F700 Brake Pedal Whistling.
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From: Northern CA.
F700 Brake Pedal Whistling.
Working out all the bugs in my new to me 1995 F700 Ford Box Truck and noticed that I get a whistling sound inside the cab when the brake pedal is depressed.
The sound varies by how much the pedal travels and sounds like it's coming from where the shaft that goes from the pedal to the master cylinder through the fire-wall is located. Sounds like a vacuum or air pressure leak.
The brakes (I assume) are the infamous Lucas-Girling system and work fine, they just make that whistling sound anytime the pedal is used (Annoying as H#%$ when waiting at a stop light).
Any ideas and suggestions as how to rectify this situation is greatly appreciated.
Thanks in advance for any help given, Al.
The sound varies by how much the pedal travels and sounds like it's coming from where the shaft that goes from the pedal to the master cylinder through the fire-wall is located. Sounds like a vacuum or air pressure leak.
The brakes (I assume) are the infamous Lucas-Girling system and work fine, they just make that whistling sound anytime the pedal is used (Annoying as H#%$ when waiting at a stop light).
Any ideas and suggestions as how to rectify this situation is greatly appreciated.
Thanks in advance for any help given, Al.
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From: Northern CA.
It's some sort of a Hydra-Boost set-up.
The power steering has it's own reservoir and pump which is gear driven.
The Hydra-Boost has its own reservoir and a belt driven pump. The master cylinder and Hydra-Boost are mounted to the fire-wall at the normal place. The Hydra-Boost has some sort of an electric motor just under it. Anytime the brake pedal is depressed, the electric motor comes on even if the ignition key is not on. There is also another aluminum assembly to the right (when viewed from the front) of the master cylinder and Hydra-Boost that is tied into the brake system. Got no idea what that is for.
I couldn't find any sort of a vacuum pump or lines going to or from the Hydra-Boost.
The more I look at it, the more I wonder what could possibly be causing the noise.
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AFAIK, the electric part of this system is a backup in case the main power is lost. I lost the belts on a GM rental once, and the electric backup handled the steering or the brakes, but not both at once! Not to much excitement, but a pita anyway. Your system has a separate pump, so I would inspect that pump, fluid level etc.
The electric backup will make a noise by design I think--to alert you to the loss of primary power.
Not sure if this is what's causing your noise, but if so, you may have:
--a problem with primary power
--a problem with the backup system, causing it to activate all the time
Usually on our stuff, the noise (of one kind or another) is caused by low fluid.
The electric backup will make a noise by design I think--to alert you to the loss of primary power.
Not sure if this is what's causing your noise, but if so, you may have:
--a problem with primary power
--a problem with the backup system, causing it to activate all the time
Usually on our stuff, the noise (of one kind or another) is caused by low fluid.
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Both the power steering and hydra-boost use power steering fluid as per the decals on the sides of the reservoirs. The fluid in the hydra-boost reservoir is above the full mark and has no burnt smell at all.
When the electric brake motor comes on, I can tell what it is by the sound it makes. The noise I'm concerned about is like a vacuum whistle that only happens when the brake pedal is applied. There is no noise until the pedal moves. I can't tell if it does it without the engine running since the second I touch the pedal the electric motor comes on.
The way I understand it, the electric motor will only come on when the the normal (hydra-boost) system fails.
I'm at a total loss on this and got no idea what it could be.
When the electric brake motor comes on, I can tell what it is by the sound it makes. The noise I'm concerned about is like a vacuum whistle that only happens when the brake pedal is applied. There is no noise until the pedal moves. I can't tell if it does it without the engine running since the second I touch the pedal the electric motor comes on.
The way I understand it, the electric motor will only come on when the the normal (hydra-boost) system fails.
I'm at a total loss on this and got no idea what it could be.
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Sounds like you have pressure bypassing in the hydraboost unit
a loss of pressure will make the electric motor come on
Try disconnecting the electric motor and see if it still makes the noise
a loss of pressure will make the electric motor come on
Try disconnecting the electric motor and see if it still makes the noise
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From: Northern CA.
Well, I just took Krewat advise (thank you!) and dug out the mechanics stethoscope.
The sound is definitely coming from the rear of the Hyra-Max Booster (dug out the factory manuals as-well to get the proper names for this stuff).
Also checked the electric motor with the engine running and brake applied, it was not running. Even unplugged it with the motor running and still got the whistling.
After looking at some of the exploded views of the system, it appears that there are two seals at the rear of the Hydra-Max Booster of which I believe are bad. It must be sucking air in past the seals but I couldn't see any bubbles in the reservoir with the brake applied and the engine running. The top of the reservoir is rather wet with fluid indicating a possibility of blowing some out at some point.
Your assistance with this has been very helpful guys, thanks again.
Any other thoughts are appreciated.
Al.
The sound is definitely coming from the rear of the Hyra-Max Booster (dug out the factory manuals as-well to get the proper names for this stuff).
Also checked the electric motor with the engine running and brake applied, it was not running. Even unplugged it with the motor running and still got the whistling.
After looking at some of the exploded views of the system, it appears that there are two seals at the rear of the Hydra-Max Booster of which I believe are bad. It must be sucking air in past the seals but I couldn't see any bubbles in the reservoir with the brake applied and the engine running. The top of the reservoir is rather wet with fluid indicating a possibility of blowing some out at some point.
Your assistance with this has been very helpful guys, thanks again.
Any other thoughts are appreciated.
Al.
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From: saxton pa.
Booster noise
On that system there is a accumulator that when the pedal is pressed will discharge and supliment hydralic pressure. Sometimes they will make the sound you describe. If the booster works OK and there are no leaks you should be allright.
Have A Great Day ----- Hotwrench
Have A Great Day ----- Hotwrench
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From: Brentwood,CA
The noise you describe is normal on these as well as most hydro boost setups when the brakes are pressed you should have a pressure whine or whistle from the unit. The noise is louder on these as the 1.76 inch piston creates a lot of force. You are dealing with almost 2900 psi the seals on the unit are bad if they are leaking. They can't suck air and make sure you check the power steering/brake reservoir its the large one for fluid. The small reservoir on top of the engine is the brake pump for the parking brake chambers and is only used for the chambers. The gear driven pump is used for main brakes and the steering.
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Thanks for the shout guys, tends to put my mind at ease.
I Googled the problem last night and found this problem is fairly common. Was actually in a Technical Service Bulletin for the same problem on Motor Coaches in 1998 (TSB 98-22-4 and 603713).
The brakes work fine in all regards, just makes that irritating whistling noise when the pedal is applied.
I apparently have a different system than the one ford390gashog describes because the steering and brake systems are exclusive of each other. No lines are shared between the two anywhere. Which pops up a huge red flag in the aspects of, if the engine dies... the power steering would instantly disappear! Can this vehicle be controlled (steered) without power steering?
Both of the systems have identical sized reservoirs and I couldn't find a small reservoir anywhere in the engine compartment for the parking brake.
The information you guys supplied has been a great help. I would have probably spent more money needlessly on fixing a perfectly fine system for no other reason than to eliminate a frickin noise.
Thanks again guys, Al.
PS; To ford390gashog, I got a 390 GAS-HOG as-well! A 72 Ford F250 4X4 "THE MONEY-PIT". The NEVER ENDING PROJECT. PLEASE buy it from me, steal it, or torch the thing and put me out of my misery!
I Googled the problem last night and found this problem is fairly common. Was actually in a Technical Service Bulletin for the same problem on Motor Coaches in 1998 (TSB 98-22-4 and 603713).
The brakes work fine in all regards, just makes that irritating whistling noise when the pedal is applied.
I apparently have a different system than the one ford390gashog describes because the steering and brake systems are exclusive of each other. No lines are shared between the two anywhere. Which pops up a huge red flag in the aspects of, if the engine dies... the power steering would instantly disappear! Can this vehicle be controlled (steered) without power steering?
Both of the systems have identical sized reservoirs and I couldn't find a small reservoir anywhere in the engine compartment for the parking brake.
The information you guys supplied has been a great help. I would have probably spent more money needlessly on fixing a perfectly fine system for no other reason than to eliminate a frickin noise.
Thanks again guys, Al.
PS; To ford390gashog, I got a 390 GAS-HOG as-well! A 72 Ford F250 4X4 "THE MONEY-PIT". The NEVER ENDING PROJECT. PLEASE buy it from me, steal it, or torch the thing and put me out of my misery!
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It will steer fine w/o PS, but will get harder and harder to steer as you slow down. You should be able to safely drive the truck just about any distance without PS--just watch your tight turns at low speed, as you won't be able to crank it as fast as you'd like.
