I have done a hydroboost conversion on my 1993 F250. I am currently having and issue with the braking system. When I hit the brake hard to do a panic stop there is a click I can faintly hear under that dash. When I hear the click I can feel a pulse in the pedal. When this happens the brake pedal goes hard and no matter how hard I push on the pedal The wheels will not lock up. If I press the pedal slowly, no click or pulse and I can lock up all the brakes. Now my goal is not to lock up the brakes but in the panic stop situation the truck takes a long time to stop. My RABS system is not working at the moment. Tonight I just found out the brake pressure switch is leaking and my connector started smoking. I have a new sensor on order. I am thinking the clicking is the RABS and is the culprit but when I unplugged the brake pressure switch and RABS unit on the frame rail of the truck I had the same issue. Just wondering if anyone has dealt with this.

 

That sounds like a defective HydroBoost unit.

And do replace the switch on the MC before it burns down your truck.

 

In the mean time disconnect the connector on the Brake Pressure Switch before the truck burns down.

That means now before it's too late.

 

Switch is unplugged and I am not going to drive the truck until I replace it. Questions......

1) Would the brake pressure switch effect the ABS?
2) If the hydroboost is faulty is there a test I can do, or is what I am experiencing "the test"? The unit I used was brand new not a reman, although I know new parts still fail.

Thanks

 

Yeah, new doesn't always mean good/functional. As far as I know, that pressure switch is only to disengage the speed control as a secondary method to the BOO (brakes on-off) switch on the pedal. No effect to the ABS.

Do you ever lose the power steering when the brakes do this little hiccup? Could be your pump isn't providing enough pressure/volume. As far as testing, not sure what to tell ya. Can you replicate this sitting in the driveway? Do you have to be moving to cause this?

With the RABS unplugged, either your MC is shot or your HydroBoost is malfunctioning. Are you using a Saginaw pump made for this or a modded Ford unit?

Man, troubleshooting across the Intarwebs is a difficult thing . . .

 

X2........

 

The pump I am using is a reman that I picked up while collecting all of the parts. I do not know its history but it looked very clean like brand new when I got it. It came as an assembly with the reservoir with the extra drain back for the hodroboost. I never had hydroboost before so I do not know what it is supposed to feel like. My previous vacuum assist was not working well and was getting scary to stop the truck when in a hurry. One thing that would happen is that if I really stepped on the brake pedal hard it would get stiff and almost seem like it would push back. Although it became hard to push I could still lock up all four if wanted. I thought that this was what hydroboost was, awesome pedal feel not spongy and would put you thru the windshield if wanted. The issues that just arrived are puzzling me. I did the following, I thought I did everything correct and tried not to cut corners. Also, steering assist does not feel to be affected with this.

1) Hydroboost power steering pump (or what I thought was)
2) New (not reman) Hydroboost assist
3) All new hydrolic hoses
4) New master cylinder
5) New rubber brake lines front and rear
6) New brake lines front and rear
7) Adjustable proportion valve for rear brakes
8) New front calipers
9) New rear wheel cylinders
10) Used synthetic brake fluid
11) ATF used in power steering pump, although first I used regular power steering fluid but it kept cavitatingand made the pump whine very loud. Pump still whines a bit but not terrible.

 

I'm not sure where you got that hydroboost has an "awesome pedal feel". Every Ford and GM truck I've ever driven with hydroboost has had an absolutely atrocious pedal feel. Overboosted, hard to modulate, lumpy pedal feel, etc..Basically the only thing hydroboost has going for it, is that it can deliver a large brake force assist - more than most vacuum boosters.

Anyways, it sounds like your hydroboost unit has an internal problem if you can feel a "click" in the pedal when you stomp it.

 

I'll X2 what Lead Head said. Years ago, the shop I worked for had a 1 ton 3500 series single rear wheel flatbed Chebbie. I6, 4 speed, no power steering(!) and hydroboost. It was almost like you were being punished if you had to drive "Ol Flattie" for the day. All you had to do was look at the pedal and it would lock up the rears. It was hard to drive, considering you had to use Armstrong power steering effort, shift that notchy transmission and keep from locking up the brakes.

So, I can postulate you need to replace that hydroboost unit. They do not click under heavy brake application. Probably has a defective pressure relief valve that goes full open when you hear that click, dumping the hydraulic assist.