks is set up for different a pressure than the earlier racks, hence the different part #s? I'm definitely not interested in going to a manual rack.

[Shakes_26]

Jeff,

I had some links bookmarked at the FFR owners/builders site (they got lost a long time ago). There had been a few discussions in the MkIII threads about hydro boost and eliminating it in some cases and adding it in others.

There's a company that sold a pressure regulating valve (or was it volume?). I may be remembering it backwards, but its been a number of years. I believe its commonly used in hot rods.

Sorry not much help. If I find anything this weekend, I'll post it up or give you a shout.

[terryr]

Originally Posted by jslindst

Its not the master cylinder I'm concerned with, its the power steering pump output. I'm curious if the steering will feel over-boosted after having new power steering hoses made to complete the circuit without the hydroboost unit.

The pump has a pressure relief valve, so it can't go higher than that. All the volume went through HB, then the PS, not Tee-d, but there's no bypass valve without HB, so there should be slightly more flow to the PS.

[Jack Hidley]

Jeff,

The high pressure outlet from the PS pump runs to the hydroboost slave cylinder, then the high pressure output continues on the steering rack. When you aren't using the brakes, the inlet and outlet pressures of the hydroboost unit will be exactly the same. When you apply the brakes, the hydroboost unit applies some of the high pressure fluid to the piston through a control valve. This results in a small transient pressure drop in the high pressure outlet of the hydroboost unit. There is also a small high pressure reservoir on the hydroboost unit that dampens this transient pressure drop and retains pressure for when the engine is off. After you release the brakes, the fluid in the piston chamber goes out the third line of the hydroboost unit back to the reservoir in the PS system.

Essentially the high pressure outlet of the PS pump is tee'd to go to the steering rack and the hydroboost unit. This tee is located inside the hydroboost unit, so it isn't physically visible.

If you bypass the high pressure section of the hydroboost, so the PS pump output goes directly to the steering rack input, the pump should work correctly. There won't be any additional pump pressure at the steering rack input.

[terryr]

Calling it tee-d is pushing it.



Even with the brakes applied, some pressure goes straight to the steering through the spool. And when the bypass closes no more fluid is being used.

And you rarely steer and brake hard at the same time anyhow.

[Blk01 Cobra]

I did it last season on a 99 Cobra that now has a Tilton race pedal setup. Went direct to the rack after removing the hydroboost. I never drove the car, but the owner never complained and the car handles great. Took a lot of weight out of the car between the hydroboost and abs.

[jslindst]

Originally Posted by Jack Hidley

Jeff,

The high pressure outlet from the PS pump runs to the hydroboost slave cylinder, then the high pressure output continues on the steering rack. When you aren't using the brakes, the inlet and outlet pressures of the hydroboost unit will be exactly the same. When you apply the brakes, the hydroboost unit applies some of the high pressure fluid to the piston through a control valve. This results in a small transient pressure drop in the high pressure outlet of the hydroboost unit. There is also a small high pressure reservoir on the hydroboost unit that dampens this transient pressure drop and retains pressure for when the engine is off. After you release the brakes, the fluid in the piston chamber goes out the third line of the hydroboost unit back to the reservoir in the PS system.

Essentially the high pressure outlet of the PS pump is tee'd to go to the steering rack and the hydroboost unit. This tee is located inside the hydroboost unit, so it isn't physically visible.

If you bypass the high pressure section of the hydroboost, so the PS pump output goes directly to the steering rack input, the pump should work correctly. There won't be any additional pump pressure at the steering rack input.

This is why I have bought & will continue to buy from MM.

Thanks Jack, I was hoping you would chime in. I was assuming that it wouldn't be an issue since the pressure from the pump had to go somewhere when the hydroboost wasn't assisting the brakes.

I'm going to try to tackle this mod sometime in the coming months and will post up tech/experience.

[Jack Hidley]

Terry,

I'm not quite sure what you meant by your "Calling it tee-d is pushing it." comment, so I'll explain what I mean with some more detail.

See the link below:

staff.wwcc.edu/james.haun/spring/hydroboost.ppt

Look at slides 8 and 9. In slide 8, the brakes are off and you can clearly see that the position of the spool valve does not restrict any flow between the HP inlet and HP outlet ports. No pressure drop = a tee, from a hydraulic standpoint.

In slide 9, the brakes are on and the spool valve has restricted some flow to the steering rack. The purpose of this is to keep the load on the PS pump constant, which means the pressure applied to the piston in the hydroboost unit will be constant and the brake pressure assist won't change. The pressure to the steering rack will decrease a little bit. How much is a function of the PS pump flow output, the crevice design of the spool valve and the required flow of the steering rack for the given steering input. It is not a simple thing to calculate. In my experience on Mustangs with hydroboost brakes, the steering feel during trail braking feels normal. The small reduction in steering assist is probably masked by the increasing slip angle of the front tires.

In any case, with respect to Jeff's original question, he can just remove the hydroboost from his car without being concerned with the operation of the PS pump, since the hydroboost doesn't affect the PS fluid pressure to the steering rack in any way that matters.

[terryr]

You appear to be saying the same as me, with more words.

It's not a 'real' tee because all, or most, of the flow goes through one then the other.

My computer can't deal with that link: staff.wwcc.edu/james.haun/spring/hydroboost.ppt No powerpoint.

[Bossbill]

http://staff.wwcc.edu/james.haun/spring/hydroboost.ppt

[terryr]

That's the same link. Still no powerpoint.

[mschlang]

Time for some computer maintenance Terry, works fine here.